A Chandra High-Resolution X-ray spectrum of KT Eri

ATel #2418; J.-U. Ness (ESA/ESAC), J. J. Drake (CfA), S. Starrfield (ASU), M. Bode (Liverpool), K. Page, A. Beardmore, J. P. Osborne (Leicester), G. Schwarz (AAS), on behalf of the Swift Nova-CV Working Group.
on 3 Feb 2010; 18:57 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Jan-Uwe Ness (Jan-Uwe.Ness@asu.edu)

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A high resolution X-ray spectrum was obtained of the Classical Nova KT Eri with the Low Energy Transmission Grating (LETG) onboard Chandra. The exposure began at 2010-01-23T21:48:52 and ended at 2010-01-24T02:25:30. This was between 70.31 to 70.49 days after optical peak (2009 Nov 14.632, IAUC 9098 . We note this was also taken as t=0 in ATel #2392, rather than outburst discovery as stated therein). The average LETGS count rate was 15 counts per second (cps), but the light curve was highly variable with count rates ranging from 5 to 25 cps. At the same time, the Swift XRT count rate was variable between 5-10 cps. The integrated spectrum is that of a bright supersoft source (SSS) with a strong continuum between 23 and 50AA plus deep absorption features. We have fit a blackbody to this spectrum and the resulting temperature and extinction is 4.4x10**5 K (37.9eV) and N_H=1.2x10**21 cm**-2, respectively. These results are similar to those obtained from Swift spectra (see ATel #2392). Caution should be exercised as, e.g., our results for blackbody fits to the LETG spectra of V4743 Sgr show that such a fit significantly underestimates the actual temperature and, thus overestimates the resulting bolometric luminosity (Ness et al. 2010, in prep). The spectrum contains deep absorption lines from nitrogen (25 and 29 A) and carbon (34 A), and perhaps silicon. The absorption lines are blue shifted by about -2500km/s. In addition to the absorption lines, a strong emission line of NVI can clearly be seen at 29 A, it is red shifted by about 1500km/s and is broader than the instrumental line broadening function. A comparison of the high-flux and the low-flux spectra (from our full data-set) indicate that the NVI emission line was stronger relative to the continuum during the times of lower average count rate. Separating the observed spectrum into 200 sec intervals indicates that this line was varying through the observation. We would like to thank Harvey Tananbaum for generously granting the DDT observation and the Chandra Observatory for their extremely rapid response.