Young Black Hole and Neutron Star Systems in the Nearby Star-forming Galaxy M33: The NuSTAR View
Abstract
We can learn about the formation and evolution of compact objects, such as neutron stars and black holes (BHs), by studying the X-ray emission from accreting systems in nearby star-forming galaxies. The hard (E > 10 keV) X-ray emission in particular allows strong discrimination among the accretion states and compact object types. We conducted a NuSTAR survey (~600 ks) of the Local Group spiral galaxy M33 to study the distribution of X-ray binary (XRB) accretors in an actively star-forming environment. We constructed color-intensity and color-color diagrams to infer XRB accretion states. Using these diagrams, we have classified 28 X-ray sources in M33 by comparing their hard X-ray colors to those of known systems. Four sources lie in the parameter space occupied by X-ray pulsars, while 8, 10, and 4 sources lie in the parameter space occupied by BHs in the hard, intermediate, and soft states, respectively. The known ultraluminous X-ray source M33 X-8 is also found to be consistent with that source type. Some sources overlap within the Z/Atoll sources due to the overlap of the two categories of BHs and Z/Atoll sources. In contrast to a similar NuSTAR survey of M31 (with a low-mass XRB-dominant population), the source population in M33 is dominated by high-mass XRBs (HMXBs), allowing the study of a very different population with similar sensitivity due to the galaxy's similar distance. This characterization of a population of HMXB accretion states will provide valuable constraints for theoretical XRB population synthesis studies to their formation and evolution.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2022
- DOI:
- 10.3847/1538-4357/ac6351
- Bibcode:
- 2022ApJ...930...64Y
- Keywords:
-
- Neutron stars;
- Compact objects;
- Black holes;
- Triangulum Galaxy;
- Accretion;
- Stellar accretion;
- Classification;
- Ultraluminous x-ray sources;
- High mass x-ray binary stars;
- X-ray binary stars;
- Stellar classification;
- 1108;
- 288;
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- 14;
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- 1907;
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