Associated Spectral and Temporal State Transition of the bright ULX NGC1313 X-1 (2009)
Dewangan, G. C., Misra, R., Rao, A. R., Griffiths, R. E.
(Abridged) Stellar mass black hole X-ray binaries exhibit X-ray spectral states which also have distinct and characteristic temporal properties. These states are believed to correspond to different...
X-ray emission from active galactic nuclei with intermediate mass black holes (2008)
Dewangan, G. C., Mathur, S., Griffiths, R. E., Rao, A. R.
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 prototype AGNs in this...
Dewangan, G. C., Griffiths, R. E., Dasgupta, Surajit, Rao, A. R.
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 delays between the...
Time lags in Narrow-line Seyfert 1 galaxies and the origin of their soft excess emission (2007)
Dewangan, G. C., Griffiths, R. E., Rao, A. R., Dasgupta, Surajit
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 alternative models for the...
Relativistic Iron K Emission and absorption in the Seyfert 1.9 galaxy MCG-5-23-16 (2007)
Braito, V., Reeves, J. N., Dewangan, G. C., George, I., Griffiths, R. E., Markowitz, A., ...
We present the results of the simultaneous deep XMM and Chandra observations of the bright Seyfert 1.9 galaxy MCG-5-23-16, which is thought to have one of the best known examples of a...
Quasi Periodic Oscillations and Strongly Comptonized X-ray emission from Holmberg IX X-1 (2006)
Dewangan, G. C., Griffiths, R. E., Rao, A. R.
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 observation. The QPO...
Evidence for a high energy curvature in the XMM-Newton spectrum of the ULX NGC1313 X-1 (2005)
Dewangan, G. C., Griffiths, R. E., Rao, A. R.
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 revealed a cool (kT...
Type 2 counterparts of narrow-line Seyfert 1 galaxies (2005)
Dewangan, G. C., Griffiths, R. E.
Unified models of Seyfert galaxies, based on viewing angles, successfully explain the observed differences between type 1 and 2 Seyferts. The existence of a range in accretion rates relative to the...
Dasgupta, Surajit, Rao, A. R., Dewangan, G. C., Agrawal, V. K.
We present the results of an analysis of data from XMM-Newton and CHANDRA observations of the high luminosity narrow-line quasar PG 1404+226. We confirm a strong soft X-ray excess in the X-ray...
Dasgupta, Surajit, Rao, A. R., Dewangan, G. C.
We present results based on an XMM-Newton observation of the high luminosity narrow-line QSO PHL 1092 performed in 2003 January. The 0.3 - 10 keV spectrum is well described by a model which includes...
Iron Kalpha emission from the low-luminosity Active Galaxies M81 and NGC 4579 (2004)
Dewangan, G. C., Griffiths, R. E., Di Matteo, T., Schurch, N. J.
We report on XMM-Newton spectroscopy of the low-luminosity active galaxies (LLAGN) M81 and NGC4579 both of which have known black hole masses and well-sampled spectral energy distributions (SED). The...
Iron Kα emission from the low-luminosity active galaxies M81 and NGC 4579 (2004)
Dewangan, G. C., Griffiths, R. E., Di Matteo, T., Schurch, N. J.
XMM-Newton view of the prototype narrow-line Seyfert 1 galaxy I Zw 1 (2003)
Dewangan, G. C., Griffiths, R. E.
We present results based on an XMM-Newton observation of the prototype narrow-line Seyfert 1 galaxy I Zw 1 performed in June 2002. The 0.6-12 keV spectrum is well described by a steep power-law...
XMM-Newton observations of Broad FeKalpha emission from a Seyfert 1.9 galaxy MCG-5-23-16 (2003)
Dewangan, G. C., Griffiths, R. E., Schurch, N. J.
XMM-Newton observations of the bright Seyfert 1.9 galaxy MCG-5-23-16 have revealed a broad FeKalpha emission line which is nearly symmetric in contrast to the broad and red-shifted asymmetric...
Soft X-ray properties of a high redshift sample of QSOs observed with ROSAT (2002)
Dewangan, G. C., Singh, K. P., Gunn, K. F., Newsam, A. M., McHardy, I. M., Jones, L. R.
