LO the Astrophysical Journal Supplement Series, 81:59-81, 1992 July © 1992

O'!PC LO The Astrophysical Journal Supplement Series, 81:59-81, 1992 July © 1992. The American Astronomical Society. All rights reserved. Printed in U.S.A. co io a CM< £ THE BROAD EMISSION LINE AND CONTINUUM VARIATIONS OF SEYFERT GALAXIES. ^ I. TIME SCALES AND AMPLITUDES

Edward I. Rosenblatt Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093 Matthew A. Malkan Department of Astronomy, University of California, Los Angeles, Los Angeles, CA 90024-1562 AND Wallace L. W. Sargent and Anthony C. S. Readhead Department of Astronomy, MS 105-24, California Institute of Technology, Pasadena, CA 91125 Received 1990 June 25; accepted 1991 November 27 ABSTRACT Spectroscopic observations of 13 Seyfert 1 galaxies made from 1979 to 1984 at Palomar and Steward Observa- tories were analyzed for Balmer-line and optical continuum variability. The majority of the galaxies showed significant variations, particularly in the continuum. Typical peak-to-peak changes for Hß and H7 integrated fine fluxes were 100%-200%, while the continua varied by 200%-350%. In several cases, Balmer-line and continuum variations were found to be strongly correlated, as expected for photoionization by a central continuum source. However, these correlations were jfound to be highly nonlinear. Significant correlations were found between variability amplitude and global AGN properties such as luminosity. Moreover, a significant number of variations occurring on short time scales constrains the size of the broad-line region in Seyfert galaxies to ^90 lt-days across or less. Subject headings: galaxies: Seyfert

1. INTRODUCTION (e.g., Clavel, Wamsteker, & Glass 1989; Masegosa, Moles, & Pension 1986; Wamsteker et al. 1985; Kollatschny & Fricke In this paper we examine the time scales and amplitudes of 1985). variations in the optical continuum and broad emission fines These studies and others have done much to advance our of a large sample of Seyfert galaxies. Recently, much attention understanding of the broad-fine region. However, given the has been devoted to variability as a means of understanding small number of objects studied in detail thus far, a broad the size and structure of the broad-fine region (BLR) in active overview of the variability properties of Seyfert galaxies has not galactic nuclei. However, only a very limited number of ob- been achieved. The large sample of objects presented in this jects have been observed with sufficient sampling to allow a study, observed using the same telescope and setup, represents detailed analysis. The Seyfert 1.5 galaxy NGC 4151 has been the most comprehensive optical variability study completed to examined by several investigators (e.g., Cherepashchuk & Lyu- date. In addition to analyzing over a dozen individual objects tyi 1973; Pension et al. 1981; Antonucci&Cohen 1983; Ulrich in detail, we have combined this internally consistent data set et al. 1984; Clavel et al. 1987). These studies have shown NGC to study global variability properties of active galactic nuclei 4151 to be highly variable in both its ultraviolet and optical (AGNs). The present paper focuses on variability time scales continuum and broad emission lines. The characteristic size of and amplitudes and their implications for models of the BLR. the BLR indicated by the lag of ultraviolet emission fines and A study of NGC 5548 (Rosenblatt & Malkan 1990) using ob- the continuum is estimated to be quite small at ~ 1 lt-week. servations taken from this large data base has already been Another Seyfert galaxy that has received much attention is published, and some of the results are incorporated here. In a NGC 5548 (e.g., Anderson 1971; Peterson, Korista, & Cota separate paper, we will examine the structure and kinematics 1987;Peterson 1987;Stirpe, de Bruyn, & van Groningen 1988; of the BLR. Peterson, Korista, & Wagner 1989; Wamsteker et al. 1990; Rosenblatt & Malkan 1990). Broad-fine profile variations have 2. OBSERVATIONS AND DATA REDUCTION been observed in both the UV and optical. A worldwide collaboration obtained UV spectra with IUE (Clavel et al. 1990) and 2.1. Instrumentation and Sample optical data with ground-based telescopes (Peterson et al. The spectra used in this study were obtained as part of a 1991a) simultaneously every 4 days to monitor NGC 5548 for long-term spectroscopic monitoring study of bright Seyfert gal- an 8 month period. These data yielded an accurate estimate of axies. The data were collected by M. A. Malkan in collabora- the time lag between ultraviolet continuum and emission-fine tion with W. L. W. Sargent and A. C. S. Readhead of the variations caused by a finite BLR size. Two other Seyfert galax- California Institute of Technology. The majority of the obser- ies that have been extensively monitored are Akn 120 (see the vations (58 nights) were obtained at Palomar Observatory review by Peterson 1988; Peterson et al. 1989) and Fairall 9 from 1979 to 1983; four nights were obtained at Steward Ob- 59

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!PC LO 60 ROSENBLATT ET AL. œ servatory during 1984. A journal of the observations is pre- the 4-5 yr monitoring period. Spectra were thus scaled by their sented in Table 1 for the 15 Seyfert galaxies included in the measured [O m] X5007 fine flux using absolute X5007 fine flux ^ sample (the data on NGC 5548 are included, although they values given by one or more of the following: de Bruyn, Sar- § were published separately; Rosenblatt & Malkan 1990). All gent, & Readhead ( 1982); Malkan & Oke ( 1983); and the pres- CT)S observations were made with the same instrumentation and ent photometric Steward data. Recent simulations by Bari- ^ setup at each site. The Silicon Intensified Target (SIT) long-slit baud & Alloin (1990) quantify the systematic errors that can spectrograph (Kent 1979) was used on the Palomar 1.5 m re- occur from [O m] scaling. These authors point out that large flector with a 600 line mm-1 grating which gave a dispersion of errors in [O m] fine flux measurements can be introduced 3.4 Â per pixel (the spectra of 1981 November 15 and 16,1982 when Hß is extremely broad and the Fe n emission is highly February 13, 14, and 17,1982 July 18, and 1982 September 30 variable, as in the case of Akn 120. Under these conditions, were obtained with a 1200 line mm“1 grating and later re- [O m] sits on top of the Hß red wing, making accurate fine flux binned to match the lower resolution data). The slit was 4" measurements quite difficult. However, the present sample of wide and 20" long, oriented east-west, providing a spectral reso- galaxies does not fall into the same category as Akn 120, since lution of 2.5 pixels (9 Â) FWHM. The 512 pixels along the Hß is not extremely broad, and, although the Fe n emission dispersion covered the spectral range from 3500 to 5300 Â. A might be variable, it is relatively weak. photon-counting Reticon spectrograph (Hege, Cromwell, & Another potential problem involved with scaling spectra by Woolf 1979) on the Steward 90 inch (2.28 m) telescope yielded their [O m] flux is that [O m] measurement errors may in turn similar spectral characteristics. affect measurements of other emission fines, thus producing correlated errors. We tested whether this was in fact occurring 2.2. Palomar Data Reduction by examining Hß and [O m] measurements for NGC 1068 and for Mrk 3. Since the emission fines in these galaxies should be The limited dynamic range of the SIT detector readout (a maximum of4095 counts) required integration times just long intrinsically constant, fine flux measurements should be unre- enough to bring [O in] X5007 nearly up to saturation. Typi- lated in principle. Indeed, we found that these fine flux measurements were in fact completely uncorrelated. Although not cally five repeated exposures each with 5-10 minute integra- definitive, this test provides good evidence that correlated tions were obtained yielding signal-to-noise ratios of ~ 15-30. Beginning in 1981 August, the SIT spectrograph was upgraded errors are not significant in the present data. Last, the spectra were not corrected for Galactic reddening, although these cor- by the addition of a television guider. The efficiency increased, rections are small and would not affect the variability results and it was then necessary, because of readout time consider- presented here. ations, to “trail” the spectra by moving the nucleus along the slit. Since the trails were 40"-70" long, there may have been increased contamination of off-nuclear starhght. However, 2.3. Steward Data Reduction comparisons with nontrailed spectra show that this contamina- Reticon spectra were reduced with C. Foltz’s 1RS program at tion is small. Moreover, with the possible exception of NGC Steward Observatory. Since they were obtained with a large 3516, we find no discontinuities in the fight curves of any of aperture (7" circular) under photometric conditions, the abso- the galaxies before and after the installation of the guider. It lute fluxes are reliable. Agreement between several standard can thus be concluded that trailing had little or no effect on stars observed on each night is better than 10%. The spectral spectra of the present sample. resolution (7.5 À FWHM) is slightly better than in the Palomar The two-dimensional images were reduced on the Caltech spectra, and the sampling is better, with a pixel spacing of 1.0 Astronomy Department VAX 11/780, using a series of Á. The wavelength coverage extends from 3600 to roughly FORTH routines written by T. Boroson. Each image had an 6600 Á, and the typical residuals to fits of comparison arc average zero exposure (“erase frame”) subtracted, and was wavelengths were 1.0 Â. then divided by the average of about a dozen flat-field exposures of the uniformly illuminated dome ceiling. Regions 60"- 3. SPECTRAL CORRECTIONS 80" east and west of the galaxy were used to measure the sky brightness, which was then subtracted from the summed spec- To isolate and measure the broad Hß and nonstellar contin- trum of the central 40" around the galactic nucleus (a wider uum fluxes of Seyfert galaxies requires several spectral correc- swath was summoned for the trailed spectra). A cubic polyno- tions, which may include the subtraction of narrow Hß, Fe n mial wavelength solution was obtained from six to eight fines XX4924, 5018, and starlight (see, e.g., Peterson 1987; Rosen- measured from a helium comparison lamp. The 1 a residuals blatt & Malkan 1990). These corrections are discussed below. from these fits indicate that relative wavelengths are typically Hy was not corrected except for NGC 5548 (see Rosenblatt & accurate to roughly 3 Á. It should be noted that wavelength Malkan 1990). calibration uncertainties will not affect the fine flux measure- In order to subtract narrow Hß, it is assumed that the intrin- ments of this study. sic profiles of the narrow component and [O m] X5007 are The conversion of the net count rates into fluxes was made identical. Since both of these narrow fines are believed to origi- by comparing measurements of two or three standard stars nate from the same region and, in any case, their profiles are each night to their “AB79” magnitudes, from Oke & Gunn dominated by instrumental resolution, this assumption is ( 1984). However, since many of the nights were not photomet- most likely valid. The subtraction is accomplished by scaling ric, the absolute flux levels are not in general reliable. The down [O m] X5007 until it matches the narrow component in spectra were normalized (as is commonly done) by assuming intensity and yields the smoothest remaining broad-fine pro- that the intrinsic [O m] X5007 fine flux remained constant over file.

