Deep Broadband Observations of the Distant Gamma-ray Blazar PKS 1424+240

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 $z\ge 0.6035$, 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 hours of VERITAS observations from three years, a multiwavelength light curve and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1$\pm 0.3$)$\times 10^{-7}$ ph m${}^{-2}$s${}^{-1}$ above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02$\pm 0.08$)$\times 10^{-7}$ ph m${}^{-2}$s${}^{-1}$ above 120 GeV. The measured differential very high energy (VHE; $E\ge 100$ GeV) spectral indices are $\Gamma =$3.8$\pm$0.3, 4.3$\pm$0.6 and 4.5$\pm$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 longer than year timescales 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.

ApJL accepted March 17, 2014

References in corpus (8)

• Fermi Large Area Telescope Bright Gamma-ray Source List
• Very-High-Energy Gamma Rays from a Distant Quasar: How Transparent Is the Universe?
• The First VERITAS Telescope
• The Imprint of The Extragalactic Background Light in the Gamma-Ray Spectra of Blazars
• Hints of the existence of Axion-Like-Particles from the gamma-ray spectra of cosmological sources
• Formation of hard VHE gamma-ray spectra of blazars due to internal photon-photon absorption
• Inspecting absorption in the spectra of extra-galactic gamma-ray sources for insight into Lorentz invariance violation
• Evidence for the Secondary Emission as the Origin of Hard Spectra in TeV Blazars

Cited by in corpus (18)

• Sensitivity of the Cherenkov Telescope Array to the detection of axion-like particles at high gamma-ray opacities
• First-Epoch VLBA Imaging of Twenty New TeV Blazars
• Testing two-component models on very-high-energy gamma-ray emitting BL Lac objects
• A Correlation Between Hard Gamma-ray Sources and Cosmic Voids Along the Line of Sight
• PKS 1424+240: yet another masquerading BL Lac object as a possible IceCube neutrino source
• Understanding the TeV emission from a distant blazar PKS 1424+240 in a lepto-hadronic jet model
• Short Timescale Photometric and Polarimetric Behavior of two BL Lacertae Type Objects
• Particle diffusion and localized acceleration in inhomogeneous AGN jets - Part I: Steady-state spectra
• First broadband characterization and redshift determination of the VHE blazar MAGIC J2001+439
• Luminous and high-frequency peaked blazars: the origin of the $\gamma$-ray emission from PKS 1424+240
• EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources
• A self-consistent interpretation of the GeV-TeV emission from a distant blazar PKS 1424+240
• Multiwavelength Observations of the Blazar VER J0521+211 During an Elevated TeV Gamma-Ray State
• Effects of Spatial Fluctuations in the Extra Galactic Background Light on Hard Gamma Ray Spectra
• Constraining the redshifts of TeV BL Lac objects
• Exploring TeV candidates of Fermi blazars through machine learning
• Redshift constrain of BL Lac PKS 1424+240
• Application of the optimised next neighbour image cleaning method to the VERITAS array