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Swift follow-up observations of renewed gamma-ray emission from the FSRQ PKS 1510-089

ATel #3939; S. Vercellone, P. Romano (INAF/IASF-Pa), F. Verrecchia, F. Lucarelli, C. Pittori (ASDC and INAF/OAR), G. Piano (INAF/IAPS), E. Striani (Univ. Roma Tor Vergata), M. Cardillo (INAF/IAPS and Univ. Roma Tor Vergata), I. Donnarumma (INAF/IAPS), A. Bulgarelli (INAF/IASF-Bo) and M. Tavani (INAF/IAPS and Univ. Roma Tor Vergata) on behalf of the AGILE Team
on 23 Feb 2012; 12:55 UT
Credential Certification: Stefano Vercellone (stefano@ifc.inaf.it)

Subjects: Optical, Ultra-Violet, X-ray, Gamma Ray, AGN, Blazar

Following the AGILE/GRID detection of renewed gamma-ray emission from the FSRQ PKS 1510-089 (Lucarelli et al. 2012, ATel #3934), we performed a Swift Target of Opportunity observation (ToO) monitoring campaign. We report the preliminary results of the observations performed from 2012-02-17 to 2012-02-19 (6.6ks on source).

The XRT spectrum obtained combining the first 3.8ks fitted with an absorbed power law with an absorbing column density fixed to the Galactic value of 6.89E20 cm-2 (Kalberla et al. 2005) yields a photon index of 1.7+/-0.1, and an average flux of F=5.1E-12 erg/cm2/s (2-10 keV, unabsorbed). The XRT spectrum obtained combining the last 2.8ks yields a photon index of 1.6+/-0.1, and an average flux of F=5.4E-12 erg/cm2/s (2-10 keV, unabsorbed).

The UVOT observed the field simultaneously with the XRT in the1 following optical and UV filters. The preliminary observed magnitudes in the Vega system are:

MJD Filter Magnitude
55974.9425+/-0.0006 B 16.52+/-0.05 (stat) +/-0.02 (sys)
55974.9407+/-0.0012 U 15.63+/-0.03 (stat) +/-0.02 (sys)
55974.9692+/-0.0345 W1 15.74+/-0.03 (stat) +/-0.03 (sys)

55976.0868+/-0.0007 B 16.55+/-0.04 (stat) +/-0.02 (sys)
55976.0853+/-0.0007 U 15.68+/-0.04 (stat) +/-0.02 (sys)
55976.0830+/-0.0015 W1 15.84+/-0.04 (stat) +/-0.03 (sys)
55976.0903+/-0.0027 W2 15.82+/-0.03 (stat) +/-0.03 (sys)

55976.5556+/-0.0719 V 16.22+/-0.06 (stat) +/-0.01 (sys)
55976.5510+/-0.0696 B 16.48+/-0.04 (stat) +/-0.02 (sys)
55976.5501+/-0.0691 U 15.60+/-0.04 (stat) +/-0.02 (sys)
55976.5489+/-0.0689 W1 15.73+/-0.04 (stat) +/-0.03 (sys)
55976.5588+/-0.0746 M2 15.67+/-0.04 (stat) +/-0.03 (sys)
55976.5540+/-0.0721 W2 15.76+/-0.03 (stat) +/-0.03 (sys)

55976.7634+/-0.0683 V 16.30+/-0.05 (stat) +/-0.01 (sys)
55976.7584+/-0.0687 B 16.52+/-0.03 (stat) +/-0.02 (sys)
55976.7574+/-0.0688 U 15.65+/-0.03 (stat) +/-0.02 (sys)
55976.7558+/-0.0694 W1 15.75+/-0.03 (stat) +/-0.03 (sys)
55976.7652+/-0.0689 M2 15.70+/-0.04 (stat) +/-0.03 (sys)
55976.7608+/-0.0699 W2 15.81+/-0.03 (stat) +/-0.03 (sys)

The magnitudes in the table are not corrected for the Galactic extinction due to a reddening of E(B-V) = 0.097 mag in the direction of the source (Schlegel et al. 1998).

We can compare our preliminary results with those reported in Vercellone et al., 2012, ATel #3910. We note that the current X-ray flux level is about a factor of two lower than that previously reported, while the photon index is marginally softer. The values reported here are in agreement with the harder-when-brighter trend reported in D'Ammando et al., (2011, A&A, 529, A145). Moreover, we report a brightening of the source in the UV-optical bands (about 0.2 - 0.3 mag) with respect to the 2012 February 2 values.

We warmly thank N. Gehrels, the Science Planners, and the Observatory Duty Scientists for having scheduled these observations.