학술논문
DEEP BROADBAND OBSERVATIONS OF THE DISTANT GAMMA-RAY BLAZAR PKS 1424+240
Document Type
article
Author
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 Bhróithe, A O'Faoláin; 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; D'Ammando, F; de Angelis, A
Source
The Astrophysical Journal Letters. 785(1)
Subject
Language
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) × 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. © 2014. The American Astronomical Society. All rights reserved..