UT Julian NGC NGC NGC NGC NGC NGC NGC NGC NGC Mrk Mrk Mrk Mrk Mrk Mrk Date Day3 1068 1275 3227 3516 4051 5548 6814 7469 7603 3 6 79 290 335 509 a 1979 Mar 3 .. 3938 1979 Mar 4 .. 3939 1979 Mar 5 .. 3940 1979 Mar 6 .. 3941 1979 May 30 . 4023 1979 May 31 . 4024 1979 Jun 1 ... 4025 1979 Jun2 ... 4026 1979 Jul 1 ... 4055 1979 Jul 2 4056 1979 Aug 16.. 4101 1979 Aug 17 . 4102 1979 Aug 20 . 4105 1979 Aug 21 . 4106 1979 Nov 22 . 4199 1979 Nov 24 . 4201 1979 Dec 24 . 4230 1980 Mar 14 . 4312 1980 Mar 15 . 4313 1980 Mar 16 . 4314 1980 Jun 13 . 4403 1980 Jun 14 . 4404 1980 Jun 16 . 4406 1980 Jun 17 . 4407 1980 Sep 15 .. 4497 1980 Sep 16 .. 4498 1980 Sep 17.. 4499 1981 Feb 27 . 4662 1981 Feb 28 . 4663 1981 Apr 4 .. 4698 1981 May 30. 4754 1981 Aug 5 .. 4821 1981 Aug 7 .. 4823 1981 Nov 3 .. 4911 1981 Nov 15 . 4923 1981 Nov 16 . 4924 1981 Nov 21 . 4929 1981 Nov 23 . 4931 1982 Feb 13 . 5013 1982 Feb 14 . 5014 1982 Feb 17 . 5017 1982 Feb 18 . 5018 1982 May 17 . 5106 1982 May 18 . 5107 1982 Jul 15 .. 5165 1982 Jul 16 .. 5166 1982 Jul 17 .. 5167 1982 Jul 18 .. 5168 1982 Sep 24.. 5236 1982 Sep 28.. 5240 1982 Sep 30.. 5242 1982 Nov 22 . 5295 1982 Nov 24 . 5297 1984b Jan 27 . 5726 1984b Feb 24 . 5754 1984b Mar 7 . 5765 1984b Apr 22 5811 1984b Jun 6 .. 5857 1984b Oct 13 . 5986 a Julian Day (+2,440,000). b Observations in 1984 were made with the 90" telescope at Steward Observatory. All other observations were made with the 60" telescope at Palomar Observatory.

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!PC LO 62 ROSENBLATT ET AL. Vol. 81 œ Hß and [O m] X5007 are each contaminated by a member of the Fe n multiplet 42 group, X4924 and X5018, respectively, o Without the removal of this Fe n contamination, Hß would S' appear to have some excess red line flux, and thus a red asym- gi metry could erroneously be measured. To remove Fe n con- ^ tamination, the methodology of De Robertis (1985) was adopted, as well as his determinations of Fe n to broad Hß Une flux ratios. The method assumes that the profiles of Hß and Fe n XX4924, 5018 resemble one another and that the intensities of Fe n X4924 and X5018 are equal. After estimating the fine strength of Fe n XX4924, 5018 from other multiplet 42 members (estimates taken from De Robertis 1985), Hß was scaled down to the appropriate intensity and subtracted off at the proper wavelengths. The continua of AGNs include stellar and nonstellar compo- nents. To measure only the nonstellar continuum requires that the starhght first be subtracted. This is also required because stellar absorption features may alter measured broad-fine profiles (Crenshaw & Peterson 1985). Since the present data lack Fig. 1.—Portion of an uncorrected spectrum of Mrk 79 centered on Hß the resolution and signal-to-noise ratios required to measure and [O m] (in the redshifted frame) observed on 1982 February 14 (solid weak stellar absorption features accurately, estimated stellar line). Narrow Hß was subtracted using a scaled-down [O m] X5007 profile. Fe il XX4924, 5018 were removed from Hß and [O m] X5007, respectively, by subtracting off a scaled Hß template at the appropriate wavelengths. The dashed line shows the resulting spectrum after narrow Hß and Fe n TABLE 2 subtraction. Spectral Corrections

Starlight continuum flux densities were taken from the literature when Object F(Fe n/Hß) ,F(HßN/X5007) (mJy) F(X5007) (1) (2) (3) (4) (5) available (e.g., Malkan & Filippenko 1983). It is assumed that the stellar population in the present sample of AGNs has the NGC 1068 . 200b same spectrum as the SO galaxy IC 4889. The template galaxy NGC 1275 . 6.0 spectrum (kindly supplied by A. V. Filippenko) was scaled to NGC 3227 . 0C 0.088d 2e 7.0 NGC 3516. 0.025c a 6f 3.0 the appropriate starhght flux density for each spectrum and NGC 4051 . 0C a 3C 4.0 then subtracted. NGC 5548 . 0.05c 0.11 ±0.02g Ie 4.4g Data for NGC 3227, NGC 3516, NGC 6814, and NGC 7603 a a h NGC 6814. l 1.5 were smoothed with a Hanning function (a binomial distribu- NGC 7469 . 0.015c 0.226i 4.3e 6.0 h tion spanning 3 pixels) to reduce the relative amplitude of NGC 7603 . l 0.7 Mrk 3 37b noise. This procedure was found not to affect fine flux or pro- Mrk 6 0.08 ±0.01 7.0j file measurements significantly. Mrk 79 .... 0.07c 0.097 ± 0.006 3.0 a Table 2 summarizes the corrections applied to each galaxy. Mrk 290 ... 0.098 ± 0.008 2.3 Figure 1 compares an uncorrected and corrected spectrum of Mrk 335 ... 0.09c 2.0 Mrk 509 ... 0.08c 7.0 Mrk 79. As shown, Fe n corrections have little effect on Hß line fluxes or profiles [the largest value of F(¥q n)/F(Hß) for any of Col. (1).—Object name. the galaxies in the present sample is only 10%, for Mrk 335]. Col. (2).—Fe n to Hß line flux ratio used to subtract Fe h XX4924,5018. However, narrow Hß is relatively strong in some of the objects, Col. (3).—Narrow Hß to [O m] X5007 line flux ratio used to subtract and thus subtraction of this component is required to obtain narrow Hß. Col. (4).—Stellar continuum flux density in mJy within a 5" circular accurate broad-line flux and profile measurements. Starhght aperture at 4900 Á used to subtract starlight. subtraction can also affect hne flux and equivalent width mea- Col. (5).—Spectra scaled by [O m] X5007 integrated Une flux in units of surements if the stellar fraction is large. However, except for 13 -1 -2 1 X 10“ ergs s cm taken from de Bruyn & Sargent 1989, (private NGC 3516, NGC 7469, and Mrk 6, the stellar fraction is less communication) unless stated otherwise. a Estimate not available or correction not necessary. than ~25%. b Due to saturated [O m] X5007, spectra were scaled using F(X4959) from de Bruyn, Sargent, & Readhead 1982. 4. ERROR ANALYSIS c De Robertis 1985. d Cohen 1983. Crucial to any variability study is an accurate estimate of e Malkan & Filippenko 1983. observational and measurement errors. Line flux and equiva- f Crenshaw & Peterson 1985. g lent width error estimates were obtained from two Seyfert 2 This paper and Peterson 1987. galaxies, NGC 1068 and Mrk 3. The emission hnes of Seyfert 2 h de Bruyn & Sargent 1989 (private communication). 1 Narrow Hß not subtracted in NGC 7469. Value from Cohen 1983 galaxies arise from a narrow-hne region of order 100 pc in size given for completeness. or greater, so that hne intensities and profiles are expected to j Malkan & Oke 1983. remain constant for a time interval much longer than our

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!PC LO No. 1, 1992 LINE AND CONTINUUM VARIATIONS OF SEYFERT GALAXIES 63 ï—I 00 TABLE 3A Seyfert 2 Emission-Line Measurements: NGC 1068 a Julian CM CO UT Date Day F(Hß/X4959) EW(Hß/X4959) F(H7/X4959) F(He H/X4959) CO (1) (2) (3) (4) (5) (6) 1979 Jul 3 ... 4056 0.266 0.249 0.181 0.072 1979 Aug 21 . 4106 0.281 0.279 0.203 0.106 1979 Nov 22 . 4199 0.267 0.256 0.166 0.090 1979 Dec 24 . 4231 0.280 0.251 0.160 0.061 1980 Mar 15 . 4313 0.237 0.231 0.197 0.080 1980 Sep 15 . 4497 0.318 0.294 0.103 0.045 1981 Aug 5 .. 4821 0.265 0.269 0.161 0.071 1981 Nov 16 . 4924 0.248 0.238 a a 1981 Nov 21 . 4929 0.184 0.188 0.134 0.073 1982 Feb 14 . 5014 0.237 0.222 a a 1982 Jul 17 .. 5167 0.261 0.264 0.149 0.067 1982 Sep 24 . 5236 0.233 0.232 0.156 0.065 1982 Nov 22 . 5295 0.210 0.212 0.125 0.076 Col. (1).—Date of observation. Col. (2).—Julian Day (+2,440,000). Col. (3).—Hß to [O in] X4959 flux ratio. Col. (4).—Hß to [O ni] X4959 equivalent width ratio. Col. (5).—Hy to [O m] X4959 flux ratio. Col. (6).—He il X4686 to [O m] X4959 flux ratio. a H7 and He n X4686 are not included in these high-resolution spectra.

