A group led by scientists from the RIKEN Cluster for Pioneering Research, using coordinated observations of the Krab pulsar in a number of frequencies has discovered that the “giant radio pulses” it emits include an increase in x-ray emissions, in addition to the radio and visible light emissions previously observed. This finding, published in Science, implies that these pulses are hundreds of times more energetic than previously believed, and that they can provide insights into the mysterious phenomenon of ‘fast radio bursts’.
Giant radio pulses – a phenomenon where extremely short pulses of radio waves of a millisecond are emitted – have been observed in conjunction with a dozen pulses in our Milky Way, but little is known about the mechanism that causes them. It has been suggested that this may also be the origin of ‘rapid radio bursts’ – rapid bursts of radio waves that are thought to have arisen from energetic events in the extragalactic universe.
To gain insight into these phenomena, the RIKEN-led group conducted coordinated observations on the Crab pulsar, one of the best known and most observed pulsars. The explosion of this star in a supernova explosion was seen by Chinese and Japanese observers in 1054 and led to the formation of the beautiful crab nebula that can still be seen today.
This new wavelength image of the Crab Nebula combines X-ray light from the Chandra X-ray Observatory (in blue) with visible light from the Hubble Space Telescope (in yellow) and infrared light seen by the Spitzer Space Telescope (in red). This particular combination of light from across the electromagnetic spectrum emphasizes the nested structure of the pulsar wind nebula. Credit: NASA, ESA, J. DePasquale (STScI), and R. Hurt (Caltech / IPAC)
The group began looking to see if there was an increase in X-ray emissions associated with giant radio pulses. In fact, despite numerous observations for several decades, researchers have so far been unable to make any unambiguous findings. The observations were based on a coordinated international campaign of simultaneous space-based X-ray and ground-based radio observations, with the space-based observations made with NICER, a new instrument aboard the International Space Station, and the radio observations made with two observatories in Japan.
Over a period of three years, the group continued the campaign and eventually found a clear signal exceeding a ‘five-sigma’ indicating an improvement in the X-ray emissions associated with the increase in radio wavelength.
Between 2017 and 2019, NASA’s Neutron star Interior Composition Explorer (NICER) and radio telescopes in Japan studied the Crab pulsar simultaneously. In this visualization, which represents only 13 minutes of NICER observations, millions of X-rays are drawn in relation to the rotational phase of the pulsar, which is central to the strongest radio emission. For clarity, two full rotations are shown. As the pulse rays sweep across our line of sight, they produce two peaks for each rotation, with the brighter one accompanied by larger numbers of giant radio pulses. For the first time, NICER data show a slight increase in X-ray emission associated with these events. Credit: NASA’s Goddard Space Flight Center / Enoto et al. 2021
The improved emission detected in the X-ray band was similar to that previously reported in the visible band, but none of the other 2,800 known pulses has ever been observed. According to Teruaki Enoto, leader of the Extreme Natural Phenomena RIKEN Hakubi Research Ream, “Our measurements imply that these giant pulses are hundreds of times more energetic than previously thought.”
Another important effect of the finding is that it places important constraints on models of the mysterious phenomenon known as ‘rapid radio bursts’. It is believed that these phenomena – mysterious extragalactic radio bursts within a millisecond, are associated with pulsars, and possibly young people such as the Crab pulsar. “However, the relationship between the two is still controversial,” says Enoto, and these findings, together with the forthcoming discoveries regarding rapid radio bursts, will help us understand the connection between these phenomena. ‘
He adds: ‘Our result not only has a wide impact on the science of the pulsar and FRB, but is also a fitting legacy for the Kashima 34-m telescope, which has been a valuable tool for the radio astronomy community, but in 2019 was irreparably damaged by a typhoon. ”
The group also included scientists from the University of Tokyo, Hiroshima University, Changhua National University of Education. JAXA, NIST, and NASA, and a number of other institutes from around the world.
Read more about this discovery Weird X-ray Surges Detected in Crab Pulsar’s Radio Bursts by NASA’s NICER.
Reference: “Enhanced x-ray emission that coincides with giant Crab Pulsar radio pulses” by Teruaki Enoto, Toshio Terasawa, Shota Kisaka, Chin-Ping Hu, Sebastien Guillot, Natalia Lewandowska, Christian Malacaria, Paul S. Ray, Wynn CG Ho, Alice K. Harding, Takashi Okajima, Zaven Arzoumanian, Keith C. Gendreau, Zorawar Wadiasingh, Craig B. Markwardt, Yang Soong, Steve Kenyon, Slavko Bogdanov, Walid A. Majid, Tolga Güver, Gaurava K. Jaisawal, Rick Foster, Yasuhiro Murata, Hiroshi Takeuchi, Kazuhiro Takefuji, Mamoru Sekido, Yoshinori Yonekura, Hiroaki Misawa, Fuminori Tsuchiya, Takahiko Aoki, Munetoshi Tokumaru, Mareki Honma, Osamu Kameya, Tomoaki Oyama, Katsuaki Asano, Shatsinaki, Science.
DOI: 10.1126 / science.abd4659