On the spin modulated circular polarization from the intermediate polars NY Lup and IGRJ1509-6649

TL;DR

This study presents high-resolution polarimetry of NY Lup and IGRJ1509-6649, revealing spin-modulated circular polarization and cyclotron emission, shedding light on their magnetic fields and accretion geometries.

Contribution

It provides new high signal-to-noise polarimetric data confirming circular polarization and spin modulation, and suggests these systems have strong magnetic fields related to polars.

Findings

Detection of wavelength-dependent spin and beat periods.

Strong spin-modulated circular polarization in IGRJ1509-6649.

Cyclotron emission signatures indicating strong magnetic fields.

Abstract

We report on high time resolution, high signal/noise, photo-polarimetry of the intermediate polars NY Lup and IGRJ1509-6649. 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 signal/noise photometry we have unambiguously detected wavelength dependent spin and beat periods and harmonics thereof. IGRJ1509-6649 is discovered to also 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 IPs. The relatively strong magnetic fields is also suggestive of them being polar progenitors.