From AAS NOVA: “An Extreme Pulsar Seen in Gamma Rays”



11 December 2019
Susanna Kohler

Artist’s illustration of a pulsar (left) and its small stellar companion (right), viewed within their orbital plane. [NASA Goddard SFC/Cruz deWilde]

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

One of the fastest spinning radio pulsars known has now been detected to pulse in gamma rays, too. What can we learn about this extreme pulsar from new observations?

Artist’s illustration of a pulsar, a fast-spinning, magnetized neutron star. [NASA]

Pushing the Record for Spin

Pulsars are rapidly spinning, magnetized neutron stars left behind at the end of a star’s lifetime. Pulsar J0952-0607, a pulsar in a binary orbit with a very low-mass companion star, has the second-fastest known pulsar spin, rotating 707 times each second. For comparison, that’s about 70 times faster spin than the fastest helicopter rotors — and it’s an object that’s 10 km across and weighs more than the Sun!

As it spins, PSR J0952-0607 flashes a beam of radio waves across the path of the Earth, radiating from a hot spot on its surface. In a recent study, a team of scientists led by Lars Nieder (Albert Einstein Institute and Leibniz University Hannover, Germany) have now hunted through years of data from the Fermi Gamma-ray Space Telescope to see if we can spot pulsations from a gamma-ray beam as well.


NASA/Fermi Gamma Ray Space Telescope

Finding High-Energy Pulses

The radio observations of PSR J0952-0607’s pulsations span only 100 days, which isn’t long enough to precisely constrain its properties. The Fermi Gamma-ray Space Telescope launched in 2008, and its Large Area Telescope (LAT) has been providing all-sky images on a regular basis since then. Nieder and collaborators reasoned that if they could spot PSR J0952-0607 in gamma rays in the Fermi LAT data, then they’d be able to observe the pulsar over a much longer baseline than its radio observations provide.

The catch? PSR J0952-0607 is very faint in gamma-rays — which is why its pulsations weren’t previously detected. Nieder and collaborators had to develop novel search and timing methods with greater sensitivity, ultimately using the computational equivalent of 24 years on a single-core computer to search for a signal. Their efforts paid off, however — they managed to detect faint gamma-ray pulsations from PSR J0952-0607 spanning from July 2011 to the end of the dataset in January 2017.

Plot of the spin-down rate vs. the spin for the known pulsar population outside of globular clusters. PSR J0952-0607 is marked by an orange star. [Nieder et al. 2019]

Some Answers and Some New Puzzles

From the gamma-ray observations, Nieder and collaborators were able to measure a precise spin-down rate for the pulsar (it slows by less than 4.6 x 10-21 seconds each second), as well as other properties. PSR J0952-0607’s inferred magnetic field is among the 10 lowest magnetic fields measured for pulsars — an extreme that is predicted by theory based on this pulsar’s remarkably fast spin.

Though we’ve gained a lot of information about PSR J0952-0607 from its gamma-ray pulsations, new mysteries have also been introduced. The fact that its pulsations are undetectable before July 2011 is one of these — could the pulsar’s flux have changed? Or its orbit around its companion star? We’ll need more data to be able to solve this puzzle.

We still have more to learn about PSR J0952-0607, but the newly discovered gamma-ray pulsations have provided us with unique insight into the extremes that arise when compact astrophysical bodies spin at such high speeds. With luck, future observations of this pulsar — and others like it — will help us to further probe the physics of these unusual sources.


“Detection and Timing of Gamma-Ray Pulsations from the 707 Hz Pulsar J0952−0607,” L. Nieder et al 2019 ApJ 883 42.

See the full article here .


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