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Swift Follow-up of the recent Gamma-ray flare in PKS 0402-362

ATel #6391; R. Ojha (NASA/GSFC/UMBC/CRESST), B. Carpenter (CUA/NASA/GSFC), F. Krauss (Remeis Observatory & ECAP, FAU Erlangen/Univ. Wuerzburg), on behalf of the Fermi LAT Collaboration.
on 15 Aug 2014; 15:06 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

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

Following a recent gamma-ray flare of the high redshift (z = 1.417, Peterson et al. 1976, ApJ, 207, 5), flat spectrum radio quasar PKS 0402-362, two Swift target of opportunity observations were performed on 2014 August 6 and 8. As a "LAT Monitored Source" a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0402-362 , hence no ATel was issued.

Swift/XRT data were taken in Photon Counting mode for a total exposure of about 4.9 ksec and 4.8 ksec, respectively. The X-ray spectrum (0.5-10 keV) can be fit by an absorbed power law model with an HI column density set to the Galactic value of 6.03x10^19 cm^-2 (Kalberla et al. 2005, A&A, 440, 775) using the abundances of Wilms et al. (2000, ApJ, 542, 914) and the cross sections of Verner et al. (1996, ApJ, 465, 487). The observed fluxes are (6.6+-0.7)x10^-12 and (6.1+-0.6)x10^-12 erg cm^-2 s^-1; while the photon indexes are 1.7+-0.1 and 1.7+-0.1, respectively. This flux is more than a factor of 2 lower than that observed on 2011 September 23 (Atel #3659) when this source had a much brighter gamma-ray flare but is about twice the flux of (3.2+/-0.2)x10^-12 erg cm^-2 s^-1 observed on 2008 Jan 1 when this object was in a gamma-ray quiet state.

Simultaneous Swift/UVOT observations are shown below, along with magnitudes from 2011 September 23 when this object exhibited another powerful gamma-ray flare and from 2008 January 01. Across all filters the current magnitudes are brighter than those observed on 2011 September 23 and 2008 January 01. All bands, except the V-magnitude, fade between 2014 Aug 06 and 2014 Aug 08. Therefore it is not clear that the gamma-ray state influences the optical band.

Filter   2008-Jan-01   2011-Sep-23   2014-Aug-06   2014-Aug-08
V       17.22+/-0.08   17.07+/-0.17   16.68+/-0.12   16.64+/-0.09
B       17.49+/-0.06   17.27+/-0.09   16.89+/-0.08   17.14+/-0.08
U       16.71+/-0.06   16.54+/-0.08   15.95+/-0.07   16.09+/-0.06
W1                           16.40+/-0.09   15.77+/-0.08   15.97+/-0.07
M2                           16.53+/-0.09   15.92+/-0.06   16.12+/-0.08
W2                           16.76+/-0.10   16.08+/-0.07   16.24+/-0.07

Further multiwavelength observations are encouraged. For this source the Fermi LAT contact person is J. Vandenbroucke (vandenbrouck@wisc.edu).

We would like to thank the Swift Team for making these observations possible, in particular D. Malesani as the Swift Observatory Duty Scientist.