# Echoes in X-ray binaries; mapping the accretion flow

Source: [Echoes in X-ray binaries; mapping the accretion flow](<https://www.sota2.com/research/paper/68fa1dea7a2b558e2931d1e7>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-23T12:35:32.916Z

Authors: K O'Brien, K Horne

Published: 2001-04-26T12:56:44.000Z

## Abstract

In X-ray binaries much of the optical/UV emission arises from X-rays reprocessed by material in the accretion disk, stream and the companion star. The resulting reprocessed variability will be delayed in time with respect to the X-ray variability by an amount depending on the position of the reprocessing regions. We can determine a range of time-delays present in the system. This time-delay transfer function can be used to \`echo-map' the geometry of the reprocessing regions in the binary system.   We present our modeling of this transfer function and show results from our echo-mapping campaign using X-ray lightcurves from RXTE, simultaneous with HST. In the X-ray transient, GRO j1655-40, shortly after the 1996 outburst, we find evidence for reprocessing in the outer regions of a thick accretion disk.

## Recorded benchmark results

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/astro-ph/0104428>)

[PDF](<https://arxiv.org/pdf/astro-ph/0104428.pdf>)