monitoring period (e.g., Oke, Sargent, & Readhead 1980). ments owing to such observational factors as seeing and slit Thus, Seyfert 2 galaxies provide an accurate and reliable esti- placement. And yet, even with these possible sources of error, 1 mate of the uncertainties associated with the entire process of a uncertainties for NGC 1068 and Mrk 3 were still 10%. In any data collection from observing, reducing, and measuring emis- case, the stellar fraction for most of the Seyfert 1 galaxies in the sion-hne and continuum strengths. present sample (^20%) is much less than in Seyfert 2 galaxies. Thirteen observations of NGC 1068 and eight of Mrk 3 were Only three of the Seyfert 1 galaxies (NGC 3516, NGC 7469, made during the same period as the remainder of the sample, and Mrk 6) have relatively large stellar contributions (—40%), using the identical setup and reduction procedure previously although these are still significantly less than for NGC 1068 described. However, because of the relative weakness of Hß in and Mrk 3. In addition, our slit size of 4" X 20,' was sufficiently these objects, [O m] A5007 was allowed to saturate, using large to observe the entire nuclear region of the Seyfert 1 galax- longer integrations to raise the signal-to-noise ratio of the other ies. Thus, such factors as seeing and slit placement should have narrow lines. Therefore, [O m] X4959 instead of X5007 was little or no effect on continuum measurements. used to estimate line flux and continuum measurement uncer- On the other hand, the relatively narrow emission fines of tainties. Seyfert 2 galaxies are easier to measure than the broad fines The measurement of line flux and equivalent width depends found in Seyfert 1 galaxies. Thus, in this sense Seyfert 2 galax- sensitively on the adopted continuum baseline. The local con- ies do not provide a complete test of emission-line measure- tinuum was represented as a straight line and, in order to better estimate measurement uncertainties, an average of three independent measurements for each emission Une was taken. H7, TABLE 3B Hß, and [O m] X4959 were measured for NGC 1068, and the Seyfert 2 Emission-Line Measurements: Marrarían 3 latter two emission lines were measured for Mrk 3 (see Tables 3 A and 3B). The resulting 1 a standard deviation values of line UT Date Julian Day T(Hß/X4959) EW(Hß/X4959) fluxes and equivalent width ratios for Hß and H7 (normalized (1) (2) (3) (4) by [O m] X4959) are 10% and 12%, respectively, for NGC 1979 Mar 3 3938 0.241 0.206 1068, while the uncertainty in Hß for Mrk 3 is 9% (see Figs. 2a 1979 Aug 16 4101 0.236 0.246 and 2b). Thus, 1 a line flux and equivalent width measurement 1979 Nov 24 4201 0.226 0.227 1979 Dec 23 4230 0.231 0.207 error values of 10% and 12% were adopted for Hß and H7, 1980 Mar 15 4313 0.232 0.225 respectively. The 1

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!PC LO 64 ROSENBLATT ET AL. Vol. 81 ï—I 00 ment stability. However, strong evidence that the above estimates are in fact accurate comes from measurements of the h) emission lines of the Seyfert 1 galaxy Mrk 335 and the Seyfert a CM 1.5 galaxies NGC 1275 and NGC 4051. The latter two galaxies CO have strong narrow lines superposed on a broad base, while Mrk 335 has strong permitted emission lines which are comparable in width to those of the other Seyfert 1 galaxies in the present sample. Thus, the emission Unes of these three galaxies (certainly Mrk 335) should be as difficult to measure as other Seyfert 1 emission lines. However, as will be shown in § 5, these three galaxies did not show any significant evidence for emission-fine variability. The fact that the rms scatter in fine flux measurements for these three galaxies is comparable to that for NGC 1068 and Mrk 3 indicates that the broad fines are not substantially more difficult to measure than the narrow fines of Seyfert 2 galaxies. The above error estimates of course depend on the signal-to- noise ratio of the particular spectrum being measured. Since galaxies in the present sample with relatively weak continua and Hß fluxes, such as NGC 6814 and NGC 7603, had lower signal-to-noise ratios, their measurement uncertainties may be larger. However, continuum and Hß 1 a errors probably do not exceed 15% in these cases. This estimate is consistent with the value given by Tohline & Osterbrock (1976) for comparable signal-to-noise spectra of NGC 7603.

5. CONTINUUM AND EMISSION-LINE INTENSITY VARIATIONS 5.1. Line Flux and Continuum Measurements Fig. 2a The major results of this variability study are summarized in Table 4. Column (1) gives the object name. Columns (2), (3), and (4) present the mean continuum, Hß, and H7 (when observed) fluxes, respectively, together with their measured 1 a rms scatter (not the 1 a uncertainties which are estimated in § 4 from NGC 1068 and Mrk 3 measurements). Continuum fluxes are in units of 10“13 ergs s“1 cm-2 Á-1, while Balmer-fine fluxes are given in units of 10-13 ergs s-1 cm-2. As a measure of an object’s variability strength, columns (5), (6), and (7) fist the 1 a rms scatter normalized by the corresponding continuum, Hß, and H7 mean flux levels, respectively, for each object. Columns (8), (9), and (10) fist the largest variation (fisted as a percentage change) that was observed between consecutive or nearly consecutive observations for the continuum, Hß, and H7, respectively. Note that consecutive observations are separated by weeks to months in most cases. Columns (11), (12), and (13) present the peak-to-peak variations (again fisted as a percentage change) for the continuum, Hß, and H7, respectively. Columns (14), (15), and (16) fist the probabilities (as given by F-tests) that the continuum, Hß, and H7, respectively, varied significantly. These tests are described in detail in 4000 4500 5000 § 5.2. Last, column (17) gives an estimate of the variability JD (+2,440,000) strength of each galaxy (this will be discussed in detail in § 5.3). Fig. 2b Individual flux measurements for each galaxy are given in Fig. 2.—(a) Light curves for NGC 1068 show 1 a rms scatter of 10%, Tables 5-17, and fight curves are presented in Figures 3-15. 11%, and 14% for continuum, Hß, and H7 measurements, respectively. Optical continuum flux densities were assumed equal to the Continuum flux densities are given in units of 1 X 10-13 ergs s-1 cm-2 Â-1, -13 -1 -2 inverse of [O m] X5007 equivalent widths (measured in star- while Hß and H7 line fluxes are given in units of 1 X 10 ergs s cm , (b) fight-subtracted spectra when appropriate) multiplied by a Light-curve data for Mrk 3 yield 1 a rms scatter of 10% and 9% for continuum and Hß measurements, respectively. Continuum flux densities are constant X5007 fine flux. All Hß fine flux and equivalent width given in units of 1 X 10“13 ergs s-1 cm-2 A-1, while Hß and H7 fluxes are values refer to measurements made on fully corrected spectra given in units of 1 X 10“13 ergs s-1 cm-2. (see § 3).

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American Astronomical Society Provided by the NASA Astrophysics Data System TABLES NGC 1275 Emission-Line and Continuum Measurements

-1 UT Date Julian Day nm FX(cont) (EW À5007) F(Hß/X5001) EW(Hj8/X5007) (2) (3) (4) (5) (6) (7) a (1) 1979 Mar 3 . 3938 1.55 0.141 -0.023 0.26 0.25 1979 Aug 17 , 4102 1.71 0.169 -0.027 0.28 0.28 1979 Aug 20 . 4105 1.75 0.180 -0.029 0.28 0.28 1979 Nov 24 . 4201 1.35 0.122 -0.020 0.22 0.21 1979 Dec 24 . 4230 1.33 0.089 -0.015 0.22 0.21 1980 Mar 15 , 4313 1.52 0.071 -0.012 0.25 0.24 1980 Sep 15 . 4497 1.35 0.131 -0.026 0.23 0.23 1981 Feb 27 . 4662 1.60 0.104 -0.017 0.26 0.25 1981 Nov 21 . 4929 1.55 0.119 -0.020 0.26 0.28 1982 Feb 13 . 5013 1.24 0.125 -0.021 0.21 0.21 1982 Sep 28 . 5240 1.30 0.123 -0.021 0.22 0.22 1982 Nov 22 . 5295 1.45 0.126 -0.021 0.24 0.24 Col. (1).—Date of observation. Col. (2).—Julian Day (+2,440,000). Col. (3).—Hß line flux in 10-13 ergs s" 1 cm 2 scaled assuming a constant [O m] X5007 line flux of 6.0 X 10 13 ergs s Col. (4).—Nonstellar continuum flux density at 5000 Â in 10"13 ergs s-1 cm-2 À” scaled assuming a constant [O m] X5007 line flux as listed in col. (5) of Table 2. Col. (5).—Inverse [O m] X5007 equivalent width in Á" indicative of the nonstellar continuum level. Col. (6).—Hß to [O m] X5007 flux ratio. Col. (7).—Hß to [O m] X5007 equivalent width ratio.

TABLE 6 NGC 3227 Emission-Line and Continuum Measurements

UT Date Julian Day F(m FX (EW X5007)- F(Hß/X5001) EW(H0/X5OO7) Fs/Ft (1) (2) (3) (4) (5) (6) (7) (8) 1979 Mar 4.. 3939 3.09 0.081 -0.012 0.44 0.43 0.23 1979 May 31 4024 3.03 0.060 -0.009 0.43 0.38 0.27 1979 Jul 3 .. 4056 4.05 0.082 -0.012 0.58 0.55 0.23 1979 Nov 22 4199 3.52 0.079 -0.011 0.50 0.47 0.23 1980 Mar 14 4312 2.83 0.059 -0.008 0.40 0.40 0.30 1980 Jun 17 4407 4.44 0.080 -0.011 0.63 0.54 0.22 1981 Apr 4 . 4698 2.25 0.085 -0.012 0.32 0.30 0.16 1981 Nov 15 4923 2.90 0.128 -0.018 0.41 0.40 0.17 1981 Nov 21 4929 2.86 0.129 -0.018 0.41 0.43 0.12 1982 Feb 17 5017 4.73 0.169 -0.024 0.68 0.66 0.15 1982 May 17 5106 4.42 0.141 -0.020 0.63 0.65 0.20 Note.—Col. (8) gives the ratio of stellar to total continuum level within a 5" circular aperture at 4900 Â. See Table 5 for definitions of other measurements.

