arXiv subjects

Jeffrey E. McClintock

Publications and source records attributed to Jeffrey E. McClintock.

At least 91 records · Page 5Linked to original sources

arXiv2004

The X-ray Outburst of H1743-322: High-Frequency QPOs with a 3:2 Frequency Ratio

We observed the 2003 X-ray outburst of H1743-322 in a series of 130 pointed observation with RXTE. We searched individual observations for high-frequency QPOs (HFQPOs) and found only weak or marginal detections near 240 and 160 Hz. We next grouped the observations in several different ways and computed the average power-density spectra (PDS) in a search for further evidence of HFQPOs. This effort yielded two significant results for those observations defined by the presence of low-frequency QPOs (0.1-20 Hz) and an absence of ``band-limited'' power continua: (1) The 9 time intervals with the highest 7-35 keV count rates yielded an average PDS with a QPO at $166 \pm 5$ Hz. ($4.1 σ$; 3--35 keV); and (2) a second group with lower 7-35 keV count rates (26 intervals) produced an average PDS with a QPO at $242 \pm 3$ Hz ($6.0 σ$; 7--35 keV). The ratio of these two frequencies is $1.46 \pm 0.05$. This finding is consistent with results obtained for three other black hole systems that exhibit commensurate HFQPOs in a 3:2 ratio. Furthermore, the occurrence of H1743-322's slower HFQPO at times of higher X-ray luminosity closely resembles the behavior of XTE J1550-564 and GRO J1655-40. We discuss our results in terms of a resonance model that invokes frequencies set by general relativity for orbital motions near a black-hole event horizon.

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arXiv2004

Black Hole Binaries

We review the properties of 40 X-ray binaries that contain either a confirmed black hole or a black hole candidate. After discussing briefly the significance of these Galactic black holes to both astronomy and physics, we present basic data for all 40 systems, review the physics of mass accretion onto black holes, and then show seven-year light curves of 20 systems. The second half of this work is a far-reaching review of the canonical emission states of black hole binaries, which is based on X-ray, radio and gamma-ray data. For several selected black holes, we show 33 pairs of X-ray energy and power density spectra and use these spectra as a basis for introducing modified definitions of the canonical X-ray emission states of an accreting black hole. We highlight the physical structures and some of the emission mechanisms associated with each emission state. In the final pages we examine both low- and high-frequency quasi-periodic oscillations. A recurring theme of the review is the importance of these black holes as potential sites for tests of general relativity. Accordingly, we stress phenomena that originate in strong gravity, such as relativistic Fe emission lines and thermal continuum emission, both of which arise in the inner accretion disk. Especially important in this regard are the high-frequency (40-450 Hz) quasi-periodic oscillations observed for seven black holes, three of which show evidence for commensurate (3:2) pairs of frequencies.

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arXiv2004

The importance of discovering a 3:2 twin-peak QPO in a ULX or how to solve the puzzle of intermediate mass black holes

Recently, twin-peak QPOs have been observed in a 3:2 ratio for three Galactic black-hole microquasars with frequencies that have been shown to scale as 1/M, as expected for general relativisitic motion near a black hole. It may be possible to extend this result to distinguish between the following two disparate models that have been proposed for the puzzling ultraluminous X-ray sources (ULXs): (1) an intermediate-mass black hole M ~1000 solar mass) radiating very near the Eddington limit and (2) a conventional black hole (M ~ 10 solar mass) accreting at a highly super-Eddington rate with its emission beamed along the rotation axis. We suggest that it may be possible to distinguish between these models by detecting the counterpart of a Galactic twin-peak QPO in a ULX: the expected frequency for the intermediate-mass black hole model is only about 1 Hz, whereas, for the conventional black hole model the expected frequency would be the ~100 Hz value observed for the Galactic microquasars.

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arXiv2003

Multiwavelength Spectrum of the Black Hole XTE J1118+480 in Quiescence

We present an X-ray/UV/optical spectrum of the black hole primary in the X-ray nova XTE J1118+480 in quiescence at L_x = 4 x 10^{-9} of the Eddington luminosity. The Chandra, HST and MMT spectroscopic observations were performed simultaneously on 2002 January 12 UT. Because this 4.1-hr binary is located at b = 62 deg, the transmission of the ISM is very high (e.g., 70% at 0.3 keV). We present many new results for the quiescent state, such as the first far-UV spectrum and evidence for an 0.35 mag orbital modulation in the near-UV flux. However, the centerpiece of our work is the multiwavelength spectrum of XTE J1118+480, which we argue represents the canonical spectrum of a stellar-mass black hole radiating at L_x = 4 x 10^{-8.5} of the Eddington luminosity. This spectrum is comprised of two apparently disjoint components: a hard X-ray spectrum with a photon index Gamma = 2.02 +/- 0.16, and an optical/UV continuum that resembles a 13,000 K disk blackbody spectrum punctuated by several strong emission lines. We present a model of the source in which the accretion flow has two components: (1) an X-ray-emitting interior region where the flow is advection-dominated, and (2) a thin, exterior accretion disk with a truncated inner edge (R_tr ~ 10^4 Schwarzschild radii) that is responsible for the optical/UV spectrum. For D = 1.8 kpc, the luminosity of the X-ray component is L_x = 3.5 x 10^{30} erg/s (0.3-7 keV); the bolometric luminosity of the optical/UV component is 20 times greater.

