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Evolution of the reverberation lag in GX 339-4 at the end of an outburst

De Marco, B and Ponti, G and Petrucci, P O and Clavel, M and Corbel, S and Belmont, R and Chakravorty, S and Coriat, M and Drappeau, S and Ferreira, J and Henri, G and Malzac, J and Rodriguez, J and Tomsick, J A and Ursini, F and Zdziarski, A A (2017) Evolution of the reverberation lag in GX 339-4 at the end of an outburst. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 471 (2). pp. 1475-1487.

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Official URL: http://doi.org/10.1093/mnras/stx1649

Abstract

We studied X-ray reverberation lags in the Black hole X-ray binary (BHXRB) GX 339-4 at the end of the 2014-2015 outburst. We analysed data from an XMM-Newton campaign covering the end of the transition from the soft to hard state, and the decrease of luminosity in the hard state. During all the observations we detected, at high frequencies, significant disc variability, responding to variations of the power-law emission with an average time delay of similar to 0.009 +/- 0.002 s. These new detections of disc thermal reverberation add to those previously obtained and suggest the lag to be always present in hard and hard-intermediate states. Our study reveals a net decrease of lag amplitude as a function of luminosity. We ascribe this trend to variations of the inner flow geometry. A possible scenario implies a decrease of the inner disc truncation radius as the luminosity increases at the beginning of the outburst, followed by an increase of the inner disc truncation radius as the luminosity decreases at the end of the outburst. Finally, we found hints of FeK reverberation (similar to 3 sigma significance) during the best quality observation of the XMM monitoring. The lag at the FeK energy has similar amplitude as that of the thermally reprocessed component, as expected if the same irradiated region of the disc is responsible for producing both the thermalized and reflected components. This finding suggests FeK reverberation in BHXRBs to be at the reach of current detectors provided observations of sufficiently long exposure are available.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the AMER SOC MICROBIOLOGY, 1752 N ST NW, WASHINGTON, DC 20036-2904 USA
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Depositing User: Id for Latest eprints
Date Deposited: 23 Sep 2017 05:12
Last Modified: 23 Sep 2017 05:12
URI: http://eprints.iisc.ac.in/id/eprint/57851

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