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Swift follow-up of the flaring high-redshift blazar PKS 0458-02

ATel #4407; F. D'Ammando (Univ. Perugia and INFN), M. Orienti (Univ. Bologna and INAF-IRA) on behalf of the Fermi Large Area Telescope Collaboration, and C. J. Mountford (Univ. Leicester)
on 21 Sep 2012; 10:13 UT
Credential Certification: Filippo D'Ammando (filippo.dammando@fisica.unipg.it)

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

Following the gamma-ray flare of the high-redshift flat spectrum radio quasar PKS 0458-02 detected by Fermi LAT on 2012 September 17 (ATel #4396) a Swift target of opportunity observation was performed on September 19.

Swift/XRT data were taken in Photon Counting mode for a total exposure of about 2.0 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 = 6.02 x 10^20 cm^-2, Kalberla et al. 2005, A&A, 440, 775) and a photon index of 1.4+/-0.2. The corresponding observed 0.3-10 keV flux is (4.6+/-0.8)x10^-12 erg cm^-2 s^-1. This flux is about a factor of two higher than that observed by Swift/XRT on 2011 September 1, (2.1+/-0.5)x10^-12 erg cm^-2 s^-1, with a photon index of 1.3+/-0.2.

Simultaneous Swift/UVOT observations on 2012 September 19 found PKS 0458-02 about 0.2 mag brighter in V-band, 0.4 mag in B-band, and 0.8 mag in U-band compared to the UVOT observations performed on 2011 September 1. The measured Vega magnitudes are:

Band 2012-09-19 2011-09-01
V 17.73+/-0.10 17.93+/-0.13
B 18.38+/-0.10 18.79+/-0.12
U 18.42+/-0.12 19.29+/-0.30

An optical brightening of the source has been reported also by Pursimo et al. (ATel #4402). In consideration of the ongoing activity of this source, confirmed also by the Swift observations, we encourage further multiwavelength observations. For this source the Fermi LAT contact person is M. Orienti (orienti@ira.inaf.it).

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