UKIDSS J Band Lookup Table for 4XMM J182531.5–144036. The red circle is centered on the XMM-Newton detected position, with a radius of 1” equal to the position error. The white circle is centered on the position detected by Chandra and has a radius of 0.6” equal to its position error. Credit: arXiv (2024). DOI: 10.48550/arxiv.2401.02468
Astronomers from the Open University in Milton Keynes, UK and elsewhere report the detection of a new Be/X-ray binary. The new system, designated 4XMM J182531.5–144036, exhibits persistent X-ray emission. The discovery was detailed in a paper published Jan. 4 on the preprint server. arXiv.
X-ray binaries consist of a normal star or white dwarf transferring mass onto a compact neutron star or black hole. Depending on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB).
Be/X-ray binaries (Be/XRB) are the largest subgroup of HMXB. These systems are made up of Be stars and, generally, neutron stars, notably pulsars. Observations have shown that most of these systems exhibit persistent weak X-ray emission, interrupted by explosions lasting several weeks.
4XMM J182531.5–144036 was initially detected as a hard X-ray source in April 2008 with ESA’s XMM-Newton satellite. Since its nature remains unknown, a team of astronomers led by Andrew Mason Jr. of the Open University analyzed available data from XMM-Newton, NASA’s Chadra spacecraft, the Very Large Telescope (VLT) and of the UKIDSS (UKIRT Infrared Deep Sky Survey) galactic plane. Investigation, in order to investigate this source.
The study found that the position of 4XMM J182531.5–144036 coincides with an infrared object exhibiting a near-infrared excess compared to the spectra of early B-type dwarf or giant stars. This object also displays a strong B-type line. hydrogen emission. The researchers noted that these properties are characteristic of Be stars.
Additionally, a coherent X-ray pulse of 4XMM J182531.5–144036 was detected, with a period of 781 seconds. The presence of such a pulsation is typical of BeXRB pulsars. The astronomers added that the profile of the X-ray pulses is asymmetric, which is observed in X-ray pulsars and can provide information about the structure of the neutron star’s magnetic field.
According to the paper, the X-ray pulsation is observed with the same profile in widely separated XMM-Newton and Chandra observations. This indicates that the X-ray emission is likely persistent.
Regarding the orbital period of 4XMM J182531.5-144036, researchers calculate that it is between 250 and 500 days. The system’s orbit was found to have low eccentricity.
“We therefore conclude that 4XMM J182531.5–144036 is a newly identified persistent, long-period Be/X-ray binary,” the study authors wrote.
Astronomers estimate the distance to 4XMM J182531.5–144036 to be between 3,300 and 23,00 light years. However, they noted that the system is too faint to be detected by ESA’s Gaia satellite and therefore no independent distance estimate is available.
More information:
AB Mason et al, 4XMM J182531.5–144036: discovery of a new persistent Be/X-ray binary
as part of the XMM-Newton chance survey, arXiv (2024). DOI: 10.48550/arxiv.2401.02468
Journal information:
arXiv
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