NICER finds amplified X-rays in the radio bursts of Crab Pulsar

Global scientific collaboration using data from NASA’s Neutron star Interior Composition Explorer (NICER) telescope on the International Space Station has discovered X-rays that follow radio bursts from pulsars in the Crab Nebula.

The discovery shows that these bursts, called giant radio pulses, release much more energy than previously thought.

The pulsar is a type of fast-spinning neutron star, a crushed core of a city-sized star that exploded like a supernova. A young, isolated neutron star can rotate tens of times every second, and its vortex magnetic field supplies rays of radio waves, visible light, X-rays, and gamma rays. If these rays pass by 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 normal pulses,” said lead scientist Teruaki Enoto of RIKEN. Pioneer Research Cluster in Waku, Saitama Prefecture, Japan. “After decades of observation, only cancer has been shown to amplify its giant radio pulses by emitting from other parts of the spectrum.”

The new study, which will appear in the April 9 issue of Science and is now available online, analyzed the largest amount of simultaneous X-ray and radio data ever collected from pulsars. It expands the observed energy range associated with this phenomenon of improvement thousands of times.

Observations by NASA’s Neutron star Interior Composition Explorer (NICER) show X-ray amplifications associated in random giant radio pulses of Crab pulsars. Watch to find out more. Credit: NASA’s Goddard Space Flight Center

Located about 6,500 light-years from us in the constellation Taurus, the Cancer Nebula and its pulsar formed in a supernova whose light reached Earth in July 1054. The neutron star rotates 30 times every second, and at X-ray and radio wavelengths it is located among the brightest pulsars in the sky.

Between August 2017 and August 2019, Enoto and his colleagues used NICER to repeatedly observe the Cancer pulsar in X-rays with energies up to 10,000 electron volts or thousands of times greater than visible light. As NICER watched, the team also studied the facility using at least one of Japan’s two terrestrial radio telescopes – a 34-meter antenna at the Kashima Space Technology Center and a 64-meter antenna at the Usuda Deep agency from the Japan Aviation Agency Space Center, both working at a frequency of 2 gigahertz.

The combined data set effectively enabled the researchers to cover X-rays and radios for almost a day. In all, they captured activity in 3.7 million pulsar rotations and networked some 26,000 giant radio pulses.

Giant pulses erupt quickly, accelerate in millionths of a second, and occur unpredictably. However, when they do occur, they coincide with regular hourly pulsations.

NICER records the arrival time of each X-ray it detects within 100 nanoseconds, but the accuracy of the telescope’s time is not the only advantage of this study.

“NICER’s capacity to observe light X-ray sources is almost four times greater than the combined brightness of both the pulsar and its nebula,” said Zaven Arzoumanian, project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Thus, these observations were largely unaffected by accumulation – where the detector counts two or more X-rays as a single event – and other issues that complicated previous analyzes.”

Unit’s team combined all the X-ray data that matched the giant radio pulses, revealing an X-ray gain of about 4% that happened synchronized with them. It is remarkably similar to a 3% increase in visible light, also associated with a phenomenon discovered in 2003. Compared to the difference in illumination between regular and giant Cancer pulses, these changes are extremely small and challenge the explanation of theoretical models.

Improvements suggest that giant pulses are a manifestation of basic processes that produce emissions that span the electromagnetic spectrum, from radios to X-rays. And since X-rays are packaged a million times more than the impact of a radio wave, even a modest increase is a great energy contribution. The researchers conclude that the total emitted energy associated with the giant pulse is tens to hundreds of times higher than previously estimated from radio and optical data alone.

“We still don’t understand how and where pulsars produce their complex and widespread show, and I’m glad we’ve contributed to another piece of the puzzle with multiple wavelengths of these fascinating objects,” Enoto said.

NICER is an astrophysical opportunity mission within NASA’s Explorers program, which provides frequent flight opportunities for world-class scientific research from space using innovative, streamlined, and efficient management approaches within the fields of heliophysics and astrophysics. NASA’s Space Technology Administration supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

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