TABLE 7 NGC 3516 Emission-Line and Continuum Measurements

1 UT Date Julian Day F(Hß) (EW X5007)" F(HjS/X5007) Fs/Ft (1) (2) (3) (4) (5) (6) (7) 1979 Mar 3 . 3938 3.83 0.051 -0.017 1.28 0.59 1979 May 31 4024 3.70 0.112 -0.037 1.23 0.40 1979 Jul3 ... 4056 5.24 0.072 -0.024 1.75 0.46 1979 Nov 24 4201 5.15 0.089 -0.030 1.72 0.45 1980 Mar 14 4312 5.17 0.053 -0.018 1.72 0.63 1980 Jun 16 . 4406 2.90 0.050 -0.017 0.97 0.57 1981 Feb 28 . 4663 2.83 0.071 -0.024 0.94 0.24 1981 Nov 23 4931 6.79 0.230 -0.077 2.26 0.32 1982 Feb 13 . 5013 4.65 0.181 -0.060 1.55 0.29 1982 May 17 5106 7.90 0.178 -0.059 2.63 0.29 1982 Jul 16 . 5166 8.02 0.166 -0.055 2.67 0.34 1982 Jul 18 . 5168 5.89 0.139 -0.046 1.96 0.35 1982 Sep 28 . 5240 7.43 0.141 -0.047 2.48 0.33 1982 Nov 24 5297 7.05 0.173 -0.058 2.35 0.61 Note.—See Tables 5 and 6 for definitions of measurements. 66

-1 UT date Julian Day mß) (EW X5007) F(Hß/\5007) EW(Hj9/X5007) Fs/Ft (2) (3) (4) (5) (6) (7) (8) a (1) 1979 Mar 4 ., 3939 2.44 0.061 -0.015 0.62 0.60 0.39 1979 Jun 1 .. 4025 3.34 0.063 -0.016 0.85 0.78 0.36 1979 Jul 3 .. 4057 3.93 0.063 -0.016 1.01 0.98 0.38 1979 Aug 21 , 4106 3.32 0.095 -0.022 0.77 0.70 0.26 1979 Nov 24 , 4201 2.97 0.068 -0.017 0.76 0.71 0.35 1980 Mar 14 . 4312 2.90 0.040 -0.010 0.73 0.64 0.47 1980 Jun 13 4403 2.94 0.065 -0.017 0.75 0.59 0.33 1981 Apr 4 . 4698 3.40 0.082 -0.021 0.88 0.84 0.32 1982 Feb 18 . 5018 3.98 0.159 -0.040 1.01 1.04 0.20 1982 May 18 , 5107 3.37 0.107 -0.027 0.85 0.92 0.28 1982 Jul 17 . 5167 4.10 0.113 -0.029 1.04 1.08 0.26 1982 Nov 24 . 5297 4.09 0.129 -0.032 1.03 1.10 0.24 1984 Mar 7 ., 5765 3.67 0.083 -0.022 0.97 0.93 0.31 Note.—See Tables 5 and 6 for definitions of measurements.

TABLE 9 NGC 5548 Emission-Line and Continuum Measurements

a UT Date Julian Day mß) (EW X5007)" jF(Hß/X5007) EW(Hj6/X5007) ^H7) Fs/Ft (1) (2) (3) (4) (5) (6) (7) (8) (9) 1979 Mar 6 . 3941 4.02 0.028 -0.006 0.91 0.77 1.58 0.11 1979 May 30 4023 6.47 0.078 -0.018 1.47 1.22 2.64 0.10 1979 Jul 2... 4055 6.71 0.068 -0.016 1.55 1.35 2.76 0.11 1979 Aug 16 4101 6.48 0.082 -0.018 1.46 1.38 2.73 0.12 1980 Mar 15 4313 5.13 0.071 -0.016 1.16 1.06 2.15 0.10 1980 Jun 14 . 4404 7.06 0.092 -0.021 1.61 1.47 2.52 0.09 1981 Feb 27 . 4662 4.20 0.066 -0.015 0.96 0.96 1.94 0.17 1981 Apr 4 .. 4698 4.52 0.072 -0.016 1.02 0.94 2.67 0.15 1981 May 30 4754 5.86 0.065 -0.015 1.33 1.21 2.61 0.22 1981 Aug 5 . 4821 5.44 0.088 -0.020 1.25 1.29 1.95 0.14 1982 Feb 17 . 5017 5.39 0.101 -0.023 1.24 1.18 b 0.07 1982 May 17 5106 6.89 0.140 -0.032 1.59 1.61 2.73 0.07 1982 Jul 15 . 5165 7.37 0.130 -0.030 1.70 1.70 2.97 0.07 1982 Jul 18 . 5168 7.86 0.110 -0.025 1.79 1.71 b 0.11 1984 Feb 24 . 5754 7.01 0.094 -0.022 1.61 1.47 3.18 0.12 1984 Jun 6 .. 5857 7.39 0.088 -0.020 1.71 1.65 3.82 0.12 Note.—See Tables 5 and 6 for definitions of measurements. a Due to Hg il X4358 skyline contamination, H line fluxes were underestimated by ~ 15%. b 7 H7 was not included in this high-resolution spectrum.

TABLE 10 NGC 6814 Emission-Line and Continuum Measurements

UT Date Julian Day FHß ^A (EW X5007)" F(Hß/\5007) EW(H/6/X5007) Fs/F, (1) (2) (3) (4) (5) (6) (7) (8) 1979 May 30 4023 0.85 0.040 -0.27 0.56 0.53 0.24 1979 Jul4 ... 4057 1.83 0.046 -0.031 1.22 1.13 0.21 1979 Aug 20 . 4105 0.91 0.046 -0.031 0.61 0.62 0.23 1980 Jun 13 . 4403 1.39 0.032 -0.021 0.92 0.89 0.28 1980 Sep 16 . 4498 1.75 0.051 -0.034 1.16 1.14 0.20 1981 Aug 5 .. 4821 2.87 0.110 -0.073 1.91 2.03 0.10 1982 May 18 5107 1.82 0.076 -0.050 1.21 1.31 0.16 1982 Jul 15 .. 5165 1.73 0.116 -0.077 1.15 1.25 0.11 1982 Jul 17 .. 5167 2.38 0.153 -0.102 1.58 1.64 0.08 1982 Sep 28 . 5240 2.13 0.091 -0.060 1.42 1.55 0.14 Note.—See Tables 5 and 6 for definitions of measurements. 67

i UT Date Julian Day m¡3) (EW X5007)- il(HiS/X5007) EW(H/8/X5007) ^H7) Fs/V a (1) (2) (3) (4) (5) (6) (7) (8) (9) CM CO 1979 May 31 4024 8.48 0.111 -0.018 1.41 1.32 3.54 0.32 CO 1979 Jul 3 ... 4056 8.96 0.114 -0.019 1.49 1.28 4.96 0.29 1979 Nov 22 4199 7.98 0.123 -0.020 1.33 1.31 3.64 0.29 1980 Jun 16 . 4406 8.51 0.109 -0.018 1.42 1.42 3.30 0.33 1980 Sep 15 . 4497 8.18 0.086 -0.014 1.36 1.22 4.86 0.36 1981 May 30 4754 7.90 0.083 -0.014 1.32 1.23 4.14 0.39 1981 Nov 3 . 4911 6.15 0.088 -0.015 1.02 0.99 2.65 0.38 1981 Nov 15 4923 5.60 0.099 -0.016 0.93 0.95 3.20 0.36 1981 Nov 21 4929 6.17 0.080 -0.013 1.03 1.07 2.36 0.39 1982 Jul 15 . 5165 7.42 0.159 -0.026 1.24 1.25 3.66 0.25 1982 Jul 17 . 5167 7.74 0.157 -0.026 1.29 1.27 3.78 0.25 1982 Jul 18 . 5168 7.60 0.135 -0.022 1.27 1.21 a 0.27 1982 Sep 28 . 5240 7.16 0.120 -0.020 1.19 1.26 3.72 0.33 1982 Nov 22 5295 8.48 0.178 -0.030 1.41 1.42 4.07 0.23 1984 Oct 13 . 5986 10.14 0.134 -0.022 1.68 1.52 4.73 0.27

aNote.—See Tables 5 and 6 for definitions of measurements. H7 was not included in this high-resolution spectrum. TABLE 12 NGC 7603 Emission-Line and Continuum Measurements

UT Date Julian Day mß) FX (EW X5007)- jFT(Hß/X5007) EW(Hß/X5007) Fs/Ft (1) (2) (3) (4) (5) (6) (7) (8) 1979 Jun 2 .. 4026 1.58 0.041 -0.058 2.25 1.92 0.24 1979 Aug 21 . 4106 1.50 0.049 -0.071 2.14 2.12 0.20 1980 Jun 16 . 4406 0.77 0.034 -0.048 1.10 1.09 0.26 1980 Sep 17 . 4499 1.56 0.051 -0.073 2.23 2.03 0.20 1981 Aug 5 .. 4821 1.35 0.061 -0.087 1.93 2.07 0.18 1982 Jul 16 .. 5166 0.97 0.069 -0.099 1.38 1.50 0.16 1982 Jul 17 .. 5167 0.89 0.068 -0.096 1.26 1.35 0.16 1982 Sep 24 . 5236 1.02 0.062 -0.088 1.46 1.56 0.18 1982 Nov 22 . 5295 1.23 0.070 -0.100 1.75 1.89 0.16 Note.—See Tables 5 and 6 for definitions of measurements. TABLE 13 Marrarían 6 Emission-Line and Continuum Measurements

