Fermi-LAT detection of renewed flaring activity from the blazar Ton 599 (4C +29.45)

ATel #14722; G. Principe (University of Trieste and INFN - Trieste, INAF - Istituto di Radioastronomia, Bologna), on behalf of the Fermi Large Area Telescope Collaboration
on 16 Jun 2021; 17:27 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 renewed gamma-ray activity from a source positionally consistent with the flat spectrum radio quasar Ton 599, also known as 4FGL J1159.5+2914 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates RA = 179.8826413 deg, Decl. = 29.2455075 deg, (J2000; Johnston et al. 1995 AJ 110, 880) at z = 0.72449 (Adelman-McCarthy et al. 2008, SDSS6).

Preliminary analysis indicates that this source has been in an elevated gamma-ray emission state since mid-April, in particular reaching on June 15, 2021, a daily averaged gamma-ray flux (E>100MeV) of (1.2+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 10 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.1+/-0.1, and is consistent with the 4FGL value of 2.19+/-0.01 within the uncertainties. GeV flaring emission in this source was previously reported in August 2010 (ATel #2795), November 2015 (ATel #8319) and November 2017 (ATel #10931). Optical flaring of Ton 599 has recently been reported ATel #14696.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is one of the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is 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 are S. Ciprini (stefano.ciprini@ssdc.asi.it) and D. J. Thompson (David.J.Thompson@nasa.gov).

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.