1,993 research outputs found
A new luminous supersoft X-ray source in NGC 300
Context. We report the discovery of a new luminous supersoft source, XMMU J005455.0−374117, in the nearby spiral galaxy GC 300, in XMM-Newton observations performed on 2005 May 22 and on 2005 November 25. The source is not present in ROSAT data nor in the previous XMM-Newton observations of 2000 December/2001 January. The unique luminous supersoft source,XMMU J005510.7−373855, detected in the 1992 May/June ROSAT data and in the 2000/2001 XMM-Newton data, fell below detectability. This source already appeared highly variable in ROSAT observations.
Aims. We report on the temporal and spectral analysis of this new supersoft source (SSS) and compare its properties with the previous known SSS.
Methods. We present the light curves of the SSS, model its spectrum and estimate the corresponding flux and luminosities.
Results. The light curve of XMMU J005455.0−374117 does not show large fluctuations in any of the observations and its spectrum can be modelled with an absorbed blackbody with kT ∼ 60 eV. The corresponding bolometric luminosity is 8.1+1.4
−4.5 × 1038 erg s−1 in the first observation and drops to 2.2+0.5 −1.4 × 1038 erg s−1 six months later. No optical source brighter than mV ∼ 21.7 mag is found coincident with its position.
Conclusions. The luminosity of these two SSSs is higher than what has been found for “classical” SSSs. Their nature could be explained by beamed emission from steady nuclear burning of hydrogen onto white dwarfs, or accretion onto stellar-mass black hole with matter outflow or observed at high inclination angle. The presence of an intermediate-mass black hole seems unlikely in our case
On the optical counterpart of NGC300 X-1 and the global Wolf-Rayet content of NGC300
(Conext:) Surveys of Wolf-Rayet (WR) populations in nearby galaxies provide
tests of evolutionary models plus Type Ib/c supernova progenitors. This
spectroscopic study complements the recent imaging survey of the spiral galaxy
NGC 300 by Schild et al. (Aims): Revisions to the known WR content of NGC 300
are presented. We investigate the WR nature of candidate #41 from Schild et al.
which is spatially coincident with the bright X-ray point source NGC 300 X-1;
(Methods:) VLT/FORS2 multi-object spectroscopy of WR candidates in NGC 300 is
obtained; (Results:) We establish an early-type WN nature of #41, i.e. similar
to the optical counterpart of IC 10 X-1, which closely resembles NGC 300 X-1.
We confirm 9 new WR stars, bringing the current WR census of the inner disk to
31, with N(WC)/N(WN)~0.9. (Conclusions:) If #41 is the optical counterpart for
NGC 300 X-1, we estimate a WR mass of 38 Msun based upon ground-based
photometry, from which a black hole mass of > 10 Msun results from the 32.8 hr
period of the system and WR wind velocity of 1250 km/s. We estimate an 95%
completeness among WC stars and 70% among WN stars, such that the total WR
content is ~40, with N(WC)/N(WN)~0.7. From the Halpha-derived star formation
rate of the inner galaxy, we infer N(WR)/N(O)~0.04Comment: 5 pages, 5 figures, accepted for A&A Letter
An ultraluminous supersoft source with a 4 hour modulation in NGC 4631
Context. Supersoft X-ray sources (SSSs) are characterised by very low
temperatures (< 100 eV). Classical SSSs have bolometric luminosities in the
range of 10^36-10^38 erg/s and are modelled with steady nuclear burning of
hydrogen on the surfaces of white dwarfs. However, several SSSs have been
discovered with much higher luminosities. Their nature is still unclear. Aims.
We report the discovery of a 4h modulation for an ultraluminous SSS in the
nearby edge-on spiral galaxy NGC 4631, observed with XMM-Newton in 2002 June.
