Swift follow-up of the gamma-ray flaring BL Lac CGRaBS J0211+1051
ATel #3129; F. D'Ammando (INAF - IASF Palermo), K. V. Sokolovsky (MPIfR/ASC Lebedev), on behalf of the Fermi Large Area Telescope Collaboration, and E. Hoversten (PSU)
on 28 Jan 2011; 02:00 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)
Subjects: Optical, Ultra-Violet, X-ray, Blazar
Following the gamma-ray flare of the BL Lac object CGRaBS J0211+1051 (also known as
MG1 J021114+1051, and 1FGL J0211.2+1049, Abdo et al. 2010, ApJS, 188, 405) detected by
Fermi LAT on 2011 January 23 (ATel #3120), we performed a Swift target of opportunity
observation on January 25.
Swift/UVOT observations found CGRaBS J0211+1051 about 1.3 mag brighter in U band
(U = 13.77+/-0.03) and 1.4 mag in W2 band (W2 = 14.44+/-0.04) compared to the UVOT
observation performed on 2010 March 5 (U = 15.02+/-0.03; W2 = 15.82+/-0.06).
On January 25 CGRaBS J0211+1051 was observed also in V band at V = 14.00+/-0.08,
making it currently one of the brightest BL Lac objects in the sky.
Swift/XRT data were taken in Photon Counting mode for a total exposure of 3.9 ksec. The
X-ray 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 = 6.16x10^20 cm^-2, Kalberla et al. 2005) and a photon index of 2.34+/-0.11.
The corresponding unabsorbed 0.3-10 keV flux is (6.8+/-0.5)x10^-12 erg cm^-2 s^-1.
The flux observed is comparable with that previously observed by Swift/XRT on 2010 March 5
(6.0+/-1.0 x10^-12 erg cm^-2 s^-1, with a photon index of 2.32+/-0.27).
Swift/UVOT observations confirmed the high activity state of the source. We encourage
further multiwavelength observations. For this source the LAT contact person is
F. D'Ammando (dammando@ifc.inaf.it).
We thank the Swift Team for their rapid scheduling of this observation.
