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Fermi LAT detection of a GeV gamma-ray flare from blazar PKS 2144+092 (OX 074)

ATel #10847; Stefano Ciprini (SSDC-ASI Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 12 Oct 2017; 21:51 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)

Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar

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 flat spectrum radio quasar object PKS 2144+092 (also known as OX 074, S3 2144+09, and 3FGL J2147.2+0929) with radio coordinates (J2000) R.A.: 326.79235 deg, Dec.: 9.49630 deg (Johnston et al. 1995, AJ, 110, 880). This blazar has a redshift z=1.113 (White et al. 1988, ApJ, 327, 561).

PKS 2144+092 (OX 074) has brightened in GeV gamma rays since 2017 October 4. In particular, preliminary analysis indicates that on 2017 October 10, PKS 2144+092 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (1.5+/-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 photon spectral index (E>100 MeV) of 2.0+/-0.1 (statistical uncertainty only) is smaller than the 3FGL catalog value of 2.38+/-0.05.

The peak 6-hour integrated gamma-ray flux (E>100 MeV) of (2.6+/-0.6) X 10^-6 photons cm^-2 s^-1 was reached by PKS 2144+092 on 2017 October 10 in the interval 12:00-18:00 UT, and was about 33 times greater than the average flux reported in the 3FGL catalog.

PKS 2144+092 (OX 074) is the identified counterpart of 3FGL J2147.2+0929 (Acero et al. 2015, ApJS, 218, 23) based on observed correlated gamma-ray and 3mm radio-band flux variability (Fuhrmann et al. 2014, MNRAS, 441, 1899). 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 almost 9.3 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 person is S. Ciprini (stefano.ciprini@ssdc.asi.it).

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.