UT Date Julian Day mß) (EW X5007)“ mß/^007) EW(Hi0/X5OO7) Fs/F, (1) (2) (3) (4) (5) (6) (7) (8) 1979 Aug 20 . 4105 2.50 0.031 -0.004 0.36 0.36 0.30 1979 Dec 23 . 4230 2.36 0.011 -0.002 0.34 0.28 0.53 1980 Mar 16 . 4314 1.61 0.008 -0.001 0.23 0.19 0.57 1980 Sep 15 . 4497 2.43 0.027 -0.004 0.35 0.34 0.32 1981 Feb 28 . 4663 1.27 0.016 -0.002 0.18 0.18 0.48 1981 Nov 3 .. 4911 1.44 0.026 -0.004 0.21 0.20 0.35 1981 Nov 23 . 4931 1.59 0.046 -0.007 0.23 0.26 0.25 1982 Sep 24 . 5236 2.08 0.035 -0.005 0.30 0.32 0.29 Note.—See Tables 5 and 6 for definitions of measurements. TABLE 14 Marrarían 79 Emission-Line and Continuum Measurements UT Date Julian Day mß) (EW X5007)- Fl(Hj3/X5007) EW(H0/X5OO7) (1) (2) (3) (4) (5) (6) (7) (8) 1979 Mar 5 .. 3940 3.52 0.031 -0.010 1.17 1.00 1.43 1979 Nov 22 , 4199 3.49 0.038 -0.013 1.17 1.11 1.29 1980 Mar 16 . 4314 3.76 0.035 -0.012 1.25 1.08 2.11 1980 Sep 17. 4499 3.46 0.038 -0.013 1.15 1.07 1.97 1981 Feb 28 4663 3.23 0.045 -0.015 1.07 1.04 1.78 1981 Nov 3 .. 4911 4.17 0.067 -0.022 1.39 1.33 2.00 1981 Nov 21 . 4929 4.78 0.055 -0.018 1.59 1.67 1.91 1982 Feb 14 . 5014 3.40 0.057 -0.019 1.13 1.12 1982 Sep 30.. 5242 4.79 0.068 -0.022 1.58 1.52 1982 Nov 24 . 5297 5.85 0.080 -0.027 1.95 1.98 2.28

aNote.—See Tables 5 and 6 for definitions of measurements. H7 was not included in these high-resolution spectra. 68

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!PC LO TABLE 15 Marrarían 290 Emission-Line and Continuum Measurements UT Date Julian Day me) (EW Â5007)- Ei(H0/X5OO7) EW(Hß/A5007) a (1) (2) (3) (4) (5) (6) (7) (8) COCM 1979 Mar 5 .. 3940 2.56 0.019 -0.008 1.11 0.85 1.47 CO 1979 Jun 2 .. 4026 2.38 0.030 -0.013 1.03 0.89 1.49 1979 Jul 3 ... 4056 2.56 0.024 -0.010 1.11 0.95 1.56 1979 Aug 21 . 4106 2.42 0.031 -0.013 1.05 0.98 1.37 1980 Jun 13 . 4403 2.64 0.027 -0.012 1.15 1.04 1.50 1980 Jun 16 . 4406 1.98 0.019 -0.008 0.87 0.86 1.28 1980 Sep 16 . 4498 2.35 0.039 -0.017 1.02 0.99 1.93 1982 Feb 18 . 5018 3.00 0.054 -0.024 1.31 1.29 1.63 1982 May 17 5106 2.97 0.044 -0.019 1.29 1.30 1.50 1982 May 18 5107 2.91 0.041 -0.018 1.26 1.23 1.51 1982 Jul 16 .. 5166 3.68 0.053 -0.023 1.60 1.61 1.80 1984 Jan 27 . 5726 2.52 0.032 -0.014 1.11 1.01 1.64 1984 Feb 24 . 5754 2.76 0.036 -0.016 1.20 1.14 1.57 1984 Apr 22 . 5812 2.59 0.033 -0.014 1.12 1.03 1.62 1984 Jun 6 .. 5857 2.86 0.036 -0.016 1.25 1.17 1.76 Note.—See Tables 5 and 6 for definitions of measurements.

TABLE 16 Marrarían 335 Emission-Line and Continuum Measurements UT Date Julian Day me) (EW A5007)- Fl(H/3/A5007) EW(H/?/A5007) my) (1) (2) (3) (4) (5) (6) (7) (8) 1979 Jun 1 .. 4025 9.23 0.104 -0.052 4.58 4.16 4.87 1979 Jul 2 ... 4055 10.56 0.134 -0.068 5.34 4.87 6.24 1979 Aug 17 . 4102 10.11 0.123 -0.062 4.82 4.66 6.50 1979 Nov 24 . 4201 8.87 0.114 -0.056 4.39 4.07 4.26 1979 Dec 23 . 4230 9.67 0.075 -0.037 4.74 4.07 4.59 1980 Sep 15 . 4497 6.83 0.067 -0.034 3.49 3.19 4.09 1981 Nov 3 .. 4911 8.59 0.094 —0.047 4.30 4.07 4.30 1981 Nov 21 . 4929 8.04 0.092 -0.045 3.95 4.10 3.44 1982 Jul 15 .. 5165 8.08 0.094 -0.048 4.10 4.18 3.61 1982 Sep 28 . 5240 7.62 0.078 -0.039 3.82 3.77 3.96 1982 Sep 30 . 5242 8.79 0.104 -0.053 4.51 4.55 a 1984 Mar 7 .. 5726 7.87 0.076 -0.038 3.94 3.85 4.19 1984 Feb 24 . 5754 10.08 0.085 -0.043 5.04 4.77 5.04 1984 Jun 6 .. 5857 7.30 0.080 -0.040 3.65 3.53 4.05 1984 Oct 13 . 5986 8.89 0.102 -0.051 4.44 3.95 5.05 Note.—See Tables 5 and 6 for definitions of measurements. a H7 was not included in this high-resolution spectrum.

TABLE 17 Marrarían 509 Emission-Line and Continuum Measurements

UT Date Julian Day F(Hß) (EW A5007)- F(H/3/\5007) EW(H0/A5OO7) fth7) (1) (2) (3) (4) (5) (6) (7) (8) 1979 Jun 1 .. 4025 12.26 0.095 -0.013 1.74 1.53 5.31 1979 Jul 2... 4055 11.88 0.108 -0.015 1.70 1.56 5.99 1979 Aug 16 4101 10.77 0.107 -0.016 1.56 1.52 5.03 1979 Nov 24 4201 9.34 0.107 -0.036 4.12 4.01 3.31 1980 Jun 13 . 4403 9.93 0.073 -0.011 1.42 1.14 7.00a 1980 Sep 15 . 4497 9.23 0.105 -0.015 1.33 1.27 3.01 1981 May 30 4754 14.69 0.115 -0.017 2.12 2.00 7.47 1981 Aug 7 . 4823 12.08 0.104 -0.015 1.71 1.65 4.43 1981 Nov 3 . 4911 12.66 0.117 -0.017 1.81 1.77 5.62 1981 Nov 21 4929 11.09 0.116 -0.017 1.60 1.69 3.73 1982 May 18 , 5107 11.20 0.121 -0.017 1.61 1.67 4.58 1982 Jul 15 . 5165 11.83 0.144 -0.021 1.72 1.76 4.68 1982 Jul 18 . 5168 12.31 0.166 -0.023 1.71 1.81 b 1984 Jun 6 .. 5857 20.77 0.190 -0.027 2.97 2.86 9.19 1984 Oct 13 . 5986 15.57 0.125 -0.018 2.22 2.00 7.64 Note.—See Tables 5 and 6 for definitions of measurements. a Measurement uncertainties may be considerably larger than 20% due to [O m] A5007 situated at the extreme red limit of this spectrum. b H7 was not included in this high-resolution spectrum. 69

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'! LO : 70 ROSENBLATT ET AL. tions were in fact detected. Because of lower signal-to-noise ratios, 1 a uncertainties of 15% were used in the F-tests for NGC 3227, NGC 3516, NGC 6814, and NGC 7603, rather than the lower Seyfert 2 measurement uncertainties.

5.3. An Estimate of the Likelihood of Detecting Variations Since this study lacks high temporal sampling, we cannot rule out the possibility of variations occurring in between our observations. However, we can set useful upper limits on the intrinsic variability strength of our sample by comparing the present data with observations obtained for NGC 5548 (Peter- son et al. 1991 a). These 129 observations obtained during an 8 month period provide the best sampled Hß and optical continuum light curves of any Seyfert galaxy available to date. By assuming that these light curves represent the variability power spectrum of Seyfert galaxies in general, the probability of detecting significant variations given the temporal sampling for each of the present galaxies can be determined. This was done for Hß by superposing the sampling of each galaxy onto the Hß light curve of NGC 5548 and then using an F-test to compute the probability that variations occurred. In this simulation the light curve of NGC 5548 was extended (by repetition) to match the 5 yr monitoring period of our data set. For comparison with the NGC 5548 rms scatter, measurement uncertainties of 10% for high signal-to-noise data and 15% for galaxies with lower signal-to-noise data were used (i.e., NGC 3227, NGC 3516, NGC 6814, and NGC 7603). 4000 4200 4400 4600 4800 5000 5200 Since our monitoring could have begun at any point on the JD (+2,440,000) Fig. 3 Figs. 3-15.—Light curves of the 13 Seyfert 1 galaxies in the present sample for the optical continuum (in units of 1 X 10"13 ergs s-1 cm-2 Â”1) and Bahner Unes (i.e., Hß and in some cases H7, in units of 1 X 1CT13 ergs s_1 cm-2).

