V745 Sco is a recurrent nova, with the most recent eruption occurring in February 2014. V745 Sco was first observed by Swift a mere 3.7 h after the announcement of the optical discovery, with the super-soft X-ray emission being detected around 4 d later and lasting for only ~2 d, making it both the fastest follow-up of a nova by Swift and the earliest switch-on of super-soft emission yet detected. Such an early switch-on time suggests a combination of a very high velocity outflowand lowejected mass and, together with the high effective temperature reached by the super-soft emission, a high mass white dwarf (> 1.3M⊙). The X-ray spectral evolution was followed from an early epoch where shocked emission was evident, through the entirety of the super-soft phase, showing evolving column density, emission lines, absorption edges, and thermal continuum temperature. UV grism data were also obtained throughout the super-soft interval, with the spectra showing mainly emission lines from lower ionization transitions and the Balmer continuum in emission. V745 Sco is compared with both V2491 Cyg (another nova with a very short super-soft phase) and M31N 2008-12a (the most rapidly recurring nova yet discovered). The longer recurrence time compared to M31N 2008-12a could be due to a lower mass accretion rate, although inclination of the system may also play a part. Nova V745 Sco (2014) revealed the fastest evolving super-soft source phase yet discovered, providing a detailed and informative data set for study.
Bibliographical noteFunding Information:
KLP, JPO, and APB acknowledge funding from the UK Space Agency. SS acknowledges partial support to ASU from NSF and NASA grants. We thank the Swift PI, Neil Gehrels, together with the Observatory Duty Scientists and Science Planners, especially for their work in scheduling the grism observations. We thank Hans Krimm for adding V745 Sco to the BAT Transient Monitor and Brad Schaefer for useful discussion. This research has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under the grants ESP2013-41268-R and ESP2014-56003-R.
© 2015 The Author.
- Novae, cataclysmic variables
- Stars: individual: V745 Sco
- Ultraviolet: stars
- X-rays: stars