Swift/XRT detection of the old symbiotic nova AG Peg.

ATel #5324; Nunez, N. E.(ICATE); Luna, G. J.M.(IAFE)
on 26 Aug 2013; 11:02 UT
Credential Certification: Natalia Edith Nuñez (nnunez@icate-conicet.gob.ar)

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We report the Swift/XRT detection of the symbiotic nova AG Peg after its recent optical brightening that started around May 18, 2013 (as reported by Munari et al. 2013, Atel #5258). Swift observed the field of AG Peg for a total of 9.5 ks on August 16, 2013 detecting the source with a signal-to-noise ratio of 11 and with a count rate of 0.020+-0.002 c/s. The X-ray source coordinates, alpha = 21h 51m 1.83s and delta = 12d 37' 25.5" (with an error radius of 3.6", at a 90% confidence), are consistent with the position of the symbiotic nova at alpha = 21h 51m 1.97s and delta = 12d 37' 32.12". Given an orbital period of 818.2 days and the time of periastron passage T(JD) = 2446812 (Fekel et al. 2000, AJ, 119, 1375), our observation took place at the binary phase phi=0.83. A preliminary fit of the X-ray spectrum, that extends up to energies of around 3 keV, suggests that it can be modeled with an absorbed (nH ~ 0.2e22 cm^-2) optically thin thermal plasma (kT ~ 0.8 keV). The unabsorbed flux in the 0.3-10.0 keV band is around 5.1e-13 erg/s/cm^2 and the luminosity in the same energy band is 2.2e31 erg/s (at a distance of 600 pc, Kenny & Taylor 2007, ApJ, 662, 1231). The source was too bright in the UV and saturated the UVOT images. AG Peg was detected with ROSAT in June 1993, declining from the previous outburst, with a X-ray luminosity of ~4e31 erg/s (Muerset et al. 1997, A&A, 319, 201), commensurate with our current measurement. Soft X-ray emission in symbiotic systems is expected to arise in a region where the winds from the white dwarf and red giant collide. The current brightening makes AG Peg an ideal system to study the development of such a region. We gratefully acknowledge the effort of the entire Swift team for the execution of our ToO request.