arXiv subjects

Charles D. Bailyn

Publications and source records attributed to Charles D. Bailyn.

At least 37 records · Page 2Linked to original sources

arXiv2010

The Spin of the Black Hole in the Soft X-ray Transient A0620--00

During its yearlong 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. We recently determined accurate values for the black hole 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 black hole 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 black hole. 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 black hole to be a*=0.12+/-0.19, with a*<0.49 and a*>-0.59 at the 3 sigma 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 black hole 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.

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arXiv2010

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photometry of the Soft X-ray Transient A0620-00 spanning nearly 30 years, including previously published and previously unpublished data.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=51 plus or minus 0.9 degrees, implying M=6.6 plus or minus 0.25 solar masses. Using our dynamical model and zero-disk stellar VIH magnitudes, we find d=1.06 plus or minus 0.12 kpc. Understanding the disk origin of non-ellipsoidal 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.

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arXiv2009

A New Dynamical Model for the Black Hole Binary LMC X-1

We present a dynamical model of the high mass X-ray binary LMC X-1 based on high-resolution optical spectroscopy and extensive optical and near-infrared photometry. From our new optical data we find an orbital period of P=3.90917 +/- 0.00005 days. We present a refined analysis of the All Sky Monitor data from RXTE and find an X-ray period of P=3.9094 +/- 0.0008 days, which is consistent with the optical period. A simple model of Thomson scattering in the stellar wind can account for the modulation seen in the X-ray light curves. The V-K color of the star (1.17 +/- 0.05) implies A_V = 2.28 +/- 0.06, which is much larger than previously assumed. For the secondary star, we measure a radius of R_2 = 17.0 +/- 0.8 solar radii and a projected rotational velocity of V_rot*sin(i) = 129.9 +/- 2.2 km/s. Using these measured properties to constrain the dynamical model, we find an inclination of i = 36.38 +/- 1.92 deg, a secondary star mass of M_2 = 31.79 +/- 3.48 solar masses, and a black hole mass of 10.91 +/- 1.41 solar masses. The present location of the secondary star in a temperature-luminosity diagram is consistent with that of a star with an initial mass of 35 solar masses that is 5 Myr past the zero-age main sequence. The star nearly fills its Roche lobe (~90% or more), and owing to the rapid change in radius with time in its present evolutionary state, it will encounter its Roche lobe and begin rapid and possibly unstable mass transfer on a timescale of a few hundred thousand years.

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arXiv2008

Outburst Morphology in the Soft X-ray Transient Aquila X-1

We present optical and near-IR (OIR) observations of the major outbursts of the neutron star soft X-ray transient binary system Aquila X-1, from summer 1998 -- fall 2007. The major outbursts of the source over the observed timespan seem to exhibit two main types of light curve morphologies, (a) the classical Fast-Rise and Exponential-Decay (FRED) type outburst seen in many soft X-ray transients and (b) the Low-Intensity State (LIS) where the optical-to-soft-X-ray flux ratio is much higher than that seen during a FRED. Thus there is no single correlation between the optical (R-band) and soft X-ray (1.5-12 keV, as seen by the ASM onboard RXTE) fluxes even within the hard state for Aquila X-1, suggesting that LISs and FREDs have fundamentally different accretion flow properties. Time evolution of the OIR fluxes during the major LIS and FRED outbursts is compatible with thermal heating of the irradiated outer accretion disk. No signature of X-ray spectral state changes or any compact jet are seen in the OIR, showing that the OIR color-magnitude diagram (CMD) can be used as a diagnostic tool to separate thermal and non-thermal radiation from X-ray binaries where orbital and physical parameters of the system are reasonably well known. We suggest that the LIS may be caused by truncation of the inner disk in a relatively high mass accretion state, possibly due to matter being diverted into a weak outflow.

