arXiv:0907.0893v1 [astro-ph.CO] 5 Jul 2009 RCEIG FTE31 THE OF PROCEEDINGS rtkMajumdar Pratik ih,aeawl salse xrglci TeV of extragalactic line established the well of a towards orientation are (jets) close sight, outflows a relativistic by their characterized (AGN) clei rcse epnil o h bevdbaa behavior? acceleration blazar remains observed hadronic question the or for important responsible leptonic most processes the the are models of unanswered: theoretical one the still constrain fully and to enough yet not γ shown. are 2007/8 from in curves 1ES1959+650 and light 501 measured Mrk on results in between addition, preliminary In variability correlation observed. flux high been have strong a emissions X-ray/TeV and 421 observa- scales Mrk such time of each different case for a flux flux Crab In a the tion. establish of to minutes. 30% allows 60 of level MAGIC to MAGIC of 30 the sensitivity of The 1ES exposures by single and observed with 501 telescope regularly Mrk bright are TeV 421, 1959+650, and (Mrk) nearby Markarian three blazars, 2006, Since emitters. eprlo ttehgl aibeVE(E VHE have variable to highly us the allowing at look part deeper took MAGIC a also [3], [5] VERITAS HESS and [4] like Atmospheric many (IACTs) Imaging Telescopes In of Cerenkov accel- blazars. generation new the in the explaining mechanisms campaigns of emission aim and the eration with performed [2]. were [1] minutes to different years in on form but second ranging frequencies, a scales observed to time and all found X-ray at was variable flux soft broad be their two to Moreover, and UV range). GeV-TeV lines the the emission in Distribution weak (one Energy or humps Earth. no Spectral the with continuous towards (SED) a oriented have jets They relativistic by terized tele- gamma-ray scopes observations; gamma-rays objects; ∗∗ ryeiso.Ufruaeytedt olce ofris far so collected data the Unfortunately emission. -ray hn-hn Hsu Ching-Cheng Abstract Keywords nrcn er ueosmliaeeghcampaigns multiwavelength numerous years recent In charac- are and AGN of class the to belong Blazars hpl bevtr,HradSihoinCne o Astr for Center Harvard-Smithsonian Observatory, Whipple ¶ lzr,acaso cieGlci Nu- Galactic Active of class a Blazars, . uraOsraoy et hsc n srnm,Universi Astronomy, and Physics Dept. Observatory, Tuorla cieGlci uli LLacertae BL Nuclei; Galactic Active : § iatmnod iia nvri` el td iSea V Siena, di Studi degli Universit`a Fisica, di Dipartimento icm Bonnoli Giacomo ∗ a-lnkIsiu urPyi,Ferne ig6 D-808 6, Ring Foehringer Physik, fuer Max-Planck-Institut .I I. oioigo rgtBaaswt MAGIC with Blazars Bright of Monitoring † noi Stamerra Antonio , NTRODUCTION ∗ osacaSatalecka Konstancja , ‡ ehiceUieste otud -42 otud Germ Dortmund, D-44221 Dortmund, Universitaet