Astronomers Precisely Measure Distance to Magnetar (Astronomy)

XTE J1810−197 (J1810), a magnetar located in the constellation of Sagittarius, was the first magnetar identified to emit radio pulses, and has been extensively studied during a radio-bright phase in 2003–2008. It is estimated to be relatively nearby compared to other Galactic magnetars, and provides a useful prototype for the physics of high magnetic fields, magnetar velocities, and the plausible connection to extragalactic fast radio bursts. Upon the re-brightening of the magnetar at radio wavelengths in late 2018, researchers of current study resumed an astrometric campaign on J1810 with the Very Long Baseline Array, and sampled 14 new positions of J1810 over 1.3 years and has made the direct geometric measurement of the distance to XTE J1810-197, a magnetar located in the constellation of Sagittarius.

An artist’s impression of a magnetar emitting a burst of radiation. Image credit: Sophia Dagnello, NRAO / AUI / NSF.

Magnetars are a variety of neutron stars — the superdense remains of massive stars that exploded as supernovae — with extremely strong magnetic fields.

A typical magnetar magnetic field is a trillion times stronger than the Earth’s magnetic field, making magnetars the most magnetic objects in the Universe.

They can emit strong bursts of X-rays and gamma rays, and recently have become a leading candidate for the sources of fast radio bursts (FRBs).

Researchers performed the phase calibration for the new observations with two phase calibrators that are quasi-colinear on the sky with J1810, enabling substantial improvement of the resultant astrometric precision. They then, combine their new observations with two archival observations from 2006 and have refined the proper motion and reference position of the magnetar and have measured its annual geometric parallax, the first such measurement for a magnetar.

This effect, called parallax, allows astronomers to use geometry to directly calculate the object’s distance. And what they found?

They found that the parallax of 0.40 ± 0.05 mas corresponds to a most probable distance 2.5 (↑+0.4 ↓−0.3) kpc for J1810. Their new astrometric results confirm an unremarkable transverse peculiar velocity of ≈200 km s−¹ km for J1810, which is only at the average level among the pulsar population. The magnetar proper motion vector points back to the central region of a supernova remnant (SNR) at a compatible distance at ≈70 kyr ago, but a direct association is disfavored by the estimated SNR age of ∼3 kyr.

References: H Ding, A T Deller, M E Lower, C Flynn, S Chatterjee, W Brisken, N Hurley-Walker, F Camilo, J Sarkissian, V Gupta, A magnetar parallax, Monthly Notices of the Royal Astronomical Society, , staa2531, https://doi.org/10.1093/mnras/staa2531

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