X-ray follow-up observation of the high-redshift, gamma-ray quasar S5 0836+710 (4C 71.07)

ATel #7898; S. Vercellone, P. Romano (INAF/IASF Palermo), C. M. Raiteri, M. Villata (INAF/OATO)
on 10 Aug 2015; 06:41 UT
Credential Certification: Stefano Vercellone (stefano@ifc.inaf.it)

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The high-redshift (z=2.172) flat-spectrum radio quasar (FSRQ) S5 0836+710 (4C 71.07) is one of the Fermi/LAT Monitored Sources (see http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/ ). On 2015 August 3, upon noticing a bright flare in the gamma-ray light curve of this source, with a flux F(E>100 MeV) > 2E-6 ph/cm2/s, we triggered a Swift Target of Opportunity monitoring. The gamma-ray flux enhancement was subsequently confirmed by Ciprini et al. (ATel #7870), and Giroletti et al. (ATel #7890) reported a high-state at radio frequency.

We report the preliminary results of the first Swift observation, performed on 2015-08-09 (MJD 57243.893751)

The XRT/PC spectrum (958 s), is fitted with an absorbed power law, with two absorbing components (NHGAL=2.8E20 cm-2; Kalberla et al. 2005; and one free NH=0.4E20 cm-2) and a photon index =1.27 (+0.23,-0.12)). The average unabsorbed flux is 2.9E-11 erg/cm2/s (0.3-10 keV).

The UVOT observed the field simultaneously with the XRT in the following optical and UV filters. The preliminary observed magnitudes in the Vega system are:
MJD Filter Magnitude
57243.9583+/-0.0004 V 16.98+/-0.15 (stat) +/-0.01 (sys)
57243.9546+/-0.0004 B 17.07+/-0.09 (stat) +/-0.02 (sys)
57243.9539+/-0.0004 U 16.37+/-0.08 (stat) +/-0.02 (sys)
57243.8901+/-0.0633 W1 17.05+/-0.07 (stat) +/-0.03 (sys)
57243.9599+/-0.0012 M2 17.40+/-0.12 (stat) +/-0.03 (sys)
57243.9565+/-0.0014 W2 17.90+/-0.11 (stat) +/-0.03 (sys)
The magnitudes are not corrected for Galactic extinction.

Our group has been regularly monitoring S5 0836+710 with Swift since October 2014. The most recent Swift/XRT observation prior to the gamma-ray flare was acquired on 2015-07-17 (MJD 57220.824013) for a total of 4834 s on source. When the spectrum is fit with the same model as described above, the average unabsorbed flux is 3.4E-11 erg/cm2/s (0.3-10 keV, power-law photon index = 1.23 +/- 0.08).

The UVOT magnitudes (not corrected for Galactic extinction) on 2015-07-17 were:
MJD Filter Magnitude
57220.8256+/-0.0966 V 16.99+/-0.06 (stat) +/-0.01 (sys)
57220.8203+/-0.0958 B 17.18+/-0.04 (stat) +/-0.02 (sys)
57220.8192+/-0.0956 U 16.29+/-0.04 (stat) +/-0.02 (sys)
57220.8177+/-0.0958 W1 17.11+/-0.05 (stat) +/-0.03 (sys)
57220.8281+/-0.0983 M2 17.67+/-0.05 (stat) +/-0.03 (sys)
57220.8232+/-0.0977 W2 18.08+/-0.05 (stat) +/-0.03 (sys)

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