arXiv subjects

R. I. Hynes

Publications and source records attributed to R. I. Hynes.

At least 55 records · Page 3Linked to original sources

arXiv2009

The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol

We present optical and infrared photometry of the low-mass X-ray binary EXO 0748-676 in quiescence for the first time in 24 years since it became X-ray active in 1985. We find the counterpart at average magnitudes of R=22.4 and J=21.3. We monitored the source approximately nightly through 2008 November to 2009 January. During this time there was considerable night-to-night optical variability but no long term trends were apparent. The night-to-night variability reveals a periodicity of P=0.159331+/-0.000012d, consistent with the X-ray orbital period to within 0.01%. This indicates that the quiescent optical modulation is indeed orbital in nature rather than a superhump. Interestingly, the modulation remains single-peaked with a deep minimum coincident with the times of X-ray eclipse, and there is no indication of a double-peaked ellipsoidal modulation. This indicates that even in `quiescence' emission from the accretion disk and/or X-ray heated inner face of the companion star dominate the optical emission, and implies that obtaining an accurate dynamical mass estimate in quiescence will be challenging.

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arXiv2008

An anti-correlation between X-ray luminosity and H-alpha equivalent width in X-ray binaries

We report an anticorrelation between continuum luminosity and the equivalent width (EW) of the H-alpha emission line in X-ray binary systems. The effect is evident both in a universal monotonic increase in H-alpha EW with time following outbursts, as systems fade, and in a comparison between measured EWs and contemporaneous X-ray measurements. The effect is most clear for black hole binaries in the low/hard X-ray state, which is prevalent at X-ray luminosities below ~1% Eddington. We do not find strong evidence for significant changes in line profiles across accretion state changes, but this is hampered by a lack of good data at such times. The observed anti-correlation, highly significant for black hole binaries, is only marginally so for neutron star systems, for which there are far less data. Comparison with previously established correlations between optical and X-ray luminosity suggest that the line luminosity is falling as the X-ray and optical luminosities drop, but not as fast (approximately as L_{H-alpha} \propto L_X^{~0.4} \propto L_{opt}^{~0.7}). We briefly discuss possible origins for such an effect, including the optical depth, form of the irradiating spectrum and geometry of the accetion flow. Further refinement of the relation in the future may allow measurements of H-alpha EW to be used to estimate the luminosity of, and hence the distance to, X-ray binary systems. Beyond this, further progress will require a better sample of spectro-photometric data.

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arXiv2008

Optical and UV Light Curves of the Accretion Disk Corona Source 4U 1822-371

The eclipsing low-mass X-ray binary 4U is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectrograms of 4U with the Hubble Space Telescope and new V- and J-band light curves with the 1.3-m SMARTS telescope at CTIO. We present an updated ephemeris for the times of the optical/UV eclipses. Model light curves do not give acceptable fits to the UV eclipses unless the models include an optically-thick ADC.

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arXiv2007

A signature of the donor star in the extra-galactic X-ray binary LMC X-2

Two nights of phase-resolved medium resolution VLT spectroscopy of the extra-galactic low mass X-ray binary LMC X-2 have revealed a 0.32+/-0.02 day spectroscopic period in the radial velocity curve of the HeII lambda4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disk in LMC X-2. This is strengthened by HeII lambda4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMC X-2,with a velocity of K_em=351+/-28 km/s, that we tentatively interpret as coming from the irradiated side of the donor star. Since K_em must be smaller than K_2, this leads to the first upper-limit on the mass function of LMC X-2 of f(M_1)>=0.86Msun (95% confidence), and the first constraints on its system parameters.

