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An 'outside-in' outburst of Aql X–1 |
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| Authors: | T Shahbaz R M Bandyopadhyay P A Charles R M Wagner P Muhli P Hakala J Casares & J Greenhill |
| Institution: | University of Oxford, Department of Astrophysics, Nuclear Physics Building, Keble Road, Oxford OX1 3RH,;Department of Astronomy, Ohio State University, 174 West 18th Avenue, Columbus, OH 43210-1106, USA,;Observatory, PO Box 14, FIN-00014 University of Helsinki, Finland,;Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain,;Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tasmania, Australia |
| Abstract: | We present optical spectroscopy and optical and infrared photometry of the neutron star soft X-ray transient Aql X–1 during its X-ray outburst of 1997 August. By modelling the X-ray, optical and IR light curves, we find a 3-d delay between the IR and X-ray rise times, analogous to the UV–optical delay seen in dwarf novae outbursts and black hole X-ray transients. We interpret this delay as the signature of an 'outside-in' outburst, in which a thermal instability in the outer disc propagates inward. This outburst is the first of this type definitively identified in a neutron star X-ray transient. |
| Keywords: | accretion accretion discs binaries: close stars: individual: Aql X–1 stars: neutron X-rays: stars |