2004A&A...423..955S


C.D.S. - SIMBAD4 rel 1.7 - 2019.11.20CET19:28:43

2004A&A...423..955S - Astronomy and Astrophysics, volume 423, 955-963 (2004/9-1)

X-ray flares from the ultra-luminous X-ray source in NGC 5408.

SORIA R., MOTCH C., READ A.M. and STEVENS I.R.

Abstract (from CDS):

We have studied an ultra-luminous X-ray source (ULX) in the dwarf galaxy NGC5408 with a series of XMM-Newton observations, between 2001 July and 2003 January. We find that its X-ray spectrum is best fitted with a power law of photon index Γ≃2.6-2.9 and a thermal component with blackbody temperature kTbb≃0.12-0.14keV. These spectral features, and the inferred luminosity ≃1040erg/s in the 0.3-12keV band, are typical of bright ULXs in nearby dwarf galaxies. The blackbody plus power-law model is a significantly better fit than either a simple power law or a broken power law (although the latter model is also acceptable at some epochs). Doppler-boosted emission from a relativistic jet is not required, although we cannot rule out this scenario. Our preliminary timing analysis shows flaring behaviour which we interpret as variability in the power-law component, on timescales of ∼102s. The hard component is suppressed during the dips, while the soft thermal component is consistent with being constant. The power density spectrum is flat at low frequencies, has a break at νb≃2.5mHz, and has a slope ≃-1 at higher frequencies. A comparison with the power spectra of Cyg X-1 and of a sample of other BH candidates and AGN suggests a mass of ∼102M. It is also possible that the BH is at the upper end of the stellar-mass class (M∼50 M), in a phase of moderately super-Eddington accretion. The formation of such a massive BH via normal stellar evolution may have been favoured by the very metal-poor environment of NGC 5408.

Abstract Copyright:

Journal keyword(s): black hole physics - galaxies: individual: NGC 5408 - X-rays: galaxies - X-ray: stars - accretion, accretion disks

Simbad objects: 7

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Number of rows : 7

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 1313 G 03 18 16.046 -66 29 53.74   10.06 10.0 9.40 10.4 ~ 587 2
2 NGC 4559 H2G 12 35 57.6399424117 +27 57 35.859639262   10.46 10.01     ~ 521 1
3 [FK2005] 25 ULX 14 03 19.63 -41 22 58.7           ~ 190 0
4 NGC 5408 EmG 14 03 20.907 -41 22 39.75   12.59   11.96 12.2 ~ 307 3
5 V* V381 Nor HXB 15 50 58.6520652623 -56 28 35.309070422   17.95 16.6     K3III 1000 0
6 Granat 1915+105 LXB 19 15 11.54938 +10 56 44.7585           ~ 2235 0
7 HD 226868 HXB 19 58 21.6758193269 +35 12 05.782512305 9.38 9.72 8.91 8.42   O9.7Iabpvar 3849 0

    Equat.    Gal    SGal    Ecl

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2019.11.20-19:28:43

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