arXiv:1111.0244v1 [astro-ph.HE] 1 Nov 2011 a nua eouino h re fsvrlarcmin- several typi- of the order Given the in utes of mechanism. resolution angular acceleration mod- cal crucial the probing and structure, of regions jet’s els emission the the misalign- identifying of the to imaging However, enables becom- challenging. ment sight, more of at sources much line oriented observer’s aligned ing typically the are from these angles AGNs appar- In larger Non- the flux. boosts [2]. ent substantially itself beaming positrons jet relativistic and the electrons pro- within shock-accelerated photons by synchrotron the duced of scattering Compton h otcmol cetdmdlt con for account to [1]. model sight accepted of the line commonly observer’s most the aligned to The is degrees hole, few black a within super-massive of accretion a the around which by matter in produced AGNs jet, of ultra-relativistic sub-category the a , are sources ovdi the in solved hrfr h oeigo h yaiso ohpopu- both of dynamics the of [4], rays modeling are cosmic the galaxies for therefore of accelerator cluster potential and be to jets believed AGN amplifica- scale field Large magnetic tion. and acceleration intra-cluster particle accompanied the by shocks energize termination jets the through powerful galax- medium Their of cluster radio [3]. in that ies seen located been preferentially has are It which galaxies in located. environment typically rich are the they also study to possible is is galaxies proceedings. radio these about in the contribution presented of dedicated substructures A the the investigate in jet. work to at strategy processes viable physical a are galaxies radio on campaigns observational (MWL) coordinated multi-wavelength through studies Correlation wavelengths. Cn C110509 eConf h ags ouaino VHE-detected of population largest The h datg fosrigrdoglxe sta it that is galaxies radio observing of advantage The γ ryeiso rmtejto Gsi inverse- is AGNs of jet the from emission -ray γ ryisrmns e usrcue r o re- not are substructures jet instruments, -ray em n EIA nbaa bevtosrsle nimport through in (EBL) resulted light observations blazar background on classification VERITAS detailed and more prog Fermi a research started AGN VERITAS and the structures successful through inner The also Nuclei galaxies. but radio Galactic project, on science Active key of blazar VERITAS study the The objects. astrophysical otenAioa t i st td h eyhg nry(VH energy high very the study to is aim Its Arizona. southern u-lse EIA icvrdas h rtextragalact first the also discovered VERITAS . sub-classes le npsil ehnssfraclrtn omcrays. cosmic VERIT accelerating by for 82 mechanisms M possible galaxy on starburst the clues from emission gamma-ray of EIA sa ra ffu 2mdaee mgn atmospheri imaging diameter 12-m four of array an is VERITAS γ ryeeg ad u hyaei other in are they but band, energy -ray .INTRODUCTION I. h EIA xrglci cec Program Science Extragalactic VERITAS The avr-mtsna etrfrAstrophysics for Center Harvard-Smithsonian 01FriSmoim oa,My 9-12 May. Roma., Symposium, Fermi 2011 o h EIA Collaboration VERITAS the for γ http://veritas.sao.arizona.edu ryosrain,ado h aaoun ftesvrlAGN several the of cataloguing the on and observations, -ray γ -ray .Galante N. i tutrswoepyisi neetn othe to interesting is physics whose structures tic radiation. expected and are gas interstellar stars with via massive interactions emission gamma-ray their formation, their diffuse the produce super- of eventually in to and death produced novae and rays of life, cosmic rate The times higher novae. 10 mass, consequent similar of about a galaxies normal rate with in rate formation the than star starburst larger a of regions have cos- active energy galaxies The ultra-high accelerators. as rays candidates mic good also are ies com- cosmic-ray the for munity. interest particular of is lations aito steeoeepce ob epnil of responsible be to expected therefore background is microwave radiation and stellar cluster. winds of globular Energetic Comptonization the pulsar through gradually magnetospheres. the diffuse pulsar leptons of the collisions inside shock and/or in the at originating millisec- leptons accelerate of waves can hundreds which host pulsars can ond They community. ray 07 EIA bevto fbaasaveraged blazars of observation VERITAS 2007, rmaehr presented. here pro- are science gram results non-blazar and extragalactic VERITAS topics the the research of on the on pro- contribution Highlights separate a ceeding. dedicated in presented is A program DM VERITAS non- extragalactic VERITAS program. the of blazar part also is dates, emission. ray ial,goua lsesaetecoetextragalac- closest the are clusters globular Finally, galax- starburst environments, AGN-related Beside ic h einn fisoeain nOctober in operations its of beginning the Since h nietsac o akmte D)candi- (DM) matter dark for search indirect The I H XRGLCI SCIENCE EXTRAGALACTIC THE II. fbaas oevr h yeg between synergy the Moreover, blazars. of cnon-AGN ic AN sitnieyprudthrough pursued intensively is (AGN) E: ag W bevtoa campaigns observational MWL large n osrit nteextragalactic the on constraints ant a a rvddisgt otejet the to insights provided has ram > E SadFripoie important provides Fermi and AS -hrno eecpslctdin located telescopes c-Cherenkov 0 GeV) 100 γ rysuc.Tediscovery The source. -ray PROGRAM .Blazars A. γ ryeiso from emission -ray γ γ ∼ - - 1 2 2011 Fermi Symposium, Roma., May. 9-12

