• Avinash A. Deshpande

      Articles written in Journal of Astrophysics and Astronomy

    • Fast Transients with the Square Kilometre Array and its Pathfinders: An Indian Perspective

      Yashwant Gupta Poonam Chandra Manjari Bagchi Niruj M. Ramanujam Yogesh Maan Avinash A. Deshpande Siddhartha Bhattacharyya

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      In the rapidly developing field of study of the transient sky,fast radio transients are perhaps the most exciting objects of scrutiny at present. The SKA, with its wide field-of-view and significant improvement in sensitivity over existing facilities, is expected to detect a plethora of fast transients which, in addition to help resolve the mysteries surrounding their nature and origin, will also lead to other interesting applications in astrophysics. We explore some of these possibilities here, and also emphasize the current status and future plans of the Indian communityworking in this area, in the context of ongoing work and extensionof this to the SKA.

    • Classical Orbital Paramagnetism in Non-equilibrium Steady State

      Avinash A. Deshpande N. Kumar

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      We report the results of our numerical simulation of classical-dissipative dynamics of a charged particle subjected to a non-Markovian stochastic forcing. We find that the system develops a steady-state orbital magnetic moment in the presence of a static magnetic field. Very significantly, the sign of the orbital magnetic moment turns out to be paramagnetic for our choice of parameters, varied over a wide range. This is shown specifically for the case of classical dynamics driven by a Kubo–Anderson type non-Markovian noise. Natural spatial boundary condition was imposed through (1) a soft (harmonic) confining potential, and (2) a hard potential, approximating a reflecting wall. There was no noticeable qualitative difference. What appears to be crucial to the orbital magnetic effect noticed here is the non-Markovian property of the driving noise chosen. Experimental realization of this effect on the laboratory scale, and its possible implications are briefly discussed. We would like to emphasize that the above steady-state classical orbital paramagnetic moment complements, rather than contradicts the Bohr–van Leeuwen (BvL) theorem on the absence of classical orbital diamagnetism in thermodynamic equilibrium.

    • The dynamic spectral signatures from lunar occultation: A simulation study


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      Lunar occultation, which occurs when the Moon crosses sight-lines to distant sources, has been studied extensively through apparent intensity pattern resulting from Fresnel diffraction, and has been successfully used to measure angular sizes of extragalactic sources. However, such observations till date havebeen mainly over narrow bandwidth, or averaged over the observing band, and the associated intensity pattern in time has rarely been examined in detail as a function of frequency over a wide band. Here, we revisit the phenomenon of lunar occultation with a view to study the associated intensity pattern as a function of both time and frequency. Through analytical and simulation approach, we examine the variation of intensity across the dynamic spectra, and look for chromatic signatures which could appear as discrete dispersed signal tracks, when the diffraction pattern is adequately smoothed by a finite source size. We particularly explore circumstances in which such diffraction pattern might closely follow the interstellar dispersion law followed by pulsars and transients, such as the Fast Radio Bursts (FRBs), which remain a mystery even after a decade of their discovery. In this paper, we describe details of this investigation, relevant to radio frequencies at which FRBs have been detected, and discuss our findings, along with their implications. We also show how a band-averaged light curve suffers from temporal smearing, and consequent reduction in contrast of intensity variation, with increasing bandwidth. We suggest a way to recover the underlying diffraction signature, as well as the sensitivity improvement commensurate with usage of large bandwidths.

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      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

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