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

ATel #4158; Stefano Ciprini (ASI Science Data Center and INAF Rome, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 7 Jun 2012; 21:53 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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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, placed 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, Lovell et al. 1998, ApJ, 508, L51) is a distant and peculiar flat spectrum radio quasar with intervening absorption systems and being subject to gravitational lensing by a galaxy placed at z=0.886 (Wiklind & Combes 1996, Nature, 379, 11). In addition to being the brightest radio source of any gravitational lens, it showed a bright GeV gamma-ray flare detected by the LAT in October 2010 (ATel #2943) and representing the highest (E>100 MeV) gamma-ray flux ever recorded for this object. High level gamma-ray activity was also detected by AGILE in October 2009 (ATel#2242) and October 2010 (ATel#2950, following up the LAT main flare detection).

Preliminary analysis indicates that the source on June 6, 2012 showed a gamma-ray daily flux (E>100MeV) of (2.2+/0.2) x10^-6 ph cm^-2 s^-1 (errors are statistical only), more than a factor of 4 greater than the average flux reported in the second Fermi LAT catalog (2FGL), reaching in two 6-hour bins of the day a flux (E>100MeV) level above 3 x 10^-6 photons cm^-2 s^-1. 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 (link: http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/ ).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we encourage multiwavelength observations. For this source the Fermi LAT contact people 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.