Multiwaveband studies of supernovae: lives of their parent stars

What are the nature and goals of multiwaveband studies?

The scientific goals of the project are to determine the radiative processes and conditions in the ionised and magnetised plasma responsible for radio and X-ray emission from the interaction of supernova and circumstellar matter; and to constrain the prior evolution of the parent star and the mass lost from it.

The work is an interaction of theoretical research and observational efforts. We have ourselves proposed and carrying out some of the latter, using telescopes like the GMRT (radio band) or Chandra X-ray Observatory or the XMM-Newton Observatory (both in the X-ray bands).

A supernova explosion from the core collapse of a massive star drives a powerful shock into the circumstellar medium that is created due to continuous mass loss from the progenitor star.

The interaction of a supernova shock with its surrounding medium produces X-ray and radio emission which probes this environment. These in turn determine the previous evolution of the pre-explosion progenitor star, since the shock quickly samples regions of the wind established by the mass-losing star. Soft X-rays arise from the heating of the exploding star's ejecta by a reverse shock propagating into it, or alternatively due to the radiative cooling of clumped, prexisting clouds crushed by the blast-wave shocked circumstellar medium. Thus, the X-ray radiation from the SN probes the outer region of the supernova ejecta, between the blast wave shock and the reverse shock.

X-ray spectroscopy of the SN can determine the element abundance pattern of the SN ejecta. The abundance pattern of core-collapse supernovae can be used to determine the mass of the progenitor star. Massive stars of varying masses produce varying amounts intermediate mass elements versus the heavier elements and this method will be used to determine the mass of the progenitor of the type IIn SN1995N. For this SN our team has successful proposals with both Chandra X-ray Observatory (PI: Poonam Chandra) as well as XMM-Newton observatory (PI: Firoza Sutaria) that will provide key inputs to this question.

A Supernova with a Gamma-Ray Burst counterpart

On 29th March 2003, a Gamma-Ray burst source (designated GRB030329) was discovered whose fluence put it among the top 0.2 \% of the nearly 2700 GRBs which was discovered previously. It also had a very energetic supernova (a hypernova) that was spatially and temporally coincident with the GRB with a redshift of z=0.1685, i.e. at cosmological distances of approximately 810 Mpc (d_L).

The supernova/GRB has been detected and observed in several bands of electromagnetic spectrum, from gamma-rays to radio. Below we show an unpublished radio map of the region around it at 1.4 GHz band made on 13th June 2003 with the Giant Metrewave Radio Telescope (GMRT) near Narayangaon, India which is a low frequency synthesis array telescope. We however did not detect it in the 610 MHz band on 17th June 2003 (2 sigma upper limit of 0.27 mJy) implying that the SN was still obscured at low frequencies by absorption of the overlying gas. This data was obtained by our collaboration (Poonam Chandra, Alak Ray and Sanjay Bhatnagar) under a Target of Opportunity Observation.

A few publications in this field:

The nature of prompt X-ray and radio emission from SN 2002ap -- F. K. Sutaria, P. Chandra, S. Bhatnagar and A. Ray Astronomy \& Astrophysics, 397, 1011 (2003).

Radio studies of young core collapse supernovae -- P. Chandra, A. Ray and S. Bhatnagar, Bull. Astr. Soc. India (2002), 30, 755.

Chandra and ASCA X-ray observation of Supernova 1979C in NGC 4321 - A. Ray, R. Petre \& E. Schlegel, Astron. J, 122, 966 (2001).

X-ray and radio bright type Ic SN 2002ap -- a hypernova without an associated GRB -- F. K. Sutaria, A. Ray and P. Chandra, in Procs ESO Workshop "From Twilight to Highlight -- The Physics of Supernovae" ESO/MPA/MPE Workshop at Garching, July 2002, p.287.

X-ray observation of radio supernova SN1979C by ASCA - A. Ray, R. Petre \& E. Schlegel, in Greatest explosions since the big bang: supernovae and gamma-ray bursts; Procs of the Space Telescope Science Institute May 1999 Workshop (ed M. Livio et al) p. 55 (1999).

Link to Homepage of Alak K. Ray given below