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Nine new and partly unusual pulsars

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Nine new and partly unusual pulsars
Editorial Board
/ Press release from the Max Planck Institute for Radio Astronomy
January 26, 2023

The nine-millisecond pulsars, which are often found in rare and sometimes unusual binary systems, were discovered in a targeted survey using the MeerKAT South African Telescope Array. For this purpose, there are 79 unknown pulsar-like sources from observations
Fermi gamma ray telescope
NASA noticed it.

This image shows a portion of the sky as seen by the Fermi Large Area Telescope.
NASA/DOE/FermiLat collaboration

“For our TRAPUM survey, we observed a selection of promising pulsar-like sources using MeerKAT, a relatively new and very sensitive radio telescope, along with proprietary analysis software,” explains Colin Clark, group leader at the Max Planck Institute for Gravitational Physics. Albert Einstein Institute; AEI) in Hanover and first author of the study now presented. “The reward for our efforts is something to be proud of: we have discovered nine new millisecond pulsars, some of them quite unusual.”

The team used a proven approach to discover new millisecond pulsars: a catalog Fermi Large Area Telescope Lists sources of gamma rays Fermi gamma ray telescope It was discovered by NASA in eight years of observation. This catalog contains information about the locations of sources in the sky, the energy distribution of gamma rays, and temporal changes in the brightness of gamma rays.

“We used machine learning methods to determine the probability that all sources in the Fermi catalog that are not associated with known celestial bodies are pulsars,” Clark explains. “So we identified the most pulsar-like sources in the Fermi catalog. Then we narrowed our list down to those most likely to be detectable by our survey. Then we observed 79 using MeerKAT.”

MeerKAT is an arrangement of 64 parabolic antennas with an effective diameter of 13.5 meters each at Karoo in South Africa. MeerKAT offers unprecedented sensitivity to celestial bodies in the Southern Hemisphere. It is able to detect sources five times fainter than those observed by the second, more sensitive telescope in the Southern Hemisphere. that TRansients and Pulsars using the MeerKAT Large Survey Project TRAPUM uses this sensitivity to search for new pulsars in parts of the sky where they are most likely to be found: globular clusters, nearby galaxies, supernova remnants and, as in this survey, unknown gamma-ray sources.

This requires the development of special computers that collect data from the MeerKAT antennas into a virtual large radio telescope capable of observing nearly 500 closely spaced celestial sites simultaneously. The TRAPUM scan of Fermi sources uses the additional sensitivity of MeerKAT to reduce the observation time to just ten minutes. This is much shorter than the observational hours previously required to find pulsars in these sources.

Short notes have several advantages: more sources can be recorded in a limited observation time. They can be observed again and again, which increases the chance of spotting a new radio pulsar, as they are not always visible when first seen. The TRAPUM pulsar survey included two observations for each source. Analysis of short observations is computationally less demanding than analysis of longer observations. In addition, orbital motion in binary star systems can complicate detection of radio pulsars. During a short observation period, the pulsar’s motion is nearly constant, minimizing the adverse effect of the variable orbital motion.

In addition to high sensitivity, the MeerKAT array offers another advantage over radio telescopes with a single parabolic antenna. MeerKAT can locate the new sources in the sky with very high accuracy because the individual antennas are separated by up to eight kilometers. This enables rapid follow-up scans at other wavelengths.

Searching for pulsars with the large amounts of data generated during TRAPUM observations requires a great deal of computing power and fast processing to free up memory for more observations. “We used specially developed data analysis methods running on 120 graphics processing units (GPUs) in a dedicated computer cluster to examine the MeerKAT observations. We quickly found nine millisecond candidate pulsars, which we analyzed all using additional MeerKAT observations,” says Iwan Parr. , group leader at the Max Planck Institute for Radio Astronomy and project scientist for TRAPUM. “It is remarkable that we were also able to use these confirmatory observations to improve sky locations, as MeerKAT is able to observe many converging sky locations simultaneously. This is invaluable for follow-up studies at different wavelengths.”

One of the finds, PSR J1526-2744, was examined in detail later. After detecting this radio pulsar in a binary star system, the researchers also detected the neutron star’s gamma-ray pulses. Using all available Fermi data, they were able to study the orbital motion in detail and determine the properties of the binary star system. Most likely, the neutron star orbits a common center of mass with a light white dwarf in just under five hours. This would be the second shortest known orbital period for this binary system.

The team also looked for persistent gravitational waves from PSR J1526-2744. If the neutron star were deformed, it would emit gravitational waves at twice the frequency of rotation. The researchers used all publicly available advanced LIGO data from O1, O2 and O3 observations. By knowing precisely the motion of the pulsar in the binary system through gamma-ray observations, the research team achieved the highest possible sensitivity to search for gravitational waves.

Although they did not observe persistent gravitational waves from PSR J1526-2744, they were able to measure how far the neutron star deviated from perfect axial symmetry. “We now know that PSR J1526-2744 is in fact very symmetric. We’ve shown that a neutron star’s equator cannot deviate from a perfect circle by more than the diameter of a human hair,” says Anjana Ashok, PhD student in the permanent education Max Planck research group. Independent “Continuous Gravitational Waves” at AEI Hannover. She led the search for gravitational waves.

Two other pulsars, PSR J1036-4353 and PSR J1803-6707, are typical pulsar systems composed of neutron stars with companion stars that are at least a quarter of the mass of our Sun. These pulsars evaporate and destroy their mates over time, similar to the eponymous Australian red spider, whose females eat males after mating.

After quickly and accurately locating pulsars using the unique capabilities of MeerKAT, the pulsar companions became the star catalog for the astrometry mission. gaia They were identified and studied in the optical spectrum using the ULTRACAM camera on ESO’s New Technology Telescope. In addition, the X-ray emission of PSR J1803-6707 was found in data from the first comprehensive survey of eROSITA. The X-rays likely come from the energetic pulsar wind colliding with the material vaporized by the companion. It is typical of Redback systems.

It is difficult to estimate the number of undiscovered pulsars hiding behind pulsar-like Fermi sources. However, experts are sure that future observations can still detect several millisecond pulsars. There are other candidates on the target list who are very likely to be superstars. However, they have not shown any pulsating radio waves or gamma rays in many surveys to date. New telescopes, methods of analysis, and repeated attempts at observation may one day prove that they are pulsars. With the increase of observation time from Fermi As the source catalog grows, more pulsar-like sources will appear and become potential targets.

“Our results, which are only the first from TRAPUM’s survey of Fermi sources, really show the great potential of MeerKAT. With MeerKAT and special software, we are not only able to detect new pulsars from milliseconds, but also quickly and accurately localize them,” says Clark. “MeerKAT observations are a great help for multiwavelength tracking, catalog search, and future observations—in other words, pulsars make milliseconds a gift that keeps gifting.”

The team writes about their observations in a specialized article published in the journal Monthly Notices of the Royal Astronomical Society He appeared.


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