arXiv:astro-ph/0604438v1 20 Apr 2006 and d 9 oaacrigt al . fWre (1995). Warner of 5.4 Table to according nova ogn igad rge(03 lomeasured also (2003) Prigge & Ringwald, Morgan, orik(03 acltdta h ierqie o a for is maximum required from time magnitudes three the of that decline Schmid- calculated & (2003) of Nielbock tobreick Association (AAVSO), American Observers the Star of Variable curve light long-term the − re htteojc sa eI-ls oaadmeasured H and nova the II-class of Fe FWHM an the is object the that firmed V at mt hlo 98.I diin eetn eea pe- (e.g., several mass detecting secondary addition, In the of 1998). Dhillon period estimate & an orbital Smith yields the nova Finding a of 2002). sec. (Warner 1365 periods of bital period a & at peak Orio highest observations, the XMM-Newton power period. with from the Sgr might spin V4743 in it of a peaks spectrum that several or suggested found pulsation (2004) and Tepedelenlioglu They sec a 1324 Sgr. either of V4743 represent period (2003) of observations a July al. and X-ray found 4 et Chandra April Ness 2003 of nights, 18, two system. of binary results the the presented of 0.281 period of orbital period They a July. with 2003 ± modulation in sinusoidal nights a three detected during taken Sgr V4743 oarpdices ntelmnst ftebnr system, outburst. binary nova the a of leads luminosity called which the is event, in This increase When rapid surface. a the the to off at blows dwarf. layer it white runaway, burning white thermonuclear the hot a for a dense ignite of and to hot dwarf star surface sufficiently gets companion the material a this onto from accreted matter systems, is binary these In 22 anre l 20)reported (2003) al. et Wagner urnl,teeaeaot5 oa ihkonor- known with novae 50 about are there Currently, oaV73Sr( Sgr V4743 Nova (CVs). variables cataclysmic of subclass a are Novae rpittpstuigL using 2021 typeset 30, Preprint March version Draft .0 67h ntedt,aditrrtdi sthe as it interpreted and data, the in h) (6.7 d 0.003 o 00 1 ≈ et fAtooy&Atohsc,Pn tt nvriy 5 University, State Penn Astrophysics, & Astronomy of Dept. ′ n20 etme 0 aoe l 20)con- (2002) al. et Kato 20. September 2002 on 5 05 httetasto hs nnvemyb eae oitreit po intermediate to related be may r qua novae headings: our Abou show in Therefore, Subject to phase nova. star). seemed transition classical Her Sgr in the th (DQ phase V4743 that of transient of polar the period curve intermediate of spin light typical an the optical as presumably the classified bea is outburst, the which be is period, should period w X-ray 24-min Sgr only the the pe that but and than 6.7-h and data, longer system the period somewhat 2003 binary that is underlying the suggest the period We in of 24-min observations. present The X-ray also year. from this is detected in period found is long period The data. 2005 )fo 03ad20.W n w eid f029 d 0.2799 of periods two find We 2005. and 2003 from 3) # t 3 ′′ epeetterslso 1ngt fCDufitrdpooer o photometry unfiltered CCD of nights 11 of results the present We . ≈ )wsdsoee yKtuiHsd (2002) Haseda Katsumi by discovered was 9) 6d hc aeV73Sravr fast very a Sgr V4743 make which d, 16 OAV73SGTAI 02 NITREIT OA CANDIDAT POLAR INTERMEDIATE