VERITAS Discovery of VHE Emission from the EHBL 1ES 1028+511
ATel #16458; Amy Furniss (UC Santa Cruz) for the VERITAS Collaboration
on 18 Feb 2024; 16:25 UT
Credential Certification: Amy Furniss (afurniss@ucsc.edu)
We report the VERITAS discovery of very-high-energy (VHE; >100 GeV) gamma-ray emission from the blazar 1ES 1028+511. This extreme high-frequency-peaked BL Lac (EHBL) object, located at redshift z = 0.361 (Polomski et al. 1997 ApJ 486, 179), is a non-variable, hard-spectrum member of all recent major Fermi-LAT catalogs, and has long been a target for VHE observations.
Approximately 59 hours of good-weather dark-time observations were collected by VERITAS between 08 November 2007 and 05 February 2024 (UTC), yielding ~43 hours of quality-selected data. A preliminary analysis of these data yields an excess of ~270 gamma-ray events above background at the position of the source, corresponding to a statistical significance of 5.5 standard deviations. The preliminary flux estimate is F(>200 GeV) = (2.4 +/- 0.5) e-12 cm^-2 s^-1, or approximately 1% of the Crab Nebula flux above the same threshold.
Prior analysis of Fermi-LAT data indicated the likely presence of VHE emission. A significant cluster of VHE photons was found at the source location (Armstrong et al. 2015 MNRAS 452, L3159), and the object was observed at ~3.6 sigma between 150 and 500 GeV in the 3FHL catalog (Ackermann et al. 2017 ApJS 232, 18). With the VERITAS discovery, 1ES 1028+511 is among the most distant EHBLs detected at VHE so far. The VERITAS flux is consistent with the 3FHL 150-500 GeV flux.
VERITAS will continue to observe 1ES 1028+511; 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).
