NuSTAR observation of V475 Sco

ATel #5913; Vikram Rana (Caltech), Marina Orio (University of Wisconsin Department of Astronomy, USA, and INAF-Padova, Italy), Jeno Sokoloski (Columbia University) and Fiona Harrison (Caltech)
on 21 Feb 2014; 19:27 UT
Credential Certification: Marina Orio (orio@astro.wisc.edu)

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V745 Sco (see ATel 5862, 5865, 5870, 5871, 5874, 5877, 5879, 5881, 5884, 5897) was observed 10 days after the announced optical discovery (R. Stubbings, AAVSO special notice #380), on 2014-02-16 at 00:51:07 UT with NuSTAR for about 25 kiloseconds. The exposure was not continuous and ended at 12:51:07 UT. A luminous hard X-ray source was detected, with a measured flux of (1.68$\pm$0.10) x 10(-11) erg/cm(2)/s in the 3-20 keV range. The spectrum can be fitted with an XSPEC "VAPEC" model of plasma in collisional ionization equilibrium at kT=2.6 keV. No harder component above 20 keV was detected. The flux and plasma temperature are consistent with those derived analysing a Swift observation done while the NuSTAR exposures were ongoing (observation id. 00033136034). Iron features are detected, the strongest of which is the unresolved iron He-like triplet at 6.73$\pm$0.02 keV, with an equivalent width of about 1 keV. The iron lines do not require enhanced iron abundance to be fitted, but they appear prominent because of the high sensitivity of NuSTAR in the 6-8 keV range. The authors are grateful to the NuSTAR team for the timely observation.