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25 papers · 2 filters
Fast Transition between High-soft and Low-soft States in GRS 1915+105: Evidence for a Critically Viscous Accretion Flow
S. Naik, A. R. Rao, Sandip K. Chakrabarti
We present the results of a detailed analysis of RXTE observations of class which show an unusual state transition between high-soft and low-soft states in the microquasar GRS…
On Variation of the Latitudinal Structure of the Solar Convection Zone
H. M. Antia, S. M. Chitre, M. J. Thompson
The latitudinal sound-speed structure of the Sun's convection zone gives insight into the physical processes occurring there, specifically the cellular convection and possibly the…
Spectral properties of the X-ray binary pulsar LMC X-4 during different intensity states
S. Naik, B. Paul
We present spectral variations of the binary X-ray pulsar LMC X-4 observed with the RXTE/PCA during different phases of its 30.5 day long third period. Only out of eclipse data wer…
Changes in Solar Dynamics from 1995 to 2002
Sarbani Basu, H. M. Antia
Data obtained by the GONG and MDI instruments over the last seven years are used to study how solar dynamics -- both rotation and other large scale flows -- have changed with time.…
Microflares in accretion disks
V. Krishan, S. Ramadurai, P. J. Wiita
We have investigated the phenomenon of explosive chromospheric evaporation from an accretion disk as a mechanism for fast variability in accreting sources such as low mass X-ray bi…
Far and mid infrared observations of two ultracompact H II regions and one compact CO clump
R. P. Verma, S. K. Ghosh, B. Mookerjea +1
Two ultracompact H II regions (IRAS 19181+1349 and 20178+4046) and one compact molecular clump (20286+4105) have been observed at far infrared wavelengths using the TIFR 1 m balloo…
The Correlation between X-ray spectral slope and FeKalpha line energy in radio-quiet active galactic nuclei
Gulab Chand Dewangan
A significant correlation between FeKalpha line energy and X-ray spectral slope has been discovered among radio-quiet active galactic nuclei. The ionization stage of the bulk of th…
X-ray and radio bright type Ic SN 2002ap -- a hypernova without an associated GRB
F. K. Sutaria, A. Ray, P. Chandra
Combined X-ray (0.3 -10 keV) and Radio (0.61 and 1.42 GHz) observations of the type Ic SN 2002ap are used here, to determine the origins of the prompt X-ray and Radio emission from…
Identification of 13 Cepheids and 333 Other Variables in M31
Y. C. Joshi, A. K. Pandey, D. Narasimha +2
We present Cousins and band photometry of variable stars in a region in the disk of M31 galaxy, obtained during 141 nights. Of the 26 Cepheid variables…
Helioseismic limit on heavy element abundance
H. M. Antia, S. M. Chitre
Primary inversions of accurately measured solar oscillation frequencies coupled with the equations of thermal equilibrium and other input physics, enable us to infer the temperatur…
Subsurface magnetic fields from helioseismology
H. M. Antia
Using even-order frequency splitting coefficients of global p-modes it is possible to infer the magnetic field in the solar interior as a function of radial distance and latitude.…
Soft X-ray properties of a high redshift sample of QSOs observed with ROSAT
G. C. Dewangan, K. P. Singh, K. F. Gunn +3
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<z<3.…
State transition between high-soft and low-soft states observed in GRS 1915+105
S. Naik, A. R. Rao, Sandip K. Chakrabarti
We present the results of a detailed analysis of RXTE observations which show an unusual state transition between high-soft and low-soft states in the microquasar GRS 1915+105. The…
Nature of the Soft Spectral Component in the X-ray Pulsars SMC X-1 and LMC X-4
B. Paul, F. Nagase, T. Endo +3
We present here the results of an investigation of the pulse averaged and pulse phase resolved energy spectra of two high luminosity accretion powered X-ray pulsars SMC X-1 and LMC…
The nature of the prompt X-ray and radio emission from SN2002ap
F. K. Sutaria, P. Chandra, S. Bhatnagar +1
We report on the combined X-ray and radio observations of the type Ic SN 2002ap, using XMM-Newton ToO observation of M74 and the Giant Metrewave Radio Telescope (GMRT). We account…
Study of Spectral Lag for Short GRBs
Varsha Gupta, Patrick Das Gupta, P. N. Bhat
This paper reports statistically significant correlations between various burst parameters, observed in a sample of 156 GRBs belonging to BATSE 4B catalog with T90 less than 2 s. T…
Seismic tests for solar models with tachocline mixing
A. S. Brun, H. M. Antia, S. M. Chitre +1
We have computed accurate 1-D solar models including both a macroscopic mixing process in the solar tachocline as well as up-to-date microscopic physical ingredients. Using sound s…
New Measurements of Orbital Period Change in Cygnus X-3
N. S. Singh, S. Naik, B. Paul +3
A nonlinear nature of the binary ephemeris of Cygnus X-3 indicates either a change in the orbital period or an apsidal motion of the orbit. We have made extended observations of Cy…
CSSs in a sample of B2 radio sources of intermediate strength
D. J. Saikia, P. Thomasson, R. E. Spencer +3
We present radio observations of 19 candidate compact steep-spectrum (CSS) objects selected from a well-defined, complete sample of 52 B2 radio sources of intermediate strength. Th…
A 10-day ASCA Observation of the Narrow-line Seyfert~1 galaxy IRAS 13224-3809
G. C. Dewangan, Th. Boller, K. P. Singh +1
(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 ba…
Evidence for Synchrotron Bubbles from GRS 1915+105
C. H. Ishwara-Chandra, J. S. Yadav, A. Pramesh Rao
We present GMRT observations of the Galactic microquasar GRS 1915+105 at 1.28 GHz for 8 days from 2001 June 18 to July 1. We have seen several isolated radio flares of varying magn…
Angular Resolution of the Pachmarhi Array of Cerenkov Telescopes
P. Majumdar, P. N. Bhat, B. S. Acharya +4
The Pachmarhi Array of Cerenkov Telescopes consists of a distributed array of 25 telescopes that are used to sample the atmospheric Cerenkov Photon showers. Each telescope consists…
Cosmic Star Formation History and Deep X-ray Imaging in the XMM-NEWTON and CHANDRA Era
Pranab Ghosh
I summarize X-ray diagnostic studies of cosmic star formation in terms of evolutionary schemes for X-ray binary evolution in normal galaxies with evolving star formation. Deep X-ra…
Spatial distribution of emission in Unidentified Infrared Bands from Midcourse Space Experiment Survey
S. K. Ghosh, D. K. Ojha
Recently the Midcourse Space Experiment (MSX) has surveyed the Galactic plane in mainly four infrared bands between 6 and 25 micron. Two of these bands cover several Unidentified I…