X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters

Kristen C. Dage; Stephen E. Zepf; Mark B. Peacock; Arash Bahramian; Omid Noroozi; Arunav Kundu; Thomas J. Maccarone

doi:10.1093/mnras/stz479

X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters

Kristen C. Dage, Stephen E. Zepf, Mark B. Peacock, Arash Bahramian, Omid Noroozi, Arunav Kundu, Thomas J. Maccarone

Physics

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7 Scopus citations

Abstract

A number of ultraluminous X-ray sources (ULXs) are physically associated with extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis of eight of the brightest of these sources. We fit the spectra of the GC ULXs to single power law and single disc models. We find that the data never require that any of the sources change between a disc and a power law across successive observations. The GC ULXs best fit by a single disc show a bimodal distribution: they either have temperatures well below 0.5 keV, or variable temperatures ranging above 0.5 keV up to 2 keV. The GC ULXs with low kT have significant changes in luminosity but show little or no change in kT. By contrast, the sources with higher kT either change in both kT and L_X together, or show no significant change in either parameter. Notably, the X-ray characteristics may be related to the optical properties of these ULXs, with the two lowest kT sources showing optical emission lines.

Original language	English
Pages (from-to)	1694-1707
Number of pages	14
Journal	Monthly Notices of the Royal Astronomical Society
Volume	485
Issue number	2
DOIs	https://doi.org/10.1093/mnras/stz479
State	Published - Feb 15 2019

Keywords

Accretion
Galaxies: individual: NGC 1399
Globular clusters:general
NGC 4472
NGC 4649
X-rays: binaries

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10.1093/mnras/stz479

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@article{985566b4b5e4401ca58288b0d03b354a,

title = "X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters",

abstract = "A number of ultraluminous X-ray sources (ULXs) are physically associated with extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis of eight of the brightest of these sources. We fit the spectra of the GC ULXs to single power law and single disc models. We find that the data never require that any of the sources change between a disc and a power law across successive observations. The GC ULXs best fit by a single disc show a bimodal distribution: they either have temperatures well below 0.5 keV, or variable temperatures ranging above 0.5 keV up to 2 keV. The GC ULXs with low kT have significant changes in luminosity but show little or no change in kT. By contrast, the sources with higher kT either change in both kT and LX together, or show no significant change in either parameter. Notably, the X-ray characteristics may be related to the optical properties of these ULXs, with the two lowest kT sources showing optical emission lines.",

keywords = "Accretion, Galaxies: individual: NGC 1399, Globular clusters:general, NGC 4472, NGC 4649, X-rays: binaries",

author = "Dage, {Kristen C.} and Zepf, {Stephen E.} and Peacock, {Mark B.} and Arash Bahramian and Omid Noroozi and Arunav Kundu and Maccarone, {Thomas J.}",

note = "Funding Information: KCD, SEZ, and MBP acknowledge support from Chandra grant GO4-15089A and NASA grant number HST-AR-13923.001-A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. SEZ and MBP also acknowledge support from the NASA ADAP grant NNX15AI71G. This research has made use of data obtained from the Chandra Data Archive and the Chandra Source Catalog. We also acknowledge use of NASA{\textquoteright}s Astrophysics Data System and Arxiv. The authors thank Claire Kopenhafer, Jay Strader, and Ryan Urquhart for helpful discussion. We also thank the anonymous referees for their suggestions to improve the paper. Publisher Copyright: {\textcopyright} 2019 The Author(s).",

year = "2019",

month = feb,

day = "15",

doi = "10.1093/mnras/stz479",

language = "English",

volume = "485",

pages = "1694--1707",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

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X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters. / Dage, Kristen C.; Zepf, Stephen E.; Peacock, Mark B.; Bahramian, Arash; Noroozi, Omid; Kundu, Arunav; Maccarone, Thomas J.

In: Monthly Notices of the Royal Astronomical Society, Vol. 485, No. 2, 15.02.2019, p. 1694-1707.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters

AU - Dage, Kristen C.

AU - Zepf, Stephen E.

AU - Peacock, Mark B.

AU - Bahramian, Arash

AU - Noroozi, Omid

AU - Kundu, Arunav

AU - Maccarone, Thomas J.

N1 - Funding Information: KCD, SEZ, and MBP acknowledge support from Chandra grant GO4-15089A and NASA grant number HST-AR-13923.001-A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. SEZ and MBP also acknowledge support from the NASA ADAP grant NNX15AI71G. This research has made use of data obtained from the Chandra Data Archive and the Chandra Source Catalog. We also acknowledge use of NASA’s Astrophysics Data System and Arxiv. The authors thank Claire Kopenhafer, Jay Strader, and Ryan Urquhart for helpful discussion. We also thank the anonymous referees for their suggestions to improve the paper. Publisher Copyright: © 2019 The Author(s).

PY - 2019/2/15

Y1 - 2019/2/15

N2 - A number of ultraluminous X-ray sources (ULXs) are physically associated with extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis of eight of the brightest of these sources. We fit the spectra of the GC ULXs to single power law and single disc models. We find that the data never require that any of the sources change between a disc and a power law across successive observations. The GC ULXs best fit by a single disc show a bimodal distribution: they either have temperatures well below 0.5 keV, or variable temperatures ranging above 0.5 keV up to 2 keV. The GC ULXs with low kT have significant changes in luminosity but show little or no change in kT. By contrast, the sources with higher kT either change in both kT and LX together, or show no significant change in either parameter. Notably, the X-ray characteristics may be related to the optical properties of these ULXs, with the two lowest kT sources showing optical emission lines.

AB - A number of ultraluminous X-ray sources (ULXs) are physically associated with extragalactic globular clusters (GCs). We undertake a systematic X-ray analysis of eight of the brightest of these sources. We fit the spectra of the GC ULXs to single power law and single disc models. We find that the data never require that any of the sources change between a disc and a power law across successive observations. The GC ULXs best fit by a single disc show a bimodal distribution: they either have temperatures well below 0.5 keV, or variable temperatures ranging above 0.5 keV up to 2 keV. The GC ULXs with low kT have significant changes in luminosity but show little or no change in kT. By contrast, the sources with higher kT either change in both kT and LX together, or show no significant change in either parameter. Notably, the X-ray characteristics may be related to the optical properties of these ULXs, with the two lowest kT sources showing optical emission lines.

KW - Accretion

KW - Galaxies: individual: NGC 1399

KW - Globular clusters:general

KW - NGC 4472

KW - NGC 4649

KW - X-rays: binaries

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U2 - 10.1093/mnras/stz479

DO - 10.1093/mnras/stz479

M3 - Article

AN - SCOPUS:85062884060

VL - 485

SP - 1694

EP - 1707

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -

X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters

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Keywords

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