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arXiv2007

Kinematical Studies of the Low Mass X-Ray Binary GR Mus (XB1254-690)

We present simultaneous high-resolution optical spectroscopy and X-ray data of the X-ray binary system GR Mus (XB1254-690), obtained over a full range of orbital phases. The X-ray observations are used to re-establish the orbital ephemeris for this source. The optical data includes the first spectroscopic detection of the donor star in this system, through the use of the Doppler Tomography technique on the Bowen fluorescence blend (~4630-4650 A). In combination with an estimate for the orbital parameters of the compact object using the wings of the He II 4686 emission line, dynamical mass constraints of 1.20 < M_X/M_{sun} < 2.64 for the neutron star and 0.45 < M_2/M_{sun} < 0.85 for the companion are derived.

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arXiv2007

Optical spectroscopy of the low mass X-ray binary GX9+9

Phase-resolved medium resolution VLT spectroscopy of the low mass X-ray binary GX9+9 has revealed narrow CIII emission lines that move in phase relative to our new estimate of the ephemeris, and show a velocity amplitude of 230+/-35 km/s. We identify the origin of these lines as coming from the surface of the donor star, thereby providing the first estimate of the mass function of f(M_1)>=0.22M_sun. Rotational broadening estimates together with assumptions for the mass donor give 0.07<q<0.35 and 182<K_2<406 km/s. Despite a low mass ratio, there is no evidence for a superhump in our dataset. Doppler maps of GX9+9 show the presence of a stream overflow, either in the form of material flowing downward along the accretion disk rim or in a similar fashion as occurs in high mass transfer rate cataclysmic variables known as the SW Sex stars. Finally we note that the Bowen region in GX9+9 is dominated by CIII instead of NIII emission as has been the case for most other X-ray binaries.

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arXiv2007

The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton

We present XMM observations of the black hole X-ray nova V404 Cygni in quiescence. Its quiescent spectrum can be best fitted by a simple power-law with slope 2. The spectra are consistent with that expected for the advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in luminosity compared to the previous observation of Chandra. We see variability of a factor of 4 during the observation. We find no evidence for the presence of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and 110 eV respectively. The limit on the fluorescent emission is improved by a factor of 15 over the previous estimate, and the restriction on H-like/He-like emission is lower than predicted from models by a factor of roughly 2.

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arXiv2006

A detection of the donor star of Aquila X-1 during its 2004 outburst?

Phase-resolved high resolution optical spectroscopy has revealed narrow N III and He II emission lines from the soft X-ray transient Aquila X-1 during its 2004 outburst that move as a function of the orbit consistent with the phasing of the donor star. Under the assumption that these lines come from the irradiated side of the donor star, we can constrain its K_2 velocity to >247+/-8 km/s, and derive a mass function of f(M_1)>1.23+/-0.12M_sun. Estimates for the rotational broadening based on the emission components suggest a possible massive neutron star of >1.6M_sun (at 95% confidence). However, an updated ephemeris and additional high resolution spectroscopy of Aql X-1 during a future outburst are warranted in order to confirm that the narrow lines indeed originate on the donor star surface, and reliably characterise the system parameters of this important X-ray binary. Spectra taken during the end of the outburst show that the morphology of the emission lines changed dramatically. No donor star signature was present anymore, while the presence of narrow low-velocity emission lines became clear, making Aql X-1 a member of the slowly growing class of low-velocity emission line sources.

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arXiv2006

Detection of the Irradiated Donor in the LMXBs 4U 1636-536 (=V801 Ara) and 4U 1735-444 (=V926 Sco)