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arXiv2007

Supplementary Information for "A 15.65 solar mass black hole in an eclipsing binary in the nearby spiral galaxy Messier 33"

This Supplementary Information provides details about the spectral extraction (crowding issues and the removal of nebular lines), a discussion about the distance to M33, a model for the O-star wind and the measurement of the true photospheric X-ray eclipse width Theta, and details about ellipsoidal modelling. It also contains five related figures, one related table, and additional references.

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arXiv2007

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.

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arXiv2007

Robust Models for Phase Shifts in Accreting Binary Stars

Radial velocity studies of accreting binary stars commonly use accretion disk emission lines to determine the radial velocity of the primary star and therefore the mass ratio. These emission line radial velocity curves are often shifted in phase from the expected motion of the primary. These phase shifts cast doubt on the use of disk emission lines in the determination of mass ratios. We present a systematic study of phase shifts, using data from the literature to distinguish between possible explanations of the phase shift. We find that one widely adopted class of models is contradicted by observations (section 2). We present a generalized form of another class of models, which we call "measurement offset models." We show that these models are quantitatively consistent with existing data (figures 2 and 3, and the discussion in section 4.4). We consider the implications of adopting measurement offset models, for both disk structure and determination of binary parameters. Specifically, we describe in section 6 how measurement offset models may be used improve determinations of the mass ratio based on disk emission lines. This could be a valuable new tool in determining masses of important astrophysical objects such as accreting neutron stars and black holes.

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arXiv2007

IR Monitoring of the Microquasar GRS 1915+105: Detection of Orbital and Superhump Signatures

We present the results of seven years of K-band monitoring of the low-mass X-ray binary GRS 1915+105. Positive correlations between the infrared flux and the X-ray flux and X-ray hardness are demonstrated. Analysis of the frequency spectrum shows that the orbital period of the system is $P_{orb}= 30.8 \pm 0.2$ days. The phase and amplitude of the orbital modulation suggests that the modulation is due to the heating of the face of the secondary star. We also report another periodic signature between 31.2 and 31.6 days, most likely due to a superhump resonance. From the superhump period we then obtain a range on the mass ratio of the system, $0.05 < q < 0.12$.

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arXiv2005

X-Ray Observations of V4641 SGR (= SAX J1819.3-2525) During the Brief and Violent Outburst of 2003

We present the results of detailed analysis of pointed X-ray observations by RXTE PCA/HEXTE of the black hole X-ray binary (BHXRB) system V4641 Sgr (= SAX J1819.3-2525) during its outburst of August 2003. Soft X-ray (3-20 keV) flux variations by factors of 10 or more on timescales of minutes or shorter were seen. The rapid and strong variability of this source sets it apart from typical XRBs. In spite of large luminosity fluctuations, the spectral state of the source did not change significantly during the dwells which suggests that the physical emission processes did not change much during the observations. The energy spectra during the dwells were dominated by a hard Comptonized powerlaw component, indicative of the canonical low/hard state observed in other BHXRBs. No soft thermal component was found in three out of the four RXTE pointings. However spectral deconvolution of the observation with largest average luminosity suggests an obscured, hot accretion disk. During one of the observations we detected a short term (about 100s) soft X-ray dropout which is apparently due to variability in the observed column density. Strong Fe K$α$ fluorescent emisssion line near 6.5 keV was detected with large equivalent widths in the range of 700 - 1000eV. In the temporal domain, the Fourier power spectra were dominated by red noise below a few Hz. Poisson noise dominated at higher frequencies and no high frequency features were detected. The strong Comptonized spectra, broad iron emission line, absence of disk component in the spectra, absence of any timing variability above few Hz and occasional large changes in the column density along the line-of-sight, all support an enshrouded black hole with occasional outflow and a very dynamic environment.

