Fermi LAT detection of increasing gamma-ray activity from the BL Lac Object S4 1749+70
ATel #3171; S. Buson, D. Bastieri (University/INFN Padova)
on 16 Feb 2011; 23:11 UT
Credential Certification: Denis Bastieri (denis.bastieri@pd.infn.it)
Referred to by ATel #: 3199
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has observed an increasing gamma-ray flux from a source positionally consistent with the BL Lac Object S4 1749+70 (also known as 1FGL J1748.5+7004, Abdo et al. 2010, ApJS, 188, 405; R.A: 17:48:32.8401 Dec.: +70:05:50.768, J2000, Stickel et al. 1993, A&AS 98, 393) at redshift z=0.77 (Hughes et al. 1992, ApJ 396, 469).
The source entered a higher state during the past week. Preliminary analysis indicates that on February 15, 2011, S4 1749+70 was detected at a gamma-ray flux (E > 100MeV) of (0.7 +/- 0.2) x 10^-6 photons/cm^2/s (errors are statistical only), which represents an increase of more than an order of magnitude with respect to the average source flux observed in the first eleven months of Fermi observations (Abdo et al. 2010), where it was detected with a photon spectral index of (2.05 +/- 0.10).
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 contact people for this source are S. Buson (buson@pd.infn.it) and D. Bastieri (bastieri@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.
