A general summary of my research:

My primary research interest is the transient high-energy phenomena known as gamma-ray bursts. These are pulses of gamma-ray radiation that are observed from all over the sky. They are primarily linked to the end of the stellar life cycle in that they are typically produced by either:

The gamma-ray burst emission itself is produced by an accretion-powered relativistic jet that is launched from the remnant object, irrespective of the progenitor system.

The emission from a GRB consists of the initial pulse of gamma-rays, called the prompt emission, which typically lasts for a timescale of seconds. The prompt emission is thought to arise from internal collisional shocks within the jet.

The prompt-phase emission is followed by a longer-lived broadband electromagnetic transient that is called the afterglow emission, which can last from hours to years post-burst and is produced by the deceleration of particles accelerated in the jet by the surrounding medium.

A neat consequence of these two separate progenitor systems is that GRBs and their resulting emission can be associated with two fundamentally very distinct environments.

  1. Collapsar-driven GRBs arise from a massive stellar progenitor and, as a result, are typically found in regions undergoing intense star formation within their host galaxies.
  2. Merger-driven GRBs, on the other hand, require two explosions of the binary star components for them to end up as compact objects. As a result, these systems are found to be at a significant offset from their host galaxies.

Collapsar GRBs as probes of their environment

Long gamma-ray bursts are powerful, high-energy explosions originating from distant galaxies and are some of the most energetic events in the universe. These bursts last longer than two seconds, distinguishing them from short gamma-ray bursts. Typically, LGRBs can last a few seconds to several minutes. Their progenitors are generally massive stars undergoing core-collapse (collapsars) at the end of their life. Collapsars are often found in regions of active star formation within galaxies, supporting the theory of their massive stellar origins.

Scientific Significance and Implications

Given their low angular offsets from their hosts, their bright and long-lived afterglow emission intercepts significant amounts of the medium along the line of sight. As a result, they can be used as probes of the medium in which the progenitor star evolved and exploded. This, coupled with their extreme brightness, means that we can use their afterglows to study the medium at very early epochs (12 Myr after the Big Bang) to understand how different it is from what we see around us today.
In particular, I use X-ray telescopes such as XMM-Newton, Chandra, Swift-XRT and the newly launched Einstein Probe to observe the afterglow spectra of LGRBs. I couple this X-ray data with optical spectra from telescopes such as VLT, GTC and Keck, to produce a complete picture of the medium along our line of sight to the GRB.

The detection of LGRBs at high redshifts helps astronomers study the universe’s evolution and the processes leading to the formation of the first stars and galaxies.