THE FIRST DETECTION OF [O IV] FROM AN ULTRALUMINOUS X-RAY SOURCE WITH SPITZER. I. OBSERVATIONAL RESULTS FOR HOLMBERG II ULX

Journal Article · Fri Jan 01 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/708/1/354· OSTI ID:21392465

Berghea, C T ^[1]; Dudik, R P ^[2]; Weaver, K A

---

1. Physics Department, Catholic University of America, Washington, DC 20064 (United States)
2. United States Naval Observatory, Washington, DC 20392 (United States)

We present the first Spitzer Infrared Spectrograph observations of the [O IV] 25.89 mum emission line detected from the ultraluminous X-ray source (ULX) in Holmberg II. This line is a well-established signature of high excitation, usually associated with active galactic nucleus (AGN). Its detection suggests that the ULX has a strong impact on the surrounding gas. A Spitzer high-resolution spectral map shows that the [O IV] is coincident with the X-ray position of the ULX. The ratios of the [O IV] to lower-ionization lines are similar to those observed in AGN, suggesting that a strong UV and X-ray source is responsible for the photoionization. The best XMM-Newton data are used to model the X-ray band which is then extrapolated into the UV. We perform infrared and ultraviolet photometry, and use previously published optical and radio data to construct the full spectral energy distribution (SED) for the ULX and its companion. The preferred model to describe the SED includes an accretion disk which dominates the soft X-rays but contributes little at UV and optical wavelengths. The optical counterpart is consistent with a B supergiant as previously suggested in other studies. The bolometric luminosity of the ULX suggests the presence of an intermediate-mass black hole with mass >85 M{sub sun} for sub-Eddington accretion or, alternatively, a stellar-mass black hole that is accreting at super-Eddington rates. In a follow-up second paper, we perform detailed photoionization modeling of the infrared lines in order to constrain the bolometric luminosity of the ULX.

• OSTI ID: 21392465
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 708; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
BOLOMETERS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
EMISSION
ENERGY SPECTRA
GALAXIES
IONIZATION
IONIZING RADIATIONS
LUMINOSITY
MEASURING INSTRUMENTS
OPTICAL PROPERTIES
PHOTOIONIZATION
PHOTOMETRY
PHYSICAL PROPERTIES
RADIATIONS
SIMULATION
SOFT X RADIATION
SPECTRA
ULTRAVIOLET RADIATION
WAVELENGTHS
X RADIATION