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) x 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) x 10-7 photons m(-2) s(-1) above 120 GeV. The measured differential very high energy (VHE; E >= 100 GeV) spectral indices are Gamma = 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 tau = 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.
DEEP BROADBAND OBSERVATIONS OF THE DISTANT GAMMA-RAY BLAZAR PKS 1424+240 / Archambault S; Aune T; Behera B; Beilicke M; Benbow W; Berger K; Bird R; Biteau J; Bugaev V; Byrum K; Cardenzana JV; Cerruti M; Chen X; Ciupik L; Connolly MP; Cui W; Dumm J; Errando M; Falcone A; Federici S; Feng Q; Finley JP; Fleischhack H; Fortson L; Furniss A; Galante N; Gillanders GH; Griffin S; Griffiths ST; Grube J; Gyuk G; Hanna D; Holder J; Hughes G; Humensky TB; Johnson CA; Kaaret P; Kertzman M; Khassen Y; Kieda D; Krawczynski H; Krennrich F; Kumar S; Lang MJ; Madhavan AS; Maier G; McCann A; Meagher K; Moriarty P; Mukherjee R; Nieto D; de Bhroithe AO; Ong RA; Otte AN; Park N; Pohl M; Popkow A; Prokoph H; Quinn J; Ragan K; Rajotte J; Reyes LC; Reynolds PT; Richards GT; Roache E; Sembroski GH; Shahinyan K; Staszak D; Telezhinsky I; Tucci JV; Tyler J; Varlotta A; Vassiliev VV; Vincent S; Wakely SP; Weinstein A; Welsing R; Wilhelm A; Williams DA; Ackermann M; Ajello M; Albert A; Baldini L; Bastieri D; Bellazzini R; Bissaldi E; Bregeon J; Buehler R; Buson S; Caliandro GA; Cameron RA; Caraveo PA; Cavazzuti E; Charles E; Chiang J; Ciprini S; Claus R; Cutini S; DAmmando F; de Angelis A; de Palma F; Dermer CD; Digel SW; Di Venere L; Drell PS; Favuzzi C; Franckowiak A; Fusco P; Gargano F; Gasparrini D; Giglietto N; Giordano F; Giroletti M; Grenier IA; Guiriec S; Jogler T; Kuss M; Larsson S; Latronico L; Longo F; Loparco F; Lubrano P; Madejski GM; Mayer M; Mazziotta MN; Michelson PF; Mizuno T; Monzani ME; Morselli A; Murgia S; Nuss E; Ohsugi T; Ormes JF; Paneque D; Perkins JS; Piron F; Pivato G; Raino S; Razzano M; Reimer A; Reimer O; Ritz S; Schaal M; Sgro C; Siskind EJ; Spinelli P; Takahashi H; Tibaldo L; Tinivella M; Troja E; Vianello G; Werner M; Wood M. - In: THE ASTROPHYSICAL JOURNAL LETTERS. - ISSN 2041-8205. - STAMPA. - 785:1(2014), pp. 785.16-785.23. [10.1088/2041-8205/785/1/L16]
DEEP BROADBAND OBSERVATIONS OF THE DISTANT GAMMA-RAY BLAZAR PKS 1424+240
D'AMMANDO, FILIPPO;
2014
Abstract
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) x 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) x 10-7 photons m(-2) s(-1) above 120 GeV. The measured differential very high energy (VHE; E >= 100 GeV) spectral indices are Gamma = 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 tau = 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
