Astronomers using the NICER X-ray monitor recorded the movement and merging of X-ray spots on a magnetar in a state of activity for the first time. It is assumed that the tectonic movement of the crust and its interaction with the stellar magnetosphere are responsible for the movement and appearance of spots.
What is a magnetar?
Magnetars are a rare type of neutron stars that have very strong magnetic fields with strengths above 1014 gausses. They can demonstrate long-term flare activity that begins with an increase in the X-ray flux by three orders of magnitude, which is accompanied by sharp changes in the properties of the radiation from the neutron star, as well as its strong temporal variability.
Bursts of activity last from several months to years, as they fade, the properties of the source return to their normal, calm state. Studies of the activity of magnetars make it possible to understand the processes taking place in its magnetosphere and on the surface of a neutron star.
Merging X-ray spots on magnetar SGR 1830-0645
A team of astronomers led by George Younes of the George Washington University published the results of an analysis of observations of the magnetar SGR 1830-0645 in the soft X-ray range using the NICER monitor installed on the ISS, from October 10 to November 17, 2020.
This magnetar was originally discovered during the outbreak of activity on October 10, 2020, by the Swift space observatory, it is located in the constellation Scutum, at a distance of about 13 thousand light-years from the Sun. The magnetar makes one revolution around its axis in 10.4 seconds, its magnetic field was estimated at 2.7×1014 gausses, and the age is 24.3 thousand years.
Scientists have found three slowly moving hot spots on the magnetar, two of which merged in the process of moving. There are two physical scenarios for the observed evolution of the soft X-ray flux from a magnetar: the plastic motion of the neutron star crust and the spinning of the magnetosphere.
Scenarios
These two scenarios suggest the two most probable causes of magnetar surface heating during flares: the release of energy in the stellar crust or the bombardment of its surface by accelerated particles in a twisted external magnetic field.
In the first case, the release of energy will be associated with the tectonic movement of the magnetar crust at a speed of less than a hundred meters per day.
In the second case, bombardment by charged particles from the magnetosphere is responsible for heating regions on the surface of the star, and hot spots are places where structures are created by the magnetic field, somewhat reminiscent of solar coronal loops, meet the surface of the magnetar.
In this case, the migration of the spot can be associated with the movement of the base point of the field lines.
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Sources:
• Reddy, F. (2022, March 7). NASA’s NICER telescope sees hot spots merge on a magnetar. NASA.
• Reddy, F. (2022, March 8). NASA’s NICER telescope sees hot spots merge on a magnetar. Phys.org.
• Sci-News. (n.d.). NICER Observes Merger of X-Ray Spots on Distant Magnetar.
• University of East Anglia. (n.d.). UEA researcher part of NASA team to discover hot spots merging on a magnetar.
• Younes, G., Lander, S. K., Baring, M. G., Enoto, T., & Kouveliotou, C. (2022, January 13). Pulse Peak Migration during the Outburst Decay of the Magnetar SGR 1830-0645: Crustal Motion and Magnetospheric Untwisting. The Astrophysical Journal Letters.