Technische st CC Ł ICRC, † EY ltnnle ,D178Zuhn Germany. Zeuthen, D-15738 6, Platanenallee DESY, § OD ´ ioaGalante Nicola , 2009 Z ´ ≥ § 0 GeV) 100 n oetWagner Robert and γ † -ray awn Thom Malwina , k deceased ∗∗ 8 pr rmago ecito fteSDstructure SED the “orphan” of the explain description also good (SPB) can a Blazar from Proton Mirror apart Synchrotron Synchrotron [8] or the [7] like reasonable (SMM) hand, Hadronic Model a other blazars. the offer of on variability and models, fast SEDs the existing describ- for the in explanation of successful very most are ing [6] (SSC) Compton Self n rdc msino iheeg neutrinos. energy high of emission predict and oresaeidpnet ogtr oioigo the of monitoring brighter term interesting long most independent, a state performing in by source participation also by but only observations, accelera- Not multiwavelength the blazars. of in understanding mechanism for tion input valuable a give te aeegh.I otx f“rhn e flares TeV valuable. at ob- especially “orphan” are observing the of observations X-ray context satellites of simultaneous a and coverage In telescopes IACTs wavelengths. time other or other the – include increase servations to trigger, allowing ToO – the the by issuing performed observations. be IACT (ToO) may observations Opportunity follow-up These of Target triggering allow and acceleration also the may about processes. knowledge activity emission our source improve different to of of periods is the study from a expected such results interest. [11] particular neutrino the observatory of as neutrino view such IceCube In observables, [10]. other the events and between of states correlations estimation possible flaring flaring the of of significance for statistical determination essential the probabilities, example: state For variou any on levels. statistics perform flux high and requires states which obtain study flux to statistical of allow distribution They unbiased observations. an such of advantages lra Goebel Florian , etncmdl,lk o xml,teSynchrotron- the example, for like models, Leptonic smnindbfr h e eeainICscan IACTs generation new the before mentioned As nte motn seto h G oioigis monitoring AGN the of aspect important Another during occurring changes spectral of Investigation pyis ..Bx9,Aao Z86509,USA. 85645-0097, AZ Amado, 97, Box P.O. ophysics, ∗ yo uk,F-01 uk,Finland. Turku, FI-20014 Turku, of ty ‡ aRm 6 -30 in,Italy. Siena, I-53100 56, Roma ia nbhl fteMGCCollaboration MAGIC the of behalf on ihe Backes Michael , I AGN II. 5Mece,Germany. Muenchen, 05 ∗k ln Lindfors Elina , γ MONITORING ryeitr.Teeaemany are There emitters. -ray any. γ ryflrs(e ..[9]) e.g. (see flares -ray ‡ ls Bernardini Elisa , ¶ , 1 s † , 2 CHING-CHENG HSU et al. MONITORING OF BRIGHT BLAZARS

