Deep Broadband Observations of the Distant Gamma-ray Blazar PKS 1424+240

S. Archambault , T. Aune , B. Behera , M. Beilicke , W. Benbow , K. Berger , R. Bird , J. Biteau , V. Bugaev , K. Byrum , J.V Cardenzana , M. Cerruti , X. Chen , L. Ciupik , M.P. Connolly , W. Cui , J. Dumm , M. Errando , A. Falcone , S. Federici , Q. Feng , J.P. Finley , H. Fleischhack , L. Fortson , A. Furniss , N. Galante , G. H. Gillanders , S. Griffin , S.T. Griffiths , J. Grube , G. Gyuk , D. Hanna , J. Holder , G. Hughes , T.B. Humensky , C.A. Johnson , P. Kaaret , M. Kertzman , Y. Khassen , D. Kieda , H. Krawczynski , F. Krennrich , S. Kumar , M.J. Lang , A.S Madhavan , G. Maier , A. Mccann , K. Meagher , P. Moriarty , R. Mukherjee , D. Nieto , A. O'Faoláin de Bhróithe , R.A. Ong , A.N. Otte , N. Park , M. Pohl , A. Popkow , H. Prokoph , J. Quinn , K. Ragan , J. Rajotte , L.C. Reyes , P.T. Reynolds , G.T. Richards , E. Roache , G. H. Sembroski , K. Shahinyan , D. Staszak , I. Telezhinsky , J.V. Tucci , J. Tyler , A. Varlotta , V. V. Vassiliev , S. Vincent , S.P. Wakely , A. Weinstein , R. Welsing , A. Wilhelm , D.A. Williams , M. Ackermann , M. Ajello , A. Albert , L. Baldini , D. Bastieri , R. Bellazzini , E. Bissaldi , J. Bregeon (1) , R. Buehler , S. Buson , G.A. Caliandro , R.A. Cameron , P.A. Caraveo , E. Cavazzuti , E. Charles , J. Chiang , S. Ciprini , R. Claus , S. Cutini , F. d'Ammando , A. de Angelis , F. de Palma , C.D. Dermer , S.W. Digel , L. Di Venere , P.S. Drell , C. Favuzzi , A. Franckowiak , P. Fusco , F. Gargano , D. Gasparrini , N. Giglietto , F. Giordano , M. Giroletti , I.A. Grenier (2) , S. Guiriec , T. Jogler , M. Kuss , S. Larsson , L. Latronico , F. Longo , F. Loparco , P. Lubrano , G.M. Madejski , M. Mayer , M.N. Mazziotta , P.F. Michelson , T. Mizuno , M.E. Monzani , A. Morselli , S. Murgia , E. Nuss (1) , T. Ohsugi , J.F. Ormes , D. Paneque , J.S. Perkins , F. Piron (1) , G. Pivato , S. Rainò , M. Razzano , A. Reimer , O. Reimer , S. Ritz , M. Schaal , C. Sgrò , E.J. Siskind , P. Spinelli , H. Takahashi , L. Tibaldo , M. Tinivella , E. Troja , G. Vianello , M. Werner , M. Wood

1 LUPM - Laboratoire Univers et Particules de Montpellier
2 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation

We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope, and Swift UV Optical Telescope data between 2009 February 19 and 2013 June 8. This blazar resides at a redshift of z ≥ 0.6035, displaying a significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production with the extragalactic background light. We present more than 100 hr of VERITAS observations over three years, a multiwavelength light curve, and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1 ± 0.3) × 10–7 photons m–2 s–1 above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02 ± 0.08) × 10–7 photons m–2 s–1 above 120 GeV. The measured differential very high energy (VHE; E ≥ 100 GeV) spectral indices are Γ = 3.8 ± 0.3, 4.3 ± 0.6 and 4.5 ± 0.2 in 2009, 2011, and 2013, respectively. No significant spectral change across the observation epochs is detected. We find no evidence for variability at gamma-ray opacities of greater than τ = 2, where it is postulated that any variability would be small and occur on timescales longer than a year if hadronic cosmic-ray interactions with extragalactic photon fields provide a secondary VHE photon flux. The data cannot rule out such variability due to low statistics.

Mots clés: BL Lacertae objects: individual (PKS 1424+240)-cosmic background radiation; gamma rays: galaxies; photon: flux; photon: absorption; gamma ray: flux; detector: optical; X-ray: detector; cosmic radiation: interaction; spectral; blazar; VHE; VERITAS; pair production; statistics; background; redshift; opacity

Domaines: Astrophysique [astro-ph]

S. Archambault, T. Aune, B. Behera, M. Beilicke, W. Benbow, et al.. Deep Broadband Observations of the Distant Gamma-ray Blazar PKS 1424+240. Astrophys.J.Lett., 2014, 785, pp.L16. ⟨10.1088/2041-8205/785/1/L16⟩. ⟨hal-02024305⟩