AN 2002: SAGITTARII V4743 NOVA 1. α A α 2 INTRODUCTION msinln f20 ms km 2400 of line emission T ocp bevtr,P o 0,Emuh 77 Australia; 6707, Exmouth, 300, Box PO Observatory, Norcape 2000 E a .Kang W. Tae tl mltajv 6/22/04 v. emulateapj style X . crto,aceindss—sas niiul 44 g oa,c novae, — Sgr V4743 individual: stars: — disks accretion accretion, 0 variable 19 = B h bn htmtyof photometry -band 01 1 m lnRetter Alon , etratopueu [email protected] and [email protected] [email protected]; 09 s . 38 δ , rf eso ac 0 2021 30, March version Draft t − 3 2000 1 ≈ From . 5d. 15 . t 0 ABSTRACT 2 1 ≈ = lxLiu Alex , 5DvyLb nvriyPr,P 60;[email protected] 16802; PA Park, University Lab, Davey 25 a sd pruepooer a sdi h reduc- filter the no in and used sec, was 120 photometry every Aperture sec times used. 60 exposure The of was an and range arcsec. in 30 3 The resulting between – 2.5 square. were arcmin was arcsec 10 data giving per the x for pixel reducer seeing 15 0.85 of focal of This view scale f5 image square. of Optec microns field an 9 image to at an attached is pixels frame is 510 telescope full x camera The The 765 is Australia. camera. Western resolution CCD Exmouth, ST7E in SBIG cou- a located telescope pho- an presents f/6.3 The 0.3-m to 1 a observations. pled with Table the out carried of was hours. schedule tometry nightly the 7.5 the of included about and summary observations total, was in The length points data mean June. 2267 and 2005 hours on 82.2 nights 6 and or- Sgr V4743 the system. that between polar propose period intermediate thus We beat an is a periods. spin and presence and photometric period the bital present orbital suggests we which an paper, Sgr, of opti- V4743 this their of In in observations curves. periodicities light for search cal to telescopes small accretion the of This the absence of or 2006). presence field disk. the magnetic al. and Warner the dwarf et 2002; white on Kang information al. 2002; valuable et Warner Warneryields Patterson & & 2001; Woudt Woudt al. 2002; 2001; et Patterson Lipkin 1999; 1999; 2001; Naylor Ret- al & Kovo-Kariti et Leibowitz 1998; & Skillman Retter, Warner Leibowitz 1999; & Retter, 1997; Patterson Patterson 1998; 1998; al. Leibowitz 1997; et & Patterson ter al. 1993; 1997; et al. Ofek et Skillman & Baptista 1989; Leibowitz Steiner Retter, superhump & Diaz permanent (e.g., or systems polars, magnetic intermediate as into such systems, system variables the cataclysmic of classifying groups in different help can novae in riodicities 44 g a bevddrn ihso 03June 2003 on nights 5 during observed was Sgr V4743 with novae observe to program ongoing an have We 2 n ecdsRichards Mercedes and , ≈ slsspottepeiu suggestion previous the support esults idct ersnsteobtlperiod orbital the represents riodicity . n .14 d 0.01642 and h 6.7 iproi siltos hc are which oscillations, si-periodic [email protected] eidct ewe h orbital the between periodicity t lars. h 2mnpro,wihwas which period, 22-min the 2. 44 g Nv g 2002 Sgr (Nova Sgr V4743 f ht wr.Tu,V4743 Thus, dwarf. white e i otsatrtenova the after months six t a vdneo h shorter the of evidence eak OBSERVATIONS ≈ 1 4mni the in min 24 E ataclysmic du; 2 Kang et al.

