Wolf-Rayet/black-hole binary

Blobrana

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Posts: 131433

Date: Jan 27 11:36 2010

NGC 300 X-1	Permalink

Title: NGC 300 X-1 is a Wolf-Rayet/Black-Hole binary Authors: P. A. Crowther (1), R. Barnard (2), S. Carpano (3), J. S. Clark (2), V. S. Dhillon (1), A. M. T. Pollock (3) ((1) Sheffield UK; (2) Open Univ UK; (3) ESAC, Spain) 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. Read more (256kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Jul 4 09:02 2008

RE: Wolf-Rayet/black-hole binary	Permalink

Title: NGC300 X-1 and IC10 X-1: a new breed of black hole binary? Authors: R. Barnard, J. S. Clark, U. C. Kolb IC10 X-1 has recently been confirmed as a black hole (BH) + Wolf-Rayet (WR) X-ray binary, and NGC300 X-1 is thought to be. IC10 X-1 and NGC300 X-1 have similar X-ray properties, with luminosities ~10^38 erg/s, and orbital periods ~30 hr. We investigate similarities between these two, as well as differences between them and the known Galactic BH binary systems. We have examined XMM-Newton observations of NGC300 X-1 and IC10 X-1. We extracted lightcurves and spectra; power density spectra (PDS) were constructed from the lightcurves, and the X-ray emission spectra were modeled. Each source exhibits PDS that are characteristic of disc-accreting X-ray binaries (XBs) in the high state. In this state, Galactic XBs with known BH primaries have soft, thermal emission; however the emission spectra of our targets are predominantly non-thermal. Furthermore, the Observation 1 spectrum of NGC300 X-1 is strikingly similar to that of IC10 X-1. The remarkable similarity between the behaviour of NGC300 X-1 in Observation 1 and that of IC10 X-1 lends strong evidence for NGC300 X-1 being a (BH+WR) binary. The unusual spectra of NGC300 X-1 and IC10 X-1 may be due to these systems existing in a persistently high state, whereas all known BH LMXBs are transient. BH XBs in a persistent high state could retain their corona, and hence exhibit a large non-thermal component. LMC X-1 is a BH XB that has only been observed in the high state, and its spectrum is remarkably similar to those of our targets. We therefore classify NGC300 X-1, IC10 X-1 and perhaps LMC X-1 as a new breed of BH XB, defined by their persistently high accretion rates and consequent stable disc configuration and corona. This scenario may also explain the lack of ultraluminous X-ray sources in the canonical soft state. Read more (66kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Mar 26 08:09 2008

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Title: IC10 X-1: the immediate progenitor of a double black hole binary
Authors: Tomasz Bulik, Krzysztof Belczynski, Andrea Prestwich

We follow the evolution of IC10 X-1, the extragalactic binary hosting the most massive known stellar black hole with the mass of at least 23 solar masses. A massive companion of this black hole is a 35 solar mass helium star that will very soon form another black hole. We demonstrate that this system will become a close double black hole binary with coalescence time of ~ 2-3 Gyr. We estimate that a detection rate of such systems is of the order of 0.5 yr^{-1} for initial LIGO and VIRGO. Additionally, we point out that the existence of a 23 solar masses black hole in the small metallicity environment of IC10 constrains the mass loss rates from massive stars to ~ 50% of currently used values.

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Blobrana

L

Posts: 131433

Date: Feb 22 17:04 2008

IC 10 X-1	Permalink

The heaviest black hole formed from the collapse of a single star weighs as much as 33 Suns - double the previous record, new measurements confirm. Black holes come in a range of sizes, from "supermassive" behemoths weighing billions of Suns to "stellar-mass" objects weighing a few times the Sun's mass. These stellar-mass black holes form when a massive star dies, sending its outer layers exploding outwards in a supernova and collapsing its core into a black hole. There are limits to how massive the objects can become, based on the mass and chemical composition of the parent star. The previous record holder is a black hole in the nearby galaxy M33. Called M33 X-7, it was measured to have 16 times the Sun's mass. Read more __________________

