Support ATel At Patreon

[ Previous | Next | ADS ]

Ultraviolet and X-ray observations of YY Her in outburst

ATel #14469; Nicola Masetti (INAF-OAS, Bologna) and Ulisse Munari (INAF-OAPadova)
on 18 Mar 2021; 10:53 UT
Credential Certification: Nicola Masetti (nicola.masetti@inaf.it)

Subjects: Ultra-Violet, X-ray, Binary, Cataclysmic Variable, Transient, Variables

Following the announcement of a new outburst of the symbiotic star YY Her (Sokolovsky et al., ATel #14458; Munari et al., ATel #14464), on 2021 March 16 we activated X-ray and ultraviolet (UV) observations of the source respectively with the instruments XRT and UVOT onboard the Neil Gehrels Swift satellite. The pointing started at 19:35 UT.

YY Her was observed in UV with UVOT in filters UVW1, UVW2 and UVM2 for 261 s, 980 s and 699 s, respectively; it was well detected, yelding Vega system magnitudes UVW1=12.33+-0.04, UVW2=12.85+-0.04 and UVM2=12.79+-0.04. These values are fully consistent with the U-band magnitude acquired on the same day and reported in ATel #14464.
Assuming a distance for the source of 8.2 kpc according to the Gaia early Third Data Release (Gaia Collaboration, 2020yCat.1350....0G) and a colour excess E(B-V)=0.20 mag (Skopal 2005, A&A, 440, 995), we estimate an integrated unabsorbed UV luminosity of ~2.8e36 erg s-1, or ~730 Lsun. This is within the range of the bolometric luminosities of the burning WD in YY Her during active phases derived by Skopal (2005) from SED modeling.

The source was instead not detected in X-rays by XRT: a simultaneous observation lasting about 2000 s did not reveal any object in the 0.3-10 keV band at the position of YY Her down to a 3-sigma limit of 2.2e-3 counts s-1. Assuming a bremsstrahlung spectrum with temperature kT=0.1 keV and a hydrogen column density 1.1e21 atoms cm-2 derived from the E(B-V) above using the prescription of Predehl & Schmitt (1995, A&A, 293, 889), this countrate corresponds to an unabsorbed flux upper limit <3e-13 erg cm-2 s-1 and to a luminosity limit <2.4e33 erg s-1.

We thank the Swift Team for the quick approval, scheduling and acquisition of the observation presented in this communication.