TABLE 1 4 The observations time table

UT Time of Start Run Time Points (yymmdd) (HJD–2452000) (Hours) number 8

030604 795.1066 6.9 192 2003 data 030605 796.0732 7.8 220 030609 800.0777 7.7 204 12 030610 801.0709 7.8 219 Magnitude 030611 802.0834 7.7 209 2005 data 050618 1540.0458 7.8 223 050619 1541.0664 7.3 203 16 050620 1542.0773 7.0 194 050624 1546.0746 7.5 202 050625 1547.0789 7.4 197 500 800 1100 1400 1700 050626 1548.0624 7.3 204 HJD (−2452000)

Fig. 1.— The long-term light curve of V4743 Sgr. Empty circles represent visual estimates made by amateur astronomers, compiled by the AAVSO. The filled circles correspond to our observations. tion, with an aperture size of 12 pixels. We estimated Our data points were shifted upwards by 1 mag to compensate for differential magnitudes with respect to the comparison the difference between visual and unfiltered data. Quasi-periodic star, “C” (Guide Star Catalog (GSC) 6294-2448) and brightness oscillations with a peak-to-peak amplitude of up to 1 mag seemed to be present between HJD 2452716 (2003 March) the check star, “K” (GSC 6294-2481). Their recorded and 2452908 (2003 December). Note that some variability could GSC magnitudes are V = 12.4 and 13.7, respectively. have been missed during the observational gap in 2002 November The magnitudes of the stars were derived from the SBIG – 2003 March. CCDOPS software. Figure 1 displays the long-term light curve of V4743 Sgr from outburst until 2005 June. The data were compiled from the AAVSO. By combining the data from To confirm that the f1 and f2 peaks are real, we per- the AAVSO with our data, we obtained 3291 individ- formed several tests. First, we checked to see if the f1 ual points. The times of our observations are marked peak in the power spectrum was an artefact of the win- on the graph as well. Since our observations were taken dow function. This was done by assigning 1 to the times with no filter, we compared our data with the AAVSO of observations of the 2005 data, and checking the result- data around the same time, and subtracted 1 mag from ing diagram. There was no evidence for significant power our estimates to compensate for the difference between at the location of the peak. the visual and unfiltered data. The resulting light curve We also checked whether the power spectrum of the suggests that the fading of the nova was not smooth. check star minus comparison star (K–C) data had a sim- Kato (2003) pointed out that quasi-periodic brightness ilar power and pattern near f1. However, the K–C power oscillations with a peak-to-peak amplitude of up to 1 spectrum did not show any strong power near this peak. mag seemed to be present in the light curve between The f1 frequency can not be a result of color effects due to the nova being bluer than the comparison star. This is HJD 2452716 (2003 March) and 2452908 (2003 Decem- −1 ber). Kiyota, Kato & Yamaoka (2004) also represented because f1 is not an harmonic of 1 d , and since there is the long-term light curve of V4743 Sgr compiled by the no evidence for such a periodicity in the power spectrum Variable Stars Network (VSNET), which displays similar of the hour angle data. To further check the significance oscillations. of f1, we used the bootstrap method. First, we scram- bled the magnitude values, arbitrarily assigned them to 3. DATA ANALYSIS the times of the observations, and calculated the cor- responding power spectrum. We then found the power 3.1. The 2005 light curve of the highest peak in the power spectrum in the fre- We first discuss our 2005 data since two periodicities quency range 2–5 d−1. Finally, we plotted the histogram were clearly detected in this season. The bottom panel of the highest peaks of the 1000 simulations. This sug- in Figure 2 shows the normalized power spectrum (Scar- gested that the f1 peak was about 59σ significant. Thus, gle 1982) of our raw data in 2005. It is dominated by we confirmed that the peak was significant. The results two similar alias patterns around two frequencies, f1 = were similar for the tests applied to the f2 peak. −1 −1 3.573 d and f2 = 60.884 d , which correspond to the periodicities P1 = 0.2799 ± 0.0002 d (6.7 h) and P2 = 3.1.2. Significance of the two peaks ± 0.016425 0.00002 d (24 min). To check the significance of two independent period- The power spectra of the raw data in 2005 zoomed icities in the light curve of the nova, we applied a few into the frequency intervals around these two peaks are tests. First, we fitted and subtracted the f2 frequency shown in Figures 3b and 4b, respectively. The power from the data using a sinusoidal fit. The power spectrum spectrum in Figure 3b clearly shows the f1 frequency f ± −1 of the residuals clearly showed 1 as the dominant peak with its 1 d aliases. Figure 4b displays the f2 peak in the graph. Conversely, when the f frequency was with its ± 1 d−1 aliases. 