The new intermediate polars from the ROSAT all-sky survey

Abstract

An overview of the soft X-ray temporal and spectral properties of the 7 new intermediate polar (IP) type cataclysmic variables, discovered up to now in the ROSAT all-sky survey, is presented. Their nature as pulsating X-ray sources with spin periods between 300 and 1400 s was revealed by follow-up ROSAT pointed and optical observations. RE0751+14, RX J0558.0+5353, RX J0512.2-3241 and probably RX J1914.4+2456 belong to the new class of soft IPs, characterized by soft X-ray spectra which are dominated by a variable blackbody-like component with kT around 60 eV. New ROSAT HRI observations of RX J1914.4+2456 confirm the spin period at 569.4 s. RX J0028.8+5917, RX J1712.6-2414 and RX J0153.3+7446 have X-ray spectra consistent with hot thermal Bremsstrahlung as it was observed from IPs known before the launch of ROSAT. These ROSAT-discovered “hard” IPs show on average however lower photo-electric absorption which varies only marginally with pulse phase. The light curve of RX J1712.6-2414 at soft X-ray energies is modulated at the beat frequency between spin and orbital period, indicating that most of the material is accreted directly via the accretion stream. New RXTE observations of RX J1712.6-2414 during a higher intensity state of the source find the X-ray modulations a factor of 5 reduced.