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Swift follow-up observations of the blazar PKS 1510-089 after a high optical flare

ATel #2047; F. D'Ammando (Univ. Tor Vergata, INAF-IASF Roma), H. Krimm (CRESST/GSFC/USRA), P. Romano, S. Vercellone (INAF-IASF Palermo)
on 15 May 2009; 21:37 UT
Credential Certification: Pat Romano (romano@ifc.inaf.it)

Subjects: X-ray, Gamma Ray, AGN

Following the extraordinary optical brightness level of the blazar PKS 1510-089 on May 08.9 (Larionov et al., ATel #2045), we report on the analysis of Swift data obtained immediately after the optical flare.

The Swift/BAT hard X-ray transient monitor detected an outburst in PKS 1510-089 in the 15-50 keV energy band. On 2009 May 10 (MJD 54961) the count rate was 0.009 +/- 0.005 cts/s/cm^2 (40 mCrab). The source then declined to background on May 11, before rising again to 0.003 +/- 0.001 cts/s/cm^2 (14 mCrab) on May 13. It has remained at nearly the same rate since then. This is roughly the same brightness as was reported in March 2009 (Krimm et al, ATel #1963).

Target of Opportunity observations with Swift/XRT were obtained on May 11, 12, 13, and 14. The first short (1.4 ks) Swift/XRT observation is strongly affected by the presence of a hot column at the center of the PSF. The spectra of the Swift/XRT following observations (4 to 5 ks each on-source time) can be fit (0.3-10 keV energy range) with an absorbed power-law model with a column density consistent with the Galactic one in the direction of the source (n_H = 6.89E20 cm^-2, Kalberla et al. 2005) and a photon index of 1.34+/-0.09, 1.51+/-0.10 and 1.41+/-0.10, respectively. The corresponding unabsorbed 0.3-10 keV fluxes are 1.3E-11, 1.0E-11, and 1.0E-11 erg cm^-2 s^-1. The X-ray flux confirms the high activity of the source at the beginning of the Swift/XRT observations.

We thank Neil Gehrels and the Swift Team for making these observations possible, in particular the duty scientists and science planners.