Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18

Yoshimoto, Marina; Yoneyama, Tomokage; Noda, Hirofumi; Odaka, Hirokazu; Matsumoto, Hironori

doi:https://doi.org/10.3847/1538-4357/ad4e34

Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18

Yoshimoto, Marina; Yoneyama, Tomokage; Noda, Hirofumi et al.

Astrophysical Journal, 2024, 970(1), 8

Number of Access:479（2025-08-16 03:18 Counts）

Identifier to cite or link to this item: https://hdl.handle.net/11094/98254

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Title	Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18
Creator	CreatorName Yoshimoto, Marina
	NRID 1000090908774 1000090908774 CreatorName Yoneyama, Tomokage
	NRID 1000050725900 1000050725900 CreatorName Noda, Hirofumi
	NRID 1000050610820 1000050610820 researchmap permalink odakahirokazu odakahirokazu CreatorName Odaka, Hirokazu
	NRID 1000090311365 1000090311365 researchmap permalink hironori_matsumoto hironori_matsumoto Scopus Author ID 56973086400 56973086400 CreatorName Matsumoto, Hironori
Description	Yoshimoto M., Yoneyama T., Noda H., et al. Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18. Astrophysical Journal 970, 8 (2024); https://doi.org/10.3847/1538-4357/ad4e34.
Abstract	We present an analysis of X-ray observations of the ultraluminous X-ray source (ULX) in I Zw 18 based on archival data taken with Chandra, XMM-Newton, and Suzaku. This ULX is considered to be an intermediate-mass black hole candidate simply because it is in the lowest-metallicity environment among ULXs, where the formation of heavy black holes is facilitated. However, actual study of the ULX based on observations spanning for a long period has been too limited to determine its nature. In this study, we investigate the spectral evolution of the ULX up to 2014, combining the previously unpublished Suzaku data with those from the other two satellites. We derive a positive correlation of L ∝ T in 2.1 ± 0.4 between the bolometric luminosity L and inner-disk temperature T in on the basis of the multicolor disk blackbody model, where we exclude the Chandra data, which have the lowest luminosity and systematic residuals in the fitting. The nominal relation L ∝ T in 4 for the standard disk is rejected at a significance level of 1.5%. These results suggest that the ULX was in the slim-disk state during these observations except at the time of the Chandra observation, in which the ULX was likely to be in a different state. The apparent inner-disk radius appears negatively correlated with the inner-disk temperature. Moreover, we find a radial dependence of the disk temperature of T(r) ∝ r −p with p < 0.75, which also supports the hypothesis that the ULX has a slim disk. Therefore, the I Zw 18 ULX is most likely to be powered by a stellar-mass compact object in supercritical accretion.
Publisher	Institute of Physics
Source Title	Astrophysical Journal
Volume (Issue)	970(1)
Page	8
Date of Issued	2024-07-11
Language	English
Handle URL	https://hdl.handle.net/11094/98254
PISSN	0004637X
eISSN	15384357
Relation.isIdenticalTo	DOI (Publisher Version) https://doi.org/10.3847/1538-4357/ad4e34
Access Rights	open access
CopyRight	This article is licensed under a Creative Commons Attribution 4.0 International License.
oaire:version	Version of Record
Category	学術雑誌論文 Journal Article

Resource Type	journal article
Local Type	Journal Article
DCTERMS.bibliographicCitation	Astrophysical Journal. 2024, 970(1), p. 8
DC.title	Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18
DC.creator	Yoshimoto, Marina
	Yoneyama, Tomokage
	Noda, Hirofumi
	Odaka, Hirokazu
	Matsumoto, Hironori
DC.publisher	Institute of Physics
DC.language' scheme='DCTERMS.RFC1766	English
DCTERMS.issued' scheme='DCTERMS.W3CDTF	2024-07-11
DC.identifier	https://doi.org/10.3847/1538-4357/ad4e34
DC.description	Yoshimoto M., Yoneyama T., Noda H., et al. Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18. Astrophysical Journal 970, 8 (2024); https://doi.org/10.3847/1538-4357/ad4e34.
DCTERMS.abstract	We present an analysis of X-ray observations of the ultraluminous X-ray source (ULX) in I Zw 18 based on archival data taken with Chandra, XMM-Newton, and Suzaku. This ULX is considered to be an intermediate-mass black hole candidate simply because it is in the lowest-metallicity environment among ULXs, where the formation of heavy black holes is facilitated. However, actual study of the ULX based on observations spanning for a long period has been too limited to determine its nature. In this study, we investigate the spectral evolution of the ULX up to 2014, combining the previously unpublished Suzaku data with those from the other two satellites. We derive a positive correlation of L ∝ T in 2.1 ± 0.4 between the bolometric luminosity L and inner-disk temperature T in on the basis of the multicolor disk blackbody model, where we exclude the Chandra data, which have the lowest luminosity and systematic residuals in the fitting. The nominal relation L ∝ T in 4 for the standard disk is rejected at a significance level of 1.5%. These results suggest that the ULX was in the slim-disk state during these observations except at the time of the Chandra observation, in which the ULX was likely to be in a different state. The apparent inner-disk radius appears negatively correlated with the inner-disk temperature. Moreover, we find a radial dependence of the disk temperature of T(r) ∝ r −p with p < 0.75, which also supports the hypothesis that the ULX has a slim disk. Therefore, the I Zw 18 ULX is most likely to be powered by a stellar-mass compact object in supercritical accretion.
DC.rights	This article is licensed under a Creative Commons Attribution 4.0 International License.
DC.format	98254
citation_title	Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18
citation_author	Yoshimoto, Marina
	Yoneyama, Tomokage
	Noda, Hirofumi
	Odaka, Hirokazu
	Matsumoto, Hironori
citation_publisher	Institute of Physics
citation_language	English
citation_date	2024-07-11
citation_journal_title	Astrophysical Journal
citation_volume	970
citation_issue	1
citation_firstpage	8
citation_doi	https://doi.org/10.3847/1538-4357/ad4e34
citation_public_url	https://hdl.handle.net/11094/98254

Possible Supercritical Accretion on the Ultraluminous X-Ray Source in the Metal-poor Galaxy I Zw 18

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