Gamma rays from the quasar PKS 1441+25: story of an escape

Creators: Abeysekara, A. U.; Archambault, S.; Archer, A.; Aune, T.; Barnacka, A.; Benbow, W.; Bird, R.; Biteau, J.; Buckley, J. H.; Bugaev, V.; Cardenzana, J. V.; Cerruti, M.; Chen, X.; Christiansen, J. L.; Ciupik, L.; Connolly, M. P.; Coppi, P.; Cui, W.; Dickinson, H. J.; Dumm, J.; Eisch, J. D.; Errando, M.; Falcone, A.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Flinders, A.; Fortin, P.; Fortson, L.; Furniss, A.; Gillanders, G. H.; Griffin, S.; Grube, J.; Gyuk, G.; Hütten, M.; Håkansson, N.; Hanna, D.; Holder, J.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Khassen, Y.; Kieda, D.; Krause, M.; Krennrich, F.; Kumar, S.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; Meagher, K.; Moriarty, P.; Mukherjee, R.; Nieto, D.; O'Faoláin de Bhróithe, A.; Ong, R. A.; Otte, A. N.; Park, N.; Perkins, J. S.; Petrashyk, A.; Pohl, M.; Popkow, A.; Pueschel, E.; Quinn, J.; Ragan, K.; Ratliff, G.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Rousselle, J.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Smith, A. W.; Staszak, D.; Telezhinsky, I.; Todd, N. W.; Tucci, J. V.; Tyler, J.; Vassiliev, V. V.; Vincent, S.; Wakely, S. P.; Weiner, O. M.; Weinstein, A.; Wilhelm, A.; Williams, D. A.; Zitzer, B.; Smith, P. S.; Holoien, T. W.-S.; Prieto, J. L.; Kochanek, C. S.; Stanek, K. Z.; Shappee, B. J.; Hovatta, T.; Max-Moerbeck, W.; Pearson, T. J.; Reeves, R. A.; Richards, J. L.; Readhead, A. C. S.; Madejski, G. M.; Djorgovski, S. G.; Drake, A. J.; Graham, M. J.; Mahabal, A.

Abstract

Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the Universe. The detection of significant emission above 100 GeV from a distant quasar would show that some of the radiated gamma rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (EBL), or the radiation near the supermassive black hole lying at the jet's base. VERITAS detected gamma-ray emission up to 200 GeV from PKS 1441+25 (z=0.939) during April 2015, a period of high activity across all wavelengths. This observation of PKS 1441+25 suggests that the emission region is located thousands of Schwarzschild radii away from the black hole. The gamma-ray detection also sets a stringent upper limit on the near-ultraviolet to near-infrared EBL intensity, suggesting that galaxy surveys have resolved most, if not all, of the sources of the EBL at these wavelengths.

Additional Information

© 2015. The American Astronomical Society. Received 2015 August 10; accepted 2015 November 17; published 2015 December 15. This research is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, and by NSERC in Canada, with additional support from NASA Swift GI grant NNX15AR38G. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument. The VERITAS Collaboration is grateful to Trevor Weekes for his seminal contributions and leadership in the field of VHE gamma-ray astrophysics, which made this study possible. ASAS-SN thanks LCOGT, NSF, Mt. Cuba Astronomical Foundation, OSU/CCAPP and MAS/Chile for their support. The observations at Steward Observatory are funded through NASA Fermi GI grant NNX12AO93G. CRTS is supported by the NSF grants AST-1313422 and AST-1413600. The OVRO 40-m monitoring program is supported in part by NASA grants NNX08AW31G and NNX11A043G, and NSF grants AST-0808050 and AST-1109911. The National Radio Astronomy Observatory is a facility of NSF operated under cooperative agreement by Associated Universities, Inc. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009).

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