Fermi-LAT detection of a GeV gamma-ray flare from the BL Lac object OT 081

ATel #9231; J. Becerra Gonzalez (NASA/GSFC/UMD/CRESST) and D. Thompson (NASA/GSFC) for the Fermi-LAT collaboration
on 11 Jul 2016; 02:42 UT
Credential Certification: Josefa Becerra Gonzalez (josefa.becerra@nasa.gov)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the BL Lac object OT 081 (also known as PKS 1749+096, 4C 09.57, 0FGL J1751.5+0935, 1FGL J1751.5+0937, 2FGL J1751.5+0938, 1FHL J1751.5+0938, 3FGL J1751.5+0939), with the radio counterpart position R.A.: 267.88674 deg, Dec.: 9.65020 deg (J2000.0, Lanyi et al. 2010, AJ, 139, 1695).

Preliminary analysis indicates that on 2016 July 9, OT 081 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (1.0+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 20 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). The corresponding daily averaged spectral photon index (E>100 MeV) of 2.24+/-0.19 (statistical uncertainty only) is compatible with the 3FGL catalog value of 2.25 for a power-law fit (although the best spectral fit in the 3FGL catalog is a log-parabola ).

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 person is J. Becerra Gonzalez (josefa.becerra@nasa.gov).

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.