Fast transients
Following up fast transients with GROWTH-India Telescope.
A diagram of a gamma-ray burst’s two stages. An initial “prompt emission” of gamma rays arises from particle jets expelled by a newborn black hole; as the jets collide with surrounding material, they create a longer-lived “afterglow” that radiates across the entire electromagnetic spectrum. Image credit: NASA GSFC
Gamma-Ray Bursts (GRBs)
Gamma-Ray Bursts (GRBs) are the most powerful explosions observed in the universe, releasing vast amounts of energy in just seconds. These high-energy events are divided into two types based on their duration:
- Short GRBs (SGRBs) – Lasting less than 2 seconds, typically associated with the mergers of neutron stars or a neutron star–black hole binary.
- Long GRBs (LGRBs) – Lasting more than 2 seconds, linked to the collapse of massive stars in supernova or hypernova events.
Orphan Afterglows: The Silent Remnants of Gamma-Ray Bursts
Not all Gamma-Ray Bursts (GRBs) are detected as bright flashes of gamma rays. Some GRB jets are misaligned from our line of sight, making the initial burst invisible while their afterglow—emission in X-ray, optical, and radio—slowly becomes detectable as the jet expands. These are known as orphan afterglows.
Unlike typical GRBs, where the gamma-ray flash triggers observations, orphan afterglows are discovered serendipitously in transient surveys like ZTF, LSST, and radio observatories. Their detection helps constrain GRB jet structures, event rates, and the physics of relativistic shocks. Studying orphan afterglows provides crucial insights into the true population of GRBs, many of which go unnoticed due to jet orientation.