1 removed from the data, the f2 frequency and its daily 3.1.1. aliases remained in the residual power spectrum. Tests To check whether uncorrelated noise could be respon- V4743 Sgr as an intermediate polar 3 sible for the presence of the candidate periods, we added 400 f (a) 2003 noise to the model light curves of the 2005 data. The 1 noise in the original data was defined as the root mean 300 square of the data minus the f1 frequency. We then 200 searched for the highest peak in a frequency interval (55– −1 65 d ) around the f2 peak. In 1000 simulations, no peak 100 reached the height of the f2 frequency. Similarly, for the 0 f frequency, we did 1000 simulations in the frequency 120 1 (b) 2005 −1 f1 interval 2–5 d . No peak reached the height of the f1 peak either. So both periods seem to be real. 80 As a final test for the presence of the two frequencies, we divided our 2005 data into two parts (first and last 40 f three nights). In the power spectra of both parts of the 2 observations, the same peaks appeared as the strongest − 0 ones in a 1 d 1 frequency interval on both sides of the 0 20 40 60 80 100 peaks (i.e., up to the 1 d−1 aliases). Thus, we concluded Frequency (cycles/day) that the two peaks in the 2005 data indicate real period- Fig. Normalized power 2.— Normalized power spectra of V4743 Sgr. (a) The power spectrum after removing the mean from the two parts of the icities. −1 data in 2003 (See Section 3.2). The f1 = 3.573 d frequency is In a search for a third frequency, we simultaneously −1 f f dominant, but the f2 = 60.884 d peak cannot be seen because it fitted and subtracted the 1 and 2 frequencies from the is too weak. (b) The power spectrum of the raw light curve in 2005. data. The power spectrum of the residuals showed a few f1 f2 − Two frequencies, and , are seen with their alias structures. See peaks in the 10–40 d 1 frequency range. To analyze these also Figures 3 and 4. peaks, we divided the 2005 data into two parts (first and last three nights). However, we did not see any consistent peak in the power spectra. Therefore, we believe that these peaks probably correspond to quasi-periodicities. 0.20 ± 0.01 mag for the 2003 and 2005 observations, re- spectively. The light curve of V4743 Sgr folded on the 3.2. The 2003 light curve 24-min period is shown in Figure 6. The top panel dis- plays the 2003 data after removing the mean from the Figure 2a shows the normalized power spectrum of our two sets of the data and binned into 15 equal bins. The 2003 data after subtracting the mean from the two parts bottom panel presents the raw data in 2005 binned into of the data (first two and last three nights). This de- 20 equal bins. The full amplitudes of the mean variations trending method was used because the first two nights were 0.007 ± 0.003 and 0.10 ± 0.01 mag, respectively. are about 0.07 mag brighter than the remaining nights. The bars in Figures 5 and 6 are 1σ uncertainties in the It displays the f1 peak with its aliases as the dominant average values. The amplitudes of the mean variations peak in the graph. were derived by fitting a sinusoidal curve to the mean The power spectra in 2003 zoomed into the frequency light curve. −1 −1 intervals 0–7 d and 57–65 d are presented in Figures The best fitted ephemerides of the periodicities from 3a and 4a, respectively. Figure 3a clearly shows the f1 the 2005 data were: frequency with its ± 1 d−1 aliases. Figure 4a displays −1 the f2 peak with its ± 1 d aliases. However, we note T1(min)(HJD) = 2453539.838(8) + 0.2799(2)E that this frequency has a very low power. T (HJD) = 2453540.046(5) + 0.01642(2)E We applied the same tests described in Section 3.1 to 2(min) the 2003 data. The results of the f1 peak were similar to where E is an integer. the 2005 data. Thus, we confirmed that the f frequency 1 A noteworthy feature seen in Figure 5b is the dip in the was also present in the 2003 data. However, the results mean light curve of the 6.7-h period at phase 1. Its relia- of the f peak were different. We concluded that this 2 bility was checked by subtracting a pure sinusoidal with peak was not significant in our 2003 data. a peak-to-peak amplitude of 0.20 mag from the folded In a search for a third frequency in the 2003 data, we and binned data, resulting in a distribution of the points fitted and subtracted the f and f frequencies from the 1 2 around zero level. This method gave an eclipse-like fea- data. The power spectrum of the residuals showed a few − ture at phase 1 with a full amplitude of about 0.15 mag. peaks in the 10–30 d 1 frequency range. To check the To confirm the presence of the eclipses, we divided the significance of these peaks, we divided the 2003 data into 2005 data into the two parts (first and last three nights). two parts (first two and last three nights). However, we We could clearly see an eclipse in the first three nights, did not see any consistent peak in the power spectra. but only found weak evidence of the eclipse during the last three nights. Therefore, this feature may be real. 3.3. The structure of the periodicities 4. In Figure 5 we present the light curve of V4743 Sgr DISCUSSION folded on the 6.7-h period. The top panel shows the Our photometric data of V4743 Sgr show the presence 2003 data after subtracting the mean from the two parts of two independent periodicities in the light curve: P1 = of the data and the bottom panel displays the raw data 6.7 h and P2 = 24 min. We suggest that P1 is the orbital in 2005. Both are binned into 40 equal bins that cover period of the underlying binary system. Our conclusion the 0–1 phase interval. The peak-to-peak amplitudes of is supported by the fact that this period was present in the mean variations were estimated as 0.065 ± 0.004 and both light curves in 2003 and 2005, with no apparent 4 Kang et al.

