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