Research Highlight

Secrets of quasars unveiled

doi:10.1038/nindia.2016.93 Published online 21 July 2016

By analyzing images captured by an array of Earth-based, high-altitude gamma-ray telescopes, researchers have gained new insights into a blazar, an extremely bright quasar that emits every kind of radiation — from radio waves to gamma rays1.

Since high-energy waves from blazars can take billions of years to reach the Earth, they provide astronomers with information about the early stages of the Universe.

Blazars show flux variability in all timescales across the electromagnetic spectrum. Previous studies analysed their short-term flares, but little work had been done to study their long-term variability.

To better understand blazars’ long-term variability, the researchers utilized the array of seven high-altitude gamma-ray telescopes at Hanle, Ladakh, to capture images of the blazar Mkn 421. They studied the long-term temporal and spectral variability in its radiation during 2009−2015.

The flux was found to be highly variable across all timescales. This variability is energy dependent and is a maximum in the X-ray and very-high-energy bands. This is the third blazar found to show this behaviour. The variations in flux states can be attributed mainly to changes in the particle distribution.

In the future, the array of telescopes at Hanle is expected to provide excellent time-resolved spectra at very-high-energy bands, which may throw new light on such emissions from blazar jets, the researchers say.


1. Sinha, A. et al. Long-term study of Mkn 421 with the HAGAR array of telescopes. Astron. Astrophys. 591, A83 (2016)