Fermi Gamma-ray Space Telescope

VERITAS detection of VHE gamma-ray emission from the blazar S3 1227+25

M. Santander (for the VERITAS Collab.)
D. Gasparrini, R. Ojha, S. Cutini, and B. Carpenter (for the Fermi-LAT Collab.), S. Jorstad, A. Marscher

Abstract:

We report on the detection of very high energy (VHE, E > 100 GeV) gamma-ray emission from the blazar S3 1227+25 (ON 246) with the VERITAS array. VERITAS observations were triggered by the detection of a hard-spectrum GeV flare from this source on May 15, 2015 using the Large Area Telescope (LAT) onboard the Fermi satellite. A two-hour VERITAS exposure on May 16th resulted in a strong 9-sigma detection of the blazar with a very soft spectrum at a flux level of 8% of the Crab nebula above 120 GeV, which was publicly announced in Astronomer's Telegram #7516. The blazar was subsequently detected during the following nights until the end of the flaring activity on May 21st. S3 1227+25 has been classified as an intermediate-synchrotron-peaked (ISP) blazar, which makes it the eighth blazar of this class to be detected in the VHE range. The detailed study of this type of object and how it compares to other ISP blazars can shed new light on the emission processes at work in blazar flares and how this class fits in the general blazar picture. This contribution summarizes the quasi-simultaneous VERITAS, Fermi-LAT, Swift, and optical polarimetry and photometry measurements performed during the May flaring period.