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. FedericiQ. 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, 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, 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, T. Ohsugi, J. F. Ormes, D. Paneque, J. S. Perkins, F. Piron, 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

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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.

Original languageEnglish (US)
Article number785
JournalAstrophysical Journal Letters
Volume785
Issue number1
DOIs
StatePublished - Apr 10 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Archambault, S., Aune, T., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Biteau, J., Bugaev, V., Byrum, K., Cardenzana, J. V., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dumm, J., Errando, M., Falcone, A., ... Wood, M. (2014). Deep broadband observations of the distant gamma-ray blazar PKS 1424+240. Astrophysical Journal Letters, 785(1), [785]. https://doi.org/10.1088/2041-8205/785/1/L16