ATel draft: Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 0446+11

ATel #16332; M. Giroletti (INAF/IRA) on behalf of the Fermi Large Area Telescope Collaboration
on 11 Nov 2023; 22:59 UT
Credential Certification: Marcello Giroletti (giroletti@ira.inaf.it)

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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 flat-spectrum radio quasar PKS 0446+11, also known as 4FGL J0449.1+1121 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 72.28196 deg, Decl. = +11.35794 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=2.153 (Shaw et al. 2012, ApJ, 748, 49). 

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on November 10, 2023, with a daily averaged gamma-ray flux (E>100MeV) of (1.1 +/- 0.2) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 18 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 photon index is 2.07 +/- 0.14, corresponding to a significantly harder spectrum than the 4FGL value of 2.51 +/- 0.02. This is the first report of enhanced activity from PKS 0446+11, although inspection of the Fermi LAT Light Curve Repository indicates that moderate activity occurred in March/April 2010.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is being added to the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available. We encourage multifrequency observations of this source, especially in light of the large redshift and hard spectrum. For this source, the Fermi-LAT contact person is Marcello Giroletti (marcello.giroletti@inaf.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.