Hy line fluxes were measured only for those galaxies with ^ relatively high signal-to-noise data (NGC 5548, NGC 7469, Mrk 79, Mrk 290, Mrk 335, and Mrk 509). However, with the exception of NGC 5548 (Rosenblatt & Malkan 1990), these line fluxes were not corrected for narrow Hy, [O m] X4363 blending, Fe n emission, or starlight.

5.2. Probability of Balmer-Line and Continuum Variability To determine objectively whether or not variations were in fact detected, an F-test was apphed to Balmer-line and continuum measurements. This test compares the variances and number of data points of two samples to determine at some confidence level whether the two are drawn from the same — parent population. Variances for Balmer-line and continuum 5, measurements for each galaxy (normalized by their mean flux ^ level) were compared with the corresponding measurement uncertainties found from NGC 1068 and Mrk 3 data (see § 4). Columns (14), (15), and (16) of Table 4 list the probabilities that the variances of continuum, Hß, and Hy flux measurements, respectively, for each Seyfert 1 galaxy are consistent with the variances of the Seyfert 2 galaxies. A high probability (>95%) means that the two samples most likely come from separate populations, and we conclude in these cases that varia-

F(Hß) F\ (CONT) Fx (CONT) 4000 © American Astronomical Society • Provided by theNASA Astrophysics Data System 4500 Fig. 5 Fig. 6 5000 5500 4000 4500 Fig. 7 Fig. 8 5000 F(Hí¡) f’x (coNT) ^(Hy) Fx (C0NT) 025 075 © American Astronomical Society • Provided by theNASA Astrophysics Data System 4500 JD (+2,440,000) Fig. 10 Fig. 9 5000 JD (+2,440,000) Fig. 12 Fig. 11 LO CO PC

F(Hr) F(H/3) Fmcont) . F(Hr) F(H0) Fx (C0NT) © American Astronomical Society • Provided by theNASA Astrophysics Data System LINE ANDCONTINUUMVARIATIONSOFSEYFERTGALAXIES Fig. 14 Fig. 13 yielded a90%chanceofdetecting Hßvariationsgiventhemea- surement uncertainties andsamphngfor eachgalaxy.For scatter normalizedbythemean Hßfluxlevel)thatwouldhave lists theamphtude(expressed inpercentagesastheHßrms with theactualobservedscatterinHßfluxes(seeTable4)as an tions weredetected.Inthesecasestheresultscanbecompared would havehada90%chanceofobservingthevariations. The the overallrmsscatterinHßfluxesnormalizedbymean indication ofthereliability thesimulation. light curvewasincreaseduntilthedetectionfraction(i.e., the simulation wasalsoapphedtothosegalaxiesinwhichvaria- strength foreachgalaxyinwhichvariationswerenotdetected, amphtude isthusaroughupperlimitonthevariability variations werenotdetected,theamphtudeofNGC5548 limit onthevariabilitystrengthofthosegalaxiesinwhichHß did notvarystronglyduringthe8monthmonitoringperiod; above the2a(i.e.,95%)confidencelevel.However,NGC5548 examined thefractionoftheseF-testprobabilitiesthatwere since ifthegalaxieshadvariedwithahigheramphtude we varied withsomeminimalamphtudetobedetermined. This expect a90%chanceofdetectingvariationsifthegalaxy had detecting variationswassignificant)90%.Thus,wewould surement uncertainties.Thus,toobtainameaningfulupper Hß fluxlevelwasonly9.6%,whichiscomparabletoourmea- axy. ToestimateourchancesofdetectingHßvariations,we Thus, 129detectionprobabilitieswerecomputedforeachgal- NGC 5548lightcurve,werepeatedthesuperpositionprocess number oftimesout129trialsinwhichtheprobability of 129 timesbysuccessivelyincrementingthesamplingpattern. The resultsarepresentedin column (17)ofTable4,which JD (+2,440,000) Fig. 15 73 O'!PC LO 74 ROSENBLATT ET AL. Vol. 81 œ those galaxies with relatively high signal-to-noise data the up- variations is most Ekely associated with the relatively narrow per Emit to the rms Hß scatter is roughly 30%. If the scatter in Hß emission Enes observed for these galaxies. If Ene width is o Hß line fluxes had been significantly larger, we would have indicative of the distance of emission-Ene gas from the contin- S' detected Hß variations with virtual certainty. On the other uum source (Shuder 1982), the lower velocity gas responsible ^ hand, the fact that continuum variations were in fact detected for generating the Ene core should be located at greater dis- ^ in ~90% of the sample suggests that the optical continuum tances, and thus vary on longer time scales. varies more strongly than Hß, with an overall scatter of at least Mrk 79.—Osterbrock & Shuder (1982) noted a ~55% de- ~ 30% in most cases. This result is consistent with the observed crease in optical continuum strength between two observa- scatter in continuum fluxes for most of our sample (see col. [5] tions made in 1975 January and 1979 November, but only a of Table 4). For the four galaxies with lower signal-to-noise 13% decrease in Hß Ene flux (specific flux values were not data, the larger measurement uncertainties do not allow the given). These findings are consistent with present variabiEty Hß and continuum variability strength to be as tightly con- results; the nonsteUar continuum varies, but Hß changes are strained. marginal. Obviously, these results depend sensitively on the measure- Mrk 335.—Shuder (1981) made three observations of Mrk ment uncertainties of any given data set. If the uncertainties 335 from 1974 November to 1976 November and observed were smaller, it would be possible to set correspondingly continuum and emission-Ene variabiEty. His [O m] X5007 tighter upper Emits on variabiEty strength for those galaxies in equivalent width measurements of 27.2 ± 8.2 Â are 21 % higher which variations were not detected or to confirm variabiEty than the 22.4 ± 4.6 Â mean value found here. This higher observations with greater certainty for those galaxies in which value is due solely to his 1975 December observation in which variations were in fact observed. Indeed, these simulations an equivalent width of 36.4 Â was found. This value is respec- show that if Seyfert galaxies vary at low amphtudes as does tively 65% and 20% higher than the mean and largest values NGC 5548 (with Hß rms scatter of only 9.6%), sampEng quar- observed in the present study. Shuder’s F(Hß)/F(X5007) mea- terly wfll not provide a high probabiEty of detecting variations surements also differ significantly from the values presented given 10% measurement uncertainties. Additional simulations here. His mean flux ratio of 3.16 ± 0.40 is 27% lower than the show that if the uncertainties were 5% and the sampEng were 4.32 ± 0.55 value obtained here. His 1975 December value of unchanged, we would have had roughly a 40% chance of de- 2.77 is respectively 35% and 15% lower than the mean and tecting variations for any given galaxy in our sample. How- lowest values of this study. Thus, the comparison of these two ever, it seems unEkely that all Seyfert galaxies vary with such data sets provides additional evidence for variabiEty in Mrk low amplitude. In fact, Peterson et al. (1991b) find that, in a 335, although our observations alone do not definitively show second year of monitoring, Hß in NGC 5548 varied twice as that Hß varied. The optical continuum, however, was found to strongly with rms scatter of over 19%. Moreover, the detection vary. of Hß variabiEty for several of the galaxies in this study provides additional evidence that Seyfert galaxies generaUy vary 6. ANALYSIS OF GLOBAL VARIABILITY CHARACTERISTICS with higher overall ampEtude than 10%. It thus seems that in 6.1. NonsteUar Continuum and Emission-Line Variability those Seyfert 1 galaxies which display Hß variabiEty, the rms scatter over time scales of a few years is between roughly 10% Most of the 13 broad-line Seyfert galaxies in the present and 30%. However, the optical continuum varies more sample showed significant continuum variabiEty. Based on F- strongly with scatter of roughly 30% or greater. These results tests (Table 4), the nonsteUar continuum varied in 12 of 13 are consistent with the mean overaE scatter in continuum and (92%) of the galaxies in the present sample. The only exception Hß strengths for the 13 Seyfert 1 galaxies in the present sample was NGC 7603, although the data were noisier than for most (33% ±11% and 21% ± 7.4%, respectively). other galaxies. Since TohEne & Osterbrock (1976) observed significant variations in their data, it appears that NGC 7603 is in fact variable. Thus, including this object as a positive detec- 5.4. Comparisons with Independent Flux Measurements tion, 100% of the galaxies showed significant continuum vari- The availabiEty of pubEshed data for NGC 4051, Mrk 79, abiEty. and Mrk 335 taken during the same period as the present ob- Assuming Ene flux measurement uncertainties of 10% and servations has allowed us to compare our measurements with 15% for high and low signal-to-noise data, respectively, we de- independent studies. The results are presented below. tected Hß variations in NGC 3516, NGC 5548, NGC 6814, NGC 4051.—Osterbrock & Shuder (1982) noted that the Mrk 6, and Mrk 509. NGC 7603 also showed evidence for Hß equivalent width of [O m] X5007 varied from 34 to 44 Â be- variabiEty with an F-test yielding a 93.5% confidence level that T tween 1977 March and 1978 April, although F (Hß)/JF(X5007) variations occurred. Moreover, high-amphtude variations changed by only 11% from 1.04 to 0.93; between 1978 April were observed for most of the galaxies in the present sample and 1978 December significant variations did not occur. These (see Fig. 16 and § 6.2), most notably NGC 3227 and Mrk 335, [O m] X5007 equivalent width and F(Hß)/F(X5007) measure- on numerous occasions during the monitoring period. These ments are within the range of values observed in the present observations indicate that real variations may in fact have oc- study. Moreover, their finding that the continuum varies but curred, but these changes cannot be statisticafly separated Hß does not is consistent with the present result. from measurement uncertainties. The overafl variabiEty characteristics of NGC 4051 closely The data for Mrk 509 are of high signal-to-noise ratio, and resemble those observed in NGC 1275. Both galaxies have an F-test indicates that Hß varied significantly. However, it continua that vary with high ampEtude, but Hß emission Enes should be noted that this result is weighted to the two Steward that do not vary significantly. The absence of Hß Ene flux Observatory observations. Excluding these two observations,

