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Flaring blazar B2 0619+33: Swift X-ray and UV/optical observations

ATEL # 2848; D. Donato (NASA/GSFC), K. V. Sokolovsky (MPIfR/ASC Lebedev), F. D'Ammando (INAF-IASF Palermo), and F. K. Schinzel (MPIfR); on behalf of the Fermi Large Area Telescope Collaboration
on 18 Sep 2010; 22:34 UT
Password Certification: Davide Donato (

Subjects: Ultra-Violet, X-ray, Gamma Ray

Following the Fermi/LAT detection of a GeV flare possibly associated with the blazar B2 0619+33 (ATel #2829) on September 01-04, 2010, we obtained Swift observations on September 09 (7.8 ks exposure) and 12 (2.9 ks) to search for signs of X-ray and UV activity in this source.

The source was detected by Swift/XRT at a count rate of about 0.01 counts/sec. The X-ray spectrum of B2 0619+33 can be fit by an absorbed power law (assuming Galactic N_HI=0.307x10^22 cm^-2, Kalberla et al. 2005, A&A, 440, 775) with the photon index of 1.7 +/-0.3 and an unabsorbed 0.3-10 keV flux of (1.1 +/-0.3)x10^-12 erg cm^-2 s^-1. The source is not listed in the ROSAT All Sky Survey catalog while the current flux in the corresponding energy range is about three times above the catalog's limit. This is a clear indication that B2 0619+33 currently shows an elevated level of X-ray activity. No significant flux or spectral variability has been detected between September 09 and 12.

B2 0619+33 has been detected by Swift/UVOT at U=18.90+/-0.05 on September 09 and U=18.35+/-0.05 on September 12 indicating a significant inter-day variability. The source has also been observed in W1 band on September 12 at W1=18.0 +/-0.1. The Swift/UVOT data confirm the high optical state of the source observed by the 1.54m Kuiper Telescope on September 07 (ATel #2831).

Overall, the elevated X-ray to optical activity of B2 0619+33 supports its identification as the source of the GeV flare observed by Fermi/LAT. We encourage further multiwavelength observations. A redshift estimation for this source would be especially useful. The Fermi LAT contact person for this source is Frank Schinzel (

We thank the Swift Team for their rapid scheduling of these observations

A 9.2'x9.2' U-band finding chart for B2 0619+33 constructed from the Swift/UVOT image obtained on September 09 (2010) is available at:

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R. E. Rutledge , Editor
ATEL Mirror v1.0 Updates