67 research outputs found
A 15.65 solar mass black hole in an eclipsing binary in the nearby spiral galaxy Messier 33
Stellar-mass black holes are discovered in X-ray emitting binary systems,
where their mass can be determined from the dynamics of their companion stars.
Models of stellar evolution have difficulty producing black holes in close
binaries with masses >10 solar masses, which is consistent with the fact that
the most massive stellar black holes known so all have masses within 1 sigma of
10 solar masses. Here we report a mass of 15.65 +/- 1.45 solar masses for the
black hole in the recently discovered system M33 X-7, which is located in the
nearby galaxy Messier 33 (M33) and is the only known black hole that is in an
eclipsing binary. In order to produce such a massive black hole, the progenitor
star must have retained much of its outer envelope until after helium fusion in
the core was completed. On the other hand, in order for the black hole to be in
its present 3.45 day orbit about its 70.0 +/- 6.9 solar mass companion, there
must have been a ``common envelope'' phase of evolution in which a significant
amount of mass was lost from the system. We find the common envelope phase
could not have occured in M33 X-7 unless the amount of mass lost from the
progenitor during its evolution was an order of magnitude less than what is
usually assumed in evolutionary models of massive stars.Comment: To appear in Nature October 18, 2007. Four figures (one color figure
degraded). Differs slightly from published version. Supplementary Information
follows in a separate postin
THE INCLINATION OF THE SOFT X-RAY TRANSIENT A0620–00 AND THE MASS OF ITS BLACK HOLE
We analyze photometry of the soft X-ray transient A0620 – 00 spanning nearly 30 years, including previously published and previously unpublished data. Previous attempts to determine the inclination of A0620 using subsets of these data have yielded a wide range of measured values of i. Differences in the measured value of i have been due to changes in the shape of the light curve and uncertainty regarding the contamination from the disk. We give a new technique for estimating the disk fraction and find that disk light is significant in all light curves, even in the infrared. We also find that all changes in the shape and normalization of the light curve originate in a variable disk component. After accounting for this disk component, we find that all the data, including light curves of significantly different shapes, point to a consistent value of i. Combining results from many separate data sets, we find i = 51fdg0 ± 0fdg9, implying M = 6.6 ± 0.25 M ☉. Using our dynamical model and zero-disk stellar VIH magnitudes, we find d = 1.06 ± 0.12 kpc. Understanding the disk origin of nonellipsoidal variability may assist with making reliable determinations of i in other systems, and the fluctuations in disk light may provide a new observational tool for understanding the three-dimensional structure of the accretion disk.National Science Foundation (U.S.) (NSF Graduate Research Fellowship DGE-0202738)National Science Foundation (U.S.) (NSF/AST grant 0407063)National Science Foundation (U.S.) (NSF/AST grant 0707627
Evidence for a black-hole in the X-ray transient XTE J1859+226
We present the results of time-resolved optical photometry and spectroscopy
of the X-ray transient XTE J1859+226 (V406 Vul). Photometric observations taken
during 2000 and 2008 reveals the presence of the secondary star's ellipsoidal
modulation. Further photometry obtained in 2010 shows the system ~1 mag
brighter than its quiescence level and the ellipsoidal modulation diluted by
strong flaring activity. Spectroscopic data obtained with the 10.4-m GTC in
2010 reveals radial velocity variations of ~500 km/s over 3 h. A simultaneous
fit to the photometry and spectroscopy using sinusoids to represent the
secondary star's ellipsoidal and radial velocity variations, yields an orbital
period of 6.58+-0.05 h and a secondary star's radial velocity semi-amplitude of
K_2= 541+-70 km/s. The implied mass function is f(M)=4.5+-0.6 Msun,
significantly lower than previously reported but consistent with the presence
of a black hole in XTE J1859+226. The lack of eclipses sets an upper limit to
the inclination of 70 degrees which yields a lower limit to the black hole mass
of 5.42 Msun.Comment: Accepted for publication in MNRAS. Contains 5 pages and 4 figure
The Mass Distribution of Stellar Black Holes
We examine the distribution of masses of black holes in transient low mass
X-ray binary systems. A Bayesian analysis suggests that it is probable that six
of the seven systems with measured mass functions have black hole masses
clustered near seven solar masses. There appears to be a significant gap
between the masses of these systems and those of the observed neutron stars.
