Magnetar Bursts

Artist’s illustration of a magnetar and its magnetic field. Credit: NASA/CXC/M. Weiss.

Outbursts from the strongest magnets in the Universe

Magnetars are neutron stars with magnetic fields up to a thousand trillion times stronger than the Earth’s. From time to time they erupt, releasing bursts of X-rays and gamma rays. Daksha will catch these outbursts from magnetars in our own galaxy, and rare giant flares from magnetars in other galaxies.

For astronomers: technical details

Magnetars (ages ≲10⁴ yr, surface fields ~10¹³–10¹⁶ G) produce short bursts, months-long outbursts and giant flares of up to ~10⁴⁶ erg in ~100 ms. Daksha’s low fluence threshold, broad band and near-all-sky coverage extend giant-flare detection to galaxies within ~100 Mpc, and its CZT polarimetry can measure the linear polarisation expected from propagation through ~10¹⁵ G fields. See Bhalerao et al. 2024, Science with the Daksha High Energy Transients Mission (Experimental Astronomy 57, 23), section “Magnetar Bursts”. All Daksha papers are listed on our Publications page.

What is a magnetar?

A magnetar is a young neutron star — the collapsed core of a massive star — with an extraordinarily strong magnetic field. A fridge magnet is about a hundred times stronger than the Earth’s magnetic field; a magnetar’s field is roughly ten trillion times stronger than a fridge magnet. Close to a magnetar, the magnetic field would distort atoms out of shape.

This enormous field stresses the star’s solid crust. Every so often the crust cracks or the field suddenly rearranges, and the magnetar releases a burst of X-rays and gamma rays. Most bursts last a fraction of a second. Rarely, a magnetar produces a giant flare: in 2004, one released more energy in a tenth of a second than the Sun gives out in 100,000 years.

What Daksha will do

Magnetar bursts can come from any direction without warning, so Daksha’s sensitivity and near-constant view of the whole sky make it well suited to catching them. It will record bursts from magnetars in our Milky Way, and spot giant flares from magnetars in other galaxies as far as about 300 million light-years away. Seen from that far, a giant flare can look like a short gamma-ray burst, so Daksha’s measurements will also help tell the two apart. Counting how often these outbursts happen, and how powerful they are, will help reveal how magnetars live and die.

For the brightest bursts, Daksha can also measure polarisation. In such extreme magnetic fields, light is expected to become strongly polarised, so these measurements test physics that cannot be recreated in any laboratory on Earth.

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