808 research outputs found
A Multi-Wavelength, Multi-Epoch Study of the Soft X-Ray Transient Prototype, V616 Mon (A0620-00)
We have obtained optical and infrared photometry of the soft x-ray transient
prototype V616 Mon (A0620-00). From this photometry, we find a spectral type of
K4 for the secondary star in the system, which is consistent with spectroscopic
observations. We present J-, H-, and K-band light curves modeled with WD98 and
ELC. Combining detailed, independently run models for ellipsoidal variations
due to a spotted, non-spherical secondary star, and the observed ultraviolet to
infrared spectral energy distribution of the system, we show that the most
likely value for the orbital inclination is 40.75 +/- 3 deg. This inclination
angle implies a primary black hole mass of 11.0 +/- 1.9 solar masses.Comment: 29 pages (preprint format), including 7 figures and 4 tables,
accepted for publication in the Nov 2001 issue of A
Determining the spectroscopic mass ratio in interacting binaries: Application to X-Ray Nova Sco 1994
We present a model for determining the mass ratio in interacting binaries by
directly fitting the observed spectrum with synthetic spectra. We make direct
use of NextGen model atmospheres intensities which are the most comprehensive
and detailed models available for cool stars. We fully take into account the
varying temperature and gravity across the secondary star's photosphere, by
incorporating the synthetic spectra into the secondary star's Roche geometry.
As a result, we determine the exact rotationally broadened spectrum of the
secondary star and so eliminate the need for a limb-darkening law, and the
uncertainties associated with it. As an example we determine the mass ratio for
the well studied soft X-ray transient Nova Sco 1994. In order to obtain a more
accurate determination of the mass ratio, which does not depend on assumptions
about the rotation profile and limb-darkening coefficients, we use our model to
compute the exact rotationally broadened model spectrum, which we compare
directly with the observed intermediate resolution spectrum of Nova Sco 1994.
We determine the mass ratio of Nova Sco 1994 to be 0.419+/-0.028 (90 percent
confidence), which is the most accurate determination of the binary mass ratio
in an X-ray binary. This result combined with the binary mass function and
inclination angle gives a refined black hole mass of 5.99+\-0.42 Mo (90 percent
confidence). We also perform simulations which show that, for an F-type
secondary star, the standard rotation profile with zero and continuum value for
the line limb-darkening coefficient gives a value for q that brackets the value
found using the full geometrical treatment.Comment: 11 pages including 5 figures, accepted by MNRA
Identification of Cohesive Ends and Genes Encoding the Terminase of Phage 16-3
Cohesive ends of 16-3, a temperate phage of Rhizobium meliloti 41, have been identified as 10-base-long, 3âČ-protruding complementary G/C-rich sequences. terS and terL encode the two subunits of 16-3 terminase. Significant homologies were detected among the terminase subunits of phage 16-3 and other phages from various ecosystems
Orbital Parameters for the Black Hole Binary XTE J1650-500
(Shortened) We present R-band photometry of the X-ray transient and candidate
black hole binary XTE J1650-500 obtained between 2003 May and August with the
6.5m Clay Telescope. A timing analysis of these data reveals a photometric
period of 0.3205 +/- 0.0007 days (i.e. 7.63 hr) with a possible alias at 0.3785
days (9.12 hr). Our photometry completely rules out the previously published
spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the
15 archival ESO/VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.)
that were the basis of the previously published spectroscopic period. We used a
``restframe search'' technique that is well suited for cases when the
signal-to-noise ratio of individual spectra is low. The results confirmed the
photometric period of 0.3205 days, and rule out the alias period near 0.38
days. The best value for the velocity semiamplitude of the companion star is
K_2 = 435 +/- 30 km/sec, and the corresponding optical mass function is f(M) =
2.73 +/- 0.56 solar masses. The amplitude of the phased R-band light curve is
0.2 magnitudes, which gives a lower limit to the inclination of 50 +/- 3
degrees in the limiting case of no contribution to the R-band light curve from
the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass
ratios of other black hole binaries like A0620-00 or GRS 1124-683 (e.g. Q >~
10), then our lower limit to the inclination gives an upper limit to the mass
of the black hole in XTE J1650-500 of M_1 <~ 7.3 solar masses. However, the
mass can be considerably lower if the R-band flux is dominated by the accretion
disk. For example, if the accretion disk does contribute 80% of the flux, as
our preliminary results suggest, then the black hole mass would be only about 4
solar masses.Comment: Accepted to ApJ. 15 pages, 5 figures (two of degraded quality).
Revised after referee's Comments, conclusions are unchange
Inclination Effects and Beaming in Black Hole X-ray Binaries
We investigate the dependence of observational properties of black hole X-ray
binaries on the inclination angle i of their orbits. We find the following: (1)
Transient black hole binaries show no trend in their quiescent X-ray
luminosities as a function of i, suggesting that the radiation is not
significantly beamed. This is consistent with emission from an accretion disk.
If the X-rays are from a jet, then the Lorentz factor gamma of the jet is less
than 1.24 at the 90% confidence level. (2) The X-ray binary 4U1543-47 with i of
order 21 degrees has a surprisingly strong fluorescent iron line in the high
soft state. Quantifying an earlier argument by Park et al. (2004), we conclude
that if the continuum X-ray emission in this source is from a jet, then gamma <
1.04. (3) None of the known binaries has cos i 75 degrees. This
fact, plus the lack of eclipses among the 20 black hole binaries in our sample,
strongly suggests at the 99.5% confidence level that systems with large
inclination angles are hidden from view. The obscuration could be the result of
disk flaring, as suggested by Milgrom (1978) for neutron star X-ray binaries.
