VERITAS Observations of a Very High Energy Gamma-ray Flare from the Blazar 3C 66A

TL;DR

This paper reports the detection of very high energy gamma-ray emission from the blazar 3C 66A by VERITAS, including flux measurement, spectral analysis, and variability, confirming its active VHE state.

Contribution

First detection of VHE gamma-ray emission from 3C 66A with detailed spectral and variability analysis using VERITAS.

Findings

Detected 1791 excess events with 21.2 sigma significance

Measured flux above 200 GeV at 6% of Crab Nebula

Observed variability on a daily timescale

Abstract

The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007 - 2008 in VHE (very high energy: E > 100 GeV) gamma-rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess of 1791 events is detected, corresponding to a significance of 21.2 standard deviations (sigma), in these observations (32.8 hours live time). The observed integral flux above 200 GeV is 6% of the Crab Nebula's flux and shows evidence for variability on the time-scale of days. The measured energy spectrum is characterized by a soft power law with photon index Gamma = 4.1 +- 0.4_stat +- 0.6_sys. The radio galaxy 3C 66B is excluded as a possible source of the VHE emission.