Increased activity of blazar SBS 1150+497 detected by Fermi LAT and Swift XRT

ATel #3353; L. Reyes (KICP - University of Chicago), F. D'Ammando (INAF-IASF Palermo and CIFS) on behalf of the Fermi-LAT Collaboration, and E. Hoversten (PSU)
on 16 May 2011; 21:00 UT
Credential Certification: Luis C. Reyes (lcreyes@uchicago.edu)

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The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed an ongoing gamma-ray flare from a source positionally consistent with the blazar SBS 1150+497 (RA: 11h53m24.4666s, Dec: +49d31m08.830s, J2000, Johnston et al. 1995, AJ, 110, 880), a quasar with a prominent radio jet detected in X-rays and at optical frequencies (Sambruna et al. 2002, ApJ, 571, 206) and located at z=0.334 (Lynds & Wills 1968, ApJ, 153, L23).

Preliminary analysis from the Fermi LAT indicates that the source has brightened in gamma rays to a flux (E>100MeV) of (3.4 +/- 0.6) x 10^-6 ph cm^-2 s^-1 (errors are statistical only) during a 12hr interval on May 15, 2011. This flux is more than two orders of magnitude higher than the average flux of the source during the first 24 months of Fermi operations of (2.6 +/- 0.4) x 10^-8 ph cm^-2 s^-1, and over a factor of two higher than the flux reported on April of this year (ATEL#3313). This source did not appear in the Fermi-LAT first source catalog (1FGL; Abdo et al. 2010, ApJS 188, 405).

Swift observed SBS 1150+497 on May 15, 2011 for a total exposure of 3.6 ksec. The Swift/XRT spectrum (0.3-10 keV) can be fit by an absorbed power law model with a HI column density consistent with the Galactic value in the direction of the source (n_H = 2.13 x10^20 cm^-2, Kalberla et al. 2005) and a photon index of 2.04+/-0.06. The corresponding unabsorbed 0.3-10 keV flux is (2.1+/-0.1) x10^-11 erg cm^-2 s^-1. The flux observed is a factor of 3 higher than that previously observed by Swift/XRT on May 2, 2011 (7.6+/-0.6 x10^-12 erg cm^-2 s^-1 with Gamma = 1.77+/-0.11) and a factor of 6 higher than that observed by Swift/XRT on November 17, 2010 (3.8+/-0.4 x10^-12 erg cm^-2 s^-1 with Gamma = 2.05+/-0.14). The contemporaneous increase in flux at GeV, X-ray and NIR (ATEL#3317) wavelengths confirms the identification of the Fermi source with the blazar SBS 1150+497.

Because Fermi operates in all-sky survey mode, 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 person for this source is E. Hays (elizabeth.a.hays@nasa.gov).

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.

We thank the Swift team for their rapid scheduling of this observation.