Irradiated Accretion Discs in Low Mass X-ray Transients

Powell, Craig Robert (2004). Irradiated Accretion Discs in Low Mass X-ray Transients. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fa07

Abstract

The disc instability model successfully explains the outbursts of dwarf novae, but modifications are required to account for the differences observed in the outbursts of Low Mass X-ray Binaries. I investigate the effects of X-ray irradiation on the accretion disc during outburst and find that the shape of the decaying lightcurve can be simply accounted for. Fitting the decay provides a new way to determine system parameters based on the accretion disc radius, supplementing existing methods. The effects of X-rays in the period following outburst allow echo outbursts to occur on timescales much longer than those of dwarf novae, as observed. In developing this work I determine a new form for the surface density profile of the disc during the decay from outburst.

I examine observations of XTE J 1118+480 taken at UKIRT to find the magnitude and spectrum of the system in its near-quiescent state. From the photometry I determine a new, more accurate orbital period. In the spectrum produced hydrogen and helium emission lines from the disc are apparent.

I also searched for the optical counterparts of two newly detected X-ray sources. Although no strong candidate was found for either, a list of less probable candidates is provided for each star.

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