arXiv subjects

Poonam Chandra

Publications and source records attributed to Poonam Chandra.

94 records · Page 6Linked to original sources

arXiv2004

Baby supernovae through the looking glass at long wavelengths

We emphasize the importance of observations of young supernovae in wide radio band. We argue on the basis of observational results that only high or only low frequency data is not sufficient to get full physical picture of the shocked plasma. In the SN 1993J composite spectrum obtained with Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT), around day 3200, we see observational evidence of synchrotron cooling, which leads us to the direct determination of the magnetic field independent of the equipartition assumption, as well as the relative strengths of the magnetic field and relativistic particles energy densities. The GMRT low frequency SN 1993J light curves suggests the modification in the radio emission models developed on the basis of VLA data alone. The composite radio spectrum of SN 2003bg on day 350 obtained with GMRT plus VLA strongly supports the internal synchrotron self absorption as the dominant absorption mechanism.

astro-ph↗

arXiv2004

Implications of aging in young supernovae

We present here the combined radio spectrum from the Giant Metrewave Radio Telescope (GMRT) and Very Large Array (VLA) of type-IIb SN 1993J (age 11 years) and a type-Ic SN 2003bg (age 1 year). In SN 1993J, we find a break in the spectrum at 4 GHz and associate it with Synchrotron cooling break. Hence, we determine the magnetic field independent of equipartition assumption between relativistic electrons and magnetic energy. We also see a hint of break in the spectrum of SN 2003bg between 22-40 GHz. The spectrum of SN 2003bg is well described by the synchrotron self absorption model.

astro-ph↗

arXiv2004

Synchrotron aging and the radio spectrum of SN 1993J

We combine the GMRT low frequency radio observations of SN 1993J with the VLA high frequency radio data to get a near simultaneous spectrum around day 3200 since explosion. The low frequency measurements of the supernova determine the turnover frequency and flux scale of the composite spectrum and help reveal a steepening in the spectral index, $Δα\sim 0.6$, in the optically thin part of the spectrum. This is the first observational evidence of a break in the radio spectrum of a young supernova. We associate this break with the phenomenon of synchrotron aging of radiating electrons. From the break in the spectrum we calculate the magnetic field in the shocked region independent of the equipartition assumption between energy density of relativistic particles and magnetic energy density. We determine the ratio of these two energy densities and find that this ratio is in the range: $8\times 10^{-6}-5\times 10^{-4}$. We also predict the nature of the evolution of the synchrotron break frequency with time, with competing effects due to diffusive Fermi acceleration and adiabatic expansion of the radiative electron plasma.

astro-ph↗

arXiv2002

Radio Studies of Young Core Collapse Supernovae

Multi-frequency observations of two radio bright SNe (SN1993J, SN1979C) carried out over a year with GMRT are presented. Their radio light curves trace the evolution of the mass loss in the stellar wind before the pre-supernova star exploded. Their spectra at low frequencies distinguish between the synchrotron self-absorption and free-free absorption based models. Two very similar type IIp SN1999gi and SN1999em were also observed and we comment on their progenitor mass. These observations of different subclasses of core-collapse supernovae will aid in defining their progenitors.

astro-ph↗