Study investigates vibrations of millisecond pulsar PSR J1023+0038

Observed in January 2020, the Aqueye+ light curve of PSR J1023+0038 is collected every 10 seconds. Count rate is normalized at maximum count rate. The vertical colored region indicates the visually defined flare range. Credits: Illiano et al., 2022

European astronomers conducted X-ray and optical observations of a transiting millisecond pulsar known as PSR J1023+0038. The results of the observational campaign, published on on November 23, provide important insights into the origins of this source’s vibrations.

Pulsars are highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation. The fastest spinning pulsars with spin periods of less than 30 milliseconds are known as millisecond pulsars (MSPs). Astronomers hypothesize that they formed in a rotating binary system when the initially larger component morphed into a neutron star and then due to the accumulation of matter from the secondary star.

Some millisecond pulsars switch between low-mass X-ray binary (LMXB) and a radio millisecond pulsar (RMSP) states. These sources were called transition millisecond pulsars (tMSPs). Observations show that tMSPs are generally fast-spinning, weakly magnetized neutron stars, oscillating between the two states within a few days. Such behaviors may be supported by different physical mechanisms.

Located about 4,000 light-years from Earth, PSR J1023+0038 is only one of three tMSPs detected so far. It has a rotation period of about 1,688 milliseconds, and its orbital period is estimated to be 0.198 days. PSR J1023+0038 is the first MSP observed as an optical pulsar.

PSR J1023+0038 exhibits optical and X-ray pulsations that are initially detected simultaneously in X-ray high modes but disappear when the source passes through low modes, suggesting a common emission mechanism. To date, this pulsar remains the only tMSP with detectable pulsed emission in the optical band.

To better understand the emission mechanism behind the optical and X-ray pulsations of PSR J1023+0038, a team of astronomers led by Giulia Illiano of the Roman Astronomical Observatory in Italy decided to examine the phase delay between pulses of PSR J1023+0038. optical and X-ray tapes, hoping to shed more light on the physical mechanisms that cause it.

“We performed a detailed timing analysis of simultaneous or quasi-synchronous observations in the X-ray band obtained with the XMM-Newton and NICER satellites, and in the optical band with fast photometers SiFAP2 (mounted on the 3.6 m Telescopio Nazionale Galileo) and Aqueye+ ( mounted on a 1.8m Copernicus Telescope),” the researchers wrote in the paper.

The study found that the total rms pulsed amplitudes of the PSR J1023+0038’s optical pulses are approximately 0.1-0.8%, while the X-ray total rms pulsed amplitudes are in the range of 4.3-10.8%. It turns out that the optical pulses lag behind the X-ray pulses by about 150 microseconds.

The results show that the phase delay between optical and X-ray oscillations is in a limited value range (0-250 microseconds) on time scales of about five years. This finding suggests that both vibrations originate from the same region and that the emission mechanisms are linked.

Astronomers assume that the shock-driven mini pulsar nebula scenario is the most plausible hypothesis to explain the source of PSR J1023+0038’s optical and X-ray pulsations. This scenario proposes that the pulses are produced by synchrotron radiation from a shock formed where the striated pulsar wind meets the accretion disk within about 100 km from the pulsar.

More information:
G. Illiano et al., Investigation of the origin of optical and X-ray vibrations of the transition millisecond pulsar PSR J1023+0038, arXiv (2022). DOI: 10.48550/arxiv.2211.12975

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Quotation: Study investigates the vibrations of the millisecond pulsar PSR J1023+0038 (2022, December 2), retrieved from on December 2, 2022 .

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