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.



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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