Pulsating Gamma-Rays Detected For Second-Fastest Spinning Pulsar

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Objects like pulsar J0952-0607 are far from common. Not only are pulsars neutron stars that pack more mass than our Sun in a sphere just 20 kilometers (12 miles) across, but they also spin on their axis at incredible speeds. This is what makes J0952-0607 truly special to astronomers: It completes 707 rotations every second, making it the second-fastest pulsar ever discovered.

As these pulsars spin, they emit radiation. From the perspective of Earth, they pulsate every time they turn in our direction, making their detection similar to the flashes from a lighthouse. In the case of J0952-0607, this happens once every 1.4 milliseconds. The pulsations are seen in radio waves, gamma-rays, or both depending on the geometry of the system. Previously, pulsar J0952-0607 had only been detected with radio observatories, but now an international team has caught this rapid pulsation in gamma rays.

As reported in The Astrophysical Journal, the team had the painstaking task of going through the data from NASA’s Fermi Large Area Telescope (LAT). The gamma-ray emissions were extremely faint over 8.5 years of observations (equivalent to about 220 billion pulses) and they detected only 200 gamma-rays. Thanks to this work, the team realized that there was an error in the original coordinates for the object and they were looking slightly off the real position of the star.

“Our discovery of the gamma-ray pulsations revealed this error,” lead author Lars Nieder, from Albert Einstein Institute, said in a statement. “This mistake was corrected in the publication reporting the radio pulsar discovery. A new and extended gamma-ray search made a rather faint – but statistically significant – gamma-ray pulsar discovery at the corrected position.”

Once the position had been corrected, the team was able to reanalyze the 8.5 years' worth of data. They were surprised to find that the pulsar didn't seem to emit gamma radiation before 2011. The reason for this is currently without an answer. The system has been observed not just in gamma-rays and radio waves but also in visible light.

J0952-0607 has a small companion star, one-fifteenth the mass of the Sun, which is tidally locked so that one side gets heated while the other side remains colder than the other. The optical observations also highlight another mystery. Based on the radio observations, the researchers estimated that the system is 4,400 light-years away. The optical detection instead puts the two stars at almost three times as far. The scientists hope that more gamma-ray data will solve this discrepancy.

“We will keep studying this system with gamma-ray, radio, and optical observatories since there are still unanswered questions about it. This discovery also shows once more that extreme pulsar systems are hiding in the Fermi-LAT catalogue,” added Professor Bruce Allen, Nieder’s PhD supervisor.

The pulsar was also studied using gravitational waves. If a millisecond pulsar such has this had a little bump or hill on its surface, it should emit gravitational waves that we can detect. No such waves have been detected, so the team believes the pulsar is close to a perfect sphere and no bump, if one exists, is higher than a millimeter.

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