410 hr per year, resulting in the detection of 20 blazars catalog [7]. (15 HBL and all 5 known IBL), including 10 discov- 1ES 0414+009 is the most distant VHE HBL with eries. a well-measured (z =0.287). It was observed Mrk 421 is the longest-known VHE blazar, and gen- by VERITAS for 55 h of quality-selected live time erally has the brightest VHE flux. It is easily the best- from January 2008 to February 2011. An excess of studied HBL at VHE, and VERITAS has acquired VHE γ-rays is detected (∼ 7σ) from this Fermi-LAT nearly 80 hr on this blazar since 2007, largely during source (ΓLAT = −1.94; [7]). The observed VERI- flaring states identified with the Whipple 10-m tele- TAS spectrum between 230 GeV and 1.8 TeV is rel- scope. A total of 47 hrs of VERITAS and 96 hrs of atively hard (Γ = 3.4 ± 0.5) considering EBL-related Whipple 10-m data taken between 2006 and 2008 are effects, and consistent with that observed during the presented in [5]. VERITAS monitoring of the VHE HESS discovery [19]. The observed VERITAS flux flux from Mrk 421 in 2009-10 reveals an elevated state is somewhat higher (1.6% Crab) than measured by during the entire season. An extreme flare was ob- HESS (0.6% Crab above 200 GeV), although the large served for nearly 5 hr live time on February 17, 2010, ∼ datasets used by both experiments are not simultane- during which the VHE flux averaged 8 Crab and ous. Results from a contemporaneous MWL observa- showed variations on timescales of approximately 5-10 tion campaign are in preparation. minutes [8]. Figure 1 shows the seasonal light curve with a zoom on the night of the flare. Variability on B2 1215+30, an IBL discovered at VHE during a the time scale of few minutes is visible. Figure 2 shows flare in January 2011 [8], was observed for 55 h of qual- a preliminary spectral analysis for two different flux ityselected live time between December 2008 and April levels: the flare happened on February 17, 2010, and 2011. The measured excess of ∼ 240 γ-rays (6.3σ) the rest of the season 2009-2010. Clear evolution of corresponds to a VHE flux of ∼ 1% Crab. There is a the spectral parameters can be seen. weak indication that the flux observed by VERITAS H 1426+428 was first detected during an outburst in 2011 may be higher than seen from 2008-10. The in 2001 [6]. This HBL was observed by VERITAS VERITAS flux is consistent with that (2 ± 1% Crab) for 22 hr quality-selected live time between 2007 and reported during the MAGIC discovery 2011. A weak excess, 5.2σ, is observed in these data, marking the first time H 1426+428 is detected since 2002. The observed flux is ¡2% Crab, well below the value (13% Crab) reported during its VHE discovery, and also below any other published VHE flux or limit B. Radio Galaxies from this source. PG 1553+113 is a hard-spectrum (ΓLAT ∼ −1.66) Fermi-LAT blazar [7]. It is likely the most distant Radio galaxies observed by VERITAS include M 87, HBL detected at VHE (see z > 0.43 from [3]). It was 3C 111 and NGC 1275. A dedicated contribution on observed by VERITAS for 60 h of quality-selected live M 87 is presented in these proceedings. A preliminary time between May 2010 and May 2011. These data analysis of 11 hr of quality-selected data of 3C 111 re- result in the most signicant VHE detection (39σ) of sults in a flux upper limit of ∼ 3% Crab flux above this HBL. The time-averaged VHE ux is 10% Crab 200 GeV. NGC 1275 is an unusual early-type galaxy above 200 GeV, higher than the archival VHE mea- located in the center of the Perseus cluster. Its radio surements, and the photon spectrum is well described emission is core dominated, but emission lines are also between 175 GeV and 500 GeV by a powerlaw func- seen, making it difficult to classify it according to the tion with photon index Γ = −4.41 ± 0.14. The VHE Faranhoff & Riley (FR) classification [12]. In Fall 2008 spectrum can be used to set an upper limit on the the Fermi γ-ray space telescope reported the detection redshift of z < 0.5. of γ-ray emission from a position consistent with the 1ES 0229+200 is one of the hardest-spectrum VHE core of NGC 1275. VERITAS observed the core region blazars known (ΓHESS = −2.5; [18]). It was observed of NGC 1275 for about 11 hr between 2009 January 15 by VERITAS as part of an intense MWL observation and February 26, resulting in 7.8 hr of quality-selected campaign for 46 h live time from 2009-11. A strong live time. No γ-ray emission is detected above the signal is detected (∼ 600 γ-rays, 9.0σ) in these ob- analysis energy threshold of ∼190 GeV, resulting in a servations corresponding to an average VHE flux of flux upper limit incompatible with the extrapolation ∼ 2% Crab above 300 GeV. The VERITAS flux is of the Fermi-LAT spectrum. Under the assumption variable on a timescale of months, and the prelimi- of a SSC emission mechanism, the VERITAS result nary VHE spectrum measured between 220 GeV and suggests the presence of a cutoff in the sub-VHE en- 15 TeV has photon index Γ = −2.44 ± 0.11. The re- ergy range [13]. The detection in Summer 2010 of sults of the MWL campaign are in preparation. It VHE γ-ray emission by MAGIC [14] has eventually is interesting to note that 1ES 0229+200 is the only included NGC 1275 among the few interesting radio VERITAS-detected blazar not included in the 1FGL galaxies for future VHE investigation. eConf C110509 2011 Fermi Symposium, Roma., May. 9-12 3

