A luminous and isolated gamma-ray flare from the blazar B2 1215+30

TL;DR

This paper reports a rare, luminous gamma-ray flare from the blazar B2 1215+30, characterized by rapid variability and multiwavelength observations, providing insights into jet emission mechanisms and relativistic beaming.

Contribution

It presents the first detailed analysis of a luminous gamma-ray flare from B2 1215+30, combining multiwavelength data and modeling to understand jet physics and emission processes.

Findings

Gamma-ray flux reached 2.4 times the Crab Nebula flux.

Variability timescale was less than 3.6 hours.

Spectral energy distribution indicates high beaming with Doppler factor > 10.

Abstract

B2 1215+30 is a BL Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes, and subsequently confirmed by the VERITAS observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B2 1215+30 during routine monitoring observations of the blazar 1ES 1218+304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of < 3.6 h. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a one-zone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor > 10, and an electron population with spectral index < 2.3.