VERITAS detection of an elevated VHE flux from the blazar H 1426+428

ATel #14501; John Quinn (University College Dublin) for the VERITAS Collaboration
on 31 Mar 2021; 22:06 UT
Credential Certification: John Quinn (john.quinn@ucd.ie)

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The VERITAS Collaboration reports an elevated very-high-energy (VHE; >100 GeV) gamma-ray flux from the BL Lac-type blazar H 1426+428 (14h28m32.6s +42d40m28.9s, J2000, z=0.129). VERITAS obtained 8h of exposure in observations between January and March 2021. Preliminary analysis results in a 9σ detection, corresponding to a flux F(>0.25 TeV) = (5.5 ± 0.8) × 10^-12 cm^-2 s^-1, or (3.2% ± 0.5%) of the Crab Nebula flux. The measured flux in 2021 is approximately double its long-term average over the last decade and a preliminary spectral analysis suggests enhanced activity at the higher energies. Swift-XRT monitoring in the 0.2-10 keV band also indicates a high count rate during March 2021 observations, with significant flux variability.

H 1426+428 is classified as an extreme BL Lac with synchrotron peak located beyond 1 keV (Costamante et al. 2001) and was routinely detected at VHE energies before 2002 at flux levels between 5% and 18% of the Crab Nebula flux (Aharonian et al. 2002; Horan et al. 2002; Djannati-Atai et al. 2002). Since 2002, VHE observations of H 1426+428 have resulted in significantly lower fluxes or flux upper limits (Mueller et al. 2011; Abeysekara et al. 2019; Acciari et al. 2020).

VERITAS will continue to observe H 1426+428 in the coming weeks. Multiwavelength observations are encouraged. Questions regarding VERITAS observations should be directed to John Quinn (john.quinn@ucd.ie). VERITAS (the Very Energetic Radiation Imaging Telescope Array System) is located at the Fred Lawrence Whipple Observatory in southern Arizona, USA, and is most sensitive to gamma rays between ∼85 GeV and ∼30 TeV. For further information see the VERITAS web site.