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 XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA . and Chandra Software provided by the Chandra X-ray Center ( CXC ) in the application package CIAO was used to obtain science data . 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 2 \sigma 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 .