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Deep broadband observations of the distant gamma-ray blazar PKS 1424+240

  • Author(s): 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, AOF
  • 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
  • et al.
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..

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