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A Strong Variation of Accretion Disc Corona Size with Luminosity in LMXB

Published online by Cambridge University Press:  22 February 2018

M. J. Church
M. J. Church*
Affiliation:
School of Physics & Astronomy, University of Birmingham, Birmingham B15 2TT, UK (mbc@star.sr.bham.ac.uk) Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland

Abstract

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The controversy that has existed for many years over the nature of the continuum X-ray emission components in X-ray binaries is reviewed, in which workers have been polarized between the Eastern model with a small central Comptonizing region around the compact object and alternative models. We present measurements of the radial extent of the Comptonizing ADC in low mass X-ray binaries which rule out the Eastern model and show that, the ADC is extended (the Birmingham model). Dip ingress timing shows conclusively that the ADC radial extent varies from 7% of the accretion disc radius in faint sources, to 65% in bright sources. Remarkably, the size depends strongly on the source luminosity suggesting that the ADC is formed by irradiation of the disc by the neutron star and the hot inner disc. These results have fundamental implications for the correct description of Comptonization in X-ray binaries, and the spectral form is derived for the Comptonized emission of an extended ADC led by soft, seed photons from the underlying disc which differs substantially from that of the Eastern model. Measured ADC electron températures provide values of the Compton radius in broad agreement with measured values of the radial extent of the ADC. Finally, we show that the results are inconsistent with the non-thermal emission being produced in a jet, and so provide evidence against the recent suggestion that all LMXB have jets.

Resumen

Resumen

Se revisa la controversia que ha existido durante años sobre la naturaleza del continuo de rayos X emitido por la binarias de rayos-X. y que ha estado polarizada entre el modelo oriental con una pequeña región afectada por efecto Compton rodeando el objeto compacto y otros modelos alternativos. Presentamos medidas de la extensión radial de esta región ADC en binarias de rayos X de baja masa, las cuales excluyen este modelo oriental y muestran que la región ADC es extensa (modelo Birmingham), mostrando los tiempos de ingresos profundos de una, manera concluyente que la, extensión radial de la zona ACD varía desde el 7% del radio del disco de acreción en fuentes débiles, hasta el 65% en fuentes brillantes. Hay que señalar que el tamaño depende fuertemente de la, luminosidad de la fuente, lo cual sugiere que la zona ADC se forma por irradiación del disco por la estrella de neutrones y el disco interno caliente. Estos resultados tienen implicaciones fundamentales para la correcta descripción del proceso de “Comptonización” en las binarias de rayos X, la cual difiere sustancialmente de la del modelo oriental. Las medidas de las temperaturas eleetrónicas de la ADC nos proporcionan valores del radio de Compton en buena consonancia con los valores medidos de la extensión radial de la ADC. Finalmente, mostramos que los resultados son inconsistantes con una emisión no térmica producida en un “jet” y por tanto proporcionan evidencia en contra de la reeiente sugerencia de que todos los LMXB tienen “jets”.

Keywords

HII Regions — ISM: Jets and Outflows
Type
The Contributed Papers
Information
International Astronomical Union Colloquium , Volume 194: Compact binaries in the galaxy and beyond , 2004 , pp. 140 - 143
Copyright
Copyright © Instituto de astronomia/revista mexicana de astronomίa y astrofίsica 2004

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