Abstract Details
| Name: Soma Mandal Affiliation: Government Girls' General Degree College, Kolkata Conference ID: ASI2025_70 Title : Broadband spectral and temporal properties of the atoll source 4U 1702-429 using AstroSat-NICER Authors and Co-Authors : Soma Mandal 1, Suchismito Chattopadhyay 1, Ranjeev Misra 2 Abstract Type : Poster Abstract Category : High Energy Phenomena, Fundamental Physics and Astronomy Abstract : We present the broadband spectro-temporal analysis of the atoll source 4U 1702-429 using an AstroSat observation and another simultaneous observation by AstroSat and NICER at two different epochs separated by a year. The photon spectra of both observations can be described by a thermal Comptonization component whose seed photons arise from a black body spectrum, a disk emission and a non-relativistic reflection component. For the first observation, the coronal temperature ~7 keV is smaller than the second ~13 keV, and the disk is truncated at a larger radius, ~150 km, compared to the second, ~25 km, for an assumed distance of 7 kpc. A kHz QPO at ~800 Hz is detected in the first and is absent in the second observation. Modeling the energy-dependent r.m.s and time lag of the kHz QPO reveals a corona size of ≤ 30 km. A similar model can explain the energy dependence of the broadband noise at ~10 Hz for the second observation. The results suggest that kHz QPOs are associated with a compact corona surrounding the neutron star and may occur when the disk is truncated at large distances. |