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Fermi LAT observed another strong GeV flare from 4C 21.35 (PKS 1222+21)

ATel #2584; D. Donato (NASA/GSFC), on behalf of the Fermi Large Area Telescope Collaboration
on 26 Apr 2010; 20:18 UT
Credential Certification: Davide Donato (davide.donato-1@nasa.gov)

Subjects: Gamma Ray, Quasar

Referred to by ATel #: 2617, 2626, 2641, 2684, 2686, 2687, 5981, 6207

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flaring activity from a source positionally consistent with 4C 21.35 (also known as PKS 1222+21, RA: 12h24m54.5s, Dec: +21d22m46.4s, J2000, Beasley et al. 2002, ApJS, 141, 13). Preliminary analysis indicates that the source on April 24 2010 showed a bright flare with a daily flux (E>100MeV) of (8.1 +/- 0.7) x 10^- 6 photons cm^- 2 s^- 1 (statistical only), which represents an increase by a factor of about 4 with respect to the average flux level in the past 2 weeks and more than twice as high as the peak reported in Atel #2349 (Dec 16th, 2009). A peak flux of (16.2 +/- 2.6) x 10^-6 photons cm^-2 s^-1 (E>100MeV, statistical only) was reached between 12:00 and 17:46 UT. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The blazar 4C 21.35 is a "LAT Monitored Source" and, consequently, a quick look estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available. In consideration of the ongoing activity of this source we encourage multiwavelength observations. For this source the Fermi LAT contact persons are D. Donato (donato@milkyway.gsfc.nasa.gov), G. Iafrate (iafrate@oats.inaf.it) and Y. Tanaka (tanaka@astro.isas.jaxa.jp). 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.