Poonam Chandra
Hi, I am an Astronomer currently working at
the
National Radio Astronomy Observatory.
I completed my Ph.D. at the Tata Institute of Fundamental Research under
Joint Astronomy Programme of
Indian Institute of Science.
After my Ph.D., I was a
a
Jansky Postdoctoral Fellow of
National Radio Astronomy Observatory at the
University of Virginia from 2005 till 2008.
Since 2008 onwards I was a Senior Research Associate and Adjunct Assistant Professor at
the
Royal Military College of Canada until 2012. I was at the
National Centre for Radio Astrophysics
of Tata Institute of Fundamental Research from 2012 until May 2022
as Reader and Associate Professor before joining the NRAO in May 2022.
You can find me at:
520 Edgemont Rd, National Radio Astronomy Observatory,
Charlottesville, VA 22903, USA
Spectropolarimetric surveys have shown that around 10 percent of all massive stars are magnetic. We have carried out a systematic study of magnetic massive stars in radio bands and discovered a rare Cyclotron Maser Emission (ECME) in a fraction of magnetic stars. Currently more than 2/3rd of all known (11 out of 15) magnetic stars exhibiting ECME have been discovered by our group with the Indian upgraded Giant Metrewave Radio Telescope (GMRT) and this has put the GMRT on the world map. The discovery of ECME has allowed us to unravel the 3D magnetic topology of the stars and plasma very close to stars, inaccessible by any other means. This has important implications of Stellar demise and end products.
Supernovae and gamma-ray burst (GRB) explosions are the main distributors of heavy
elements (responsible for life) in the universe,
uniquely synthesised inside their progenitor stars, and play decisive role in the galaxy evolution.
Hence they hold the key to the Universe, yet remain poorly understood and the very last
moments of stellar deaths leading to supernovae are not well understood. Studying the
supersonically moving supernova ejecta’s interaction with the surrounding slow winds, which reveals
itself in radio and X-ray emission, enables one to study the stellar evolution just before the explosion.
This is because the winds are formed by the mass-lost from the star and their evolution
carry the unique footprints of the progenitor star’s history, hence work as a “Time Machine”. We are
using this novel technique and has several highly significant findings in this field. Our most notable
contributions came in supernovae exploding in dense environments, where we unravelled the presence of
rare internal absorption, previously only speculative in one case, confirming the asymmetry in the explosion,
and non-smooth mass-loss history. We also found the mass-loss rates in these stars to be 3-4 orders of
magnitude higher than the ones predicted from stellar evolution models, an open problem in the field.
Our X-ray observations of SN 2010jl have revealed the direct presence of the circumstellar medium due to
mass loss by measuring 1000 times higher column density in SN medium than the Galactic one.
Recently we have proposed a realistic inhomogeneous radio emission caused by varying magnetic fields in
stripped supernovae.
We also collected 15 years of data on a special stripped envelope supernova (supernovae arising from stars which have lost their Hydrogen and Helium envelope at the time of explosion) in radio, optical and X-ray bands and have shown that such explosions occur via common envelope scenario in a binary system.
We are carrying out the first systematic low frequency survey of supernovae with the GMRT
under project
GLIMPSE.
Our group was the first one to carry out the first statistical study of the complete sample of the radio afterglows of the gamma-ray bursts (GRB). Our team has also discovered the radio emission from the farthest GRB so far (GRB 090423 at redshift 8.3), allowing to constrain the circumburst density while Universe was in it’s infancy (0.63 billion years). Recently we have worked on sub-GHz evolution of a gamma-ray burst GRB 171205A and shown the inhomogeneous density surrounding the GRB along with variable mass loss rate.
Another most important finding by us is in the field of electromagnetic (EM) counterparts of gravitational waves (GWs), discovered first in Sep 2015, nearly 100 years after the prediction of their existence by Einstein. We studied the the GW event of 2017 Aug 17 (GW170817; the only GW event from neutron stars’ merger) with the upgraded GMRT and several other radio telescopes across the world. This research has made fundamental contributions in our understanding of merger environments producing GWs, implications for short GRBs, and the evolution of the jet. Our work has defied previous jet models in favour of a wide cocoon breaking out of polar region and emitting across the EM bands. The upgraded GMRT observations provided the lowest frequency observations till date, putting the best constraints on the density.
Contact information: Email: pchandra at nrao dot edu