400 5

f (a) 2003 1 4 (a) 2003 300

f1−1 3 f +1 f2 200 1 f +1 2 2 f2 −1 100 1

0 0 120 (b) 2005 (b) 2005 f1 f −1 30 1 f2 f +1 80 2 f +1 1 20 f2 −1

40 10

0 0 0 1 2 3 4 5 6 7 57 59 61 63 65 Frequency (cycles/day) Frequency (cycles/day) Normalized power Fig. 3.— The power spectra (Fig. 2) zoomed into the 0–7 d−1 Fig. 4.— Normalized power The power spectra (Fig. 2) zoomed into the 57–65 d−1 −1 1 ± range of frequencies. They clearly show the f2 frequency with its range of frequencies. They show the f frequency with its 1 d −1 aliases. (a) The power spectrum of the 2003 observations after ± 1 d aliases in 2005, but in the 2003 data, this peak is very subtracting the mean from the two sets of the data. (b) The power weak. spectrum of the raw data in 2005.

change in the frequency from the relation between fre- change in its value. Wagner et al. (2003) also reported a quency and temperature for stellar oscillations (Eq. 10 detection of a 6.7 h periodicity in three nights of photom- in Kjeldsen & Bedding 1995). Thus, we estimated that, etry in 2003 July using a B-filter, and interpreted this as if interpreted as a pulsation, the 22-min period, which the orbital period. was found in 2003 April, should have increased to about 38 min in 2005 June. Since we did not detect any period- The full amplitude of P1 increased from 0.065 in 2003 to 0.2 mag in 2005 in our data. A similar behavior was icity around 38 min, we believe that the 22-min period observed in two other novae, V838 Her and V1494 Aql. found in the X-ray band is the spin period, and not a Leibowitz et al. (1992) performed photometric observa- pulsation period. tions of nova V838 Herculis 1991. They detected eclipses Wagner et al. (2003) reported continuous photometric with a period of 7.1 h in the light curve and thus inter- observations of V4743 Sgr using a B-band during three preted the periodicity as the obital period. They also nights in 2003 July. In addition to the presence of the found that the eclipse depth increased from about 0.1 long-term period of 6.7 h, they argued that another pe- mag in 1991 April to more than 0.4 mag in 1991 July. riodicity of 69 min existed in the data. Our observa- Bos et al. (2002) analyzed photometry of nova V1494 tions could not confirm the presence of such a coherent Aql 1999 #2 during 12 nights in 2001. They found that period (Section 3), thus we believe that this is a quasi- the eclipse depth of the 3.2-h period was 10 times larger periodicity. than in mid-2000. Both Leibowtiz et al. (1992) and Bos 4.1. et al. (2002) interpreted the phenomenon as an eclipse An Intermediate Polar model of the accretion disk by the secondary star. Similarly, we The AM Her stars (magnetic CVs) differ from the non- propose to explain the 6.7-h variation in the light curve magnetic systems in two important qualitative respects: of V4743 Sgr as an eclipse of the accretion disk by the (1) a strong magnetic field on the primary star fun- companion star or as a combination of an eclipse and as- nels the infalling gas onto one or two localized accretion pect variations of the side of the comparison star, which shocks near the white dwarf’s magnetic pole(s), where is heated by the white dwarf (See also Balman, Retter & X-ray bremsstrahlung and polarized optical/infrared cy- Bos 2006). clotron emission arise; and (2) the white dwarf spin and Within the errors, P2 is the beat period between the binary orbital motions are locked in a rigid corotating orbital period and the spin period, which we take as the geometry (e.g., Schmidt & Stockman 1991). mean of the two values given for the X-ray period (Ness Intermediate polars (also known as DQ her stars) are et al. 2003; Orio & Tepedelenlioglu 2004): 1344 ± 21 binary systems, which are a subclass of the AM Her stars. sec ≈ 22 min. Ness et al. (2003) argued that the 22-min Unlike in other members of the AM Her class, in inter- period could either be a pulsation or a spin period. How- mediate polars the rotation of the primary white dwarf ever, if this periodicity represents the pulsation of the hot is not synchronized with the orbital motion of the binary white dwarf, it should change as the temperature of the system. The spin periods found in intermediate polars white dwarf cools down (e.g., Somer & Naylor 1999). We are usually much shorter than their orbital periods (Pat- estimated the ratio of the luminosity in 2003 April (when terson 1994; Hellier 1996). the X-ray period was detected) to 2005 June (when our One of the major observational characteristics of inter- observations ended). Using the relation between the lu- mediate polars is the presence of multiple periodicities in minosity and temperature of the white dwarf (Eq. 21 the power spectra of their light curves, emanating from in Prialnik 1986), we estimated the change in the ef- the non-synchronous rotation of the primary with the or- fective temperature. Then, we calculated the expected bital revolution. In fact, this characteristic has become, V4743 Sgr as an intermediate polar 5

