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Deep Broadband Observations of the Distant Gamma-Ray Blazar PKS 1424+240
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2014 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 785, no 1, article id L16Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2014. Vol. 785, no 1, article id L16
Keywords [en]
BL Lacertae objects: individual (PKS 1424+240)-cosmic background radiation, gamma rays: galaxies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
URN: urn:nbn:se:lnu:diva-42782DOI: 10.1088/2041-8205/785/1/L16OAI: oai:DiVA.org:lnu-42782DiVA, id: diva2:807510
Available from: 2015-04-23 Created: 2015-04-23 Last updated: 2017-12-04Bibliographically approved

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Prokoph, Heike

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