×10-6

-1 18 ×10-6 VERITAS Mrk 421 lightcurve E>300 GeV s -1 s -2 25 17 February 2010 flare E>300 GeV -2 m m 16

20 14

15 12

10 hLightCurve

Entries 11038 10 hLightCurve Mean 5.524e+04

Entries 5900

RMS 0.0622 5 Mean 5.522e+04 PRELIMINARY 8 55244.35 55244.4 55244.45 55244.5 RMS 41.4 MJD 6

4

2

0 55160 55180 55200 55220 55240 55260 MJD

FIG. 1: Nigthly lightcurve of Markarian 421 during the VERITAS 2009-2010 monitoring campaign. The source is detected at an average flux level of approximatively 2 Crab units over the entire season. On February 17, 2010 the source is observed in flaring state at a flux level of ∼ 8 Crab units. A zoom of the intra-night 2-minute bins lightcurve of the flaring event is shown. During the flaring event the source and intra-night variability is seen.

C. Clusters of Galaxies tionally interacting with its nearby companion M 81. This interaction has deformed M 82 in such a way Observation of clusters of galaxies is done unavoidly that an active starburst region in its center with ∼ during the observation of many radio galaxies. This a diameter of 1000 light years has been devel- is the case for NGC 1275 and M 87 where the Perseus oped [21, 22]. Throughout this compact region stars and Virgo clusters respectively are observed during are being formed at a rate approximately 10 times the radio galaxy observation. However, up to now a faster than in entire “normal” galaxies like the Milky dedicated study of the clusters themselves has been Way. Hence the supernovae rate is 0.1 to 0.3 per done only on the Coma cluster. The Coma cluster is year [23, 24]. The high star formation rate in M 82 a nearby cluster of galaxies which is well studied at implies the presence of numerous shock waves in su- all wavelengths [16]. It is at a distance of 100 Mpc pernova remnants and around massive young stars. 15 (z =0.023) and has a mass of 2 × 10 M⊙. Its X-ray Similar shock waves are known to accelerate electrons and radio features suggest the presence of accelerated to very high energies, and possibly ions too. The in- electrons in the intergalactic medium emitting non- tense radio-synchrotron emission observed in the cen- thermal radiation. Beside relativistic electrons, there tral region of M 82 suggests a very high cosmic-ray may also be a population of highly energetic protons. energy density, about two orders of magnitude higher Both high energy electrons and protons are known than in the Milky Way [25]. Acceleration and propa- to be able to produce VHE photons. A total of 19 gation of cosmic rays in the starburst core are thus ex- hr of data have been recorded between March and pected to be responsible for VHE γ-ray emission. The- May 2008. No evidence for point-source emission was oretical predictions include significant contributions observed within the field of view and a preliminary from both leptonic and hadronic particle interactions. ∼ Cosmic-ray ions create VHE gamma rays through col- upper limit of 3% of the Crab flux is given for a 0 moderately extended region centered on the core [17]. lisions with interstellar matter, producing π which decay into γ-rays. Alternatively, accelerated cosmic- ray electrons may inverse-Compton scatter ambient X-ray photons up to the VHE range [22, 26, 27, 28]. D. Starburst Galaxies VERITAS observed M 82 for a total of 137 hours of M 82 a prototype small starburst galaxy, located quality-selected live time between January 2008 and approximately 3.7 Mpc from Earth, in the direction April 2009 at a mean zenith angle of 39◦. An ex- of the . M 82 is gravita- cess of 91 gamma-ray-like events (∼0.7 photons per eConf C110509 4 2011 Fermi Symposium, Roma., May. 9-12

process responsible for the VHE emission [29].

