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Short-period X-ray oscillations in super-soft novae and persistent super-soft sources

Ness, J.-U. and Beardmore, A. P. and Osborne, J. P. and Kuulkers, E. and Henze, M. and Piro, A. L. and Drake, J. J. and Dobrotka, A. and Schwarz, G. and Starrfield, S. and Kretschmar, P. and Hirsch, M. and Wilms, J. (2015) Short-period X-ray oscillations in super-soft novae and persistent super-soft sources. Astronomy and Astrophysics, 578 . Art. No. A39. ISSN 0004-6361.

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Context. Transient short-period (<100 s) oscillations have been found in the X-ray light curves of three novae during their super-soft source (SSS) phase and in one persistent SSS. Aims. We pursue an observational approach to determine possible driving mechanisms and relations to fundamental system parameters such as the white dwarf mass. Methods. We performed a systematic search for short-period oscillations in all available XMM-Newton and Chandra X-ray light curves of persistent SSS and novae during their SSS phase. To study time evolution, we divided each light curve into short time-segments and computed power spectra. We then constructed a dynamic power spectrum from which we identified transient periodic signals even when only present for a short time. We base our confidence levels on simulations of false-alarm probability for the chosen oversampling rate of 16, corrected for multiple testing based on the number of time segments. From all time segments of each system, we computed fractions of time when periodic signals were detected. Results. In addition to the previously known systems with short-period oscillations, RS Oph (35 s), KT Eri (35 s), V339 Del (54 s), and Cal 83 (67 s), we found one additional system, LMC 2009a (33 s), and also confirm the 35 s period from Chandra data of KT Eri. The oscillation amplitudes are of about <15% of the respective count rates and vary without any clear dependence on the X-ray count rate. The fractions of the time when the respective periods were detected at 2σ significance (duty cycle) are 11.3%, 38.8%, 16.9%, 49.2%, and 18.7% for LMC 2009a, RS Oph, KT Eri, V339 Del, and Cal 83, respectively. The respective highest duty cycles found in a single observation are 38.1%, 74.5%, 61.4%, 67.8%, and 61.8%. Conclusions. Since fast rotation periods of the white dwarfs as origin of these transient oscillations are speculative, we concentrate on pulsation mechanisms. We present initial considerations predicting the oscillation period to scale linearly with the white dwarf radius (and thus mass), weakly with the pressure at the base, and luminosity. Estimates of the size of the white dwarf could be useful for determining whether these systems are more massive than typical white dwarfs, and thus whether they are growing from accretion over time. Signs of such mass growth may have implications for whether some of these systems are attractive as Type Ia supernova progenitors.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Henze, M.0000-0001-9985-3406
Piro, A. L.0000-0001-6806-0673
Drake, J. J.0000-0002-0210-2276
Kretschmar, P.0000-0001-9840-2048
Wilms, J.0000-0003-2065-5410
Alternate Title:Short-period X-ray oscillations in super-soft novae and persistent SSS
Additional Information:© 2015 ESO. Article published by EDP Sciences. Received 19 October 2014; Accepted 25 February 2015; Published online 1 June 2015. A. P. Beardmore and J. P. Osborne acknowledge support from the UK Space Agency. M. H. acknowledges support from an ESA fellowship. A. L. Piro is supported through NSF grants AST-1205732, PHY-1151197, PHY-1404569, and the Sherman Fairchild Foundation. A. Dobrotka was supported by the Slovak grant VEGA 1/0511/13. S. Starrfield gratefully acknowledges partial support from NSF and NASA grants to ASU.
Funding AgencyGrant Number
United Kingdom Space Agency (UKSA)UNSPECIFIED
European Space Agency (ESA)UNSPECIFIED
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:novae, cataclysmic variables – stars: oscillations – white dwarfs – X-rays: stars
Record Number:CaltechAUTHORS:20150811-104628162
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Official Citation:J.-U. Ness, A. P. Beardmore, J. P. Osborne, E. Kuulkers, M. Henze, A. L. Piro, J. J. Drake, A. Dobrotka, G. Schwarz, S. Starrfield, P. Kretschmar, M. Hirsch and J. Wilms A&A 578 A39 (2015) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59392
Deposited By: Tony Diaz
Deposited On:11 Aug 2015 17:57
Last Modified:17 Dec 2019 22:46

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