Enhanced HE and VHE gamma-ray activity from the FSRQ PKS 0346-27

ATel #15020; S. Wagner (U. Heidelberg, Germany), for the H. E.S. S. collaboration and B. Rani (KASI, S. Korea), on behalf of the Fermi Large Area Telescope Collaboration
on 6 Nov 2021; 18:38 UT
Credential Certification: Stefan J. Wagner (swagner@lsw.uni-heidelberg.de)

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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 0346-27, also known as 4FGL J0348.5-2749 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates RA=03h 48m 38s, Dec=-27d 49' 14'' (J2000; Beasley et al. 2002 ApJS, 141, 13), and a reported redshift of z=0.991 (White et al. 1988 ApJ, 327, 561).

The H.E.S.S. array of imaging atmospheric Cherenkov telescopes was used to carry out observations of PKS 0346-27. On November 03 (MJD 59521.9), a two hour observation shows a >5 sigma excess in the very-high-energy gamma-ray band compatible with the direction of PKS 0346-27. Preliminary analysis shows a very soft power law (photon spectral index > 4). H.E.S.S. observations are ongoing.

Preliminary analysis of the data obtained with the Fermi/LAT instrument indicates that this source was in an elevated gamma-ray emission state on November 02, 2021, with a daily averaged gamma-ray flux (E>100MeV) of (1.8+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 200 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 1.8+/-0.1, and is significantly smaller than the 4FGL value of 2.5+/-0.1. Previous enhanced gamma-ray activity in the source was detected on February 20, 2020 (ATel#13521).

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Since PKS 0346-27 is in the list of monitored sources, its light curve can be found at this link https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0346-27. For this source, the Fermi-LAT contact person is Roberto Angioni (roberto.angioni@ssdc.asi.it). We encourage multifrequency observations of this source.

H.E.S.S. is an array of five imaging atmospheric Cherenkov telescopes for the detection of very-high-energy gamma-ray sources and is located in the Khomas Highlands in Namibia. It was constructed and is operated by researchers from Armenia, Australia, Austria, France, Germany, Ireland, Japan, the Netherlands, Poland, South Africa, Sweden, UK, and the host country, Namibia. For more details see https://www.mpi-hd.mpg.de/hfm/HESS/.

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.