Fermi-LAT detection of enhanced gamma-ray activity from the high-redshift FSRQ PKS 0438-43

ATel #14446; I. Mereu (INFN Perugia) on behalf of the Fermi Large Area Telescope Collaboration
on 8 Mar 2021; 09:14 UT
Credential Certification: Isabella Mereu (mereuisabella@gmail.com)

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The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed strong gamma-ray emission from a source positionally consistent with the flat-spectrum radio quasar PKS 0438-43, also known as 4FGL J0440.3-4333 (The Fermi-LAT Collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 70.0715829 deg, Decl. = -43.5523894 deg (J2000; Johnston et al. 1995 AJ 110, 880) at redshift, z=2.852 (Morton et al. 1978 MNRAS 185, 735).

Preliminary analysis indicates that PKS 0438-43 was in an elevated gamma-ray emission state on 2021 March 6, with a daily averaged gamma-ray flux (E>100MeV) of (4.7+/-1.7) X 10^-7 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 2.2+/-0.3, and is smaller than the 4FGL value of 2.76 +/- 0.16. This is the second time that the Fermi-LAT Collaboration has announced flaring gamma-ray behavior from PKS 0438-43 (see ATel#9854).

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. PKS 0438-43 is one of the "LAT Monitored Sources" (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0438-43). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is C. C. Cheung (Teddy.Cheung at nrl.navy.mil).

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.