DEEP BROADBAND OBSERVATIONS OF THE DISTANT GAMMA-RAY BLAZAR PKS 1424+240

Journal Article · Thu Apr 10 04:00:00 EDT 2014 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/785/1/L16· OSTI ID:22365911

Archambault, S. ^[1]; Aune, T. ^[2]; Behera, B.; Chen, X.; Federici, S. ^[3]; Beilicke, M.; Bugaev, V. ^[4]; Benbow, W.; Cerruti, M. ^[5]; Berger, K. ^[6]; Bird, R. ^[7]; Biteau, J. ^[8]; Byrum, K. ^[9]; Cardenzana, J. V ^[10]; Ciupik, L. ^[11]; Connolly, M. P. ^[12]; Cui, W. ^[13]; Dumm, J. ^[14]; Errando, M. ^[15]; others, and

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1. Physics Department, McGill University, Montreal, QC H3A 2T8 (Canada)
2. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
3. DESY, Platanenallee 6, D-15738 Zeuthen (Germany)
4. Department of Physics, Washington University, St. Louis, MO 63130 (United States)
5. Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645 (United States)
6. Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States)
7. School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland)
8. Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States)
9. Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)
10. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States)
11. Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605 (United States)
12. School of Physics, National University of Ireland Galway, University Road, Galway (Ireland)
13. Department of Physics, Purdue University, West Lafayette, IN 47907 (United States)
14. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)
15. Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027 (United States)

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{sup –7} photons m{sup –2} s{sup –1} above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02 ± 0.08) × 10{sup –7} photons m{sup –2} s{sup –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.

• OSTI ID: 22365911
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 785; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
BACKGROUND RADIATION
BL LACERTAE OBJECTS
COMPARATIVE EVALUATIONS
COSMIC PHOTONS
DIAGRAMS
GALAXIES
GAMMA RADIATION
GEV RANGE
HADRONS
OPACITY
PAIR PRODUCTION
QUASARS
RED SHIFT
TELESCOPES
VISIBLE RADIATION
X RADIATION