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arXiv2005

Low-Intensity States in the Neutron Star X-ray Binary Aql X-1

Aql X-1 was observed in a Low Intensity State (LIS), a state that is usually characterized by high optical but low X-ray flux. Our daily monitoring of the source using the 1.3m telescope in Cerro Tololo Inter-America Observatory operated by the Small and Moderate Aperture Research Telescope System (SMARTS) was used to trigger a series of target-of-opportunity (ToO) observations of the source using the Rossi X-ray Timing Explorer satellite (RXTE). The X-ray colors and temporal variability studies suggest that the source was in a powerlaw dominated state featuring high rms variability in the lightcurve and dominance of hard photons during this LIS. The ToO observations were continued until the source made a transition to the canonical thermal dominated or high/soft state.

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arXiv2005

Rapid Spectral Variability during the 2003 Outburst of V4641 Sgr (= SAX J1819.3-2525)

The black hole candidate V4641 Sgr (= SAX J1819.3-2525) went through a brief outburst during 2003 Aug 01 to Aug 08. During the outburst, activity was noted in optical, radio as well as X-rays. Here we present results of Spectral and Temporal analysis of a pointed Rossi X-ray Timing Explorer (RXTE) observation of the source during the outburst. During this pointing we observed flaring activities with associated X-ray luminosity variations over factors of 5 or more in timescales of few tens of seconds. The observed flares during are intrinsically different in their spectral and temporal properties. We see evidence of variable column density during one of the flares. The spectral and temporal analyses of the data suggest occasional outflow/mass ejection.

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arXiv2005

Multi-wavelength observations of the 2002 outburst of GX 339-4: two patterns of X-ray-optical/near-infrared behavior

(Abridged) We report on RXTE and optical/near-infrared (nIR) observations of the black hole transient GX 339-4, made over a time span of 8 months in 2002 and covering the initial rise and transition from a hard to a soft spectral state. Two patterns of correlated X-ray-optical/nIR behavior were found. During the hard state the optical/nIR and X-ray fluxes correlated well, with a nIR vs. X-ray flux relation similar to the relation between X-ray and radio fluxes found in previous studies of GX 339-4 and other black hole binaries. As GX 339-4 went through an intermediate state the optical/nIR fluxes decreased rapidly and once it had entered the spectrally soft state, the optical/nIR spectrum was much bluer and the ratio of X-ray to nIR flux was higher by a factor of more than 10 compared to the hard state. In the spectrally soft state nIR-changes preceded those in the X-rays by more than 2 weeks, indicating a disk origin of the nIR. We present SEDs, including radio data, and discuss possible sources for the optical/nIR emission. We conclude that in the hard state this emission probably originates in the optically thin part of a jet and that in none of the X-ray states X-ray reprocessing is the dominant source of optical/nIR emission. Finally, comparing the light curves from the ASM and PCA instruments, we find that the X-ray/nIR delay depends critically on the sensitivity of the X-ray detector, with the delay inferred from the PCA (if present at all) being a factor of 3-6 times shorter than the delay inferred from the ASM; this may be important in interpreting previously reported X-ray-optical/nIR lags.

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arXiv2001

Dynamical Evidence for a Black Hole in the Microquasar XTE J1550-564

Optical spectroscopic observations of the companion star (type G8IV to K4III) in the microquasar system XTE J1550-564 reveal a radial velocity curve with a best fitting spectroscopic period of P_sp = 1.552 +/- 0.010 days and a semiamplitude of K_2 = 349 +/- 12 km/s. The optical mass function is f(M) = 6.86 +/- 0.71 solar masses (1 sigma). We tentatively measure the rotational velocity of the companion star to be V_rot*sin(i) = 90 +/- 10 km/s, which when taken at face value implies a mass ratio of Q = M_1/M_2 = 6.6 (+2.5 / -1.6) (1 sigma), using the above value of K_2. We derive constraints on the binary parameters from simultaneous modelling of the ellipsoidal light and radial velocity curves. We find the most likely value of the mass of the compact object is 9.41 solar masses with a 1 sigma range of 8.36 < M_1 < 10.76 solar masses. If we apply our tentative value of V_rot*sin(i) = 90 +/- 10 km/s as an additional constraint in the ellipsoidal modelling, we find the most likely value of the mass of the compact object is 10.56 solar masses with a 1 sigma range of 9.68 < M_1 < 11.58 solar masses. In either case the mass of the compact object is well above the maximum mass of a stable neutron star, and we therefore conclude XTE J1550-564 contains a black hole.

