13 papers · 1 filter
X-ray emission from active galactic nuclei with intermediate mass black holes
G. C. Dewangan, S. Mathur, R. E. Griffiths +1
We present a systematic X-ray study of eight AGNs with intermediate mass black holes (M_BH 8-95x10^4 Msun) based on 12 XMM-Newton observations. The sample includes the two prototyp…
Time lags in Narrow-line Seyfert 1 galaxies and the origin of their soft excess emission
G. C. Dewangan, R. E. Griffiths, A. R. Rao +1
The origin of soft X-ray excess emission from type 1 active galactic nuclei has remained a major problem for the last two decades. It has not been possible to distinguish alternati…
An investigation of the origin of soft X-ray excess emission from Narrow-line Seyfert 1 galaxies Akn564 and Mrk1044
G. C. Dewangan, R. E. Griffiths, Surajit Dasgupta +1
We investigate the origin of the soft X-ray excess emission from narrow-line Seyfert 1 galaxies Akn564 and Mrk1044 using XMM-Newton observations. We find clear evidence for time de…
Suzaku Observation of Two Ultraluminous X-Ray Sources in NGC 1313
T. Mizuno, R. Miyawaki, K. Ebisawa +19
Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposur…
Quasi Periodic Oscillations and Strongly Comptonized X-ray emission from Holmberg IX X-1
G. C. Dewangan, R. E. Griffiths, A. R. Rao
We report the discovery of a 200mHz quasi-periodic oscillation (QPO) in the X-ray emission from a bright ultra-luminous X-ray source (ULX) Holmberg IX X-1 using a long XMM-Newton o…
Evidence for a high energy curvature in the XMM-Newton spectrum of the ULX NGC1313 X-1
G. C. Dewangan, R. E. Griffiths, A. R. Rao
ASCA X-ray spectra of many ULXs were described in terms of optically thick emission from hot (kT ~1-2keV) accretion disks, while recent XMM-Newton and Chandra observations have rev…