Fermi LAT detection of a GeV flare from the gravitationally lensed FSRQ PKS 1830-211

ATel #6361; F. Krauss (Remeis Observatory & ECAP, FAU Erlangen/Univ. Wuerzburg), J. Becerra (NASA/GSFC/UMCP/CRESST), B. Carpenter (CUA/NASA/GSFC), R. Ojha (NASA/GSFC/UMBC/CRESST), S. Buson (INFN & Univ. of Padova) on behalf of the Fermi Large Area Telescope Collaboration
on 2 Aug 2014; 14:37 UT
Credential Certification: Felicia Krauss (Felicia.Krauss@fau.de)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with PKS 1830−211 (also known as 2FGL J1833.6−2104, Nolan et al. 2012, ApJS, 199, 31). It is located at RA: 18h 33m 39.9s, Dec −21d 03m 40s, J2000 (van Ommen et al., 1995, ApJ, 444, 561). PKS 1830−211 (z=2.507; Lidman et al. 1999, ApJ, 514, 57) is a flat spectrum radio quasar located behind the southern Galactic Bulge with gravitational magnification and absorption features. It is gravitationally lensed by a galaxy at z=0.886 (Wiklind & Combes 1996, Nature, 379, 11).

Preliminary analysis indicates that the source was in a high state with a peak gamma-ray flux (E>100MeV) of (2.1 ± 0.3) × 10^−6 photons cm^−2 s^−1 (errors are statistical only) on July 28. It was also detected on July 27 and July 29 at lower fluxes. Two previous flaring episodes of PKS 1830−211 have occurred during the Fermi mission: June 2012 (ATel #4158) and October 2010 (ATel #2943). This source was also detected previously by AGILE (ATel #2950 and ATel #2242). If this flare is lensed, as has been seen at other wavelengths (Lovell et al. 1998; Wiklind & Combes 2001), then we would expect another flare in about 27 days i.e. around Aug 22-31. In anticipation of this delayed flare from this source we strongly encourage multiwavelength observations.

Because Fermi 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 at http://fermi.gsfc.nasa.gov/FTP/glast/data/lat/catalogs/asp/current/lightcurves/PKS1830-211_86400.png. For this source the Fermi LAT contact persons are S. Ciprini (stefano.ciprini@asdc.asi.it) and L.C. Reyes (lreyes04@calpoly.edu).

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.