| Name: | Kavita Kumari |
| Affiliation: | IUCAA |
| Conference ID : | ASI2024_724 |
| Title : | Probing the X-ray and UV connection in type 1 AGNs using AstroSat observations |
| Authors : | Kavita Kumari1, G. C. Dewangan1, I. E. Papadakis2,3, Max W. J. Beard4, I. M. Mc Hardy4,
K. P. Singh5, D. Bhattacharya6, S. Bhattacharyya7, S. Chandra8,9, Daniel Kynoch4, Mayukh Pahari4 |
| Authors Affiliation: | 1 Inter-University Center for Astronomy and Astrophysics, Pune 411007, India
2 University of Crete, 71003 Heraklion, Greece
3 Institute of Astrophysics, FORTH, GR-71110 Heraklion, Greece
4 University of Southampton, University Road, Southampton SO17 1BJ, UK
5 IISER Mohali, Knowledge City, Sector 81, Manauli PO, SAS Nagar, Punjab 140306, India
6 Ashoka University, National Capital Region P.O. Rai, Sonepat Haryana 131029, India
7 Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
8 South African Astronomical Observatory, Cape Town 7925, South Africa
9 Center for Space Research, North-West University, Potchefstroom 2520, South Africa |
| Mode of Presentation: | Poster |
| Abstract Category : | Galaxies and Cosmology |
| Abstract : | Understanding the geometry of the corona, the process of accretion and the interplay between these two in the inner region of Active Galactic Nuclei (AGNs) are well-known challenges due to limitations in the telescopic techniques. However, reverberation mapping between the X-ray and UV continuum light curves provides an in-direct method to probe this region. In principle, if the X–ray emission from the corona and Ultraviolet (UV) emission from the accretion-disc are coupled, the study of their cross-correlations (and time-lags) can provide essential clues on their connections and information about the disc-corona geometry. The different lag behaviours obtained from the previous studies of various sources indicate that the UV/X-ray emission mechanism is complex and more study using long, well-sampled data is required. For analysis, we have utilized the multi-wavelength capabilities of the AstroSat mission i.e. data acquired with the Soft X-ray Telescope (SXT) and the Ultra-Violet Imaging Telescope (UVIT) in far and near UV bands. We have computed the X-ray/UV cross-correlation and time-lags for NGC 4593, NGC 7469, NGC 4051 and NGC 6814, using different robust techniques such as Interpolation Cross-Correlation Function (ICCF), and Discrete CCF (DCF). We found that variations in the UV band are lagging those in the X-rays in NGC 4593, NGC 4051 and NGC 6814, this supports the 'thermal disc reprocessing model'. Interestingly, we found an opposite trend in NGC 7469 in which UV is leading X-rays and supports the 'thermal comptonization model'. The non-detection of the thermal reverberation signal in NGC 7469 is intriguing and the observed UV variability is most likely intrinsic to the disk. This result makes our observation important because it is generally difficult to detect the intrinsic disk emission due to the combined effect of X-ray variations. Our results can constrain the current models regarding X–ray and UV/optical delays. |
