dorsal/arxiv
View SchemaHow Beaming Shapes the Demographics of Ultraluminous X-ray Sources?
| Authors | Ying-Han Mao, Xiang-Dong Li |
|---|---|
| Categories | |
| ArXiv ID | 2601.09425vv1 |
| URL | https://arxiv.org/abs/2601.09425 |
| License | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
Abstract
Ultraluminous X-ray sources (ULXs) are off-nuclear compact objects with apparent luminosities above 10^39 erg/s, often exceeding the Eddington limit for stellar-mass black holes. Beaming is a commonly invoked mechanism to explain their extreme brightness, and the dependence of the beaming factor on accretion rate is a critical parameter. In this work, we investigate how different beaming prescriptions affect the predicted properties of ULX populations. Using binary population synthesis, we construct synthetic X-ray luminosity functions (XLFs) for both classical and log-modified beaming models at solar and sub-solar metallicities. The classical model predicts a larger intrinsic number of bright ULXs, but strong beaming reduces their observable fraction, resulting in fewer visible ULXs compared to the log-modified model. The log-modified prescription yields a shallower slope at high-luminosity, aligning better with observed XLFs, and increases the fraction of observable neutron star ULXs above 10^39 erg/s. These results underscore the significant role of the beaming law in shaping ULX statistical distributions and assessing neutron star contributions to the population.
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"abstract": "Ultraluminous X-ray sources (ULXs) are off-nuclear compact objects with apparent luminosities above 10^39 erg/s, often exceeding the Eddington limit for stellar-mass black holes. Beaming is a commonly invoked mechanism to explain their extreme brightness, and the dependence of the beaming factor on accretion rate is a critical parameter. In this work, we investigate how different beaming prescriptions affect the predicted properties of ULX populations. Using binary population synthesis, we construct synthetic X-ray luminosity functions (XLFs) for both classical and log-modified beaming models at solar and sub-solar metallicities. The classical model predicts a larger intrinsic number of bright ULXs, but strong beaming reduces their observable fraction, resulting in fewer visible ULXs compared to the log-modified model. The log-modified prescription yields a shallower slope at high-luminosity, aligning better with observed XLFs, and increases the fraction of observable neutron star ULXs above 10^39 erg/s. These results underscore the significant role of the beaming law in shaping ULX statistical distributions and assessing neutron star contributions to the population.",
"arxiv_id": "2601.09425",
"authors": [
"Ying-Han Mao",
"Xiang-Dong Li"
],
"categories": [
"astro-ph.HE"
],
"license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
"title": "How Beaming Shapes the Demographics of Ultraluminous X-ray Sources?",
"url": "https://arxiv.org/abs/2601.09425",
"version": "v1"
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