AR-2019-2020

2 3 4 5 6 7 8 9 10 2.5 3 3.5 4 4.5 5 5.5 6 QPO frequency (Hz) / Mdot (10 18 g/s) Radius (r g ) χ class IMS HS a=0.97, N=0.22 a=0.91, N=0.35 a=0.99, N=0.17 Figure 13: Variation of QPO frequency divided by the accretion rate with inner disk radii. The lines represent the predictions by the relativistic standard accretion disk model for dimensionless spin parameter a = 0.973 (best fit) and for comparison, a = 0.91 and 0.99. AstroSat observations AstroSat observed the galactic micro-quasar system GRS 1915+105 when the system exhibited C- type Quasi-periodic Oscillations (QPOs) in the frequency range of 2-6 Hz. For these observations, Ranjeev Misra , D. Rawat, J.S. Yadav and P. Jain showed that the broad band spectra (1-50 keV) obtained from simultaneous LAXPC and SXT, can be well described by a dominant relativistic truncated accretion disk along with thermal Comptonization and reflection. They found that while the QPO frequency depended on the inner radii with a large scatter, a much tighter correlation has been obtained when both the inner radii and accretion rate of the disk was taken into account (See Fig. (13). In fact, the frequency varies just as the dynamic frequency (i.e., the inverse of the sound crossing time) as predicted decades ago by the relativistic standard accretion disk theory for a black hole with spin parameter, a ∼ 0.9. Thus, a general relativistic prediction has been tested using X-ray data analysis. This identification has been possible due to the simultaneous broad band spectral coverage with temporal information as obtained from AstroSat. Comparative study of a sample of narrow-line and broad-line Seyfert 1 Vineet Ojha, Hum Chand, Gulab C. Dewangan and Suvendu Rakshit performed a detailed com- parative systematic study of a sample of 221 narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift-matched sample of 154 Broad-line Seyfert 1 (BLSy1) galaxies based on ROSAT and XMM-Newton telescopes. Based on their homogeneous analysis, they investigated correlations be- tween the soft X-ray spectral shape, Eddington ratios, bolometric luminosity, black hole masses, and the widths of the broad component of optical Hbeta line. They found clear evidence for the difference in the distributions of soft X-ray spectral shape and Eddington ratio among NLSy1 and BLSy1 galaxies, with steeper soft X-ray spectrum and higher Eddington ratio for the former. Such a difference also exists in the hard X-ray spectral index distribution. These results suggests that the higher Eddington ratio in NLSy1 is responsible for the steeper X-ray spectral slope compared to the BLSy1, consistent with the disc-corona model as proposed for the luminous AGNs. Detection of a type C quasi-periodic oscillation Swadesh Chand, Vivek Agrawal, Gulab C. Dewangan and P. Thakur reported the detection of a type C quasi-periodic oscillation (QPO) along with an upper harmonic in two observations of the low-mass black hole transient H 1743-322 jointly observed by XMM-Newton and NuSTAR