(4) Transient black hole binaries with i ~ 70-75 degrees have significantly
more complex X-ray light curves than systems with i < 65 degrees. This may be
the result of variable obscuration and/or variable height above the disk of the
radiating gas.Comment: 26 pages, to appear in The Astrophysical Journal, vol. 624, May 1,
200
Chandra observation of the fast X-ray transient IGR J17544-2619: evidence for a neutron star?
IGR J17544-2619 belongs to a distinct group of at least seven fast X-ray
transients that cannot readily be associated with nearby flare stars or
pre-main sequence stars and most probably are X-ray binaries with wind
accretion. Sofar, the nature of the accretor has been determined in only one
case (SAX J1819.3-2525/V4641 Sgr). We carried out a 20 ks Chandra ACIS-S
observation of IGR J17544-2619 which shows the source in quiescence going into
outburst. The Chandra position confirms the previous tentative identification
of the optical counterpart, a blue O9Ib supergiant at 3 to 4 kpc (Pellizza,
Chaty & Negueruela, in prep.). This is the first detection of a fast X-ray
transient in quiescence. The quiescent spectrum is very soft. The photon index
of 5.9+/-1.2 (90% confidence error margin) is much softer than 6 quiescent
black hole candidates that were observed with Chandra ACIS-S (Kong et al. 2002;
Tomsick et al. 2003). Assuming that a significant fraction of the quiescent
photons comes from the accretor and not the donor star, we infer that the
accretor probably is a neutron star. A fit to the quiescent spectrum of the
neutron star atmosphere model developed by Pavlov et al. (1992) and Zavlin et
al. (1996) implies an unabsorbed quiescent 0.5--10 keV luminosity of
(5.2+/-1.3) x 10^32 erg/s. We speculate on the nature of the brief outbursts.Comment: accepted for publication 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
Optical and Infrared Photometry of the Micro-Quasar GRO J1655-40 in Quiescence
We present BVIJK photometry of the black-hole candidate GRO J1655-40 in full
quiescence. We report a refined orbital period of 2.62191 +/- 0.00020 days. The
light curves are dominated by ellipsoidal variations from the secondary star.
We model the light curves with an upgraded code which includes a more accurate
treatment of limb darkening. Previous models containing a large cool disk are
ruled out, and indeed our data can be fit with a pure ellipsoidal light curve
without any disk contribution. In general agreement with previous results, we
derive a confidence region of the correlated quantities of inclination and mass
ratio, centered on an inclination of 70.2 +/ 1.9 degrees, and mass ratio 2.6
+/- 0.3, resulting in a primary mass M = 6.3 +/- 0.5 Mo (all 95% confidence).
The complex limits and errors on these values, and on the possible disk
contribution to the light curve, are discussed.Comment: 14 pages, 5 figures. To be published in The Astrophysical Journa
A Swift survey of accretion onto stellar-mass black holes
We present a systemic analysis of all of the stellar mass black hole binaries
(confirmed & candidate) observed by the Swift observatory up to June 2010. The
broad Swift bandpass enables a trace of disk evolution over an unprecedented
range in flux and temperature. The final data sample consists of 476 X-ray
spectra containing greater than 100 counts, in the 0.6 -- 10 keV band. This is
the largest sample of high quality CCD spectra of accreting black holes
published to date. In addition, strictly simultaneous data at optical/UV
wavelengths are available for 255 (54%) of these observations.
The data are modelled with a combination of an accretion disk and a hard
spectral component. For the hard component we consider both a simple power-law
and a thermal Comptonization model. An accretion disk is detected at greater
than the 5sigma confidence level in 61% of the observations. Lightcurves and
color-color diagrams are constructed for each system. Hardness luminosity and
disk fraction luminosity diagrams are constructed and are observed to be
consistent with those typically observed by RXTE, noting the sensitivity below
2 keV provided by Swift. The observed spectra have an average luminosity of ~
1% Eddington, though we are sensitive to accretion disks down to a luminosity
of 10^{-3} L_Edd. Thus this is also the largest sample of such cool accretion
disks studied to date. (abridged)Comment: 28 pages, 5 tables, 21 figures, Accepted for publication in ApJ. This
is the final revised versio
Suzaku Observations of the Galactic Center Microquasar 1E 1740.7-2942
We present two Suzaku observations of the Galactic center microquasar 1E
1740.7-2942 separated by approximately 700 days. The source was observed on
both occasions after a transition to the spectrally hard state. Significant
emission from 1E 1740.7-2942 is detected out to an energy of 300 keV, with no
spectral break or turnover evident in the data. We tentatively measure a lower
limit to the cut-off energy of ~ 380 keV. The spectra are found to be
consistent with a Comptonized corona on both occasions, where the high energy
emission is consistent with a hard power-law (\Gamma ~ 1.8) with a significant
contribution from an accretion disc with a temperature of ~ 0.4 keV at soft
X-ray energies. The measured value for the inner radius of the accretion disc
is found to be inconsistent with the picture whereby the disc is truncated at
large radii in the low-hard state and instead favours a radius close to the
ISCO (R_in ~ 10 - 20 R_g).Comment: 8 pages, 4 figures, formatted using emulateapj.cls. Accepted for
publication in Ap
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