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Fermi-LAT and Swift observations of flaring activity from the FSRQ PKS 0346-27

ATel #15092; G. La Mura (LIP, Portugal) on behalf of the Fermi Large Area Telescope Collaboration, R. Prince (CFT, Poland)
on 8 Dec 2021; 16:28 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)

Subjects: X-ray, Gamma Ray, >GeV, AGN, Blazar, Transient

On November 24, 2021, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed increased 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 R.A. = 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). Enhanced gamma-ray flux, with high-energy photon emission detected by the LAT and the H.E.S.S. observatory, had already been reported on November 6 (Wagner and Rani, ATel #15020), leading to the activation of Swift ToO programs (ToO IDs 16630 and 16639). Following a preliminary analysis that resulted in a daily average flux 50 times brighter than the 4FGL catalogue average value, an additional Swift ToO request was submitted (ToO ID 16640).

Swift executed three observations of the source in photon counting mode, on November 24, 26 and 28, accumulating, respectively, 2500s, 2180s, and 1865s of exposure. An X-ray source positionally consistent with PKS 0346-27 was detected by XRT in all visits. Preliminary analysis suggests that the source could be modelled with an absorbed power-law, using a fixed Galactic Hydrogen column density of 8.36 X 10^19 cm^-2 (HI4PI Collaboration 2016, A&A, 594, 116). On November 24, the X-ray data in the 0.3-10keV band resulted in a flux of (2.32+/-0.28) X 10^-12 erg cm^-2 s^-1, with a photon index of 1.67+/-0.35. On November 26, the estimated flux had decreased to (1.52+/-0.38) X 10^-12 erg cm^-2 s^-1, with a photon index of 2.45+/-0.89. Finally, the source was detected again on November 28 with a flux of (1.50+/-0.25) X 10^-12 erg cm^-2 s^-1 and a photon index of 1.82+/-0.53 (statistical uncertainties only). The source is listed in the 2SXPS catalogue with a flux estimate of (2.75+/-0.08) X 10^-12 erg cm^-2 s^-1 (Evans et al. 2020, ApJS, 247, 54).

The LAT monitoring provided simultaneous coverage of the gamma-ray evolution of this flare. On November 24, the source was detected with a daily averaged gamma-ray flux (E>100MeV) of (2.19+/-0.36) X 10^-6 photons cm^-2 s^-1 and a spectral index of 1.85+/-0.07. On November 26, it was detected with an average daily flux of (0.83+/-0.20) X 10^-6 photons cm^-2 s^-1 and a spectral index of 2.08+/-0.17. Finally, on November 28, it was detected with a flux of (0.13+/-0.08) X 10^-6 photons cm^-2 s^-1 and a spectral index of 2.21+/-0.41 (statistical uncertainties only). The 4FGL average flux and spectral index are, respectively, (0.044+/-0.002) X 10^-6 photons cm^-2 s^-1 and 2.18+/-0.02.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is included in the "LAT Monitored Sources" and, consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available ( http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/ ). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Bindu Rani ( binduphysics@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. We further acknowledge commitment of the Swift Team, Observatory Duty Scientists, and PI, who made these observations possible.