The only way to measure a star's magnetic field is to look at the absorption lines in their X-ray energy spectrum. A cyclotron absorption line with an energy of 146 keV has been discovered by the Insight-HXMT team. The world records for the highest energy cyclotron absorption line and the strongest magnetic field in the universe have been broken.
The findings were obtained by the Key Laboratory for Particle Astrophysics at the Institute of High Energy Physics at the Chinese Academy of Sciences and the Institute for Astronomy and Astrophysics. The paper is written by Dr. Kong Lingda, Prof. Shu, and Prof. Shuangnan. Dr. Victor Doroshenko from the University of Tbingen was a significant contributor to the discovery.
There is a neutron star and a companion star. An accretion disk is formed by the gas of the companion star falling towards the neutron star. Powerful X-ray radiation is released when the accretion disk falls along magnetic lines. The name "X-ray pulsar accretion" was given to these objects due to the periodic X-ray pulse signals.
The cyclotron absorption lines are thought to be the cause of the absorption of X-rays by electrons in these objects. This phenomenon can be used to measure the strength of the magnetic field near the surface of a neutron star.
The X-ray luminosity of ultraluminous X-ray pulsars is much higher than that of X-ray accretion pulsars They have been found in a number of different places. Astronomers think that their pulsars have high magnetic field strengths.
Insight-HXMT made detailed and broadband observations of the eruption of Swift J0243.6+6124. The line showed energy up to 146 keV, which corresponds to a surface magnetic field of more than 1.6 billionTesla. The first detection of an electron cyclotron absorption line in an ultraluminous X-ray source is the strongest magnetic field directly measured in the universe.
It is thought that the surface magnetic fields of neutron stars have complex structures, ranging from dipole fields far from the star to multipole fields only affecting the area close to the star. Most previous estimates of the magnetic fields of the stars have only looked at the dipole fields.
The direct magnetic field measurement by Insight-HXMT based on the cyclotron absorption line is about an order of magnitude greater than the estimates. The first concrete evidence that a neutron star's magnetic field structure is more complex than a traditional symmetric field is provided by this.
Insight-HXMT is the first Chinese satellite. A high-energy telescope, medium-energy telescope, low-energy telescope, and a space environment monitor are included. Insight-HXMT has advantages over other X-ray satellites in terms of broadband, high time resolution, low dead-time, and no pile-up effects for bright sources, thus opening up a new window for observing.
A world record for direct measurement of a surface magnetic field was set in 2020 by the Insight-HXMT team. A new record for a cyclotron absorption line with its highest energy around 100 keV was found by Insight-HXMT. Insight-HXMT broke its own records for cyclotron line discoveries.
More information: Ling-Da Kong et al, Insight-HXMT Discovery of the Highest-energy CRSF from the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac7711 Journal information: Astrophysical Journal Letters
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