Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 0903-57
ATel #15666; G. La Mura (LIP, Portugal) on behalf of the Fermi Large Area Telescope Collaboration
on 11 Oct 2022; 20:25 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, >GeV, AGN, Quasar
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 0903-57, also known as 4FGL J0904.9-5734 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 136.22158 deg, Decl. = -57.58494 deg (J2000; Fey et al. 2004, AJ, 128, 2593), and tentative 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 October 10, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (2.5+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 20 relative to the average flux reported in the third release of the fourth Fermi-LAT catalog (4FGL-DR3, Abdollahi et al. 2022, ApJS, 260, 53). The corresponding photon index is 2.02+/-0.08, and is significantly smaller than the 4FGL-DR3 value of 2.21+/-0.01, similarly to what has been previously observed (e.g. ATel #15057). The spectral hardening is further confirmed by the detection of a high-energy photon of 10 GeV, observed at 12:03:17.960 UT with an association probability p = 0.9997.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source belongs to the list of daily monitored LAT sources, therefore a preliminary gamma-ray light curve is available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0903-57. Its light curve can also be accessed through the Fermi-LAT Light Curve Repository (LCR) at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J0904.9-5734. 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.
