Fermi LAT Detection of the brightest gamma-ray flare from PKS 1156-221
ATel #13533; J. Sinapius (Univ. of Wuerzburg) and R. Ojha (NASA/GSFC/UMBC) on behalf of the Fermi-LAT Collaboration
on 28 Feb 2020; 23:10 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)
Subjects: Gamma Ray, >GeV, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a gamma-ray flare from a source positionally consistent with the quasar PKS 1156-221, associated with the gamma-ray source 4FGL J1159.2-2227 (The Fermi-LAT collaboration 2019, arXiv:1902.10045) at RA = 11h59m11.2672s, Dec = -22d28m36.902s (J2000, Beasley et al. 2002 ApJS, 141, 13). This source has a measured redshift of z = 0.565 (Wright et al. 1979, ApJ 229, 73).
Preliminary analysis indicates that on 2020 February 27, PKS 1156-221 reached a daily averaged gamma-ray flux (E>100MeV) of (1.4+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 80 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.1+/-0.1, significantly smaller than the 4FGL value of 2.4+/-0.1.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue and the daily and weekly automated flux values will be added to the Monitored Source List, https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Jonas Sinapius (jonas.sinapius@stud-mail.uni-wuerzburg.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.
