Scientists from the RIKEN Innovative Research Cluster have observed a new magnetar called Swift J1818.0-1607. The new data casts doubt on current knowledge of two types of extreme stars, magnetars and pulsars. The study, published in the Astrophysical Journal, was conducted using the Neutron Star Interior Composition Explorer (NICER), an X-ray instrument aboard the International Space Station.
Magnetars are a subtype of pulsars, which are neutron stars. These are degenerate stars that failed to become black holes, and instead became extremely dense bodies made up mostly of neutrons. Magnetars, as well as some young pulsars with rotational force (this is a different type of pulsar), emit powerful X-rays. However, it is believed that the emission mechanism of these pulsars is different. Scientists believe that in such magnetars, the rays are powered by extremely strong magnetic fields, while in canonical pulsars they are powered by the rapid rotation of the star. However, much in these phenomena is not entirely clear. More recently, it was discovered that several magnetars emit radio waves. This property was previously considered limited for canonical pulsars with rotational force, blurring the line between different types of stars.
As part of the current study, work by Chin-Ping Hu, a visiting researcher on the RIKEN Hakubi Natural Extreme Research Group, and his colleagues, has identified the missing link between the two types of pulsars.
On March 12, a new GRB was detected by the Burst Alert Telescope (BAT) aboard the Neil Gerels Swift Observatory, the space-based gamma ray observatory. The object considered to be a magnetar was named Swift J1818.0-1607. The RIKEN group and the NICER team quickly took action. Four hours after the discovery, scientists began follow-up X-ray observations with NICER.
They found that this magnetar had a pulsation period of 1.36 seconds, the shortest observed so far for stars of this type. Further observations showed that the object exhibits slow rotation. Its surface magnetic field indicated that it was a young magnetar, formed about 420 years ago. Studies of sudden changes in rotational speed (which are important for understanding neutron stars) have shown that this star is indeed a young magnetar. However, it turned out that its X-ray emission is lower than that of other magnetars. This suggests that this star has the attributes of both magnetars and rotating pulsars.
This research gave scientists new insights into neutron stars with strong magnetic fields. Recent radio observations show that magnetars can be responsible for mysterious phenomena such as fast radio bursts. The team is looking forward to further research on the facility.
According to Teruaki Enoto, head of the RIKEN Hakubi extreme natural phenomena research team, “The discovery of a new magnetar is exactly what our NICER research team has been waiting for, studying such stars and magnetosphere. The NICER observatory is very well suited for monitoring X-ray pulsations from magnetars and the ‘bridge’ between the two types of pulsars that we have discovered has contributed to our understanding of these mysterious objects”.