Revealing the nature of the ULX and X-ray population of the spiral galaxy NGC 4088

Journal Article · Sun Apr 20 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/785/2/121· OSTI ID:22357107

Mezcua, M. ^[1]; Fabbiano, G. ^[2]; Gladstone, J. C. ^[3]; Farrell, S. A. ^[4]

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1. Instituto de Astrofísica de Canarias (IAC), E-38200 La Laguna, Tenerife (Spain)
2. Harvard-Smithsonian Center for Astrophysics (CfA), 60 Garden Street, Cambridge, MA 02138 (United States)
3. Department of Physics, University of Alberta, 11322-89 Avenue, Edmonton, Alberta T6G 2G7 (Canada)
4. Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, NSW 2006 (Australia)

We present the first Chandra and Swift X-ray study of the spiral galaxy NGC 4088 and its ultraluminous X-ray source (ULX N4088-X1). We also report very long baseline interferometry (VLBI) observations at 1.6 and 5 GHz performed quasi-simultaneously with the Swift and Chandra observations, respectively. Fifteen X-ray sources are detected by Chandra within the D25 ellipse of NGC 4088, from which we derive the X-ray luminosity function (XLF) of this galaxy. We find the XLF is very similar to those of star-forming galaxies and estimate a star-formation rate of 4.5 M {sub ☉} yr{sup –1}. The Chandra detection of the ULX yields its most accurate X-ray position, which is spatially coincident with compact radio emission at 1.6 GHz. The ULX Chandra X-ray luminosity, L {sub 0.2-10.0} {sub keV} = 3.4 × 10{sup 39} erg s{sup –1}, indicates that N4088-X1 could be located at the high-luminosity end of the high-mass X-ray binary (HMXB) population of NGC 4088. The estimates of the black hole (BH) mass and ratio of radio to X-ray luminosity of N4088-X1 rule out a supermassive BH nature. The Swift X-ray spectrum of N4088-X1 is best described by a thermal Comptonization model and presents a statistically significant high-energy cutoff. We conclude that N4088-X1 is most likely a stellar remnant BH in an HMXB, probably fed by Roche lobe overflow, residing in a super-Eddington ultraluminous state. The 1.6 GHz VLBI source is consistent with radio emission from possible ballistic jet ejections in this state.

• OSTI ID: 22357107
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 785; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
DETECTION
EMISSION
GALAXIES
GHZ RANGE
INTERFEROMETRY
LUMINOSITY
MASS
ROCHE EQUIPOTENTIALS
STARS
X RADIATION
X-RAY SOURCES
X-RAY SPECTRA