] -3 -1 10 VERITAS Mrk 421 Season 2009-2010 s -1 10-4 III. CONCLUSIONS Flare 17 Feb 2010 TeV -2 10-5

10-6 2009-2010 Season (no Flare) The VERITAS extragalactic science program is well established. The study of the AGN physics develops -7 dN/dE [ m 10 through two complementary observational programs 10-8 of blazars and non-blazar (radio galaxies) AGN. Γ = -1.90 ± 0.02 -9 Several blazars have been detected or discovered, and 10 E = 5.8 ± 0.4 cut a new catalog of a sub-class of AGN, the IBL catalog, -10 10 was started by VERITAS. The VHE-IBL catalog Γ ± 10-11 = -2.01 0.02 ± consists entirely in VERITAS-discovered blazars. Ecut = 3.4 0.2 PRELIMINARY 10-12 Distant blazars are also studied, resulting in signif- icant measurements for the EBL characterization. 10-1 1 10 E [ TeV ] Non-AGN sources are also investigated. A dedicated VHE study on the Coma cluster of galaxies resulted in a flux upper limit on the extended region centered FIG. 2: VERITAS preliminary spectral analysis of Markarian 421 for two different flux levels: the flare on on the core. The first detection of γ-ray emission February 17, 2010 (red dots) and the rest of the 2009-2010 from a starburst galaxy established a connection season (black dots). between cosmic-ray acceleration and star formation.

This research is supported by grants from the US hour) are detected for a total 4.8σ statistical post- Department of Energy, the US National Science Foun- trials significance above 700 GeV. The observed dif- dation, and the Smithsonian Institution, by NSERC in ferential VHE gamma-ray spectrum is best fitted us- Canada, by Science Foundation Ireland, and by STFC ing a power-law function with a photon index Γ = in the UK. We acknowledge the excellent work of the 2.5 ± 0.6stat ± 0.2sys. Comparison of the VERITAS technical support staff at the FLWO and at the collab- VHE spectrum with predictions of the theoretical orating institutions in the construction and operation models supports a hadronic scenario as the dominant of the instrument.

[1] Urry, C., & Padovani, P., PASP, 1995, 107, 803 [18] Wilson, A. S., & Yang, Y., ApJ, 2002, 568, 133-140 [2] Jones, T. W., O’dell, S. L., Stein, W. A., ApJ, 1974, [19] Acciari, V. A., et al., Science, 2009, 325, 444 188, 353-368 [20] Harris, D. E., Cheung, C. C., & Stawarz, L., ApJ, [3] Prestage R. M., Peacock J. A., MNRAS, 1988, 230, 2009, 699, 305-314 131-160 [21] Yun, M. S., Ho, P. T. P., Lo, K. Y., Nature, 1994, [4] Dermer, C. D., et al., NJPh, 2009, 11, 5016 372, 530-532 [5] Acciari, V. A., et al., ApJ, 2011, 738 25 [22] V¨olk, H. J., Aharonian, F. A., Breitschwerdt, D., [6] Horan, D., et al., ApJ, 2002, 571, 753 Space Science Reviews, 1996, 75, 279-297 [7] Abdo, A., et al., ApJS, 2010, 188, 405 [23] Kronberg, P. P., Biermann, P., & Schwab, F. R., ApJ, [8] Mariotti, M., Astronomers Telegram, 2011, #3100 1985, 291, 693-707 [9] Aharonian, F., et al., A&A, 2003, 403, L1-L5 [24] Fenech, D. M., et al., MNRAS, 2008, 391, 1384-1402 [10] Aharonian, F., et al., Science, 2006, 314, 1424-1427 [25] Rieke, G. H., et al., ApJ, 1980, 238, 24-40 [11] Acciari, V. A., et al., ApJ, 2008, 679, 397-403 [26] Pohl, M., A&A, 1994, 287, 453-462 [12] Fanaroff, B. F., & Riley, J. M., MNRAS, 1974, 167, [27] Persic, M., Rephaeli, Y., Arieli, Y., A&A, 2008, 486, 31 143-149 [13] Acciari, V. A., et al., ApJ, 2009 706, L275-L280 [28] de Cea del Pozo, E., Torres, D. F., Marrero, A. Y. R., [14] Mariotti M., 2010, Astr. Telegram, 2916 ApJ, 2009, 698, 1054-1060 [15] Albert, J., et al., ApJ, 2008, 685, L23-L26 [29] Acciari, V. A., et al., Nature, 2009, 462, 770-772 [16] Neumann, D. M., et al., A&A, 2003, 400, 811 [17] Perkins, J. S., AIPC, 2008, 1085, 569-572

eConf C110509