Fermi-LAT observation of increased gamma-ray activity from PKS 2155-304
ATel #6148; S. Cutini (ASDC/INAF), on behalf of the Fermi-LAT collaboration
on 20 May 2014; 09:05 UT
Credential Certification: Dario Gasparrini (dario.gasparrini@asdc.asi.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar
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 well-known
blazar PKS 2155-304, R.A. = 21h58m52.0651s, Dec. =-30d13m32.118s (J2000, Fey et al. 2004, AJ, 127, 3587), classified as a TeV BL Lac object with redshift z=0.116 (Falomo et al. 1993, ApJ, 411, L63).
Preliminary analysis indicates that on 2014 May 17 the source was detected in a high state with an average daily flux (E>100 MeV) of (1.6+/-0.3) x10^-6 ph cm^-2 s^-1 and a hard spectrum with a photon index of 1.8 +/- 0.1 (statistical uncertainties only).
Fermi-LAT already reported enhanced gamma-ray activity from this object in October 2010 (ATel#2944) and January 2013 (ATel#4755).
PKS 2155-304 is one of the "LAT Monitored Sources", and consequently a preliminary estimate of the daily gamma-ray flux observed by Fermi LAT is publicly available at: http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_2155-304
The Fermi-LAT contact persons for this source are B. Giebels (berrie@llr.in2p3.fr) and D. Sanchez (david.sanchez@lapp.in2p3.fr).
Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the 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.
