SWIFT X-RAY OBSERVATIONS OF CLASSICAL NOVAE. II. THE SUPER SOFT SOURCE SAMPLE

Abstract

The Swift GRB satellite is an excellent facility for studying novae. Its rapid response time and sensitive X-ray detector provides an unparalleled opportunity to investigate the -2previously poorly sampled evolution of novae in the X-ray regime. This paper presents Swift observations of 52 Galactic/Magellanic Cloud novae. We included the XRT (0.3-10 keV) X-ray instrument count rates and the UVOT (1700-8000Å) filter photometry. Also included in the analysis are the publicly available pointed observations of 10 additional novae the X-ray archives. This is the largest X-ray sample of Galactic/Magellanic Cloud novae yet assembled and consists of 26 novae with super soft X-ray emission, 19 from Swift observations. The data set shows that the faster novae have an early hard X-ray phase that is usually missing in slower novae. The Super Soft X-ray phase occurs earlier and does not last as long in fast novae compared to slower novae. All the Swift novae with sufficient observations show that novae are highly variable with rapid variability and different periodicities. In the majority of cases, nuclear burning ceases less than 3 years after the outburst begins. Previous relationships, such as the nuclear burning duration vs. t 2 or the expansion velocity of the eject and nuclear burning duration vs. the orbital period, are shown to be poorly correlated with the full sample indicating that additional factors beyond the white dwarf mass and binary separation play important roles in the evolution of a nova outburst. Finally, we confirm two optical phenomena that are correlated with strong, soft X-ray emission which can be used to further increase the efficiency of X-ray campaigns.

X-RAY FLASHES IN RECURRENT NOVAE: M31N 2008-12a AND THE IMPLICATIONS OF THE SWIFT NONDETECTION

“…Hachisu & Kato 2006, 2010, 2015, 2016aOsborne 2015;Schwarz et al 2011, and references therein). The evolution of novae has been modeled by the optically thick wind theory (Kato & Hachisu 1994), and their theoretical light curves for D-E-F have successfully reproduced the observed light curves including NIR, optical, UV, and supersoft X-rays.…”

On the narrow emission line components of the LMC novae 2004 (YY Doradus) and 2009a

“…Among these novae, the appearance of the narrow He ii emission matched the start of the SSS phase (Schwarz et al 2011) in LMC 2009a, U Sco, and KT Eri. Therefore, on one side it is tempting to suggest that the appearance of the He ii 4686 is the optical marker of the start of the SSS phase in all the objects listed above.…”

Unbeamed tidal disruption events at hard X-rays

“…The low mass X-ray binary 4U 1735-44, located 31 arcmin away, is much brighter but did not contaminate the flare significantly. (Bode et al 2010) and reached an X-ray maximum in January 2010 (Schwarz et al 2011). The hard X-ray flare detected by BAT is, therefore, not related to PGC 016029.…”

“…Very large (>20 arcmin) differences indicate that the flare image is far from a point source and most likely related to instrumental or image cleaning problems. Nolan et al 2012), the second Fermi/GBM GRB catalogue (blue crosses; von Kienlin et al 2014), the list of supernovae observed by Swift/XRT (cyan x; Russell & Immler 2012), the Swift X-ray observations of classical novae II (magenta x; Schwarz et al 2011), the Swift/BAT hard X-ray transient monitor catalogue (magenta stars; Krimm et al 2013), the second Swift/BAT GRB catalogue (red +; Sakamoto et al 2011), the 70 month Swift-BAT all-sky hard X-ray survey (red x; Baumgartner et al 2013) obtained through the Vizier service 3 . As very bright sources might affect the whole field of view of the BAT instrument and the source cleaning might be imperfect, we also checked whether our flare candidates occurred when any of the BAT bright sources were present within 60 degrees and flaring at the same time.…”