Located 6,500 light-years away in the constellation of Taurus, the Crab Nebula and its pulsar formed in a supernova whose light reached Earth in July 1054; the neutron star spins 30 times each second, and at X-ray and radio wavelengths it is among the brightest pulsars in the sky. Dr. Teruaki Enoto from the RIKEN Cluster for Pioneering Research and colleagues observed the Crab pulsar simultaneously with X-ray and radio telescopes and found that X-rays during so-called ‘giant radio pulses’ — sporadic bursts emitted by some pulsars that last a few microseconds — were slightly brighter than that during normal pulses.
This is a mosaic image, one of the largest ever taken by Hubble of the Crab Nebula, a 6-light-year-wide expanding remnant of a star’s supernova explosion. Japanese and Chinese astronomers recorded this violent event nearly 1,000 years ago in 1054, as did, almost certainly, Native Americans. Image credit: NASA / ESA / J. Hester / A. Loll, Arizona State University.
Pulsars are spinning, magnetized neutron stars that are observed as a regular sequence of radio pulses.
Most pulses are of consistent intensity, but occasionally one is brighter by orders of magnitude.
The cause of these unpredictable giant radio pulses is unknown.
“Out of more than 2,800 pulsars cataloged, the Crab pulsar is one of only a few that emit giant radio pulses, which occur sporadically and can be hundreds to thousands of times brighter than the regular pulses,” Dr. Enoto said.
“After decades of observations, only the Crab has been shown to enhance its giant radio pulses with emission from other parts of the spectrum.”
Between August 2017 and August 2019, Dr. Enoto and colleagues used NASA’s Neutron star Interior Composition Explorer (NICER) telescope on the International Space Station to repeatedly observe the Crab pulsar in X-rays with energies up to 10,000 electron volts, or thousands of times that of visible light.
While NICER was watching, the astronomers also studied the object using at least one of two ground-based radio telescopes in Japan: the 34-m dish at the Kashima Space Technology Center and the 64-m dish at JAXA’s Usuda Deep Space Center.
The combined dataset effectively gave the astronomers nearly a day and a half of simultaneous X-ray and radio coverage.
All told, they captured activity across 3.7 million pulsar rotations and netted some 26,000 giant radio pulses.
They combined all of the X-ray data that coincided with giant radio pulses, revealing an X-ray boost of about 4% that occurred in synch with them.
It’s remarkably similar to the 3% rise in visible light also associated with the phenomenon, discovered in 2003.
Compared to the brightness difference between the Crab’s regular and giant pulses, these changes are remarkably small and provide a challenge for theoretical models to explain.
The enhancements suggest that giant pulses are a manifestation of underlying processes that produce emission spanning the electromagnetic spectrum, from radio to X-rays.
And because X-rays pack millions of times the punch of radio waves, even a modest increase represents a large energy contribution.
The researchers conclude that the total emitted energy associated with a giant pulse is dozens to hundreds of times higher than previously estimated from the radio and optical data alone.
“We still don’t understand how or where pulsars produce their complex and wide-ranging emission, and it’s gratifying to have contributed another piece to the multiwavelength puzzle of these fascinating objects,” Dr. Enoto said.
The results are published in the journal Science.
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Teruaki Enoto et al. 2021. Enhanced X-ray emission coinciding with giant radio pulses from the Crab Pulsar. Science 372 (6538): 187-190; doi: 10.1126/science.abd4659
The Link LonkApril 10, 2021 at 03:48AM
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Study: Crab Pulsar's X-rays Brighter during 'Giant Radio Pulses' | Astronomy - Sci-News.com
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