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arXiv2002

X-ray QPOs in Black-Hole Binary Systems

We briefly review the properties and physical consequences of quasiperiodic oscillations (QPOs) seen on many occasions in the X-ray emission from black-hole binary systems. We also report on the discovery of QPOs at 164 and 328 Hz in GRS1915+105. These appear to be analogous to the harmonic systems of high-frequency QPOs seen in XTEJ1550-564 and GROJ1655-40.

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arXiv2002

Evidence for Harmonic Relationships in the High Frequency QPOs of XTE J1550-564 and GRO J1655-40

We continue to investigate the X-ray timing and spectral properties of the black hole binary, XTE J1550-564. For three different groups of observations, we show evidence that two high-frequency QPOs (HFQPOs) occur simultaneously near 184 and 276 Hz. In one group, there is also evidence of a broad feature at 92 Hz. In each case, we can model the QPO profiles while assuming that the central frequencies are related as integral harmonics of a single frequency. We next investigate the X-ray energy spectra, and we find a systematic increase in the strength of the power-law component as the stronger of the two HFQPOs shifts from 276 to 184 Hz. A strikingly similar result is seen for GRO J1655-40 when the stronger HFQPO shifts from 450 to 300 Hz. The fundamental HFQPO frequencies for the two X-ray sources scale inversely with black hole mass, which is consistent with the hypotheses that these HFQPOs represent some oscillation rooted in general relativity (GR) and that the two black holes have similar values of the dimensionless spin parameter. We discuss physical mechanisms that may explain these HFQPOs. In particular, a resonance between the orbital and radial coordinate frequencies in the innner accretion disk, as proposed by Abramowicz & Kluzniak, would imply moderate values for the dimensionless spin parameter (0.1 < a < 0.6) for both black holes.

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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

X-ray Novae and the Evidence for Black Hole Event Horizons

We discuss new observations of X-ray novae which provide strong evidence that black holes have event horizons. Optical observations of 13 X-ray novae indicate that these binary stars contain collapsed objects too heavy to be stable neutron stars. The objects have been identified as black hole candidates. X-ray observations of several of these X-ray novae in quiescence with the Chandra X-ray Observatory show that the systems are approximately 100 times fainter than nearly identical X-ray novae containing neutron stars. The advection-dominated accretion flow model provides a natural explanation for the difference. In this model, the accreting gas reaches the accretor at the center with a large amount of thermal energy. If the accretor is a black hole, the thermal energy will disappear through the event horizon, and the object will be very dim. If the accretor is a neutron star or any other object with a surface, the energy will be radiated from the surface, and the object will be bright. We discuss alternate interpretations of the data that eliminate the need for advection-dominated accretion. Most of these alternatives still require an event horizon to explain the unusually low X-ray luminosities of the black hole candidates. Some of the alternatives are also inconsistent with observations.

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arXiv2001

Chandra and RXTE Observations of X-ray Novae

We discuss new observations of X-ray novae with Chandra which provide strong evidence that black holes have event horizons. The evidence is based on the finding that black hole X-ray novae in quiescence are approximately 100 times fainter than equivalent neutron star X-ray novae. The advection-dominated accretion flow model provides a natural explanation for this difference. RXTE observations of XTE J1550-564 in the very high state, which were obtained during the 1998-1999 outburst of the source, reveal an extraordinarily tight correlation between the central frequency of the low frequency QPO and the soft, non-power-law flux in the 2-20 keV band. We discuss the nature of this soft spectral component and suggest the importance of obtaining direct observations of it at low energies (E < 2 keV) at the first available opportunity.

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arXiv2001

Characterizing the QPO Behavior of the X-ray Nova XTE J1550--564

For all 209 RXTE observations of the X-ray nova XTE J1550-564 during its major outburst of 1998-1999, we have analyzed the X-ray power spectra, phase lags, and coherence functions. The phase lags and coherence measures are used to distinguish three types of low-frequency QPOs (one more than those reported by Wijnands, Homan, & van der Klis 1999). For the most common type, the phase lag is correlated with both the QPO frequency and the amplitude. The physical significance of the QPO types is evident in the relationships between QPO properties and the apparent temperature and flux from the accretion disk. There is also a clear pattern in how the QPO types relate to the presence of high-frequency QPOs. In general, both the amplitude and the Q value (freq./FWHM) of low-frequency QPOs decrease as the high-frequency oscillations increase in frequency (100 to 284 Hz) and in Q value. We speculate that the antagonism between low-frequency and high-frequency QPOs arises from competing structures in a perturbed accretion disk. However, we find that the frequencies of slow (< 20 Hz) and fast (> 100 Hz) QPOs are not correlated. In addition, we encounter systematic problems in attempting to reliably compare the QPO frequencies with broad features in the power continuum, since there are a variable number of such features in the power spectra. These results cast some doubt on the reported global relationship between QPOs from neutrons stars and those from black hole systems.