The remaining source, V404 Cyg, has a mass significantly larger than the
others, and our analysis suggests that it is probably drawn from a different
distribution. Selection effects do not appear to play a role in producing the
observed mass distribution, which may be explained by currently unknown details
of the supernova explosions and of binary evolution prior to the supernova.Comment: 22 pages including figures, submitted to Ap
The Spin of the Black Hole in the Soft X-Ray Transient A0620-00
During its year-long outburst in 1975–76, the transient source A0620–00 reached an intensity of 50 Crab, an all-time record for any X-ray binary. The source has been quiescent since then. We have recently determined accurate values for the black hole (BH) mass, orbital inclination angle, and distance. Building on these results, we have measured the radius of the inner edge of the accretion disk around the BH primary by fitting its thermal continuum spectrum to our version of the relativistic Novikov–Thorne thin-disk model. We have thereby estimated the spin of the BH. Although our spin estimate depends on a single high-quality spectrum, which was obtained in 1975 by OSO-8, we are confident of our result because of the consistent values of the inner-disk radius that we have obtained for hundreds of observations of other sources: H1743-322, XTE J1550-564, and notably LMC X-3. We have determined the dimensionless spin parameter of the BH to be a∗ = 0.12 ± 0.19, with a∗ −0.59 at the 3σ level of confidence. This result takes into account all sources of observational and model-parameter uncertainties. Despite the low spin, the intensity and properties of the radio counterpart, both in outburst and quiescence, attest to the presence of a strong jet. If jets are driven by BH spin, then current models indicate that jet power should be a steeply increasing function of a∗. Consequently, the low spin of A0620–00 suggests that its jet may be disk driven.Astronom
REFINED ORBITAL SOLUTION AND QUIESCENT VARIABILITY IN THE BLACK HOLE TRANSIENT GS 1354-64 (= BW Cir)
In Casares et al. we presented the first radial velocity curve of the companion star to BW Cir which demonstrates the presence of a black hole in this historical X-ray transient. But these data were affected by aliasing and two possible periods at 2.5445 days and 2.5635 days were equally possible. Here we present new spectroscopic data that enable us to break the 1-year aliasing and confirm 2.5445 days as the correct orbital period. We also present R-band photometry over 14 years, which reveals the presence of important flaring activity dominating the light curves.Spain. Ministerio de Ciencia y Tecnología (Spanish MCYT grant AYA2002-0036)Spain. Ministerio de Ciencia y Tecnología (programme Ramon y Cajal)Chandra X-ray Center (U.S.) (NASA Contract NAS8-03060
BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
During the last ~50 years, the population of black hole candidates in X-ray
binaries has increased considerably with 59 Galactic objects detected in
transient low-mass X-ray binaries, plus a few in persistent systems (including
~5 extragalactic binaries). We collect near-infrared, optical and X-ray
information spread over hundreds of references in order to study the population
of black holes in X-ray transients as a whole. We present the most updated
catalogue of black hole transients, which contains X-ray, optical and
near-infrared observations together with their astrometric and dynamical
properties. It provides new useful information in both statistical and
observational parameters providing a thorough and complete overview of the
black hole population in the Milky Way. Analysing the distances and spatial
distribution of the observed systems, we estimate a total population of ~1300
Galactic black hole transients. This means that we have already discovered less
than ~5% of the total Galactic distribution. The complete version of this
catalogue will be continuously updated online and in the Virtual Observatory,
including finding charts and data in other wavelengths.Comment: http://www.astro.puc.cl/BlackCAT - Accepted for publication in
Astronomy & Astrophysics. 20 pages, 8 figures, 5 Table
A Black Hole in the Superluminal source SAX J1819.3-2525 (V4641 Sgr)
(shortened) Spectroscopic observations of the fast X-ray transient and
superluminal jet source SAX J1819.3-2525 (V4641 Sgr) reveal a best fitting
period of P_spect=2.81678 +/- 0.00056 days and a semiamplitude of K_2=211.0 +/-
3.1 km/sec. The optical mass function is f(M)=2.74 +/- 0.12 solar masses. We
