Peering into a baby magnetar with Chandra eyes

Magnetars and rotation-powered pulsars are particular kinds of neutron stars, left after a massive star goes supernova and explodes. They are roughly 12 miles across and among the densest objects in the universe, with a teaspoonful of a neutron star material weighing billions of tons. Magnetars possess the most extreme magnetic fields in the Universe, about a quadrillion times Earth’s magnetic field strength, and can erupt with enormous amounts of high-energy X-rays and gamma-rays. In rare cases, they also emit powerful, regularly timed pulses of radio waves. They are believed to be powered by their ultra-high magnetic fields while the pulsars are powered by their spin and emit long-lived radio beams.

 Multi-Wavelength Image of the Environment of J1818 in Radio (red), Infrared (green) and X-Ray (blue). Image courtesy of Loren Anderson (West Virginia University).

The baby magnetar, named Swift J1818.0-1607 (or J1818 for short), lies in our galaxy and was discovered in March of 2020 by NASA’s Neil Gehrels Swift Observatory. In the middle of the pandemic, when the whole world was under lockdown, the magnetar decided to make an appearance by suddenly lighting up in X-rays and soft gamma rays. The Swift detection caught astronomers’ attention because the source launched a series of intense, millisecond duration high-energy bursts in our direction, announcing the discovery of this new kid on the block. Scientists have identified only 31 magnetars, while there are over 3,000 known neutron stars.

“We have a very young magnetar emitting both in high-energy and radio, one of only five such sources known so far. Our Chandra study reveals that J1818 is a transient source behaving both like a young rotation-powered pulsar and a magnetar, a rare scenario where its powering engine swings between rotation and magnetic energy,” said Harsha Blumer of West Virginia University’s Center for Gravitational Waves and Cosmology and lead author of the Astrophysical Journal Letters paper publishing these results.

“J1818 is a newly discovered magnetar with a super strong magnetic field and may be the youngest of its kind known—only about 470 years old, which is a ‘baby’ compared with the age of other objects in the universe that can be millions of years old or older. The fact that J1818 is the youngest discovered allows astronomers to watch it ‘grow up,’ as most magnetars are already at an advanced age when they are first seen,” explains co-author Samar Safi-Harb of the University of Manitoba.

"This discovery underscores how much we still have to learn about the magnetar population" Duncan Lorimer

“This is a really unusual object in that we can study it across the electromagnetic spectrum - with each new frequency of observation, we’ll learn more about its emission mechanism and environment, and the exotic physics at play” notes Maura McLaughlin, Director for the Center for Gravitational Waves and Cosmology.  “Dr. Blumer’s paper will be an extremely valuable contribution to our understanding of these objects. ”

Blumer notes that Chandra’s high arcsecond resolution enabled them to study its complex environment and discover a compact, tiny nebula that would have been easily missed with any other telescope. The nebula is believed to be the dust scattering halo from the magnetar burst, but there could be a weak pulsar wind nebula—charged particles outflowing from the pulsar—hidden underneath.  

The interdisciplinary collaborations within the Center for Gravitational Waves and Cosmology are evident including the expertise from Center researcher, Loren Anderson.  Since the unknown is intriguing, he further notes that “magnetars are created in supernova explosions.  Since magnetars are young, they may still be associated with the debris from such explosions.  There is a candidate supernova remnant (SNR) in the vicinity of J1818, although without knowing the distance to either the SNR or J1818, we cannot say if they are related.  Future observations will hopefully allow us to determine the association, possibly shedding light on the birth of J1818.”

Blumer concludes “We learn new and exciting things about space every day and discovering more such sources would also be key to understanding the connection between magnetars and fast radio bursts.” Fast radio bursts, or FRBs, are powerful millisecond duration flashes of radio waves from space discovered in 2007 by a team led by Duncan Lorimer at WVU, but their origin is still a mystery.

"This discovery underscores how much we still have to learn about the magnetar population," said Lorimer, WVU Associate Dean for Research, who along with McLaughlin, co-discovered the first FRB with former WVU undergraduate student David Narkevic.