Bibcode
Mezcua, M.; Fabbiano, G.; Gladstone, J. C.; Farrell, S. A.; Soria, R.
Bibliographical reference
The Astrophysical Journal, Volume 785, Issue 2, article id. 121, 9 pp. (2014).
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4
2014
Journal
Citations
6
Refereed citations
5
Description
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 ☉ yr–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 0.2-10.0 keV = 3.4 ×
1039 erg s–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.
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