Fermi LAT detection of a very intense GeV flare from 4C +21.35 (PKS 1222+21)

ATel #2687; G. Iafrate (INAF - OATs Trieste), F. Longo (INFN Trieste), F. D'Ammando (INAF - IASF Palermo) on behalf of the Fermi Large Area Telescope Collaboration
on 19 Jun 2010; 20:40 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Francesco Longo (francesco.longo@ts.infn.it)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a source positionally consistent with 4C +21.35 (also known as PKS 1222+21 and PKS B1222+216, RA: 12h24m54.5s, Dec: +21d22m46.4s, J2000, Beasley et al. 2002, ApJS, 141, 13) at z=0.43.

Preliminary analysis indicates that the source on June 18, 2010 showed a bright flare with a daily flux (E>100MeV) of (12.46 +/- 0.79) x 10^- 6 photons cm^- 2 s^- 1 (statistical only), which represents an increase by a factor of about 3 with respect to the average flux level in the past week. A peak flux (E>100MeV) of (16.42 +/- 1.89) x 10^-6 photons cm^-2 s^-1 (statistical only) was reached between 12:00 and 17:01 UT.

This is the fourth time that Fermi is announcing a GeV flare from this blazar (Apr 2009 ATel #2021, Dec 2009 ATel #2349, Apr 2010 ATel #2584). This source was also previously detected by AGILE (ATel #2641, ATel #2348). Flaring activity from this source has been detected in the past few days by the MAGIC (ATel #2684) and AGILE (ATel #2686) telescopes.

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", public light curves are 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.