Temporal and spectral analysis of the source is performed. Methods. We use a
Lomb-Scargle periodogram analysis for the period search and evaluate the
confidence level using Monte-Carlo simulations. We measure the source
temperature, flux and luminosity through spectral fitting. Results. A
modulation of 4.2+-0.4 h (3 sigma error) was found for the SSS with a
confidence level >99%. Besides dips observed in the light curve, the flux
decreased by a factor of 3 within ~10h. The spectrum can be described with an
absorbed blackbody model with kT~67eV. The absorbed luminosity in the 0.2-2 kev
energy band was 2.7x10^38 erg/sec while the bolometric luminosity was a hundred
time higher (3.2x10^40 erg/s), making the source one of the most luminous of
its class, assuming the best fit model is correct. Conclusions. This source is
another very luminous SSS for which the standard white dwarf interpretation
cannot be applied, unless a strong beaming factor is considered. A stellar-mass
black hole accreting at a super Eddington rate is a more likely interpretation,
where the excess of accreted matter is ejected through a strong optically-thick
outflow. The 4 h modulation could either be an eclipse from the companion star
or the consequence of a warped accretion disk.Comment: 4 pages, 4 figures, accepted as a Letter in Astronomy & Astrophysic
NGC 300 X-1 is a Wolf-Rayet/Black-Hole binary
We present VLT/FORS2 time-series spectroscopy of the Wolf-Rayet star #41 in
the Sculptor group galaxy NGC 300. We confirm a physical association with NGC
300 X-1, since radial velocity variations of the HeII 4686 line indicate an
orbital period of 32.3 +/- 0.2 hr which agrees at the 2 sigma level with the
X-ray period from Carpano et al. We measure a radial velocity semi-amplitude of
267 +/- 8 km/s, from which a mass function of 2.6 +/- 0.3 Msun is obtained. A
revised spectroscopic mass for the WN-type companion of 26+7-5 Msun yields a
black hole mass of 20 +/- 4 Msun for a preferred inclination of 60-75 deg. If
the WR star provides half of the measured visual continuum flux, a reduced WR
(black hole) mass of 15 +4 -2.5 Msun (14.5 +3 -2.5 Msun) would be inferred. As
such, #41/NGC 300 X-1 represents only the second extragalactic Wolf-Rayet plus
black-hole binary system, after IC 10 X-1. In addition, the compact object
responsible for NGC 300 X-1 is the second highest stellar-mass black hole known
to date, exceeded only by IC 10 X-1.Comment: 5 pages, 6 figures, MNRAS Letters in press. Images and animations
available from http://www.eso.org/public/news/eso1004/ at 11am GMT on 27 Jan
1
X-ray properties of NGC 300. I, Global properties of X-ray point sources and their optical counterparts
We present X-ray properties of NGC 300 point sources, extracted from 66 ks of XMM-Newton data taken in 2000 December and 2001 January. A total of 163 sources were detected in the energy range of 0.3–6 keV. We report on the global properties of the sources detected inside the D 25
optical disk, such as the hardness ratio and X-ray fluxes, and on the properties of their optical counterparts found in B, V, and R images from the 2.2 m MPG/ESO telescope. Furthermore, we cross-correlate the X-ray sources with SIMBAD, the USNO-A2.0 catalog, and radio catalogues
UTM, a universal simulator for lightcurves of transiting systems
The Universal Transit Modeller (UTM) is a light-curve simulator for all kinds
of transiting or eclipsing configurations between arbitrary numbers of several
types of objects, which may be stars, planets, planetary moons, and planetary
rings. Applications of UTM to date have been mainly in the generation of
light-curves for the testing of detection algorithms. For the preparation of
such test for the Corot Mission, a special version has been used to generate
multicolour light-curves in Corot's passbands. A separate fitting program, UFIT
(Universal Fitter) is part of the UTM distribution and may be used to derive
best fits to light-curves for any set of continuously variable parameters.
UTM/UFIT is written in IDL code and its source is released in the public domain
under the GNU General Public License.Comment: 4 pages, 2 figures, to appear in Proc. of'Transiting Planets', IAU
Symposium 25
Optical Spectra of SNR Candidates in NGC 300
We present moderate-resolution (<5A) long-slit optical spectra of 51 nebular
objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter
Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting
the criterion of [SII]/Ha>=0.4 to confirm supernova remnants (SNRs) from
optical spectra, we find that of 28 objects previously proposed as SNRs from
optical observations, 22 meet this criterion with six showing [SII]/Ha of less
than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated
with the 28 previously proposed SNRs. Of these four, three (included in the 22
above) meet the criterion. In all, 22 of the 51 nebular objects meet the
[SII]/Ha criterion as SNRs while the nature of the remaining 29 objects remains
undetermined by these observations.Comment: Accepted for publication in Astrophysics & Space Scienc
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