−0.10 −0.010 2003 6.7 h period 2003 24 min period −0.05 −0.005

0.00 0.000

0.05 0.005

2005 2005 −0.15 −0.05

0.00 0.00

0.15 0.05

0.30 0.1 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 Phase Phase Relative magnitude Fig. 5.— The light curves of V4743 Sgr obtained in 2003 (top Fig.6.— Relative magnitude The light curves of V4743 Sgr obtained in 2003 (top panel) and 2005 (bottom panel) folded on the 6.7-h period and panel) and 2005 (bottom panel) folded on the 24-min period and binned into 40 equal bins. Two cycles are shown for clarity. Note binned into 15 equal bins for the 2003 data and 20 equal bins for the different scale in the y-axis and the dip at phase 1 in the bottom the 2005 data. Two cycles are shown for clarity. Note the different panel, which may indicate an eclipse. scale in the y-axis.

together with the presence of X-ray modulations, a ma- phase, and showed that a steady-state super Eddington jor criterion for membership in the intermediate polar stage could be maintained in a few novae. group. Retter, Liller, & Gerradd (2000b) observed LZ Mus, a We found several characteristics of the intermediate nova that erupted in 1998, and clearly showed oscillations polars in V4743 Sgr. First, we detected several periodic- during the transition phase. They found several periods ities in the light curve. Second, the orbital period (6.7 h) in its light curve. Therefore, they suggested that LZ Mus is much longer than the spin period (22 min). Third, the is an intermediate polar system. They further proposed a spin period was found in X-ray observations. Fourth, new solution to the transition phase in novae by invoking the short term periodicity f2 shows up about where it a possible connection between the transition phase and should be for an orbital sideband of the X-ray pulse (See intermediate polars. It was also found that LZ Mus was above). Finally, the orbital period and the spin period ≈ a strong X-ray source in 2001, which is consistent with roughly fit the relation Pspin 0.1Porb, which applies to the idea that the white dwarf has a strong magnetic field many other known intermediate polars (Norton, Wynn, (Hernanz & Sala 2002). & Somerscales 2004). We thus suggest that V4743 Sgr Retter (2002) argued that the observations are con- should be classified as an intermediate polar. sistent with the proposed link between the transition 4.2. phase in novae and intermediate polars. For exam- The Transition Phase in novae ples, nova GK Per 1901 showed transition phase oscilla- The optical light curves of classical novae are typically tions. Its orbital period was found in optical observations characterized by a smooth decline. However, certain no- and the spin period was detected in X-ray observations vae show a deep minimum in the light curve while others (Bianchini & Sabadin 1983). V603 Aql 1918 was an- have slow oscillations with amplitudes of 1–2 mag typ- other transition-oscillation nova. It was suggested several ically a few weeks–months after maximum, during the times as an intermediate polar and showed strong vari- so called ‘transition phase’. The deep minimum (e.g., in ations in its X-ray light curve. However, there has been DQ Her 1934 – Walker 1958) is understood by the for- an extended discussion whether this nova is indeed an in- mation of an optically thick dust envelope around the termediate polar (e.g., Borczyk, Schwarzenberg-Czerny, binary system. Several models for the oscillations during & Szkody 2003). the transition phase have been proposed: oscillations of Retter (2002) pointed out that about 10% of the cat- the common envelope, dwarf-nova outbursts, pulsations aclysmic variable population are classified as intermedi- of the hot white dwarf, and winds, but there is still not ate polars, which is consistent with the rarity (∼ 15%) enough observational evidence to understand this phe- of the transition phase in novae. Note that these values nomenon (see Retter 2002 for a review). Retter (2002) are low limits due to the lack of observations. He hy- argued that the explanation by oscillations of the com- pothesized that the accretion disks in intermediate po- mon envelope can be easily rejected since this phase lasts lars are easy to destroy in the nova outburst unlike other only about 1–2 days after the nova event. He further con- systems because the mass of the accretion disk in inter- cluded that dwarf nova outbursts can be ruled out as well mediate polars is much lower than in non-magnetic CVs. because the accretion disks in young post-novae are ther- Observational evidence for the presence of the accretion mally stable (e.g., Retter & Naylor 2000; Schreiber, Gan- disk was found in a few novae several weeks–months af- sicke, & Cannizzo 2000). Shaviv (2001) proposed that ter eruption (e.g., Leibowitz