find a photometric period of P_photo=2.81730 +/- 0.00001 days using a light
curve measured from photographic plates. The folded light curve resembles an
ellipsoidal light curve with two maxima of roughly equal height and two minima
of unequal depth per orbital cycle. The secondary star is a late B-type star
which has evolved off the main sequence. Using a moderate resolution spectrum
(R=7000) we measure T_eff=10500 +/- 200K, log(g)=3.5 +/- 0.1, and
V_rot*sin(i)=123 +/- 4 km/sec (1 sigma errors). Assuming synchronous rotation,
our measured value of the projected rotational velocity implies a mass ratio of
Q=M_1/M_2=1.50 +/- 0.08 (1sigma). The lack of X-ray eclipses implies an upper
limit to the inclination of i<70.7 deg. On the other hand, the large amplitude
of the folded light curve (about 0.5 mag) implies a large inclination (i>60
deg). Using the above mass function, mass ratio, and inclination range, the
mass of the compact object is in the range 8.73 < M_1 < 11.70 solar masses and
the mass of the secondary star is in the range 5.49 < M_2 < 8.14 solar masses
(90% confidence). The mass of the compact object is well above the maximum mass
of a stable neutron star and we conclude that V4641 Sgr contains a black hole.Comment: 17 pages, 12 figures, emulateapj5.sty, submitted to Ap
Orbital Parameters for the Soft X-ray Transient 4U 1543-47: Evidence for a Black Hole
(shortened) Spectroscopic observations of the soft X-ray transient 4U 1543-47
reveal a radial velocity curve with a period of P=1.123 +/- 0.008 days and a
semi-amplitude of K_2 = 124 +/- 4 km/sec. The mass function is f(M) = 0.22 +/-
0.02 solar masses. We derive a distance of d = 9.1 +/-1.1 kpc if the secondary
is on the main sequence. The V and I light curves exhibit two waves per orbital
cycle with amplitudes of about 0.08 mag. We modeled the light curves as
ellipsoidal variations in the secondary star and derive extreme inclination
limits of 20 <= i <= 40 deg and formal 3 sigma limits of 24 <= i <= 36 deg for
a mass ratio Q = M_1/M_2 > 1. However, there are systematic effects in the data
that the model does not account for, so the above constraints should be treated
with caution. We argue that the secondary star is still on the main sequence
and if the secondary star has a mass near the main sequence values for early
A-stars (2.3 <= M_2 <= 2.6 solar masses), then the best fits for the 3 sigma
inclination range (24 <= i <= 36 deg) and the 3 sigma mass function range (0.16
<= f(M) <= 0.28 solar masses) imply a primary mass in the range 2.7 <= M_1 <=
7.5 solar masses. Thus the mass of the compact object in 4U 1543-47 is likely
to be in excess of approximately 3 solar masses and we conclude 4U 1543-47 most
likely contains a black hole.Comment: 18 pages, 9 figures, LaTeX (uses the standard AAS style file
aas2pp4.sty), accepted for publication in the Ap
Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
The optical/near-infrared (OIR) region of the spectra of low-mass X-ray
binaries appears to lie at the intersection of a variety of different emission
processes. In this paper we present quasi-simultaneous OIR - X-ray observations
of 33 XBs in an attempt to estimate the contributions of various emission
processes in these sources, as a function of X-ray state and luminosity. A
global correlation is found between OIR and X-ray luminosity for low-mass black
hole candidate XBs (BHXBs) in the hard X-ray state, of the form L_OIR is
proportional to Lx^0.6. This correlation holds over 8 orders of magnitude in Lx
and includes data from BHXBs in quiescence and at large distances (LMC and
M31). A similar correlation is found in low-mass neutron star XBs (NSXBs) in
the hard state. For BHXBs in the soft state, all the near-infrared (NIR) and
some of the optical emission is suppressed below the correlation, a behaviour
indicative of the jet switching off/on in transition to/from the soft state. We
compare these relations to theoretical models of a number of emission
processes. We find that X-ray reprocessing in the disc and emission from the
jets both predict a slope close to 0.6 for BHXBs, and both contribute to the
OIR in BHXBs in the hard state, the jets producing ~90 percent of the NIR
emission at high luminosities. X-ray reprocessing dominates the OIR in NSXBs in
the hard state, with possible contributions from the jets (only at high
luminosity) and the viscously heated disc. We also show that the optically
thick jet spectrum of BHXBs extends to near the K-band. (abridged)Comment: Accepted for publication in MNRAS; 19 pages, 7 figure
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