Gamma Ray Bursts

What is a gamma-ray burst?

A gamma-ray burst (GRB) is a brief, intense flash of gamma rays from a distant galaxy. It happens when a newborn black hole or a rapidly spinning neutron star launches two narrow jets of matter moving at more than 99.99% of the speed of light. If one of those jets happens to point towards the Earth, we see a gamma-ray burst.

Gamma Ray Bursts are of two types. Long bursts, lasting more than about two seconds, typically come from massive stars whose cores collapse at the end of their lives. Short bursts, lasting less than about two seconds, typically come from collisions of neutron stars: the same events that produce gravitational waves.

A flash, then an afterglow

Every burst has two acts. First comes the prompt emission: the main flash of gamma rays, lasting from a fraction of a second to a few minutes. Then, as the jet slams into the gas around it, it produces an afterglow that fades over days to weeks, seen in X-rays, visible light and radio waves.

Afterglows are fairly well understood. The prompt flash is not: astronomers still debate what the jets are made of and exactly how they produce such powerful gamma rays. Answering these questions needs many bursts, measured in fine detail and over a wide range of energies – all the way from soft X-rays to Gamma rays. Current missions can see only some of these emissions, and there is no guarantee that any particular burst will have been detected in all those bands.

What Daksha adds

• Numbers: About 500 long and 50 short bursts a year, including many from the distant, early Universe.

• Colour: Each burst will be measured from soft X-rays to gamma rays at once, revealing features in its spectrum that current missions struggle to see.

• Timing: Every X-ray and gamma ray timed to a millionth of a second, so changes during the flash can be followed in fine detail.

• Polarisation: For the brightest bursts, a measurement of how their light is polarised. For more details see GRB polarisation.

Support Daksha

If you would like to see Daksha fly, please take a minute to fill in our short support form. Every response helps show the scientific community’s interest in the mission.