The symbiotic recurrent nova V745 Sco is confirmed as a bright super-soft source.
ATel #5877; K. L. Page, J. P. Osborne, A. P. Beardmore (U. Leicester), K. Mukai (NASA & UMBC) and S. Starrfield (ASU)
on 11 Feb 2014; 20:57 UT
Credential Certification: Kim Page (kpa@star.le.ac.uk)
On 2014-02-10, Swift-XRT data collected on the recurrent nova
V745 Sco showed an increase in soft counts, suggesting the onset
of the super-soft source phase (Page et al., ATel #5870). Further
data collected approximately 24 hours later
showed a dramatic increase in the source count rate, almost
entirely due to counts below 1 keV. We therefore confirm that
V745 Sco is now in the supersoft emission phase.
The 0.3-1 and 1-10 keV keV count rates for the past couple of days are
tabulated below. T0 is taken as 2014 Feb 6.694 UT (AAVSO Special Notice 380).
| UT Date | Day since detection | 0.3-1 keV XRT count
s-1 | 1-10 keV XRT count s-1 |
| 2014-02-10T03:07 | 3.44 | 0.095 +/- 0.007 |
1.17 +/- 0.02 |
2014-02-10T12:27 | 3.83 | 0.48 +/- 0.02 | 1.36
+/- 0.03 |
2014-02-10T17:16 | 4.03 | 4.28 +/- 0.16 | 1.64
+/- 0.10 |
2014-02-10T22:03 | 4.23 | 9.54 +/- 0.09 | 1.52
+/- 0.04 |
2014-02-10T03:08 | 4.44 | 13.4 +/- 0.1 | 1.54
+/- 0.04 |
2014-02-10T08:02 | 4.64 | 25.7 +/- 0.2 | 1.73
+/- 0.04 |
Duerbeck (1989, ESO Messenger 58, 34) notes that in the 1989 outburst V745 Sco appears similar to RS Oph, but the optical spectrum evolves about three times faster. The super-soft phase in RS Oph was
first detected
26 days after the optical eruption (Osborne et al., 2011, ApJ, 727,
124);
the much earlier detection of the super-soft phase in V745 Sco at ~3
days suggests an even faster evolution.
The supersoft component of V745 Sco is detected up to E ~ 1 keV, suggestive of a
high temperature, and, consistent with the rapid turn-on, that the white dwarf is
very massive (see e.g. Wolf et al., 2013 ApJ 777, 136).
We thank the Swift PI and operations team for their support of these
observations.
