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Swift follow-up of a new gamma-ray source positionally associated to the blazar PKS 0646-306

ATel #3894; D. Gasparrini (ASDC-INAF), S. Ciprini (ASDC-INAF) on behalf of the Fermi Large Area Telescope Collaboration, M. Capalbi (ASDC-INAF), and J. A. Kennea (Penn State Univ.)
on 28 Jan 2012; 15:16 UT
Credential Certification: Dario Gasparrini (dario.gasparrini@asdc.asi.it)

Subjects: Ultra-Violet, X-ray, Blazar

Following the reported detection of a gamma-ray flaring source in the vicinity of the flat spectrum radio quasar PKS 0646-306 (redshift z=1.153, Jackson et al. 2002, A&A, 386, 97) in the GeV band (ATel#3878), Swift ToO observation was requested and promptly performed on 2012 Jan 23. Swift XRT data were taken in photon counting mode for a net exposure of about 5 ksec.

The X-ray spectrum can be fit by an absorbed power law with the HI column density fixed to the Galactic value of N(HI) = 1.26 x 10^21 cm^-2 (Kalberla et al. 2005, A&A, 440, 775) and a photon index of 1.50 (+0.61, -0.35). The unabsorbed 0.3-10 keV flux is (2.42 +/-0.40) x10^-12 erg cm^-2 s^-1 that corresponds to a unabsorbed 0.1-2.4 keV flux of 1.31x10^-12 erg cm^-2 s^-1 which is a factor of about 7 higher than that previously detected by ROSAT.

Swift UVOT found an observed UV magnitude W2=18.01 +/-0.04 (statistical only).

Synergetic Fermi-Swift observations of simultaneous high brightness states at GeV and X-ray bands on Jan 23 identify the flaring source as the flat spectrum radio quasar PKS 0646-306.

We thank the Swift Team and the Observation Duty Scientists (ODS) for the rapid scheduling of this observation.