The major part of the monitoring (∼60%) has been performed under moderate moonlight or twilight, keep- ing the impact on the overall observation schedule low and allowing to maximize the available duty cycle up to ∼12%.

V. RESULTS In this section we present the preliminary results of the MAGIC AGN monitoring program for the observation season 2007/2008 together with some previously taken, published MAGIC data on the same objects. The data have been processed with the standard MAGIC analysis tools [4]. A fraction of the data has been removed due to poor observation conditions. All cuts were optimized Fig. 1. MAGIC sensitivity corresponding to a 5 σ detection [15] as and verified with Crab Nebula data. a function of exposure time. A. Mrk 421 Between February 2007 and June 2008 82 hours of III. THE MAGIC TELESCOPE data from Mrk 421 were taken. The observations were MAGIC is currently the largest single-dish IACT for mostly performed in wobble mode, which allows to VHE γ-ray astronomy. It is located on the Canary Island simultaneously collect signal and background events. of La Palma, at an altitude of 2200m a.s.l and has been About 66 hours of good quality data (80%) were used in scientific operation since summer 2004. In January for further analysis. It should be noted that about 70% of 2007 a major upgrade of the MAGIC Telescope with these data were taken due to the ongoing flaring activity a Multiplexed Fiber-Optic 2 GSamples/s FADC Data of the source and are actually not part of the monitoring Acquisition system took place [12]. The fast readout campaign. minimizes the influence of the background from the All observations of Mrk 421, performed by MAGIC light of the night sky and the additional information on since 2004 [16] [17], are shown in Fig.2. The source the time structure of the shower signal helps to reduce was very active in 2008: many flares were observed and the hadronic background [13]. The trigger threshold flux rarely decreased below 1 Crab level (FE>300 GeV ± × −10 −2 −1 of MAGIC is around 60GeV1. A source emitting γ- = 1.23 0.10) 10 ph/cm s [4]). According to rays at a flux level of 1.6% of the Crab Nebula can a ToO agreement with HESS and VERITAS, MAGIC be detected with 5 σ significance within 50 hours of issued several alerts during this time of high activity. A observation time. This sensitivity is sufficient to establish detailed analysis of the collected data, such as a study a flux level of about 30% of the Crab flux above on the intra-night variability is discussed in [18]. 300GeV for a 30min observation (Fig.1). A quick on- As mentioned before, possible correlations between line analysis system allows to estimate the flux level different wavelengths, in particular TeV γ-rays and X- of the observed source and send ToO triggers on high rays, are an interesting subject to investigate. We there- flux levels during data taking. At present MAGIC is the fore searched for X-ray and optical measurements which only IACT which can observe under moderate moon and are within 6h before or after the TeV observations. twilight conditions with only slightly lower sensitivity. In this work we used the X-ray data taken by the The construction of a second telescope (MAGIC-II) is ASM instrument aboard of the RXTE satellite, which 2 being finalized and it is planned to start stereoscopic are publicly available on the project web page. The observations in autumn 2009 [14]. averages and errors of ASM data points were calculated on a dwell-by-dwell (90 seconds) data basis. If the number of dwells were fewer than five, we discarded IV. MONITORING STRATEGY that data point. We finally selected 75 pairs of TeV-X- In order to achieve a dense sampling, up to 40 short ray measurements for further analysis. observations per source are scheduled, evenly distributed The 1.03m telescope at the Tuorla Observatory Fin- over the observable time by MAGIC. Three sources were land and the 35cm KVA telescope at La Palma, Canary chosen for a regular monitoring: Mrk 421, Mrk 501 and Islands provided us with the optical R-band data from 1ES 1959+650. The first two are relatively bright and their Blazar Monitoring Program3. The optical flux was usually 15-30min observations are scheduled for them. corrected for the flux of the host galaxy and the flux 1ES 1959+650 being fainter requires longer observation contribution from the companion galaxies [19]. In the times, at least 30 minutes per single exposure. end, 56 measurements pairs were found.

1The trigger threshold is defined as the peak of the energy distribu- 2http://xte.mit.edu/ASM lc.html tion of the triggered events. 3http://users.utu.fi/kani/1m/ PROCEEDINGS OF THE 31st ICRC, ŁOD´ Z´ 2009 3

4

3.5 2005 2006 2007 2008

3

2.5

2 PRELIMINARY

1.5

1 Crab level 1 Integral Flux >300GeV [Crab] 0.5

0

53200 53400 53600 53800 54000 54200 54400 54600

MJD [days]

Fig. 2. Mrk 421 light curve showing all data collected by MAGIC [16] [17] so far.

