An ultra-long period magnetar?
An international team led by Curtin University and the International Centre for Radio Astronomy Research including scientists from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has discovered a new type of stellar object that challenges our understanding of the physics of neutron stars. The object could be an ultra-long period magnetar, a rare type of star with extremely strong magnetic fields that can produce powerful bursts of energy. Until recently, all known magnetars released energy at intervals ranging from a few seconds to a few minutes. The newly discovered object emits radio waves every 22 minutes, making it the longest period magnetar ever detected.
A new type of stellar object was discovered using the Murchison Widefield Array (MWA) in Western Australia by an international research group led by Dr Natasha Hurley-Walker (Curtin University & ICRAR, Australia). The source, probably a magnetar, a rotating neutron star with extremely strong magnetic fields more than a billion times stronger than the most powerful magnetic field created on Earth, was labeled GPM J1839−10. It is at a distance of 15,000 light-years away from Earth in the Scutum constellation. It is only the second ultra-long period magnetar ever detected, described as an enigmatic transient object that would intermittently appear and disappear, emitting powerful beams of energy three times per hour.
"This remarkable object challenges our understanding of neutron stars and magnetars, which are some of the most exotic and extreme objects in the Universe," says Natasha Hurley-Walker.”The first of these enigmatic transient objects took us by surprise. We were stumped and thus started searching for similar objects to find out if it was an isolated event or just the tip of the iceberg."
Scanning the skies using the MWA telescope the team soon found another source, GPM J1839−10, emitting bursts of energy that last up to five minutes, five times longer than the first object. Follow-up observations with other telescopes confirmed the discovery and provided details about the magnetar's unique characteristics.
“GPM J1839−10 is quite the intriguing source, seemingly too slowly spinning to be a typical radio pulsar yet, but also too stably emitting to be a radio magnetar. In seeking to understand its true nature, we sampled the signal from the source every few milliseconds using the high-time resolution pulsar and fast transient searching instruments developed by our team”, adds Ewan Barr from the Max Planck Institute for Radio Astronomy (MPIfR), a co-author of the publication. “The observations revealed fine pulse substructure, exhibiting quasi-periodic oscillations. Whether these are an intrinsic property of the source or of its surroundings remains to be determined.”
The team also began searching the observational archives of the world's premier radio telescopes for additional information.
"It showed up in observations by the Giant Metre wave Radio Telescope (GMRT) in India, and the Very Large Array (VLA) in the USA had observations dating as far back as 1988," explains Natasha Hurley-Walker. "That was quite an incredible moment for me. I was five years old when our telescopes first recorded pulses from this object, but no one noticed it, and it stayed hidden in the data for 33 years.”
Not all magnetars produce radio waves. Some fall below the so-called 'death line', a critical threshold where a star's magnetic field becomes too weak to generate radio emission. Lying far below the death line, GPM J1839−10 should be spinning too slowly for it to produce radio pulses, yet we see them as regular as clockwork.
Every 22 minutes, the source emits a five-minute pulse of radio wavelength energy, and it has been doing for at least 33 years. Whatever mechanism may be behind this is extraordinary. The discovery has important implications for the understanding of the physics of neutron stars and the behaviour of magnetic fields in extreme environments. It also raises new questions about the formation and evolution of magnetars and could shed light on the origin of mysterious phenomena such as fast radio bursts.
The research team plans to conduct further observations of the magnetar to learn more about its properties and behaviour. They also hope to discover more ultra-long period magnetars in the future, which could help to refine our understanding of these fascinating and enigmatic objects.
The Murchison Wide-field Array (MWA) where the source GPM J1839−10 was discovered is a precursor to the world's largest radio astronomy observatory, the SKA Observatory (SKAO), which is under construction in Australia and South Africa.
Follow-up observations included three radio telescopes in Australia (Parkes, ASKAP, ATCA), MeerKAT in South Africa, the mid-frequency precursor for the SKAO, and the XMM-Newton X-ray space telescope.
The authors of the paper are N. Hurley-Walker, N. Rea, S. J. McSweeney, B. W. Meyers, E. Lenc, I. Heywood, S. D. Hyman, Y. P. Men, T. E. Clarke, F. Coti Zelati, D. C. Price, C. Horvath, T. J. Galvin, G. E. Anderson, A. Bahramian, E. D. Barr, N. D. R. Bhat, M. Caleb, M. Dall’Ora, D. de Martino, S. Giacintucci, J. S. Morgan, K.M. Rajwade, B. Stappers and A. Williams. Yunpeng Men and Ewan Barr are affiliated with the Max Planck Institute for Radio Astronomy.
Dr. Ewan Barr
Group Leader: Electronics, Software Development
Max-Planck-Institut für Radioastronomie, Bonn
Fon: +49 228 525-535
Dr. Yunpeng Men
Max-Planck-Institut für Radioastronomie, Bonn
Fon: +49 228 525-533
N. Hurley-Walker et al.: A long-period radio transient active for three decades, Nature July 19, 2023