Abstract Details
| Name: Radhika D Affiliation: Dayananda Sagar University Bengaluru Conference ID: ASI2019_91 Title : AstroSat observations of persistent black holes GRS 1758-258 and 1E 1740.7-2942 Authors and Co-Authors : Radhika D. (Author), Anuj Nandi, Aneesha U., Samir Mandal, H. Sreehari Abstract Type : Oral Abstract Category : Stars, ISM and Galaxy Abstract : We present the results of the analysis performed for the AstroSat observations of the persistent black holes GRS 1758-258 and 1E 1740.7-2942. Broad-band observations of these sources were performed by AstroSat during the different AO cycles. GRS 1758-258 was observed for a total duration of 30 ksec (October 2016), 20 ksec each (July & September 2017), while 1E 1740.7-2942 was looked into for a total of 10 ksec duration during October 2016. SXT observations of GRS 1758-258 in the energy range of 0.3 – 6 keV, shows spectral state transition along-with aperiodic variability signatures in the light curve. During the first day of observation, the source exists in the dim soft state as indicated by a dominating Keplerian disc component of temperature 0.45 keV, while the transition to the hard intermediate state with a photon index of 2.0 is observed around 270 days later. This is followed by another spectral softening within another 100 days. For the source 1E 1740.7-2942, from the combined SXT (0.3 – 6 keV) and LAXPC (3 – 80 keV) spectra, we observe significant spectral transition within the duration of a day. The spectral photon index is observed to vary from 2.6 (soft) to 1.7 (hard) in 4 hours duration. Such spectral transition occurring within a shorter duration has not been observed previously in this source. We also observe temporal variability in the source light curve & power spectra. We find significant variabilities in the source characteristics during short duration observations (within a day), and also long-term (spanning over several months). We will be discussing the spectral and temporal variations observed for these sources, considering the scenario of accretion disc dynamics. |