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

ATel #10931; C. C. Cheung (NRL), D. Gasparrini (ASI SSDC & INFN Perugia, Italy), S. Buson (NASA-GSFC), on behalf of the Fermi Large Area Telescope Collaboration
on 6 Nov 2017; 20:42 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed bright gamma-ray flaring activity from the flat spectrum radio quasar Ton 599, also known as 4C +29.45 and 1156+295 (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 from 2017 Oct 28 to Nov 5, the source has been in a high state with average daily gamma-ray fluxes (E>100MeV) exceeding 1 x 10^-6 photons cm^-2 s^-1, and peaking at (2.3 +/- 0.3) x 10^-6 photons cm^-2 s^-1 (photon index 1.9 +/- 0.1; statistical uncertainties only throughout) on Oct 31, about 20 times greater than the average flux reported in the third Fermi-LAT source catalog (3FGL J1159.5+2914; Acero et al. 2015, ApJS 218, 23). During this time interval, there has been an increased incidence of detections of >10 GeV photons, with the highest energy photon of 77 GeV found on 2017 Nov 2.

GeV flaring in this source was previously reported in August 2010 (ATel #2795) and Nov 2015 (ATel #8319). Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is a member of the "LAT Monitored Sources", with preliminary, uncalibrated estimation of the daily gamma-ray flux observed by Fermi LAT publicly available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/Ton_599 .

In consideration of the ongoing activity of this source we encourage multiwavelength observations. For this source the Fermi LAT contact persons 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.