We used the Pearson’s method (see section 14.5 in 12.7 hours of data taken in 2007 and 3.6 hours of data [20]) to calculate the correlation coefficients. For the X- taken in 2008 were analyzed. ray/TeV data set (shown in Fig.3 left), the correlation In 2007 a clear γ-ray signal of 9.0 σ is seen. How- coefficient value is r = 0.77±0.05 and for optical/TeV ever, the mean 1ES1959+650 γ-ray flux above 300GeV data (Fig.3 right), the coefficient becomes r = 0.03±0.14. during this observations period with MAGIC was only The significant (8 σ) correlation with X-rays we found (0.92 ± 0.12) × 10−11 ph/cm−2s−1, i.e. ∼10% Crab. might point to a leptonic origin of the emission (see e.g. The overall light curve for 1ES1959+650 in 2007 is [21] and references therein) but certain hadronic models shown in Fig. 5, all measurements with significances also predict such a correlation (see e.g. [8] or [22]). In below 1 σ were converted to flux upper limits. The any case, conclusions on the origin or mechanism of the light curve indicates no major changes of the flux level emission should be made very carefully because the data and no significant flares. The overall significance of were not taken strictly simultaneously. the data sample from 2008 is 2.6 σ, which allows us to set an upper limit on the flux above 300GeV of B. Mrk 501 1.54×10−11 ph/cm−2s−1 at 90% C.L. In comparison to Fig. 4 shows all the data collected from Mrk 501 previous observations [24] [25] it can be concluded that by the MAGIC telescope since 2005, when the source MAGIC observed 1ES1959+650 in 2007/2008 during its was found in a flaring state and doubling times as short usual quiescent state. as few minutes were observed [2]. The new results presented here are based on the data collected between VI. CONCLUSIONS February 2007 and August 2008. As in the case of the During the observational season 2007/2008 three Mrk 421, the observations were performed in wobble blazars were regularly monitored by MAGIC: Mrk 421, mode, mostly during moderate moonlight or twilight in Mrk 501 and 1ES 1959+650. Here we presented pre- order to maximize the time coverage of this source (56% liminary results of the measured flux levels for all three of the total observation time). After quality selection 16 sources. Mrk 501 and 1ES 1959+650 were found in a hours of data remained and were analyzed. A part of the low state, but the dense sampling of Mrk 501 provides light curve presented in Fig. 4 was taken during a mul- valuable material for further statistical studies. Mrk 421 tiwavelength campaign (MJD 54550-54602) described has shown an interesting flaring activity in 2008. We in more detail in [23]. Similar to the year 2006 [17] also investigated possible correlations of the TeV and in the 2007/2008 observational period Mrk 501 was in X-ray/optical flux levels for Mrk 421. We found a a relatively low state (below 1Crab). Thanks to good significant correlation between TeV and X-rays but no weather conditions at the site a dense sampling was correlation with the optical R-band. Parts of the data obtained. A statistical analysis, e.g. estimation of the collected from Mrk 421 and Mrk 501 are discussed in source state probability, is in progress. more detail in dedicated contributions [18] [23].

C. 1ES 1959+650 VII. THE ACKNOWLEDGMENTS MAGIC monitored 1ES 1959+650 from April 2007 We would like to thank the Instituto de Astrofisica till October 2008 for 27 hours under large zenith angle de Canarias for the excellent working conditions at the (35◦-50◦) conditions. The source was observed in wob- Observatorio del Roque de los Muchachos in La Palma. ble mode. After quality selection mainly based on bad The support of the German BMBF and MPG, the Italian atmospheric conditions and unstable, low event rates, INFN and Spanish MCINN is gratefully acknowledged. 4 CHING-CHENG HSU et al. MONITORING OF BRIGHT BLAZARS

×10-9 ×10-9 ] 0.5 ] 0.5 -1 -1 s s -2 -2 0.45 0.45 [cm [cm

0.4 0.4 E>300 GeV E>300 GeV

F F Mrk421 Optical/TeV Correlation 0.35 0.35 2008 March-April Preliminary 0.3 Preliminary 0.3

0.25 Two Crab 0.25 Two Crab

0.2 0.2

0.15 0.15 One Crab One Crab 0.1 0.1

0.05 Mrk421 X-ray/TeV Correlation 0.05 2006 - 2008 0 0 -2 -1 0 1 2 3 4 5 6 7 8 0.01 0.012 0.014 0.016 0.018 0.02 0.022 0.024 0.026 0.028 0.03 -1 ASM 2-10 keV photons [counts s ] R-band flux FO [Jy]

Fig. 3. Left: VHE γ-ray (MAGIC) - X-ray (ASM) correlation plot for Mrk 421. Right: VHE γ-ray (MAGIC) - R-band (KVA) correlation plot for Mrk 421.

5

4 2005 2006 2007 2008

3

2 PRELIMINARY

1 Crab level 1 Integral Flux >300GeV [Crab]

0

53600 53800 54000 54200 54400 54600

MJD [days]

Fig. 4. Mrk 501 light curve showing all data collected by MAGIC [17] [2] so far.