Blobrana

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Posts: 131433

Date: Feb 21 07:34 2008

RE: Wolf-Rayet/black-hole binary	Permalink

Title: On IC 10 X-1, the Most Massive Known Stellar-Mass Black Hole Authors: Jeffrey M. Silverman, Alexei V. Filippenko IC 10 X-1 is a variable X-ray source in the Local Group starburst galaxy IC 10 whose optical counterpart is a Wolf-Rayet (WR) star. Prestwich et al. (2007) recently proposed that it contains the most massive known stellar-mass black hole (23-34 M_sun), but their conclusion was based on radial velocities derived from only a few optical spectra, the most important of which was seriously affected by a CCD defect. Here we present new spectra of the WR star, spanning one month, obtained with the Keck-I 10 m telescope. The spectra show a periodic shift in the He II 4686 Ang. emission line as compared with IC 10 nebular lines such as [O III] 5007 Ang. From this, we calculate a period of 34.93±0.04 hr (consistent with the X-ray period of 34.40±0.83 hr reported by Prestwich et al. 2007) and a radial-velocity semi-amplitude of 370±20 km/s. The resulting mass function is 7.64±1.26 M_sun, consistent with that of Prestwich et al. (2007) (7.8 M_sun). This, combined with the previously estimated (from spectra) mass of 35 M_sun for the WR star, yields a minimum primary mass of 32.7±2.6 M_sun. Even if the WR star has a mass of only 17 M_sun, the minimum primary mass is 23.1±2.1 M_sun. Thus, IC 10 X-1 is indeed a WR/black-hole binary containing the most massive known stellar-mass black hole. Read more (34kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 31 01:25 2007

IC10 X-1 black hole	Permalink

Scientists estimate that the host star from which the black hole formed had a mass of about 60 solar masses. Most stars shed most of their mass when they explode as supernovas prior to becoming black holes. The host star was likely deficient in heavier elements than hydrogen and helium, which are more prone to being swept away by stellar winds. "Massive stars in our galaxy today are probably not producing very heavy stellar-mass black holes like this one. But there could be millions of heavy stellar-mass black holes lurking out there that were produced early in the Milky Way's history, before it had a chance to build up heavy elements" - Roy Kilgard, study team member at Wesleyan University in Middletown, US. __________________

Blobrana

L

Posts: 131433

Date: Oct 30 16:55 2007

IC 10 X-1 black hole	Permalink

Astronomers, using two NASA satellites, have discovered a black hole that smashes a record announced just two weeks ago. The new black hole, with a mass 24 to 33 times that of our Sun, is the heftiest known black hole that orbits another star. The record-breaker belongs to the category of "stellar-mass" black holes. Formed in the death throes of massive stars, they are smaller than the monster black holes found in galactic cores. The previous record holder for largest stellar-mass black hole is a 16-solar-mass black hole in the galaxy M33, announced on October 17. Expand (1.1mb, 2184 x 472) The galaxy IC 10 is an irregular dwarf galaxy about 1.8 million light years from Earth. Image left: The galaxy IC 10 is an irregular dwarf galaxy about 1.8 million light-years from Earth. Credit: Adam Block/NOAO/AURA/NSF. "We werent expecting to find a stellar-mass black hole this massive. We now know that black holes that form from dying stars can be much larger than we had realised" - Andrea Prestwich of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Mass., lead author of the discovery paper in the November 1 Astrophysical Journal Letters. The black hole is located in the nearby dwarf galaxy IC 10, 1.8 million light-years from Earth in the constellation Cassiopeia. Prestwichs team could measure the black holes mass because it has an orbiting companion: a hot, highly evolved star. The star is ejecting gas in the form of a wind. Some of this material spirals toward the black hole, heats up, and gives off powerful X-rays before crossing the point of no return. In November 2006, Prestwich and her colleagues observed the dwarf galaxy with NASAs Chandra X-ray Observatory. The group discovered that the galaxys brightest X-ray source, IC 10 X-1, exhibits sharp changes in X-ray brightness. Such behaviour suggests a star periodically passing in front of a companion black hole and blocking the X-rays, creating an eclipse. In late November, NASAs Swift satellite confirmed the eclipses and revealed details about the stars orbit. The star in IC 10 X-1 appears to orbit in a plane that lies nearly edge-on to Earths line of sight, so a simple application of Keplers Laws show that the companion black hole has a mass of at least 24 Suns. There are still some uncertainties in the black holes mass estimate. "Future optical observations will provide a final check. Any refinements in the IC 10 X-1 measurement are likely to increase the black holes mass rather than reduce it" - Andrea Prestwich. The black holes large mass is surprising because massive stars generate powerful winds that blow off many Suns worth of gas before the stars explode. Calculations suggest massive stars in our galaxy leave behind black holes no heavier than about 15 Suns. The IC 10 X-1 black hole has gained mass since its birth by gobbling up gas from its companion star, but the rate is so slow that the black hole would have gained no more than 1 or 2 solar masses. "This black hole was born fat; it didnt grow fat" - astrophysicist Richard Mushotzky of NASA Goddard Space Flight Centre in Greenbelt, Md., who is not a member of the discovery team. The progenitor star probably started its life with 60 or more solar masses. Like its host galaxy, it was probably deficient in elements heavier than hydrogen and helium. In massive, luminous stars with a high fraction of heavy elements, the extra electrons of elements such as carbon and oxygen feel the outward pressure of light and are more susceptible to being swept away in stellar winds. But with its low fraction of heavy elements, the IC 10 X-1 progenitor shed comparatively little mass before it exploded, so it could leave behind a heavier black hole. "Massive stars in our galaxy today are probably not producing very heavy stellar-mass black holes like this one. But there could be millions of heavy stellar-mass black holes lurking out there that were produced early in the Milky Ways history, before it had a chance to build up heavy elements" - coauthor Roy Kilgard of Wesleyan University in Middletown, Connecticut, US. Read more __________________

