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Fermi LAT detection of an intense GeV flare from the high-redshift and gravitationally lensed blazar PKS 1830-211

ATel #2943; S. Ciprini (Perugia Univ. / ASI-INAF, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 15 Oct 2010; 16:52 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Stefano Ciprini (stefano.ciprini@pg.infn.it)

Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar

Referred to by ATel #: 2950, 4158, 6361

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a rapidly increasing gamma-ray flux from a source positionally consistent with PKS 1830-21 (also known as 3EG J1832-2110, 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 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). In addition to being the brightest radio source of any gravitational lens, it has an intervening absorption system and showed a large gamma-ray inverse Compton dominance during the EGRET era. This source was well observed in the past by hard-X-ray and soft-gamma-ray instruments like COMPTEL, Swift-BAT, INTEGRAL (Zhang et al. 2008, ApJ, 683, 400).

Preliminary analysis indicates that the source on October 14, 2010 showed a bright gamma-ray outburst with a daily flux (E>100MeV) of (5.2+/-1.1) x10^-6 ph cm^-2 s^-1 (errors are statistical only), more than a factor of 12 greater than reported in the Fermi-LAT 1st year catalog (1FGL J1833.6-2103, Abdo et al. 2010, ApJS 188, 405). A peak flux (E>100MeV) of (14+/-5) x 10^-6 photons cm^-2 s^-1 (statistical only) was reached between 06:00 and 11:17 UT.

The Fermi-LAT contact people for this source are L. C. Reyes (lreyes@kicp.uchicago.edu), A. Tramacere (Andrea.Tramacere@unige.ch) and S. Ciprini (stefano.ciprini@pg.infn.it) . 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 strongly encourage multiwavelength observations.

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.