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arXiv2001

The Quiescent Emission Spectrum of Cen X-4 and other X-ray Transients containing Neutron Stars

We use the observed optical-UV and X-ray emission spectrum of Cen X-4 during quiescence to constrain models for the accretion flow in this system. We argue that the optical-UV emission is not due to an optically-thick quiescent accretion disk, nor due to synchrotron emission from an Advection-Dominated Accretion Flow (ADAF). Emission from the bright spot could account for the observed optical-UV component if the mass transfer rate in Cen X-4 is >~ 2.10^16 g/s. Although the presence of an ADAF around the neutron star leads to Compton upscattering of the soft X-ray photons radiated from the stellar surface, we find that this process alone cannot account for the power law component seen in the quiescent X-ray spectrum of Cen X-4 and other X-ray transients containing neutron stars; this result is independent of whether the source of soft photons is incandescent thermal emission or accretion-powered emission. We conclude that, in models which invoke the presence of an ADAF and a propeller effect for the quiescence of X-ray transients containing neutron stars, the intrinsic emission from the ADAF must contribute very little to the optical-UV and X-ray emission observed. If these ADAF+propeller models are correct, the X-ray power law component observed must arise from regions where the gas impacts the neutron star surface. Variability studies could greatly help clarify the role of the various emission mechanisms involved.

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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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arXiv2000

New Evidence for Black Hole Event Horizons from Chandra

Previously we claimed that Black Hole X-ray Novae (BHXN) in quiescence are much less luminous than equivalent Neutron Star X-ray Novae (NSXN). This claim was based on the quiescent detection of a single short period BHXN (A0620-00, P(orb)=7.8 hrs) and two longer period BHXN (GRO J1655-40, P(orb)=62.9 hrs; V404 Cyg, P(orb)=155.3 hrs), along with sensitive upper limits. We announce the detection of two more short period BHXN (GRO J0422+32, P(orb)=5.1 hrs; GS 2000+25, P(orb)=8.3 hrs), an upper limit for a third which is improved by two orders of magnitude (4U 1543-47, P(orb)=27.0 hrs) and a new, much lower quiescent measurement of GRO J1655-40. Taken together, these new Chandra measurements confirm that the quiescent X-ray luminosities of BHXN are significantly lower than those of NSXN. We argue that this provides strong evidence for the existence of event horizons in BHXN.

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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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arXiv2000

Characterizing the Low-Frequency QPO behavior of the X-ray Nova XTE J1550-564

For all 209 RXTE observations of the 7-Crab X-ray nova XTE J1550-564, we analyzed the X-ray power spectra, phase lags, and coherence functions. These observations cover the entire 250 day outburst cycle of the source and are the most complete and arguably the richest data set for any black hole X-ray nova. We find that there are three fundamental types of QPO behavior--one more than reported by Wijnands, Homan, & van der Klis (1999, ApJ, 526, 33). The new type occurred during the first half of the outburst. These three types of QPO behavior can be grouped according to the relative contributions of the disk and power-law components to the total flux.

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arXiv2000

A First Look at the Nuclear Region of M31 with Chandra

We report on the first observation of the nuclear region of M31 with the Chandra X-ray Observatory. The nuclear source seen with the Einstein and ROSAT HRIs is resolved into five point sources. One of these sources is within 1'' of the M31 central super-massive black hole. As compared to the other point sources in M31, this nuclear source has an unusual x-ray spectrum. Based on the spatial coincidence we identify this source with the central black hole, and note that the unusual spectrum is a challenge to current theories. A bright transient is detected ~26'' to the west of the nucleus, which may be associated with a stellar mass black hole.

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arXiv1999

Optical Lightcurves of the Black Hole Binaries GRS 1124-68 and A0620-00 in Outburst: the Importance of Irradiation

We test whether the model proposed by Esin et al. to explain X-ray observations of the black hole soft X-ray transient GRS 1124-68 in outburst can also explain the optical lightcurves of a similar object A0620-00. We show that to reproduce the observed X-ray to optical flux ratio in A0620-00, we need to assume X-ray irradiation of the outer disk that is significantly in excess of what is expected for a standard planar disk. With enhanced irradiation, the Esin et al. model can reproduce the optical evolution of A0620-00 in outburst very well. Though we find that optical observations of GRS 1124-68 also imply enhanced X-ray heating of the outer disk, the irradiation appears to be a factor of roughly 3 weaker in this system than in A0620-00. This is surprising, since GRS 1124-68 has a larger disk. We speculate that enhanced irradiation may be due to disk warping, and that the degree of warping differs between the two binaries.

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