Blobrana

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Posts: 131433

Date: Sep 19 05:14 2007

IC 10 X-1	Permalink

Title: The Orbital Period of the Wolf-Rayet Binary IC 10 X-1; Dynamic Evidence that the Compact Object is a Black Hole Authors: A. H. Prestwich, R. Kilgard, P. A. Crowther, S. Carpano, A. M. T. Pollock, A. Zezas, S. H. Saar, T. P. Roberts, M. J. Ward IC 10 X-1 is a bright (Lx=10^38 ergs/s) variable X-ray source in the local group starburst galaxy IC 10. The most plausible optical counterpart is a luminous Wolf-Rayet star, making IC 10 X-1 a rare example of a Wolf-Rayet X-ray binary. In this paper, we report on the detection of an X-ray orbital period for IC 10 X-1of 34.4 hours. This result, combined with a re-examination of optical spectra, allow us to determine a mass function for the system f(m)=7.8 Msun and a probable mass for the compact object of 24-36 Msun. If this analysis is correct, the compact object is the most massive known stellar black hole. We further show that the observed period is inconsistent with Roche lobe overflow, suggesting that the binary is detached and the black hole is accreting the wind of the Wolf-Rayet star. The observed mass loss rate of [MAC92] 17-A is sufficient to power the X-ray luminosity of IC 10 X-1. Read more (44kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Apr 6 18:27 2007

SN 2006jc	Permalink

A star that survived a massive explosion only to be destroyed in a second blast just two years later has piqued the curiosity of astronomers. Its bizarre death might be due to the production of antimatter in its core towards the end of its life. The star that exploded appears to have been a massive type called a Wolf-Rayet star, which begin their lives with more than 40 times the mass of the Sun. It exploded in a galaxy 77 million light years from Earth, with the first blast occurring on 20 October 2004. It was so bright that the amateur astronomer who first noticed it initially mistook it for a supernova the final blast that ends a star's life. But the 2004 explosion was not fatal. The star was observed undergoing a second explosion on 11 October 2006. This one was indeed a supernova, and was named SN 2006jc. This is the first time that astronomers have witnessed a star suffer a pair of explosions, with the second one ending its life. Read more __________________

Blobrana

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Posts: 131433

Date: Mar 13 10:57 2007

NGC 300 X-1	Permalink

Title: A 33 hour period for the Wolf-Rayet/black hole X-ray binary candidate NGC 300 X-1 Authors: S. Carpano, A.M.T. Pollock, A. Prestwich, P. Crowther, J. Wilms, L. Yungelson, M. Ehle Context. NGC 300 X-1 is the second extragalactic candidate, after IC 10 X-1, in the rare class of Wolf-Rayet/compact object X-ray binary systems exemplified in the Galaxy by Cyg X-3. From a theoretical point of view, accretion onto a black hole in a detached system is possible for large orbital periods only if the mass of the relativistic object is high or the velocity of the accreted wind is low. Aims. We analysed a 2 week SWIFT XRT light curve of NGC 300 X-1 and searched for periodicities. Methods. Period searches were made using Lomb-Scargle periodogram analysis. We evaluated the confidence level using Monte Carlo simulations. Results. A period of 32.8+-0.4h (3 sigma error) was found for NGC 300 X-1 with a confidence level >99%. Furthermore, we confirm the high irregular variability during the high flux level, as already observed in the XMM-Newton observations of the source. A folded XMM-Newton light curve is shown, with a profile that is in agreement with SWIFT. The mean absorbed X-ray luminosity in the SWIFT observations was 1.5x10^38 erg/s, close to the value derived from the XMM-Newton data. Conclusions. While Cyg X-3 has a short period of 4.8 h, the period of NGC 300 X-1 is very close to that of IC 10 X-1 (34.8+-0.9 h). These are likely orbital periods. Possibility of formation of accretion disk for such high orbital periods strongly depends on the terminal velocity of the Wolf-Rayet star wind and black-hole mass. While low masses are possible for wind velocities < 1000 km/s, these increase to several tens of solar masses for velocities > 1600 km/s and no accretion disk may form for terminal velocities larger than 1900 km/s. Read more (130kb, PDF) __________________

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