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Fermi-LAT detection of renewed gamma-ray activity from PKS 0903-57

ATel #13599; I. Mereu (INFN Perugia) on behalf of the Fermi Large Area Telescope Collaboration
on 29 Mar 2020; 21:37 UT
Credential Certification: Roberto Angioni (r.angioni90@gmail.com)

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

Referred to by ATel #: 13602, 13604, 13638, 15057

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray flaring activity from a source positionally consistent with the blazar PKS 0903-57, also known as 4FGL J0904.9-5734 (The Fermi-LAT collaboration 2020, ApJS, 247, 1), with coordinates R.A. = 136.2215792 deg, Decl. = -57.5849397 deg (J2000; Fey et al. 2004, AJ, 128, 2593), and redshift z=0.695 (Thompson et al. 1990, PASP, 102, 1235).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on March 28, 2020, with the emission of two E > 10 GeV photons (E = 37 GeV; time : 2020-03-28 16:18:16.961 UTC; E = 81 GeV; time : 2020-03-28 21:58:54.228 UTC) and with a daily averaged gamma-ray flux (E>100MeV) of (3.8 +/- 0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). The latter corresponds to a flux increase of a factor of 60 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 1.94 +/- 0.06, and is significantly smaller than the 4FGL value of 2.30 +/- 0.03. The peak 6-hour integrated gamma-ray flux (E>100 MeV) of (5.3 +/- 0.9) X 10^-6 photons cm^-2 s^-1 was reached by PKS 0903-57 in the interval 06:00-12:00 UT, with corresponding photon spectral index of 2.1 +/- 0.2. This is the third time that the Fermi-LAT Collaboration has announced flaring GeV gamma-ray behavior from PKS 0903-57 (see ATel#11644 and ATel#7704). This source is one of the "LAT Monitored Sources" (http://fermi.gsfc.nasa.gov/FTP/glast/data/lat/catalogs/asp/current/lightcurves/PKS0903-57_86400.png). This flare was also reported in the LAT GCN 1585493148.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Bryce D. Carpenter (carpbr01@gmail.com).

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.