VERITAS Detection of Gamma-ray Flaring Activity from BL Lacertae

ATel #16854; Amy Furniss (UC Santa Cruz) for the VERITAS Collaboration
on 8 Oct 2024; 19:35 UT
Credential Certification: Amy Furniss (afurniss@ucsc.edu)

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We report the VERITAS detection of very-high-energy (VHE; E> 100 GeV) flaring activity in BL Lacertae (z=0.0668, RA: 22 02 43.29 Dec: +42 16 39.98, J2000). Following the GeV gamma-ray activity observed by Fermi-LAT (reported in ATel #16849), approximately 3.5 hours of observations were collected by VERITAS between October 5, 2024, and October 7, 2024 (UTC). A preliminary analysis of the data yields significant detection on Oct 5 and 6, with a preliminary flux above 200 GeV of F = (4.1+/-0.7)e-7 m^-2 s^-1 or ~20% of the Crab Nebula flux, decreasing to <10% of the Crab Nebula flux on Oct 7. Intra-night light curves above 200 GeV show evidence for sub-hour variability on October 5, 2024. Gamma-ray activity above 1 TeV was also reported by LHAASO during this time (ATel #16850). VERITAS will continue to observe BL Lac as long as observations are feasible. Multi-wavelength observations are encouraged. Questions regarding the VERITAS observations should be directed to Amy Furniss (afurniss@ucsc.edu). VERITAS (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 (http://veritas.sao.arizona.edu).