et al. 1992; Skillman et steady-state winds of systems with super Eddington lu- al. 1997; Retter et al. 1997, 1998; Retter 1999, Iijima minosities can be a natural explanation for the transition & Esenoglu 2003; Retter 2004; Kang et al 2006). The 6 Kang et al. fact that the accretion disk is recovered around the same bital periods were found from optical photometry (Ak et time the transition phase occurs supports a connection al. 2005), but no short-term periodicities were detected. between the two phenomena. To our knowledge, no X-ray observations of these two Cs´ak et al. (2005) found that spectra obtained during novae were made. Another example of an old transition- the maxima of the oscillations in the transition phase oscillation nova is V373 Sct (Mattei 1975). In the light of V4745 Sgr are similar to spectra taken just after its curve of V373 Sct, Woudt & Warner (2003) detected nova eruption in 2003. Therefore, they proposed to ex- a period of 258 sec, which is very likely the spin pe- plain the oscillations by several episodes of mass ejec- riod of the white dwarf, but no long-term period was tion, which they called mini nova-outbursts. This can be found. Thus, the intermediate polar model for V2540 understood by the repeated destruction of the accretion Oph, V4745 Sgr and V373 Sct has yet to be confirmed. disk and its re-establishment because of high mass trans- fer rates. The material accumulated on the surface of the white dwarf heats it and then another mini nova-outburst 5. SUMMARY AND CONCLUSION occurs. We note that the critical mass required for the (1) We found two periods of 0.2799 d ≈ 6.7 h and mini-outburst is lower than the nova event because the 0.01642 d ≈ 24 min in the 2005 photometric observations white dwarf is hotter than before eruption. of V4743 Sgr. In the 2003 data, we also detected the The proposed link between the transition phase in no- longer periodicity, but only found weak evidence of the vae and intermediate polars (Retter et al. 2000b; Ret- shorter period. ter 2002) makes a simple prediction: novae whose light (2) We interpret the 6.7-h period as the orbital period curves show transition phase oscillations should be in- of the binary system and the 24-min period as the beat termediate polars. Iijima & Esenoglu (2003) presented periodicity between the orbital period and the spin pe- a spectroscopic coverage of the transition phase in nova riod, which was found in X-ray observations. We thus V1494 Aql 1999 and displayed its optical light curve. Its suggest that V4743 Sgr should be classified as an inter- transition stage started a month after maximum bright- mediate polar. ness (Kiss & Thompson 2000), and the amplitude of the (3) The light curve of V4743 Sgr seemed to show quasi- oscillations during the transition phase was ∼1 mag sim- periodic oscillations that are typical of the transition ilar to V4743 Sgr (see Fig. 1). A period of 3.2 h was phase in novae. Thus, our results support the previously discovered in its optical light curve (Retter et al. 2000a) suggested link between transition-oscillation novae and and was interpreted as the orbital period of the binary intermediate polars. system. Drake et al. (2003) detected a 2523 sec pe- (4) In three cases (V1494 Aql, V1039 Cen and riodicity in two X-ray runs using Chandra. Therefore, V4743 Sgr) the proposed connection between transition- V1494 Aql may be an intermediate polar, but Drake et oscillation novae and intermediate polars seems to be al. (2003) interpreted this period as the pulsation period vaild. However, more observations in the X-ray and opti- of the white dwarf. cal bands are required to confirm or refute the proposed V1039 Cen 2001 is another nova that showed oscil- link, and to follow the evolution in time of the periodic- lations in its optical light curve during the transition ities in V4743 Sgr. phase (Kiyota, Kato & Yamaoka 2004). Woudt, Warner & Spark (2005) found two periodicities, 5.92 h and 719 s, We thank the anonymous referee for very useful com- in its light curve, which they respectively interpreted as ments that improved the paper. We acknowledge the the orbital and spin periods. Therefore, they concluded amateur observers of the AAVSO who made the obser- that the transition-oscillation nova V1039 Cen is an in- vations that comprise the long-term light curve of nova termediate polar system as well. V4743 Sgr used in this study. TWK was supported by Two more examples of recent transition-oscillation no- a REU supplement to NSF grant AST – 0434234 (PI – vae are V2540 Oph 2002 (Ak, Retter, & Liu 2005) and G. J. Babu). AR was partially supported by a research V4745 Sgr 2003 (Cs´ak et al. 2005). In both cases, the or- associate fellowship from Penn State University.

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