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Fermi LAT detection of a GeV flare from FSRQ 4C +38.41

ATel #5232; D. Gasparrini (ASDC) on behalf of the Fermi LAT collaboration
on 29 Jul 2013; 06:59 UT
Credential Certification: Dario Gasparrini (dario.gasparrini@asdc.asi.it)

Subjects: Gamma Ray, >GeV, AGN, Blazar, Quasar

Referred to by ATel #: 5234, 5236

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 coincident with 4C +38.41 (RA: 16h 35m 15.493s, Dec. +38d 08m 04.50s (J2000); Johnston et al. 1995, AJ, 110, 880). This is a flat spectrum radio quasar also known as B2 1633+38, OS 356 and 3EG J1635+3813, with a redshift of 1.814 (Adelman-McCarthy et al. 2008, ApJS, 175, 297).

Preliminary analysis indicates that the source on July 27, 2013, was in a high state with a gamma-ray flux (E>100 MeV) of (2.9 +/- 0.3) x 10^-6 photons/cm^2/s (statistical uncertainty only), about a factor of 10 higher than the average flux reported in the second Fermi-LAT catalog (2FGL J1635.2+3810, Nolan et al. 2012, ApJS 199, 31) and reaching the highest daily flux level seen by Fermi-LAT to date (see also Raiteri et al. 2012, A&A, 545, 48). Fermi-LAT already detected enhanced gamma-ray activity from this object in May 2011 (ATel #3333), February 2010 (ATel #2456) and July 2009 (ATel #2136) while AGILE reported a similar gamma ray flare in September 2012 (ATel #4389).

Since Fermi operates in an all-sky scanning mode, regular 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 ( http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/1633p382 ).

In consideration of the ongoing activity of this source we strongly encourage multiwavelength observations. The Fermi LAT contact persons are S. Ciprini (stefano.ciprini@pg.infn.it) and S. Buson (buson@pd.infn.it).

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.