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Evolving early, hard X-ray emission of V745 Sco

ATel #5862; K. Mukai (NASA & UMBC), K. L. Page, J. P. Osborne (Leicester), and T. Nelson (Minnesota)
on 7 Feb 2014; 20:40 UT
Credential Certification: Koji Mukai (mukai@milkyway.gsfc.nasa.gov)

Subjects: Ultra-Violet, X-ray, Nova

Referred to by ATel #: 5870, 5874, 5920

We, on behalf of both the Swift Nova-CV group and the E-Nova collaboration, have initiated high cadence X-ray and UV monitoring of the symbiotic recurrent nova, V745 Sco, with Swift, shortly after the announcement by R. Stubbings of the first outburst since 1989 (AAVSO Special Notice #380). Here we report on the preliminary results from the first 3 pointings.

Start TimeExposure0.3-10 keV rateUVM2 mag
2014-02-06T20:20:370.98 ks0.49+/-0.0212.70+/-0.02
2014-02-07T05:56:500.98 ks0.62+/-0.0312.99+/-0.03
2014-02-07T13:57:170.92 ks0.81+/-0.0313.07+/-0.03

The first spectrum is highly absorbed, shows a prominent Fe K alpha line, and can be fitted with an APEC model with kT=8+4-2 keV and NH=(1.3+/-0.2)x1023 cm-2. The subsequent spectra can also be fitted with absorbed, hard, APEC models, but with declining NH: 5.2+0.9-0.8x1022 cm-2 and 3.5+0.5-0.4x1022 cm-2, respectively. The increasing count rate appears mostly, if not exclusively, due to the declining NH.

V745 Sco is a system similar to RS Oph in many ways, and the early, hard X-ray emission we have observed so far is no exception. In the case of RS Oph, the evolution of its hard X-ray emission was used to infer the properties of the ejecta and the ejecta-M giant wind interaction (Sokoloski et al. 2006, Nature, 442, 276; Bode et al. 2006, ApJ 652, 659).

High cadence Swift monitoring is scheduled to continue through at least 2014-02-10, and probably beyond although we may reconsider the cadence and other parameters. We encourage high cadence observations at other wavelengths.

We thank the Swift PI, Neil Gehrels, for a generous allocation of TOO time, and the operations team for implementing these high cadence observations at a short notice.