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LOFAR Radio Telescope Identifies the Second-Fastest-Spinning Pulsar

A pulsar spinning at more than 42,000 revolutions per minute has been identified by the Netherlands-based Low Frequency Array (LOFAR) radio telescope by following up on mysterious high-energy sources mapped out by NASA's Fermi Gamma-ray Space Telescope. This pulsar is considered to be the second-fastest known.

The Low-Frequency Array (LOFAR), a network of thousands of linked radio antennas, primarily located in the Netherlands, has discovered two new millisecond pulsars by investigating previously unknown gamma-ray sources uncovered by NASA's Fermi Gamma-ray Space Telescope. Pulsar J0952-0607, highlighted near center right, rotates 707 times a second and now ranks as second-fastest pulsar known. The location of LOFAR's first millisecond pulsar discovery, J1552+5437, which spins 412 times a second, is shown at upper left. Radio emission from both pulsars dims quickly at higher radio frequencies, making them ideally suited for LOFAR. The top of this composite image shows a portion of the gamma-ray sky as seen by Fermi. At the bottom is the LOFAR "superterp" near Exloo, the Netherlands, which houses the facility's core antenna stations. Credits: NASA/DOE/Fermi LAT Collaboration and ASTRON

A pulsar refers to the core of a massive star that exploded as a supernova. In this stellar remnant, also known as a neutron star, the equivalent mass of half a million Earths is crushed into a magnetized, spinning ball no larger than Washington, D.C. Beams of gamma rays, X-rays, visible light and radio waves are powered by the rotating magnetic field. Astronomers observe steady pulses of emission and classify the object as a pulsar if a beam happens to sweep across Earth.

Roughly a third of the gamma-ray sources found by Fermi have not been detected at other wavelengths. Many of these unassociated sources may be pulsars, but we often need follow-up from radio observatories to detect the pulses and prove it. There's a real synergy across the extreme ends of the electromagnetic spectrum in hunting for them.

Elizabeth Ferrara, a member of the discovery team at NASA's Goddard Space Center, Greenbelt, Maryland

The new object, called PSR J0952–0607 (J0952 for short) is categorized as a millisecond pulsar and is positioned between 3,200 and 5,700 light-years away in the constellation Sextans. The pulsar comprises of about 1.4 times the sun's mass. A companion star that has been whittled away to less than 20 times the mass of the planet Jupiter orbits the pulsar every 6.4 hours. The findings have been reported by the Scientists in a paper published in the Sept 10th edition of The Astrophysical Journal Letters and presently available online.

At some specific point in this system's history, matter started streaming from the companion and onto the pulsar, slowly increasing its spin to 707 rotations a second, or more than 42,000 rpm and majorly increasing its emissions. The pulsar eventually started evaporating its companion, and this process still continues. Systems like J0952, because of their likeness to spiders that consume their mates, are known as redback or black widow pulsars, based on how much of the companion star remains. Several of the known systems of these types were detected by following up Fermi unassociated sources.   

The potential to discover a new population of ultra-fast pulsars is further hinted by the LOFAR discovery.

LOFAR picked up pulses from J0952 at radio frequencies around 135 MHz, which is about 45 percent lower than the lowest frequencies of conventional radio searches. We found that J0952 has a steep radio spectrum, which means its radio pulses fade out very quickly at higher frequencies. It would have been a challenge to find it without LOFAR.

Cees Bassa, Lead Author, the Netherlands Institute for Radio Astronomy (ASTRON)

According to Theorists, pulsars are capable of rotating as fast as 72,000 rpm prior to breaking apart, however the fastest spin known — by PSR J1748–2446ad, reaching approximately 43,000 rpm — is just 60% of the theoretical maximum. Pulsars with faster periods maybe just cannot form. However, the gap between theory and observation may also result from the complexity in detecting the fastest rotators.

"There is growing evidence that the fastest-spinning pulsars tend to have the steepest spectra," stated Co-author Ziggy Pleunis, a Doctoral Student at McGill University in Montreal. J1552+5437, the first millisecond pulsar discovered with LOFAR, which was found by Pleunis, spins at 25,000 rpm and also shows a steep spectrum. "Since LOFAR searches are more sensitive to these steep-spectrum radio pulsars, we may find that even faster pulsars do, in fact, exist and have been missed by surveys at higher frequencies," he explained.

Fermi, during its nine years in orbit, played a role in the discovery of more than 100 pulsars, either via direct detection of gamma-ray pulses or radio follow-up of unassociated sources.

LOFAR is a radio telescope made up of an international network of antenna stations designed for observing the universe at frequencies between 10 and 250 MHz. The network, operated by ASTRON, comprises of stations in Germany, the Netherlands, Ireland, Poland, France, the U.K. and Sweden.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, created in collaboration with the U.S. Department of Energy and with vital contributions from academic institutions and partners in the United States, Sweden, Japan, Italy, Germany and France.

This animation shows a black widow pulsar like J0952 together with its small stellar companion, as seen from within their orbital plane. Powerful radiation and the pulsar's "wind" — an outflow of high-energy particles — strongly heat the facing side of the companion, evaporating it over time. (Credits: NASA's Goddard Space Flight Center/Cruz deWilde)

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