Fermi LAT detection of a GeV gamma-ray flare from the high-energy peaked BL Lac object 1ES 1215+303 (B2 1215+30, ON 325)

ATel #10270; Stefano Ciprini (ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 15 Apr 2017; 15:28 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray emission from a source positionally consistent with the very-high energy peaked BL Lac object 1ES 1215+303 (also known as ON 325, Ton 605, B2 1215+30 and 3FGL J1217.8+3007, Acero et al. 2015, ApJS 218, 23) with radio coordinates (J2000) R.A.: 184.467008 deg, Dec.: 30.116843 deg (Petrov & Taylor 2011, AJ, 142, 89). This blazar has a redshift z=0.131 (Paiano et al. 2017, ApJ, 837, 144; Bade et al. 1998, A&A, 334, 459).

1ES 1215+303 has brightened on average in GeV gamma rays since the beginning of the Fermi survey, with GeV flares recorded on October 2008 and February 2014, and now has been consistently brightening since March 2017. In particular on April 13, 2017 the daily gamma-ray flux (E>100MeV) of 1ES 1215+303 was (0.8+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) with corresponding hard hard photon spectral index (E>100MeV) of 1.7+/-0.1.

Peak 6-hour integrated gamma-ray fluxes (E>100 MeV) of (1.0+/-0.4) X 10^-6 and (1.0+/-0.5) X 10^-6 photons cm^-2 s^-1, corresponding to about a factor of 18 increase relative to the 4-year average flux reported in the 3FGL catalog, were reached by 1ES 1215+303 on April 13, 2017 in the intervals 12:00-18:00 UT and 18:00-24:00 UT respectively.

This is the first time that an increasing gamma-ray flux trend for this source is announced with a telegram by the Fermi LAT Collaboration after about 8.7 years of Fermi LAT all-sky survey observations. The source will be inserted in the "LAT Monitored Sources" table at FSSC and consequently preliminary estimations of the daily and weekly gamma-ray flux observed by Fermi LAT will be publicly available.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations.  For this source the Fermi LAT contact persons are J. Valverde (valverde@llr.in2p3.fr) and D. Horan (deirdre@llr.in2p3.fr).

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.