A global scientific collaboration using data from the NICER (Interior Composition Explorer) telescope of the NASA neutron star on the International Space Station has discovered x-ray surges accompanying pulsar radio bursts in the Crab Nebula. The discovery shows that these bursts, called giant radio pulses, release much more energy than previously suspected.
A pulsar is a type of rapidly spinning neutron star, the crushed nucleus, the size of a city, of a star that has exploded into a supernova. A young, isolated neutron star can spin dozens of times per second, and its swirling magnetic field powers beams of radio waves, visible light, x-rays and gamma rays. If these beams sweep across the Earth, astronomers observe clock-like emission pulses and classify the object as a pulsar.
“Of the more than 2,800 cataloged pulsars, the Crab pulsar is one of the few to emit giant radio pulses, which occur sporadically and can be hundreds to thousands of times brighter than regular pulses,” said the Senior Scientist Teruaki Enoto at the RIKEN Cluster for Pioneering Research in Wako, Saitama Prefecture, Japan. “After decades of observations, it has been shown that only the crab enhances its giant radio pulses with emissions from other parts of the spectrum.”
The new study, which will appear in the April 9 edition of Science and is now available online, analyzed the largest amount of simultaneous radiographic and radio data ever collected from a pulsar. It extends the observed energy range associated with this improvement phenomenon by thousands of times.
Located about 6500 light years away in the constellation Taurus, the Crab Nebula and its pulsar formed in a supernova whose light reached Earth in July 1054. The neutron star rotates 30 times per second, and at X-ray and radio wavelengths, it is among the brightest pulsars in the sky.
Between August 2017 and August 2019, Enoto and his colleagues used NICER to repeatedly observe the crab pulsar in x-rays with energies of up to 10,000 electron volts – thousands of times that of visible light. While NICER watched, the team also studied the object using at least one of two ground-based radio telescopes in Japan – the 34-meter dish at the Kashima Space Technology Center and the 64-foot dish. meters to Usuda of the Japan Aerospace Exploration Agency. Deep Space Center, both operating at a frequency of 2 gigahertz.
This combined data set effectively gave researchers nearly a day and a half of simultaneous x-ray and radio coverage. In total, they captured activity over 3.7 million pulsar rotations and generated some 26,000 giant radio pulses.
Giant pulses erupt rapidly, reaching thousandths of a second, and occur unpredictably. However, when they do occur, they coincide with the regular clockwork pulses.
NICER records the arrival time of each detected X-ray to less than 100 nanoseconds, but the telescope’s timing accuracy is not its only advantage for this study.
“NICER’s ability to observe bright X-ray sources is almost four times the combined brightness of the pulsar and its nebula,” said Zaven Arzoumanian, project scientist at NASA’s Goddard Space Flight Center in Greenbelt , Maryland. “So these observations were largely unaffected by stacking – where a detector counts two or more x-rays as a single event – and other issues that have complicated previous analyzes.
The Enoto team combined all the x-ray data that coincided with giant radio pulses, revealing an increase in x-rays of around 4% that occurred in synchronization with them. This is remarkably similar to the 3% increase in visible light also associated with the phenomenon, discovered in 2003. Compared to the difference in brightness between the regular and giant pulses of the Crab, these changes are remarkably small and challenging. for theoretical models to be explained.
The improvements suggest that giant pulses are a manifestation of underlying processes that produce emissions spanning the electromagnetic spectrum, from radio to x-rays. And since x-rays contain millions of times more power than radio waves, even a modest increase represents a significant energy contribution. The researchers conclude that the total energy emitted associated with a giant pulse is tens to hundreds of times higher than what was previously estimated from radio and optical data alone.
“We still don’t understand how or where pulsars produce their complex and extensive emission, and it is gratifying to have contributed to another piece of the multi-wavelength puzzle of these fascinating objects,” said Enoto.
NICER is an opportunity astrophysics mission within NASA’s Explorers program, which provides frequent flight opportunities for world-class scientific investigations from space using innovative, streamlined and efficient management approaches in fields of heliophysical and astrophysical sciences. The leadership of the NASA Space Technology Mission is supporting the SEXTANT component of the mission, demonstrating the navigation of pulsar-based spacecraft.