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  4. Deep Broadband Observations of the Distant Gamma-Ray Blazar PKS 1424+240
 
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Deep Broadband Observations of the Distant Gamma-Ray Blazar PKS 1424+240

Author(s)
Archambault, S.
Aune, T.
Behera, B.
Cavazzuti, Elisabetta  
Ciprini, Stefano  
more
Subjects

BL Lacertae objects i...

gamma rays galaxies

Date Issued
2014-04-01
Mission(s)
Fermi  
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<SUP>-7</SUP> photons m<SUP>-2</SUP> s<SUP>-1</SUP> above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02 0.08) 10<SUP>-7</SUP> photons m<SUP>-2</SUP> s<SUP>-1</SUP> above 120 GeV. The measured differential very high energy (VHE; E >= 100 GeV) spectral indices are Gamma = 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 tau = 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.
URI
https://hdl.handle.net/20.500.13025/3643
DOI
10.1088/2041-8205/785/1/L16
URL
http://adsabs.harvard.edu/abs/2014ApJ...785L..16A
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