Fermi-LAT detection of renewed gamma-ray activity from the gravitationally lensed FSRQ PKS 1830-211

ATel #12601; R. Angioni (MPIfR-Bonn) on behalf of the Fermi-LAT collaboration
on 20 Mar 2019; 18:03 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)

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The Large Area Telescope (LAT), one of the two instruments onboard the Fermi Gamma-ray Space Telescope, has observed renewed gamma-ray flaring activity from a source positionally consistent with PKS 1830-211 (also known as 4FGL J1833.6-2103, The Fermi-LAT collaboration 2019, arXiv:1902.10045), with coordinates RA = 18h 33m 39.9s, Dec = -21d 03m 40s, (J2000, van Ommen et al., 1995, ApJ, 444, 561). PKS 1830-211 (z=2.507, Lindman et al. 1999, ApJ, 514, 57) is a flat spectrum radio quasar located behind the southern Galactic Bulge. It is gravitationally lensed by a galaxy at z=0.886 (Wiklind & Combes 1996, Nature, 379, 139).

Preliminary analysis indicates that the source is undergoing a long term brightening since October 2018 (ATels #12136 and #12252), and on 19 March 2019 reached a daily averaged gamma-ray flux (E>100MeV) of (8.4+/-0.7) X 10^-6 photons cm^-2 s^-1 and a photon index of 2.28+/-0.07 (statistical uncertainty only). The latter corresponds to a flux increase of a factor 19 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the brightest and longest outburst from PKS 1830-211 recorded by the Fermi-LAT so far. Several GeV gamma-ray flares from this source have been detected by the LAT previous to this long term flaring state: in October 2010 (ATel #2943), June 2012 (ATel #4158) and July 2014 (ATel #6361). Gamma-ray flares were also detected by AGILE in October 2009 (ATel #2242) and, during the ongoing flare, March 2019 (ATel #12541 and #12594). PKS 1830-211 is included in the Fermi-LAT monitored sources list, therefore a preliminary estimation of its daily gamma-ray flux observed by Fermi-LAT will be publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/).

Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. Optical-UV and X-rays observations with the Neil Gehrels Swift Observatory have already been triggered by the Fermi-LAT team, and have been granted until the end of March 2019. We encourage further multi-wavelength observations. For this source, the Fermi-LAT contact persons are S. Ciprini (stefano.ciprini@ssdc.asi.it) and S. 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.