WAVELENGTH (Â) WAVELENGTH (Â) Fig. 16.—Although the overall scatter in Hß line flux for several of the galaxies in the present sample was not significant or only marginally so, large-amplitude variations between individual observations were observed for every galaxy studied. Four examples are shown here. These spectra have been corrected when appropriate (see § 3), and a baseline continuum has been subtracted. The observation of Mrk 335 on 1979 December 12 was 40% stronger than the 1980 September 15 observation. This is a 4 <7 variation in Hß line flux. The 1984 June 6 observation of Mrk 509 was 75% stronger than the 1982 July 18 observation. An even larger variation of 140% occurred between the observations of 1981 February 28 and 1981 November 23 for NGC 3516. Last, Hß increased by 60% in only 95 days between 1980 March 14 and 1980 June 17 for NGC 3227.

the confidence level that Hß variations occurred becomes insig- probability of 99.6% that H7 varied, and 98.1% excluding the nificant, although the probability that the continuum varied two Steward observations. NGC 5548 showed marginal evi- remains reasonably high at 97.8%. Thus, we include Mrk 509 dence for H7 variability with a confidence level of 91.9%. as a positive Hß variability detection with this caveat. The NGC 7469, Mrk 79, Mrk 290, and Mrk 335 also showed only F-test applied to Mrk 6 Hß flux data indicates that variations marginal or no evidence of H7 variability. Rather than actual occurred at a high confidence level. Although Hß is dominated nonvariability, larger Hy measurement uncertainties most by a strong, narrow component, there can be little doubt that likely prevented the positive detection of variations compara- the broad Hß component varied significantly in this object. ble in strength to the observed Hß variations. Data for NGC 5548 also show positive variations. The formal The mean overall scatter in continuum strengths for the 13 F-test confidence level for Hß variations in NGC 5548 is galaxies (33% ± 11%) was higher than for Hß (21% ± 7.4%). 96.2% (which remains unchanged when the two Steward ob- Peak-to-peak continuum variations are also higher compared servations are excluded). Moreover, a number of large-ampli- with Hß. Consistent with the present results, previous studies tude variations were observed, including a 65% change in line (e.g., Peterson et al. 1982; Peterson et al. 1984) using a large flux that occurred within only 4 months between JD 3941 and sample of Seyfert galaxies (but usually only two observations JD 4055. Last, we note that Hß in NGC 1275 and NGC 4051 is per galaxy separated by one or more years) have also found dominated by a narrow component that may have masked that most (^75%) broad-fine galaxies vary in their optical con- small-amplitude variations in the weak, broad Hß component. tinuum and emission lines. Nevertheless, variations in the broad component, if any, must Strong correlations were found between Hß and Hy fine flux have been of low amplitude, since none were detected in these for both NGC 5548 and Mrk 509, although Hy variations for two objects. NGC 5548 were only marginal. A Pearson r-test gives the prob- Of the six galaxies in which H7 was measured, only Mrk 509 ability that a correlation does not exist between these Balmer showed significant fine-strength variations. An F-test yielded a fines as P(null) = 7 X 10“4 and 3 X 10"4 for NGC 5548 and

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!pc LO : 76 ROSENBLATT ET AL. Vol. 81 œ Mrk 509, respectively. Balmer-line fluxes are also correlated correlations (see Fig. 18) provide evidence for a relationship ; for NGC 7469 and Mrk 335 [P(null) = 2 X 10~3 and 9 X 10"4, between Hß and continuum variations as expected for o respectively], although variations were again only marginal photoionization by a central continuum source. However, the < (see Fig. 17). As expected, Mrk 79 and Mrk 290 showed no best-fit slopes are nonlinear, indicating that the continuum evidence for any significant correlation [P(null) = 0.10 and tends to vary with higher amphtude than Hß. However, this ^ 0.09, respectively], since significant line-strength variations nonhnearity may also be due to a time-lag effect between Hß were not detected in either galaxy. The best fits to the correla- and continuum variations, since observed Hß strengths may tions for NGC 5548 and Mrk 509 [log = 0.92 log FHy + reflect previous continuum levels (see Peterson et al. 1984). 0.40 and log FHß = 0.60 log FHy + 0.65, respectively, computed Additionally, the nonhnearity may be due to atomic physics, assuming equal uncertainties in both Hß and H7 fine flux; since Hß may not intrinsically respond linearly to continuum Barlow 1989] provide some evidence that H7 varies more variations (Mushotzky & Ferland 1984). strongly than H0. The fits for NGC 7469 and Mrk 335 [log Fm = 0.70 log FHy + 0.49 and log F^ = 0.65 X 6.2. Short Time Scale Variability and the Size of the BLR log FHy + 0.51, respectively] also support this conclusion. Four galaxies (NGC 3516, NGC 5548, NGC 6814, and Mrk Since significant variations cannot occur on a time scale 335) showed strong correlations (>99% confidence level) be- much shorter than the BLR light-crossing time, an examina- tween Hß and continuum flux measurements. These positive tion of short time scale variability in the present sample can

LOG F(Hr) LOG F(Hr) Fig. 17.—Strong correlations were observed between Hß and H7 line fluxes (in units of 1 X 1013 ergs s-1 cm-2) for NGC 5548 (see also Rosenblatt & Malkan 1990), NGC 7469, Mrk 335, and Mrk 509. H7 varied significantly in Mrk 509, but only marginally in NGC 5548, NGC 7469, and Mrk 335. The slopes of these correlations suggest that H7 varies more strongly than Hß. The best-fitting fines are shown in each case.

LOG F(Hß) LOG F(Hß) Fig. 18.—Strong correlations were observed between Hß line flux (in units of 1 X lO-13 ergs s_1 cm-2) and the optical continuum (in units of 1 X ICT13 ergs s"1 cm-2 À-1) for NGC 3516, NGC 5548 (see also Rosenblatt & Malkan 1990), Mrk 335, and NGC 6814. Continuum strengths were obtained from the inverse equivalent width of [O m] Á5007 assuming a constant [O m] Une flux. The slopes of these correlations suggest that the continuum varies more strongly than Hß. The best-fitting lines are shown in each case.

constrain the BLR size in Seyfert galaxies. To determine A K-S test (using unbinned data) indicates that the probabil- whether significant variations occurred on relatively short time ity that the distribution of 3 o' continuum variations and the scales, all possible pairs of observations made 120 days or less total observational sample with At < 120 days are equivalent is apart were analyzed as in the study of Akn 120 made by Peter- only 6 X 10-4, while the probability for 3 aHß variations is 1 X son et al. (1989). Figure 19 shows changes in continuum and 10-3. Thus, the observed high-amphtude variations are not Hß flux as a function of the time interval ( Ai) between pairs of simply a subset of the total observational sample. However, as observations for the 13 Seyfert 1 galaxies in the present sample. may be expected, the high-amplitude continuum and Hß dis- The figure shows that continuum flux changes observed for tributions were not found to differ significantly from each At < 20 days tend to be smaller than changes observed for 20 < other. At < 120 days. Figure 20a shows continuum changes binned At least one significant (^3 a) continuum flux variation was (arbitrarily) for At < 20 days {hatched bins) and 20 < A/ < 120 observed with At < 120 days for 12 of the 13 galaxies in the days {unhatched bins), A Kolmogorov-Smimov (K-S) test indi- present sample (see Fig. 20c). The only exception was Mrk 79, cates that the two distributions are not drawn from the same although only four pairs of observations with A/ < 120 days are parent population at the 95.5% confidence level. Excluding the available in this case. All of the galaxies which showed some five extremely high amplitude variations shown in Figure 20a evidence for Hß variability (NGC 3227, NGC 3516, NGC decreases the confidence level to 93.1%. Thus, there is evi- 5548, NGC 6814, Mrk 6, Mrk 335, and Mrk 509) had at least dence that continuum variations occurring on a time scale one (and usually many more than one) high-amplitude (^3 a) shorter than 20 days are less frequent. The same analysis was Hß variation detected for At < 120 days. The two exceptions performed on Hß flux variations (Fig. 206). However, in this are Mrk 335 and Mrk 509, although two Hß variations of 2.8

© American Astronomical Society • Provided by the NASA Astrophysics Data System O'!PC LO 78 ROSENBLATT ET AL. 6.3. Long-Term Variability As noted by Osterbrock & Shuder (1982), line fluxes in Sey- fert galaxies can vary on short time scales (months) but tend to fluctuate about a mean level which remains roughly constant on longer time scales (years), although a notable exception not studied here is Fairall 9 (Clavel et al. 1989). The above result, however, appears to hold for most of galaxies in the present sample, for both Hß fine fluxes and the optical continuum. The slopes of the Hß and continuum light curves (i.e., the slopes ofHß and continuum flux versus time) found from a least- squares fit do not significantly differ from unity to within the formal uncertainties of thefit. The only exception is the continuum of Mrk 79, which our data show steadily increased during the monitoring period. However, undersampfing of the Mrk 79 continuum might have produced this apparent steady rise. Our data thus indicate that relatively little power appears to exist on long time scales, and therefore much of the continuum and Balmer-fine variability power spectrum can be well sampled by monitoring for periods of ~3-4 yr.

