Articles written in Journal of Astrophysics and Astronomy
Volume 1 Issue 1 September 1980 pp 25-32
We use the recently introduced concept of a ‘window’ of magnetic field strengths in which pulsars can be active to explain the variation in morphology of supernova remnants. The striking difference between shell-type and filled-type remnants is attributed to differences in he magnetic field strengths of the neutron stars left by the respective Supernovae. Field strengths of a value permitting pulsar activity result in particle production and Crab-like centrally concentrated remnants. Other field values lead to strong magnetic dipole radiation and consequent shell formation (
Volume 1 Issue 1 September 1980 pp 47-66
A 21 cm absorption measurement over a long path length free of the effects of differential galactic rotation indicates the existence of two distinct cloud populations in the plane. One of them consisting of cold, dense clouds has been well studied before. The newly found hot clouds appear to be at least five times more numerous. They have a spin temperature of ~ 300 K, an rms velocity of ~ 35 km s-1, twice the total mass, and hundred times the kinetic energy of the cold clouds. Over long path lengths, the hot clouds have
Volume 3 Issue 3 September 1982 pp 351-361
We have reanalysed a homogeneous catalogue of shell-type supernova remnants and we find that the radio data are consistent with a birthrate of one in 22±3 yr. Our approach is based on the secular decrease of surface brightness of the historical remnants whose ages are precisely known. The abovementioned birthrate is significantly higher than most previous estimates which range from one in 50–150 yr, and is consistent with the supernova rate in our galaxy derived from historical observations, as well as with recent estimates of the pulsar birthrate.
Volume 5 Issue 4 December 1984 pp 403-423
We conclude that pulsar-driven supernova remnants (SNRs) are extremely rare objects. Indeed an analysis of the known sample of plerions suggests a very low birthrate ∼ 1 in 240 years. Long-lived and bright plerions like the Crab nebula are likely to be produced only when the pulsar has an initial period ∼ 10–20 milliseconds and a field ∼ 1012 G. Such pulsars inside rapidly expanding shell remnants should also produce detectable plerions. The extreme rarity of SNRs with such hybrid morphology leads us to conclude that these pulsars must have been born with an initial period larger than ∼ 35–70 milliseconds.
Volume 13 Issue 1 March 1992 pp 1-1
Volume 16 Issue 1 March 1995 pp 53-67
A detailed statistical analysis of pulsar
Volume 16 Issue 2 June 1995 pp 69-88
Volume 16 Issue 3-4 December 1995 pp 326-326
Volume 17 Issue 3-4 December 1996 pp 53-76
Volume 19 Issue 3-4 December 1998 pp 79-96
We present a survey of molecular gas in the
Volume 19 Issue 3-4 December 1998 pp 97-116
This investigation is aimed at clarifying the nature of the interstellar gas seen in absorption against bright O and B stars. Towards this end we have obtained for the first time HI absorption spectra towards radio sources very close to the lines of sight towards twenty five bright stars previously studied. In this paper we describe the selection criteria, the details regarding our observations, and finally present the absorption spectra. In the accompanying paper we analyse the results and draw conclusions.
Volume 19 Issue 3-4 December 1998 pp 117-131
In the preceding paper (Paper I), we presented HI absorption spectra towards radio sources very close to the lines of sight towards twenty five bright stars against which optical absorption spectra had been obtained earlier, In this paper we analyse the results and draw some conclusions.
To summarize briefly, in most cases we found HI absorption at velocities corresponding to the optical absorption features provided one restricted oneself to velocities ≲10 kms-1. At higher velocities we did not detect any HI absorption down to an optical depth limit of 0.1 (except in four cases which we attribute to gas in systematic motion rather than clouds in random motion). After discussing various scenarios, we suggest that this trend should perhaps be understood in terms of the high velocity interstellar clouds being accelerated, heated and ablated by expanding supernova remnants.
Volume 22 Issue 1 March 2001 pp 35-50
Nearby interstellar clouds with high (|ν|≥10km s−1) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption) in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope (GMRT) HI absorption observations toward radio sources with small angular separation from bright O and B stars whose spectra reveal the presence of intervening high random velocity CaII absorbing clouds. In 5 out of the 14 directions searched we detect HI 21cm absorption features from these clouds. The mean optical depth of these detections is ∼0.09 and FWHM is ∼10km s−1, consistent with absorption arising from CNM clouds.
Volume 25 Issue 3-4 September 2004 pp 143-183
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum sources, located at high (
Volume 25 Issue 3-4 September 2004 pp 185-201
We have carried out a sensitive high-latitude (
Volume 40 | Issue 4
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