Fermi LAT detections of gamma ray activity in three blazars: 3C 66A, PKS 0208-512, PKS 0537-441

ATel #1759; G. Tosti (INFN/University Perugia) on behalf of the Fermi Large Area Telescope Collaboration
on 3 Oct 2008; 22:42 UT
Credential Certification: Gino Tosti (tosti@pg.infn.it)

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The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST) (launched June 11, 2008), has observed, since September 15, 2008, an increase of the gamma-ray activity in three sources positionally consistent with the blazars 3C 66A (RA: 02h22m39.6114s DEC: +43d02m07.799s), PKS 0208-512 (RA: 02h10m46.2004s DEC:-51d01m01.891s) and PKS 0537-441 (RA: 05h38m50.3614s DEC: -44d05m08.934s).

Of these three sources, 3C 66A was already reported in a high state in the TeV band by VERITAS (Atel #1753) and in optical by Larionov et al. (Atel #1755), while PKS 0208-512 was reported in a high optical state by Buxton et al. (Atel #1751).

3C 66A is a well known BL Lac object, with an adopted z=0.44 (but see, e.g. Finke, J.D. et al. 2008, A&A, 477, 513), marginally detected by EGRET as 3EG J0222+4253 (Hartman et al., 1999, ApJS, 123, 79), at a lower flux than the current one (EGRET average flux: 1.9x10-7 photons cm-2 s-1; peak flux 2.5x10-7 photons cm-2 s-1).

PKS 0208-512 is a flat spectrum radio quasar (z=0.999, Wisotzki et al. 2000, A&A, 358, 77) detected by EGRET as 3EG J0210-5055. The current value of the flux is comparable to the average flux detected by EGRET (average flux: 8.5x10-7 photons cm-2 s-1; peak flux 1.3x10-6) photons cm-2 s-1). This source is one of the "LAT Monitored Sources" (http://fermi.gsfc.nasa.gov/ssc/data/policy/LAT_Monitored_Sources.html), and consequently, a preliminary, uncalibrated estimation of the gamma-ray flux observed by Fermi LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/).

PKS 0537-441 is one of the most variable BL Lac objects (z=0.894, Peterson et al. 1976, ApJ, 207, L5-L8) and was detected by EGRET as 3EG J0540-4402. Fermi LAT observations indicate that the flux of this source is close to the maximum value observed by EGRET (average flux: 2.5x10-7 photons cm-2 s-1; peak flux 9.1x10-7 photons cm-2 s-1).

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 these sources we strongly encourage multiwavelength observations. The Fermi LAT contact persons for these sources are Luis C. Reyes (lreyes@kicp.uchicago.edu) for 3C 66A, Werner Collmar (wec@mpe.mpg.de) for PKS 0208-512 and Gino Tosti (tosti@pg.infn.it) for PKS 0537-441.

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.