Swift follow-up of the flaring blazar PKS 0250-225

ATel #4601; Michael Dutka (Catholic University of America), Roopesh Ojha (NASA/GSFC), and Davide Donato (CRESST-UMBC/NASA-GSFC) on behalf of the Fermi Large Area Telescope Collaboration and Katja Pottschmidt (CRESST-UMBC/NASA-GSFC).
on 22 Nov 2012; 22:05 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

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Following the gamma-ray flaring activity of the flat spectrum radio quasar PKS 0250-225 (also known as 2FGL J0252.7-2218, Nolan et al. 2012, ApJS, 199, 31) detected by Fermi LAT on 2012 November 13 (ATel #4574) two Swift target of opportunity observations were performed on November 14 and 16. As no significant differences were found between the two epochs the combined results are reported here.

Swift/XRT data were taken in Photon Counting mode for a total exposure of about 7.4 ksec. Preliminary analyses of these data were done using data analysis tools of the UK Swift Science Data Centre (Evans et al. 2009, MNRAS, 397, 1177). The X-ray spectrum (0.3-10 keV) can be fit by an absorbed power law model with an HI column density consistent with the Galactic value in the direction of the source (N_H = 2.4 x 10^20 cm^-2, Kalberla et al. 2005, A&A, 440, 775) and a photon index of 1.7+/-0.3. The corresponding unabsorbed 0.3-10 keV flux is (4.9+/-1.2) x10^-13 erg cm^-2 s^-1.

The XRT spectrum of archival Swift data obtained on 2009 February 20 has a photon index of 1.3+/-0.3 and the corresponding unabsorbed 0.3-10 keV flux is (9.4+/-1.9) x10^-13 erg cm^-2 s^-1 (results from these data for a different energy range are reported in ATel #2039). This Swift observation was triggered by the detection of an earlier Fermi LAT flare on 2009 February 17 (ATel #1933) that had a peak daily averaged Fermi LAT flux about half that of the current flare.

Simultaneous Swift/UVOT observations (not corrected for extinction and in the AB system) show
B = 19.6+/-0.3 (SMARTS reported B = 19.8 on 16 November 2012; ATel #4584)
U = 19.0+/-0.3
V = 18.5+/-0.3
W1 = 19.8+/-0.4
This source was not detected in the M2 and W2 filters. These magnitudes were obtained by combining data from 2012 November 14 and 2012 November 16 for reaching a significance of three sigma.

Similarly reduced archival Swift/UVOT data from 2009 February 20 shows
B = 19.0 +/- 0.3
U = 18.2 +/- 0.2
V = 17.9 +/- 0.2
W1 = 18.7 +/- 0.2
M2 = 19.3 +/- 0.2
with no detection in the W2 filter.

Hence the 2012 November gamma-ray flare appears to have been accompanied by significantly different X-ray (softer photon index and lower flux) and optical activity (half to a full magnitude dimmer) than the 2009 February activity. Further multiwavelength observations are encouraged. For this source the LAT contact person is William McConville (e-mail: wmcconvi@umd.edu).

We would like to thank the Swift Team for making these observations possible.