Haverford Astronomers Help Understand Irregular Emission from Crab Pulsar
The multiwavelength Crab Nebula. Image Credit: NASA, ESA, G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; A. Loll et al.; T. Temim et al.; F. Seward et al.; VLA/NRAO/AUI/NSF; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; Hubble/STScI.
Natalia Lewandowska and Wynn Ho were part of an international team of scientists that published new findings about the Crab Pulsar’s Giant Radio Pulses in Science.
The Crab Pulsar releases irregular emissions known as giant radio pulses (GRPs)—in fact, it was first detected in 1968 by those very GRPs. For many years scientists have tried to understand those GRPs, and, by extension, the Crab Pulsar. Part of that work has included looking for GRP counterparts at other wavelengths, such as X-ray emissions. A new paper published in the journal Science on April 9, co-authored by an international team including two Haverford astronomers, documents a new equivalence.
“The detection of an optical counterpart was reported in 2003,” said Natalia Lewandowska, visiting assistant professor of astronomy and one of the paper’s co-authors. “Since then we have been searching at pretty much all other wavelengths by using different instruments. With the Neutron Star Interior Composition Explorer (NICER), we have been finally able to detect a correlation between radio giant pulses and X-ray photons. That result gives us further constraints on how the Crab Pulsar is generating that particular form of irregular emission.”
Pulsars are fast-rotating and highly magnetized neutron stars born in supernova explosions.They have the size of a city (ranging from 6 to 7.5 miles in diameter), but are more massive than the Sun. The Crab Pulsar is just one of about 2900 known pulsars in our Galaxy, but it’s one of the most famous. It is unique in its GRP emissions, and those emissions are unique in their brightness and ease of detection.
“The electronics of a radio telescope [used to detect pulsars] also produce noise,” said Lewandowska. “The radio emission from pulsars is in most cases not bright enough to be visible above that noise level. GRPs are an exception. Since they are about a 1000 times brighter than the regular radio emission, they can be easily detected above that noise level by observing the Crab Pulsar just for a couple of minutes. This is very unusual.”
“Because X-rays are much more energetic than radio waves, this means a lot more energy is emitted during GRPs than previously known, and this has implications for our theoretical understanding of how pulsars and other classes of astronomical objects emit radiation,” said Wynn Ho, a research associate in the Haverford College Department of Physics and Astronomy and a science team member of NASA’s NICER project who also contributed to the paper.
In addition to helping craft the paper, Lewandowska advised the team in the development of a correlation search approach, which she originally developed for her Ph.D. thesis and also applied for her correlation search of the GRP and gamma-ray emission from the Crab pulsar, and Ho worked on theoretical interpretations of the results.
Haverford students are currently working on similar research with Lewandowska. Lydia Guertin '24 and Logan de Raspide Ross '23 are currently working on a corresponding correlation search in another pulsar, known as PSR B1937+21, which has also been reported to be a source of GRPs and, with a rotational frequency of about 641 Hz, was the fastest pulsar known for a very long time.
“Both students are analyzing the corresponding radio data taken with the Sardinia Radio Telescope that we took simultaneously with NICER,” said Lewandowska. “They are extracting and characterizing the radio giant pulses from this source, contributing actively to this research project.”