Phase-resolved VLT spectroscopy of the bursting Low Mass X-ray Binaries 4U 1636-536/V801 Ara and 4U 1735-444/V926 Sco is presented. Doppler images of the NIII 4640 Bowen transition reveal compact spots which we attribute to fluorescent emission from the donor star and enable us to define a new set of spectroscopic ephemerides. We measure Kem=277+-22 km/s and Kem=226+-22 km/s from the NIII spots in V801 Ara and V926 Sco respectively which represent strict lower limits to the radial velocity semi-amplitude of the donor stars. Our new ephemerides provide confirmation that lightcurve maxima in V801 Ara and likely V926 Sco occur at superior conjunction of the donor star and hence photometric modulation is caused by the visibility of the X-ray heated donor. The velocities of HeII 4686 and the broad Bowen blend are strongly modulated with the orbital period, with phasing supporting emission dominated by the disc bulge. In addition, a reanalysis of burst oscillations in V801 Ara, using our spectroscopic T0, leads to K1=90-113 km/s. We also estimate the K-corrections for all possible disc flaring angles and present the first dynamical constraints on the masses of these X-ray bursters. These are K2=360+-74 km/s, f(M)=0.76+-0.47 Msun and q=0.21-0.34 for V801 Ara and K2=298+-83 km/s, f(M)=0.53+-0.44 Msun and q=0.05-0.41 for V926 Sco. Disc flaring angles alpha>12 deg and q~0.26-0.34 are favoured for V801 Ara whereas the lack of K1 constraint for V926 Sco prevents tight constraints on this system. Although both binaries seem to have intermediate inclinations, the larger equivalent width of the narrrow NIII line in V801 Ara at phase 0.5 relative to phase 0 suggests that it has the higher inclination of the two.

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arXiv2006

Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst

We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ~10s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHKs photometry, as in the previous outburst, exhibits especially large amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power-law of slope alpha=-0.78 where Fnu is proportional to nu^alpha. There is no compelling evidence for evolution in the slope over five nights, during which time the source brightness decayed along almost the same track as seen in variations within the nights. We conclude that both short-term variability, and longer timescale fading, are dominated by a single component of constant spectral shape. We cannot fit the SED of the IR variability with a credible thermal component, either optically thick or thin. This IR SED is, however, approximately consistent with optically thin synchrotron emission from a jet. These observations therefore provide indirect evidence to support jet-dominated models for XTE J1118+480 and also provide a direct measurement of the slope of the optically thin emission which is impossible based on the average spectral energy distribution alone.

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arXiv2006

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)

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arXiv2006

Multiwavelength Observations of EXO 0748--676 -- II. Emission Line Behavior

We present optical and ultraviolet spectra, lightcurves, and Doppler tomograms of the low-mass X-ray binary EXO 0748-676. Using an extensive set of 15 emission line tomograms, we show that, along with the usual emission from the stream and ``hot spot'', there is extended non-axisymmetric emission from the disk rim. Some of the emission and Halpha and beta absorption features lend weight to the hypothesis that part of the stream overflows the disk rim and forms a two phase medium. The data are consistent with a 1.35M_sun neutron star with a main sequence companion and hence a mass ratio q~0.34.

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arXiv2006

Multiwavelength Observations of EXO 0748-676 - I. Reprocessing of X-ray Bursts

We present the first high time-resolution simultaneous X-ray, ultraviolet, and optical observations of X-ray bursts in UY Vol, the optical counterpart of the low mass X-ray binary EXO 0748-676, obtained with RXTE, HST, and Gemini-S. Strong reprocessed signals are present in the ultraviolet (a factor of 4) and optical (a factor of 2.5). These signals are lagged with respect to the X-rays and appear significantly smeared as well. The addition of far-ultraviolet coverage for one burst, together with the high quality of the dataset, allow much tighter constraints upon the temperature and geometry of the reprocessing region than previously possible. A single-zone black body reprocessing model for this burst suggests a rise in temperatures during the burst from 18,000 to 35,000K and an emitting area comparable to that expected for the disk and/or irradiated companion star. The lags, a mean of 4.0s and range of 2.5s, are consistent with those expected within the binary. The single-zone black body model cannot reproduce the ratio of optical to ultraviolet flux during the burst, however. The discrepancy, corresponding to underpredicting the optical by more than a factor of two, seems too large to explain with deviations from a local black body spectrum and more likely indicates that a range of reprocessing temperatures are required, as would be expected, with cooler regions not contributing to the UV. Comparable results are derived from other bursts, and in particular the lag and smearing both appear shorter when the companion star is on the near side of the disk as predicted. The burst observed by HST also yielded a spectrum of the reprocessed light. [Abridged]

