Swift/XRT observation of the old symbiotic nova AG Peg during its current outburst.

ATel #7741; Luna, G. J. M. (IAFE), Nunez, N. E. (UNSJ), Sokoloski, J. L. (U. of Columbia), Montane, B. (UNLP)
on 1 Jul 2015; 15:37 UT
Credential Certification: Gerardo Juan Manuel Luna (gluna@cfa.harvard.edu)

Tweet

We report results from the latest Swift/XRT observation of the symbiotic nova AG Peg after its recently reported optical brightening (AAVSO, alert notice 521). Swift observed the field of AG Peg on June 28-July 1st, 2015 for 11.37 ks and detected the source at a count rate of 0.047 -+ 0.002 c/s. During a previous observation on August 16-29 2013 (Atel #5324), AG Peg was detected with a count rate of 0.017+-0.002 c/s. A preliminary fit of the most recent X-ray spectrum, which extends upto energies of around 5 keV, suggests that it can be modeled with an absorbed (nH ~ 0.4e22 cm^-2), two-temperature optically thin thermal plasma (kT1 ~ 0.9 keV and kT2 > 0.15 keV) plus a super-soft black-body type component (kT ~ 0.02 keV and Lx ~1.5e34 ergs/s at a distance of 600 pc). The hardness ratio (HR[2.0-10.0/0.3-2.0 keV]~ 0.04) has increased since the observations on August 2013 (HR~0.012), indicating that the X-ray emission is becoming harder, possibly due to the development of a region where winds from the two stars are colliding. Since outflows are often detected from white dwarfs in symbiotic stars when they are in outburst, the current brightening makes AG Peg an ideal system for the study of the development of a colliding-winds region. The source was so bright in the UV that it saturated the UVOT images. We gratefully acknowledge the effort of the entire Swift team for the execution of our ToO request.