Breaking the world record! The Insight-HXMT satellite “saw”…

Recently, my country's Insight-HXMT team discovered a cyclotron absorption line with an energy of up to 146 keV in a neutron star X-ray binary numbered Swift J0243.6+6124, and the corresponding neutron star surface magnetic field strength exceeds 1.6 billion Tesla. The relevant research results were published online in the Astrophysical Journal Letters.

"This is the second time that the Insight-HXMT satellite has significantly refreshed the world record for direct measurement of the highest energy cyclotron absorption line and the strongest magnetic field in the universe, following the direct measurement of the strongest magnetic field in the universe of about 1 billion Tesla in 2020."

On July 5, in an interview with Science and Technology Daily, Zhang Shuangnan, chief scientist of the Insight-HXMT satellite and researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences, pointed out.

Artistic image of the Insight-HXMT satellite observing an accreting pulsar. Image courtesy of the Institute of High Energy Physics, Chinese Academy of Sciences.

Neutron stars are the celestial bodies with the strongest magnetic fields in the universe. Neutron star X-ray binary systems consist of a neutron star and its companion star. Under the strong gravitational force of the neutron star, the gas of the companion star will fall towards the neutron star, forming a gas disk that rotates at high speed around the neutron star, which is also called an accretion disk. The matter on the accretion disk will fall to the surface of the neutron star along the magnetic field lines and emit strong X-ray radiation. This radiation will form a periodic X-ray pulse signal as the neutron star rotates, so this type of celestial body is also called an "X-ray accretion pulsar."

A large number of observations have found that this type of celestial body will have a "concave" structure in the X-ray radiation energy spectrum. Theoretically, this is caused by the electron resonance scattering of electrons whirling in the magnetic field. Therefore, this "concave" structure is called a cyclotron absorption line. The energy at the absorption line corresponds to the magnetic field strength. This phenomenon can be used to directly measure the magnetic field strength near the surface of a neutron star.

"The magnetic field strength corresponding to the energy at the cyclotron absorption line is the magnetic field strength on the surface of a neutron star. This is currently the only way to directly measure the magnetic field strength on the surface of a neutron star," said Zhang Shuangnan.

In the past, astronomers have discovered ultra-bright X-ray pulsars in multiple galaxies outside the Milky Way and speculated that the magnetic field intensity of these pulsars is very high, but they have not found direct measurement evidence.

"This discovery is not only the highest record for direct measurement of the magnetic field of celestial bodies in the universe to date, but also the first direct measurement of the surface magnetic field of a neutron star in an ultra-bright X-ray source," said Zhang Shuangnan.

In Zhang Shuangnan's view, this achievement is inseparable from the unique advantages of the Insight-HXMT satellite. The Insight-HXMT satellite is my country's first X-ray astronomical satellite, carrying three scientific payloads: a high-energy X-ray telescope, a medium-energy X-ray telescope and a low-energy X-ray telescope, as well as a space environment monitor.

"Compared with foreign X-ray satellites, the Insight-HXMT satellite has outstanding advantages such as wide coverage of the energy band, the largest effective area in the high-energy X-ray energy band, high time resolution, and no photon pile-up effect when observing strong sources. It has opened a new window for observing the rapid light changes and energy spectrum research of hard X-rays from black holes and neutron stars," said Zhang Shuangnan.

Source: Science and Technology Daily