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Fermi-LAT detection of increased activity from the FSRQ OK 630

ATel #11039; R. Angioni (MPIfR-Bonn) on behalf of the Fermi-LAT Collaboration
on 7 Dec 2017; 22:57 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)

Subjects: Gamma Ray, >GeV, AGN, Blazar, 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 OK 630, also known as 3FGL J0921.8+6215 (Acero et al. 2015, ApJS, 218, 23), with coordinates R.A. = 140.4009629 deg, Decl. = 62.2644944 deg (J2000; Massaro et al. 2014 ApJ, 213, 3), and a redshift of 1.446 (Stickel & Kuhr 1993 A&AS, 101, 521).

Preliminary analysis indicates that this source went into a high-flux state starting from 3 December 2017, and continued to brighten steadily over the following days, reaching a peak daily averaged gamma-ray flux (E>100MeV) of (1.14+/-0.14) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) on 6 December. The latter corresponds to a flux increase of a factor of about 30 relative to the average flux reported in the third Fermi-LAT catalog (3FGL). The corresponding photon spectral index of 1.81+/-0.08 is significantly harder than the 3FGL value of 2.45+/-0.05. Therefore OK 630 is another example of the "harder-when-brighter" behavior observed in several flaring FSRQs.

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. The Fermi LAT contact person is R. Angioni (angioni at 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.