G. C. Dewangan
Articles written in Journal of Astrophysics and Astronomy
Volume 32 Issue 4 December 2011 pp 451-455
We describe the serendipitous discovery of a very steep-spectrum radio point source in low-frequency Giant Metrewave Radio Telescope (GMRT) images of the supernova remnant (SNR) G76.9+1.0. The steep spectrum, as well as the location of the point source near the centre of this SNR confirm that this indeed is the pulsar J2022+3842. Archival
Volume 38 Issue 2 June 2017 Article ID 0029 Review Article
K. P. Singh G. C. Stewart N. J. Westergaard S. Bhattacharayya S. Chandra V. R. Chitnis G. C. Dewangan A. T. Kothare I. M. Mirza K. Mukerjee V. Navalkar H. Shah A. F. Abbey A. P. Beardmore S. Kotak N. Kamble S. Vishwakarama D. P. Pathare V. M. Risbud J. P. Koyande T. Stevenson C. Bicknell T. Crawford G. Hansford G. Peters J. Sykes P. Agarwal M. Sebastian A. Rajarajan G. Nagesh S. Narendra M. Ramesh R. Rai K. H. Navalgund K. S. Sarma R. Pandiyan K. Subbarao T. Gupta N. Thakkar A. K. Singh A. Bajpai
The Soft X-ray focusing Telescope (SXT), India’s first X-ray telescope based on the principle of grazing incidence, was launched aboard the AstroSat and made operational on October 26, 2015. X-rays in the energy band of 0.3–8.0 keV are focussed on to a cooled charge coupled device thus providing medium resolution X-ray spectroscopy of cosmic X-ray sources of various types. It is the most sensitive X-ray instrument aboard the AstroSat. In its first year of operation, SXT has been used to observe objects ranging from active stars, compact binaries, supernova remnants, active galactic nuclei and clusters of galaxies in order to study its performance and quantify its characteriztics. Here, we present an overview of its design, mechanical hardware, electronics, data modes, observational constraints, pipeline processing and its in-orbit performance based on preliminary results from its characterization during the performance verification phase.
Volume 42 All articles Published: 31 May 2021 Article ID 0028 Mission
AstroSat is India’s first dedicated multi-wavelength space observatory launched by the Indian Space Research Organisation (ISRO) on 28 September 2015. After launch, the AstroSat Science Support Cell (ASSC) was set up as a joint venture of ISRO and the Inter-University Centre for Astronomy and Astrophysics (IUCAA) with the primary purpose of facilitating the use of AstroSat, both for making observing proposals and for utilising archival data. The ASSC organises meetings, workshops and webinars to train users in these activities, runs a help desk to address user queries, provides utility tools and disseminatesanalysis software through a consolidated web portal. It also maintains the AstroSat Proposal Processing System (APPS) which is deployed at ISSDC, a software platform central to the workflow management of AstroSat operations. This paper illustrates the various aspects of ASSC functionality.
Volume 42 All articles Published: 10 June 2021 Article ID 0038 SCIENCE RESULTS
We present the detection of type C quasi-periodic oscillation (QPO) along with upper harmonic at respective frequencies of $\sim$0.6 Hz and $\sim$1.2 Hz in the single AstroSat observation taken during the 2016 outburst of the low-mass black hole X-ray binary H 1743-322. These frequencies are found to be shifted by $\sim$0.4 Hz for the QPO and $\sim$0.8 Hz for the upper harmonic with respect to that found in the simultaneous
Volume 42 All articles Published: 14 June 2021 Article ID 0046 SCIENCE RESULTS
We report the discovery of a bright, compact ultraviolet source at a projected separation of 1.1 kpc from the known active galactic nucleus (AGN) in Mrk 766 based on AstroSat/UVIT observations. We perform radial profile analysis and derive the UV flux almost free from the nearby contaminating sources. The new source is about 2.5 and 5.6 times fainter than the AGN in the far and near UV bands. The two sources appear as a pair of nuclei in Mrk 766. We investigate the nature of the new source based on the UV flux ratio, X-ray and optical emission. The new source is highly unlikely to be another accreting supermassive black hole in Mrk 766 as it lacks X-ray emission. We find that the UV/optical flux of the new source measured at four different bands closely follow the shape of the template spectrum of starburst galaxies. This strongly suggests that the new source is a compact star-forming region.
Volume 42 All articles Published: 16 June 2021 Article ID 0049 PAYLOAD CALIBRATION
AstroSat/UVIT carries two gratings in the FUV channel and a single grating in the NUV channel. These gratings are useful for low resolution, slitless spectroscopy in the far and near UV bands of a variety of cosmic sources such as hot stars, interacting binaries, active galactic nuclei, etc. We presentcalibration of these gratings using observations of UV standards NGC 40 and HZ 4. We perform wavelength and flux calibration and derive effective areas for different grating orders. We find peak effective areas of $\sim$18.7 cm$^2$ at 2325 Å for the $\sim$1 order of NUV-Grating, $\sim$4.5 cm$^2$ at 1390 Å for the $-$2 order of FUVGrating1, and $\sim$4.3 cm$^2$ at 1500 Å for the $-$2 order of FUV-Grating2. The FWHM spectral resolution of the FUV gratings is $\approx$14.6 Å in the $-$2 order. The $-$1 order of NUV grating has an FWHM resolution of $\approx$33 Å. We find excellent agreement in flux measurements between the FUV/NUV gratings and all broadband filters. We have generated spectral response of the UVIT gratings and broadband filters that can directly be used in the spectral fitting packages such as XSPEC, Sherpa and ISIS, thus allowing spectral analysis of UVIT data either separately or jointly with X-ray data from AstroSat or other missions.
Volume 42 All articles Published: 21 July 2021 Article ID 0081 SCIENCE RESULTS
We present a detailed timing and spectral study of an extremely variable narrow-line Seyfert 1 galaxy NGC 4748 using observations in the year 2017 and 2014 performed with AstroSat and
Volume 42, 2021
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