Investigating the coronal structure by studying time lags in the Atoll source 4U 1705-44 using AstroSat

Abstract

We performed a detailed timing study of the Atoll source 4U 1705-44 in order to understand the accretion disk geometry. Cross correlation function (CCF) studies were performed between soft (3-5 keV) and hard energy (15-30 keV) bands using the AstroSat LAXPC data. We detected hard as well as soft lags of the order of few ten to hundred seconds. A dynamical CCF study was performed in the same energy bands for one of the light curves and we found smaller lags of few tens of seconds ($<$ 50 s) suggesting that the variation is probably originating from the corona. We found a broad noise component around $\sim$ 13 Hz in the 3-10 keV band which is absent in 10-20 keV band. We interpret the observed lags as the readjustment timescales of the corona or a boundary layer around the neutron star and constrain the height of this structure to few tens of km. We independently estimated the coronal height to be around 15 km assuming that the 13 Hz feature in the PDS is originating from the oscillation of the viscous shell around the neutron star.

Published in Astrophysics and Space Science

References in corpus (11)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• The corona contracts in a black-hole transient
• Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
• AstroSat/LAXPC reveals the high energy variability of GRS 1915+105 in the chi class
• A relativistically smeared spectrum in the neutron star X-ray Binary 4U 1705-44: Looking at the inner accretion disc with X-ray spectroscopy
• Suzaku broad-band spectrum of 4U 1705-44: Probing the Reflection component in the hard state
• BeppoSAX observation of 4U 1705-44: detection of hard X-ray emission in the soft state
• An explanation of the Z-track sources
• Evolution of cross-correlation and time lag of Cyg X-2 along the branches
• Detection of anti-correlated hard X-ray time lag in Cygnus X-3
• Cross-correlations between soft and hard light curves depending on luminosity in the transient neutron star XTE J1701-462