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Fermi-LAT detection of increased gamma-ray activity from the FSRQ OT 355 (B2 1732+38A)

ATel #11249; R. Angioni (MPIfR-Bonn) on behalf of the Fermi-LAT Collaboration
on 1 Feb 2018; 20:29 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)

Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Transient

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray emission from a source positionally consistent with the flat-spectrum radio quasar OT 355, also known as B2 1732+38A and 3FGL J1734.3+3858 (Acero et al. 2015, ApJS, 218, 23), with coordinates R.A. = 263.585744 deg, Decl. = 38.964290 deg (J2000; Lanyi et al. 2010 AJ, 139, 1695), and a redshift of 0.975 (Shaw et al. 2012 ApJ, 748, 49).

Preliminary analysis indicates that this source went into a high-flux state starting on 22 January 2018, and brightened over the following days, reaching a peak daily averaged gamma-ray flux (E>100MeV) of (1.2+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) on 31 January. The latter corresponds to a flux increase of a factor of about 25 relative to the average flux reported in the third Fermi-LAT catalog (3FGL). This is the highest LAT daily flux ever observed for this source. OT 355 is also detected in the 6-hour interval between 12:00 UTC and 18:00 UTC of the same day, with an integrated gamma-ray flux (E>100MeV) of (2.0+/-0.8) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), corresponding to about 40 times the 3FGL flux level.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is being added to the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/). We encourage further multifrequency observations of this source. For this source the Fermi-LAT contact person is R. Angioni (angioni@mpifr-bonn.mpg.de).

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.