0.35

0.3 2007 [7] A. Reimer, M. Bottcher, and S. Postnikov, Astrophys. J. 630, 186

0.25 (2005). PRELIMINARY

0.2 [8] A. Muecke, et al., Astropart. Phys. 18, 593 (2003).

0.15 [9] H. Krawczynski, et al., Astrophys. J. 601, 151 (2004).

0.1 Crab level 0.1 [10] K. Satalecka, et al., in Proc. 30th ICRC, Merida, Mexico, Vol.5,

Integral Flux >300GeV [Crab] 0.05 1353 (2007), preprint arXiv:0711.0353.

0 [11] J. Ahrens, et al., Astropart. Phys. 20, 507 (2004).

54200 54250 54300 54350 54400 [12] F. Goebel, et al., in Proc. 30th ICRC, Merida, Mexico, Vol.3, MJD [days] 1481 (2007), preprint arXive:0709.2363. [13] E. Aliu, et al., Astropart. Phys. 30, 293 (2009). Fig. 5. 1ES 1959+650 light curve showing MAGIC data from the [14] J. Cortina et al., these proceedings (ID 0752) (2009). year 2007. The arrows denote upper limits at 90% C.L. [15] T. Li, and Y. Ma, Astrophys. J. 273, 317 (1983). [16] J. Albert, et al., Astrophys. J. 663, 125 (2007). [17] F. Goebel, et al., in Proc. 30th ICRC, Merida, Mexico, Vol.3, 1025 (2007), preprint arXive:0709.2032. This work was also supported by ETH Research Grant [18] G. Bonnoli, et al., these proceedings (ID 1401) (2009). TH 34/043, by the Polish MNiSzW Grant N N203 [19] K. Nilsson, et al., Astron. Astrophys. 475, 199 (2007). [20] W. H. Press, et al., SIGSOFT Softw. Eng. Notes 28, 36 (2003), 390834, and by the YIP of the Helmholtz Gemeinschaft. ISSN 0163-5948. [21] R. Wagner, PoS(BLAZARS2008)013 (2008). REFERENCES [22] F. A. Aharonian, New Astron. 5, 377 (2000). [23] D. Kranich, et al., these proceedings (ID 1346) (2009). [1] F. Aharonian, et al., Astrophys. J. 664, L71 (2007). [24] F. Aharonian, et al., Astron. Astrophys. 406, L9 (2003). [2] J. Albert, et al., Astrophys. J. 669, 862 (2007). [25] K. Gutierrez, et al., Astrophys. J. 644, 742 (2006). [3] F. Aharonian, et al., Astron. Astrophys. 457, 899 (2006). [4] J. Albert, et al., Astrophys. J. 674, 1037 (2008). [5] V. A. Acciari, et al., Astrophys. J. 679, 1427 (2008). [6] F. Tavecchio, L. Maraschi, and G. Ghisellini, Astrophys. J. 509, 608 (1998). 4

3.5 2007 2008

3

2.5 PRELIMINARY

2

1.5

1 Crab level 1 Integral Flux >300GeV [Crab] 0.5

0

54100 54200 54300 54400 54500 54600 54700

MJD [days] 5

4 2005 2006 2007 2008

3 PRELIMINARY 2

1 Crab level 1 Integral Flux >300GeV [Crab]

0

53600 53800 54000 54200 54400 54600

MJD [days] 4

3.5 2005 2006 2007 2008

3

2.5

2

1.5 PRELIMINARY

1 Crab level 1

0.5 Integral Flux >300GeV [Crab]

0

-0.5 53600 53800 54000 54200 54400 54600

MJD [days] 2

2007 2008

1.5 PRELIMINARY 1 Crab level

1

0.5 Integral Flux >300GeV [Crab]

0

54250 54300 54350 54400 54450 54500 54550 54600 54650 54700

MJD [days]