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arXiv2001

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.

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arXiv2001

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.

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arXiv2000

Optical Observations of the Black Hole Candidate XTE J1550-564 During Re-Flare and Quiescence

We report optical monitoring of the soft X-ray transient XTE J1550-564 during the 1999 season (4 January 1999 to 24 August 1999). The first optical observations available in 1999 show that the peak ``re-flare'' brightness had exceeded the peak brightness of the initial optical flare in September 1998 by over half a magnitude. We compare the optical re-flare light curves with the total X-ray flux, the power-law flux and disk flux light curves constructed from the spectral fits to RXTE/PCA data made by Sobczak et al. (1999, 2000). During the first 60 days of the observed optical re-flare, we find no correspondence between the thermal component of the X-rays often associated with a disk and the optical flux -- the former remains essentially flat whereas the latter declines exponentially and exhibits three substantial dips. However, the power law flux is anti-correlated with the optical dips, suggesting that the optical flux may by up-scattered into the X-ray by the hot corona. Periodic modulations were discovered during the final stage of the outburst (May to June), with P=1.546+/-0.038 days, and during quiescence (July and August), with P=1.540+/-0.008 days. The analysis of the combined data set reveals a strong signal for a unique period at P=1.541+/-0.009 days, which we believe to be the orbital period.

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arXiv2000

Complete RXTE Spectral Observations of the Black Hole X-ray Nova XTE J1550-564

We report on the X-ray spectral behavior of the exceptionally bright X-ray nova XTE J1550-564 during its 1998-99 outburst. Our study is based on 209 pointed observations using the PCA and HEXTE instruments onboard the Rossi X-ray Timing Explorer spanning 250 days and covering the entire double-peaked eruption that occurred from 1998 September until 1999 May. The spectra are fit to a model including multicolor blackbody disk and power-law components. The source is observed in the very high and high/soft outburst states of black hole X-ray novae. During the very high state, when the power-law component dominated the spectrum, the inner disk radius is observed to vary by more than an order of magnitude; the radius decreased by a factor of 16 in one day during a 6.8 Crab flare. If the larger of these observed radii is taken to be the last stable orbit, then the smaller observed radius would imply that the inner edge of the disk is inside the event horizon! However, we conclude that the apparent variations of the inner disk radius observed during periods of increased power-law emission are probably caused by the failure of the multicolor disk/power-law model; the actual physical radius of the inner disk may remain fairly constant. This interpretation is supported by the fact that the observed inner disk radius remains approximately constant over 120 days in the high state, when the power-law component is weak, even though the disk flux and total flux vary by an order of magnitude. The mass of the black hole inferred by equating the approximately constant inner disk radius observed in the high/soft state with the last stable orbit for a Schwarzschild black hole is M_BH = 7.4 M_sun (D/6 kpc) (cos i)^{-1/2}.

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arXiv1999

Correlations between Low-Frequency QPOs and Spectral Parameters in XTE J1550-564 and GRO J1655-40

Utilizing observations obtained with the Rossi X-ray Timing Explorer, we examine correlations between the properties of 0.08-22 Hz variable frequency QPOs and the X-ray spectral parameters for the black hole candidates XTE J1550-564 and GRO J1655-40. The spectra were fitted to a model including a multi-temperature blackbody disk and a power-law component. We find that the QPO frequency and amplitude are well correlated with the spectral parameters, although the correlations found for XTE J1550-564 are generally opposite to those for GRO J1655-40. There is one exeption: Both sources exhibit a general increase in the QPO frequency as the disk flux increases (or as the mass accretion rate through the disk increases). In addition, these QPOs are observed only when the power-law component contributes more than 20% of the 2-20 keV flux, which indicates that both the disk and the power-law components are linked to the QPO phenomenon.

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