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Fermi LAT observations of enhanced gamma-ray activity of blazar PKS 2155-304

ATel #2944; S. Ciprini (Perugia Univ. / ASI-INAF, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 15 Oct 2010; 17:13 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@pg.infn.it)

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

Referred to by ATel #: 2947, 4755, 6148

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed on October 13, 2010, an increase in gamma-ray activity from the well-known blazar PKS 2155-304, classified as a TeV BL Lac object, with redshift z=0.116 (Falomo et al. 1993, ApJ, 411, L63). 

Preliminary analysis indicates that the source reached a daily integrated flux (E>100MeV) of (1.0+/-0.3) x10^-6 ph cm^-2 s^-1 (errors are statistical only), more than a factor of 4 greater than reported in the Fermi-LAT 1st year catalog (1FGL J2158.8-3013, Abdo et al. 2010, ApJS 188, 405). A preliminary estimate of the photon index (2.6+/-0.3) points out a rather soft gamma-ray spectrum on this daily interval, unusual for this type of BL Lac objects. 

The Fermi-LAT contact people for this source are B. Giebels (berrie@llr.in2p3.fr) and D. Sanchez (dsanchez@llr.in2p3.fr). 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.