Fermi-LAT detection of renewed gamma-ray activity from PKS 0903-57
ATel #15057; Stefano Ciprini (INFN Roma Tor Vergata, & ASI Space Science Data Center, Rome, Italy), on behalf of the the Fermi Large Area Telescope Collaboration
on 23 Nov 2021; 06:01 UT
Credential Certification: Teddy Cheung (Teddy.Cheung@nrl.navy.mil)
Subjects: Gamma Ray, >GeV, AGN, Blazar
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 (Abdollahi et al. 2020, ApJS, 247, 33), with coordinates R.A. = 136.2215792 deg, Dec. = -57.5849397 deg (J2000; Fey et al. 2004, AJ, 128, 2593), and a tentative redshift z=0.695 (Thompson et al. 1990, PASP, 102, 1235).
Preliminary analysis indicates that this source was in a very bright gamma-ray emission state on 2021 November 19 and 20, with the emission of several E>15 GeV-energy photons, in particular a 56 GeV photon (at time: 2021 November 19, 20:41:37 UTC) and a 51 GeV photon (at time: 2021 November 20, 09:16:01 UTC), and with daily averaged gamma-ray fluxes (E>100MeV) of (2.0+/-0.2) X 10^-6 photons cm^-2 s^-1 and (3.1+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), respectively. The corresponding photon index on both days is 1.7+/-0.1, significantly smaller than the 4FGL value of 2.30+/-0.03. The peak 6-hour integrated gamma-ray flux (E>100 MeV) of (4.6+/-0.6) X 10^-6 photons cm^-2 s^-1 was reached in the interval 06:00-12:00 UT of November 20, with a corresponding photon index of 1.7+/-0.1. This flux level corresponds to an increase of a factor of about 70 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is a renewed outburst activity for PKS 0903-57 continuing since late October 2021.
This is the fifth time that the Fermi-LAT Collaboration has announced an intense GeV gamma-ray flare from PKS 0903-57 (ATel#13604, ATel#13599, ATel#11644, ATel#7704), and after them gamma-ray detection by DAMPE (ATel#13643), H.E.S.S. (ATel#13632), and AGILE (ATel#13602). This source is included in the "LAT Monitored Sources" list and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0903-57). 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 Isabella Mereu (mereuisabella@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.
