Fermi-LAT detection of gamma-ray flaring activity from the high-redshift FSRQ PKS B1149-084

ATel #14450; R. Angioni (SSDC/INFN) on behalf of the Fermi Large Area Telescope Collaboration
on 9 Mar 2021; 22:20 UT
Credential Certification: Roberto Angioni (r.angioni90@gmail.com)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS B1149-084, also known as 4FGL J1152.3-0839 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 178.071706 deg, Decl. = -8.684254 deg (J2000; Beasley et al. 2002 ApJS, 141, 13), and redshift z=2.37 (Ellison et al. 2001 A&A, 379, 393).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 8 March 2021, with a daily averaged gamma-ray flux (E>100MeV) of (6.3+/-1.6) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 30 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 2.7+/-0.3, providing a hint of spectral softening compared with the 4FGL value of 2.38+/-0.06.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Target of Opportunity observations with the Neil Gehrels Swift Observatory are being proposed. We encourage further multifrequency observations of this source. For this source, the Fermi-LAT contact person is Roberto Angioni (roberto.angioni@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.