6.4. Correlations between Variability and Global AGN Properties A major advantage of this study is that a sufficiently large sample of objects is available to search for and analyze statistical correlations between variability and other AGN properties. Hß fine-strength variability (0^) is represented by the overall rms scatter in Hß flux measurements for each galaxy normalized by the mean Hß flux level as given in column (6) of Table Fig. 19.—All observations taken 120 days apart or less for the entire sample were paired to analyze short time scale variability. Percent changes 4. Similarly, continuum variability (0^) is indicated by the in continuum strength (AFX) and Hß line flux (AF^) as a function of the rms scatter in continuum measurements normalized by the time interval (AO between pairs of observations are shown. Variations in mean continuum flux level (see col. [5] of Table 4). These continuum strength for At < 20 days tend to be smaUer than for 20 < At < variability indicators were compared with mean Hß and con- 120 days. The two distributions for Hß, however, are not significantly -1 -1 diflerent. tinuum luminosities assuming H0 = 50 km s Mpc . Least- squares fits to the äata were obtained assuming equal uncertainties in both parameters of the relationship. A Pearson r variations was 0.27 (33 of 123 total pairs of observations), linear correlation test was used to determine the significance of while the fraction having significant Hß variability was 0.20 possible correlations between parameters. (25 of 123). These fractions far exceed the statistically expected A positive correlation [P(null) = 0.01] was found between value (^0.003 for random 3 a variations), thus providing (jnß and (Tcont (Fig. 2\a) using all 13 Seyfert 1 galaxies as the strong evidence that continuum and Hß variations occur on sample. This correlation is not linear (0^ = 1.68 0^ - 2.28), time scales of 120 days or less in Seyfert galaxies. Moreover, providing additional evidence that the optical continuum typi- there is comparably strong evidence that continuum and Hß cally varies more strongly than Hß, as the data in Figure 18 variations occur on time scales of 90 days or less as well. show. The present study thus provides strong evidence that most When NGC 1275 and NGC 4051 are excluded (these galax- Seyfert galaxies vary on time scales of a few months or less, ies have emission lines dominated by a narrow component and since a large number of significant (3 a) Hß and continuum only an extremely weak broad component), an inverse correla- variations were detected for At < 90 days (Fig. 20c). There is tion (Fig. 2\b) was found between average Hß luminosity and some evidence that variations occurring in ~20 days or less Hß variability fP(null) = 0.04 and <7^ = -13.9 log + 601]. are not as common. These data thus constrain variability time Significant inverse correlations were also found between con- scales for a large number of objects to roughly an order of tinuum variability and both Hß (excluding NGC 1275 and magnitude shorter than in previous studies (e.g., Peterson et al. NGC 4051) and continuum luminosity (using the entire sam- 1982). Although the BLR size of a few objects has already been ple). The confidence levels and best fits for these two correla- constrained to a relatively small size (e.g., Gaskell & Sparke tions (see Figs. 21c and 2\d) are P(null) = 0.02, <7^ = 1986; Peterson & Gaskell 1986), the present data strongly sug- -20.4 log Lh^ + 885 and P(null) = 0.01, <7^ = -21.7 X gest that a BLR size of at most a few fight-months across is log Lcont + 656, respectively. Thus, less luminous galaxies are typical of most Seyfert galaxies. The central continuum source more strongly variable in their fines and continuum. This is is also constrained to a size no larger than a few fight-months not surprising, since nuclear luminosity is directly related to across. BLR size and thus tö variability time scales as well. Low-lu-

h) a CM CO cz CO u PQ D

& op D ^i

AFh, (%) 26 1 r T I I I I I I I I I I I I I I I I I I I r c) Total Spectroscopic Sample (open) 20 - 3<7 Continuum Flux Changes (hatched) 3o H/9 Flux Changes (dotted) 01 16 - Cd a D 'Z 10 -

5 -

0 L 0 10 20 30 40 60 60 70 60 90 100 110 120 At (days) Fig. 20.—(a) Continuum changes binned for At < 20 days {hatched bins) and 20 < At < 120 days {unhatched bins). A K-S test indicates that the two distributions are not drawn from the same parent population at the 95.5% confidence level. Excluding the five extremely high-amplitude variations shown in the figure affects this result only slightly by decreasing the confidence level to 93.1%. {b) The same analysis performed on Hß flux variations. However, in this case a K-S test indicates that the two distributions are not significantly different, (c) Comparison of the distribution of high-amplitude continuum and Hß variations with the total sample of observations with At < 120 days. The observed number of 3

Fig. 21.—{a-d) Correlations are shown between H/3 and optical continuum specific luminosities (in units of ergs s-1 cm-2 Hz-1) and their variability amplitudes; is the overall rms scatter in Hß line flux normalized by the mean Hß flux level (each point in the figure represents a single distinct galaxy), while an analogous definition holds for the continuum variability amplitude of each galaxy given by The best-fitting line is shown for each correlation. minosity objects will therefore have shorter variability time 1. The continuum varied in 12 of 13, or 92%, of the Seyfert scales, resulting in a higher probability of detecting variations. galaxies (100% varied if NGC 7603 is included; see Tohline & Edelson & Malkan (1986) fitted the ultraviolet to far-in- Osterbrock 1976). Significant variations in Hß line flux were frared spectral energy distributions of several AGNs with detected in five of 13 galaxies (NGC 3516, NGC 5548, NGC various thermal and nonthermal models. There were no signifi- 6814, Mrk 6, and Mrk 509). In particular, strong evidence was cant correlations between Hß and continuum variability and observed for Hß line flux variations in NGC 5548 and Mrk 6. their parameters Tbb (the temperature of the ultraviolet black- H7 was observed to vary significantly in Mrk 509. NGC 5548 body continuum component) and apl (the spectral slope of the also showed some evidence for H7 variability. fitted infrared power law). 2. Hß and continuum strengths were strongly correlated for several galaxies in the present sample (NGC 3516, NGC 5548, 7. SUMMARY AND CONCLUSIONS and NGC 6814). Mrk 509 showed a strong correlation, but this was heavily weighted to one data point. These positive correla- We have analyzed the variability characteristics of a large tions provide evidence for photoionization of BLR gas by the sample of AGNs monitored quarterly from 1979 to 1983 at continuum source. Moreover, the correlations are highly non- Palomar Observatory using the same instrumentation and linear, indicating that the continuum varies with larger ampli- setup (a small number of observations were also made at tude than Hß. As suggested by Peterson et al. (1984), this non- Steward Observatory in 1984 using a similar setup). When linearity may also be due to a time-lag effect between Hß and appropriate, spectra were corrected for narrow Hß, Fe il continuum variations, since observed Hß strengths may reflect XA4924, 5018, and starlight contamination. This paper focuses a previous continuum level. Additionally, the nonlinearity on variability time scales, amplitudes, and their implications may be due to atomic physics, since Hß may not intrinsically for models of the BLR. The major findings are summarized respond linearly to continuum variations (Mushotzky & Fer- below. land 1984).

© American Astronomical Society • Provided by the NASA Astrophysics Data System O)PC 1 No. 1, 1992 LINE AND CONTINUUM VARIATIONS OF SEYFERT GALAXIES 81 œ 3. Strong correlations were found between Hß and H7 line ies more strongly than Hß. Additionally, inverse correlations ; fluxes for the two cases, NGC 5548 and Mrk 509, in which were found between Hß variability and Hß luminosity ^ evidence for H7 variations was detected. The probability that [/(null) = 0.04], continuum variability and continuum lumi- < the two Balmer lines were not correlated is /’(null) = 7 X 10-4 nosity [/(null) = 0.01], and continuum variability and Hß lu- ^ and 3 X 10"4 for NGC 5548 and Mrk 509, respectively. minosity [/(null) = 0.03]. ^ Balmer-line fluxes were also correlated for NGC 7469 and Mrk 6. The present sample of Seyfert galaxies (with the possible 335 [/(null) = 1.5 X 10-3 and 9 X 10-4, respectively], although exception of the continuum of Mrk 79) shows little Hß or variations were marginal. The best linear fits of the correla- continuum variability power on long time scales. The slopes of tions for NGC 5548 and Mrk 509 (with slopes of 0.92 ±0.16 the Hß and continuum light curves do not significantly differ and 0.60 ± 0.12, respectively) provide some evidence that H7 from unity. Our data thus indicate that much of the contin- varies more strongly than Hß (Fig. 17). The best-fit slopes for uum and Balmer-line variability power spectrum can be well NGC 7469 and Mrk 335 (0.70 ± 0.14 and 0.65 ± 0.13, respec- sampled by monitoring for periods of —3-4 yr. tively) also support this finding. 4. The fraction of observed short time scale variations E. I. R. thanks his thesis adviser, Matt Malkan, for his sup- (^20%) greatly exceeds the statistically expected value (^1%), port (both moral and financial) and encouragement through- thus providing strong evidence that continuum and Hß varia- out the three years of their collaboration. E. I. R. also gratefully tions occur on times scales of 90 days or less in Seyfert galaxies. acknowledges NASA for their generous support under the There is some evidence that variations occurring in —20 days Graduate Student Research Fellowship Program (training or less are not as common. This represents an improvement in grant NGT-70039). Thanks are due to the members of constraining variability time scales for a large number of ob- E. I. R.’s thesis committee for their time and valuable sugges- jects of roughly an order of magnitude compared with most tions: M. A. Malkan, W. G. Mathews, J. S. Miller, and D. E. previous studies. The present data thus strongly suggest that a Osterbrock. E. I. R. kindly thanks B. M. Peterson, who infor- BLR size of at most a few light-months across is typical of most mally served on the committee and who provided several in- Seyfert galaxies. The central continuum source is also con- sightful discussions during the course of this work. The anony- strained to a size no larger than a few light-months across. mous referee also contributed many useful comments that 5. Hß and continuum variability were found to correlate improved this paper. E. I. R. also benefited from valuable dis- with several global AGN properties. The overall rms scatter in cussions with D. Alloin, R. Edelson, J. Krolik, G. Shields, and Hß line flux measurements correlated with the rms scatter in M. Whittle. Also, we are grateful to Carl Henney, who assisted continuum strength [/(null) = 0.01 ] for the sample as a whole. in the measurement of much of the data presented in this However, the relationship is nonlinear (<7^ = 1.68 (rUß - paper. M. A. M. acknowledges the support of NSF grant AST- 2.28), adding further evidence that the optical continuum var- 86-14510.

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