In order to study systematically the soft X-ray emission of Active Galactic Nuclei (AGNs) at medium to high redshifts, we have analyzed ROSAT PSPC and HRI data of QSOs at 0.26
A 10-day ASCA Observation of the Narrow-line Seyfert~1 galaxy IRAS 13224-3809 (2002)
Dewangan, G. C., Boller, Th., Singh, K. P., Leighly, K. M.
(Abridged) We present an analysis of a 10-day continuous ASCA observation of the narrow-line Seyfert 1 galaxy IRAS 13224-3809. The soft (0.7-1.3 keV) and hard (1.3-10 keV) X-ray band light curves...
A 10-day ASCA observation of the narrow-line Seyfert 1 galaxy IRAS 13224-3809 (2002)
Dewangan, G.C, Boller, T., Singh, K.P, Leighly, K.M
We present an analysis of a 10-day continuous ASCA observation of the narrow-line Seyfert 1 galaxy IRAS 13224-3809. The total band (0.7-10 keV) light curve binned with 500 s reveals trough- to-peak...
Optical and X-ray characteristics of a newly discovered narrow-line QSO : RX J1334.2+3759 (2001)
Dewangan, G. C., Singh, K. P., Jones, L. R., McHardy, I. M., Mason, K. O., Newsam, A. M.
We report the discovery of a narrow-line QSO (NLQSO) RX J1334.2+3759 with a steep soft X-ray spectrum. Soft X-ray emission from the NLQSO is highly variable. Changes in the intensity by a factor of...
Soft X-ray properties of a complete sample of QSOs (2001)
In order to study systematically the soft X-ray emission of AGNs, we have analyzed ROSAT PSPC spectra of 22 QSOs. The QSOs form a complete sample with soft X-ray flux ??1.4 x 10-14 erg cm-2 s-1 in...
Discovery of a new NLQSO: RX J1334.2+3759 (2001)
Dewangan, G. C, Singh, K. P, Jones, L. R, McHardy, I. M, Newsam, A. M, Mason, K. O
A new narrow-line QSO, RX J1334.2+3759, has been identified at a redshift of 0.3858. The QSO has intrinsic soft X-ray luminosity ~ 2.8 x 1044 erg s-1. Soft X-ray emission from the QSO is highly...
Narrow-line Seyfert 1 galaxies (2001)
Narrow-line Seyfert 1 (NLS1) galaxies form a distinct subclass of Seyfert 1 galaxies. Optical spectroscopic and X-ray spectral and timing results on NLS1 and the plausible underlying physical...
A New Narrow-Line Seyfert 1 galaxy : RXJ1236.9+2656 (2000)
Dewangan, G. C., Singh, K. P., Szkody, Paula, Hoard, D. W.
We report identification of a narrow-line Seyfert 1 galaxy RXJ1236.9+2656. X-ray emission from the NLS1 galaxy undergoes long-term variability with 0.1--2.0 keV flux changing by a factor of 2 within...
Active Nucleus in a Poststarburst Galaxy : KUG 1259+280 (2000)
Dewangan, G. C., Singh, K. P., Mayya, Y. D., Anupama, G. C.
We report the discovery of an active nucleus in a poststarburst galaxy, KUG1259+280. High resolution X-ray imaging observations with ROSAT HRI show that X-ray emission from KUG1259+280 is unresolved....
The 1999 Outburst of the Recurrent Nova U Scorpii (2000)
The optical spectra of the recurrent nova U Sco obtained in five epochs 0.45-42.35 days after the 1999 outburst maximum are presented here. For the first time, an outburst spectrum of U Sco has been...
Multicolour broadband study of a lenticular galaxy : NGC 4753 (2000)
Dewangan, G. C, Singh, K. P, Bhat, P. N
Based on VBT observations, we report multicolour broadband study of a lenticular galaxy, NGC 4753 with prominent dust lanes. The extinction curve derived for NGC 4753 is similar to the Galactic...
Dust Properties of NGC4753 (1999)
Dewangan, G. C., Singh, K. P., Bhat, P. N.
We report BVR surface photometry of a lenticular galaxy, NGC4753 with prominent dust lanes. We have used the multicolor broadband photometry to study dust-extinction as a function of wavelength and...