Fermi-LAT detection of the first flaring activity from the FSRQ PKS 1954-388 and an enhanced gamma-ray activity from the high redshift blazar 4C +01.02

ATel #15274; G. Principe (University of Trieste and INFN - Trieste, INAF-IRA Bologna), S. Garrappa (DESY-Zeuthen), on behalf of the Fermi Large Area Telescope Collaboration
on 13 Mar 2022; 00:29 UT
Credential Certification: Giacomo Principe (giacomo.principe@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 the first gamma-ray flaring activity from a source positionally consistent with the flat-spectrum radio quasar PKS 1954-388, also known as 4FGL J1958.0-3845 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 299.499247 deg, Decl. = -38.751766 deg (J2000; Ma et al., 1998 AJ, 116 516), and redshift z=0.63 (Gattano et al., 2018, A&A, 618, 80). In addition, it has detected enhanced gamma-ray activity from a source positionally consistent with the high-redshift blazar 4C +01.02, also known as 4FGL J0108.6+0134 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 17.161546 deg, Decl. = 1.583421 deg (J2000; Johnston et al., 1995 AJ, 110 880), and redshift z=2.099 (Grasha et al., 2019, ApJS, 245, 3).

Preliminary analysis indicates that PKS 1954-388 was in an elevated gamma-ray emission state on March 11, 2022 with a daily averaged gamma-ray flux (E>100MeV) of (6.7+/-1.9) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 12 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 corresponding photon index is 2.1+/-0.2, compared to the 4FGL value of 2.35+/-0.02. On the same day, 4C +01.02 showed a daily averaged gamma-ray flux (E>100MeV) of (2.4+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 11 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.46+/-0.14 and is consistent with the 4FGL value of 2.35+/-0.01 within the uncertainties. (Previous ATels: #15213,#8319,#6844,#5394)

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The high-redshift blazar 4c+01.02 is on the list of "LAT Monitored Sources" and a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/4C_p01d02. We encourage multifrequency observations of PKS 1954-388 and 4C +01.02. For PKS 1954-388, the Fermi-LAT contact person is Giacomo Principe (giacomo.principe@ts.inf.it) while for 4C +01.02 the Fermi-LAT contact person is Sara Buson (sara.buson@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.