On the spin modulated circular polarization from the intermediate polars NY Lup and IGR J15094-6649

Abstract

We report on high-time-resolution, high-signal-to-noise ratio (S/N), photopolarimetry of the intermediate polars NY Lup and IGR J15094-6649. Our observations confirm the detection and colour dependence of circular polarization from NY Lup and additionally show a clear white dwarf, spin modulated signal. From our new high-S/N photometry, we have unambiguously detected wavelength-dependent spin and beat periods and harmonics thereof. IGR J15094-6649 is also discovered to have a particularly strong spin modulated circularly polarized signal. It appears double peaked through the I filter and single peaked through the B filter, consistent with cyclotron emission from a white dwarf with a relatively strong magnetic field. We discuss the implied accretion geometries in these two systems and any bearing this may have on the possible relationship with the connection between polars and soft X-ray-emitting intermediate polars. The relatively strong magnetic fields are also suggestive of them being polar progenitors. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.