Chandra detection of X-ray emission lines from the blast wave of V745 Sco

ATel #5920; J. J. Drake (Smithsonian Astrophysical Observatory), S. Starrfield (Arizona State U.), J-U. Ness (ESA/ESAC) J. P. Osborne and K. Page (U. Leicester), S. N. Shore (U. Pisa), R. M. Wagner (Ohio State U.), C. E. Woodward (U. Minnesota)
on 25 Feb 2014; 04:45 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Jeremy J. Drake (jdrake@cfa.harvard.edu)

Tweet

The recurrent nova V745 Sco was discovered in outburst on 2014 Feb 6 (CBET #3803) and was observed by the Chandra X-ray Observatory Low-Energy (LETG) grating on 2014 February 22.52 and 23.43 UT, and by the High-Energy (HETG; HEG and MEG) gratings on February 23.59 UT. The total net exposures were 45ks and 39ks for the LETG and HETG, respectively. The LETG spectra obtained with the HRC-S detector are dominated by emission lines in the 5-15 A range, with a first order count rate of 0.29 count/s. We detect emission lines, from short to long wavelengths, of S XV, Si XIV, Si III, Mg XII, Mg XI, Ne X, Ne IX, Fe XVII, O VIII, and additional Fe lines. A lack of significant emission at wavelengths longward of 20 A indicates that the supersoft source phase (ATEL #5877) has ended. This result is consistent with the report in ATEL #5897 of a strongly declining soft X-ray signal in Swift observations. HETG spectra, obtained with the ACIS-S detector on day 17 of the outburst, had 1st order count rates of 0.22 and 0.54 count/s in the HEG and MEG, respectively. The spectra resemble the Chandra spectra of the blast wave of the recurrent nova RS Ophiuchi obtained on day 14 of its 2006 outburst (Drake et al, 2009, ApJ 691, 418), and also show prominent emission lines from H-like and He-like ions of Ne, Mg, Si, S, Ca and Fe. Analogous to that event, we interpret the emission as originating from the continuing evolution of the interaction of the explosion ejecta and the atmosphere of the red giant secondary observed earlier by Swift (ATEL #5862), Fermi (ATEL #5879) and NuSTAR (ATEL #5913). Spectral lines are broadened by approximately 1500 km/s at FWHM. Ne X and O VIII resonance lines exhibit some evidence of net blueshifts indicating absorption of redshifted emission from receding gas by intervening material.