Issue |
A&A
Volume 693, January 2025
|
|
---|---|---|
Article Number | A107 | |
Number of page(s) | 10 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/202451217 | |
Published online | 09 January 2025 |
A deep Chandra study confirms diffuse nonthermal X-ray emission from the globular cluster Terzan 5
Physics Department, CCIS 4-183, University of Alberta,
Edmonton,
AB,
T6G 2E1,
Canada
★ Corresponding authors; jzhao11@ualberta.ca; heinke@ualb erta.ca
Received:
21
June
2024
Accepted:
2
December
2024
Context. Diffuse X-ray emission has been detected from a few Galactic globular clusters (GCs), but its nature remains largely unclear. The GC Terzan 5 was previously found to show a significant diffuse thermal X-ray excess from its field, likely contributed by the Galactic background, and a nonthermal component described by a power-law model with photon index Γ ~ 1.
Aims. With over 16 times the accumulated Chandra exposure time compared to a prior study, we reexamined and verified the diffuse X-ray emission from the field of Terzan 5, which enabled us to place constraints on its nature.
Methods. We analyzed all available useful Chandra observations of Terzan 5, including 18 observations over a span of 13 years, with a total exposure time of 641.6 ks. To study the diffuse X-ray emission, we focused on four annular regions with an equal width of 0.72 arcmin centered on Terzan 5 (0.72–3.60 arcmin), from which we extracted and analyzed the X-ray spectra after removing point sources and instrumental backgrounds.
Results. We confirm a significant diffuse X-ray excess from the field of Terzan 5 in the band 0.8–3 keV. After constraining the contribution from the local X-ray background, we find a diffuse X-ray component that is genuinely associated with Terzan 5 and can be well described by a power-law model. More interestingly, the fitted photon indices show a significant increase from Γ = 1.96 ± 0.18 in the inner region to Γ = 3.48 ± 0.71 in the outer region. The diffuse X-rays are also well fit by a thermal bremsstrahlung model, with plasma temperatures declining from kT ∼ 3 keV to kT ∼ 1 keV.
Conclusions. We suggest that synchrotron radiation from the combined pulsar winds of Terzan 5’s millisecond pulsar population is a possible origin of the observed diffuse X-ray emission but that the sharp steepening in the spectra cannot be produced solely by synchrotron cooling. Other radiation processes, like thermal bremsstrahlung, may also contribute to the diffuse X-rays.
Key words: X-rays: diffuse background / globular clusters: individual: Terzan 5
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.