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arXiv2005

ULTRACAM observations of the black hole X-ray transient XTE J1118+480 in quiescence

We present high time-resolution multicolour observations of the quiescent soft X-ray transient XTE J1118+480 obtained with ULTRACAM. Superimposed on the double-humped continuum g' and i'-band lightcurves are rapid flare events which typically last a few minutes. The power density spectrum of the lightcurves can be described by a broken power-law model with a break frequency at ~2 mHz or a power-law model plus a broad quasi-periodic oscillation (QPO) at ~2 mHz. In the context of the cellular-automaton we estimate the size of the quiescent advection-dominated flow (ADAF) region to be ~10^4 Schwarzschild radii, similar to that observed in other quiescent black hole X-ray transients, suggesting the same underlying physics. The similarites between the low/hard and quiescent state PDS suggest a similar origin for the optical and X-ray variability, most likely from regions at/near the ADAF.

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arXiv2005

Observational Constraints Upon Cool Disk Material in Quiescent Black Hole Binaries

We consider current observational constraints on the presence of cool, optically thick disk material in quiescent black hole binaries, specifically focusing on a case study of the prototypical system A0620-00. Such material might be expected to be present theoretically, but is usually claimed to make a negligible contribution at optical and infrared wavelengths. The primary argument is based on measurements of the veiling of stellar photospheric absorption lines, in which it is assumed that the disk spectrum is featureless. We use simulated spectra to explore the sensitivity of veiling measurements to uncertainties in companion temperature, gravity, and metallicity. We find that the derived veiling is extremely sensitive to a mismatch between the temperature and metallicity of the companion and template, but that the effect of a plausible gravity mismatch is much smaller. In general the resulting uncertainty in the amount of veiling is likely to be much larger than the usually quoted statistical uncertainty. We also simulate spectra in which the disk has an emergent spectrum similar to the star and find that in this case, optical veiling constraints are moderately robust. This is because the rotational broadening of the disk is so large that the two line profiles effectively decouple and the measurement of the depth of stellar lines is largely unbiased by the disk component. We note, however, that this is only true at intermediate resolutions or higher, and that significant bias might still affect low resolution IR observations. [Abridged]

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arXiv2004

The Optical and Ultraviolet Spectral Energy Distributions of Short Period Black Hole X-ray Transients in Outburst

We compile optical and UV spectra of a sample of 'typical' short period black hole X-ray transients in outburst. We also survey determinations of interstellar extinction and distance in order to deredden spectra and compare absolute fluxes. Hence we perform a comparative study of the broad-band spectral energy distributions (SED). We find that given such a homogeneous sample of typical sources, the optical SEDs form a relatively uniform set, all exhibiting quasi-power-law spectra with Fnu proportional to nu^alpha, where 0.5<alpha<1.5 (steeper than the canonical nu^1/3 disk spectrum). All become flatter in the UV, although there is more diversity here. The SEDs studied can be broadly divided into two optical-UV spectral states. The UV-hard spectra, e.g. A0620-00 and X-ray Nova Muscae 1991, continue to rise in the far-UV. The UV-soft spectra, e.g. GRO J0422+32, drop off. XTE J1859+226 evolved from UV-soft to UV-hard as it decayed indicating that this effect is a real difference, not a dereddening artifact. All of the spectra can be fitted by a generalized black body disk model with two forms of heating, resulting in the two states. The UV-soft state is consistent with a disk illuminated by a central point source, with irradiative heating dominating over viscous. The UV-hard state is well described by a viscously heated disk, although this requires very high mass flow rates in the case of Nova Muscae. Alternatively, a UV-hard spectrum can be produced if the disk is illuminated by a vertically extended X-ray source such as a central scattering corona or jet. [Abridged]

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arXiv2004

Time-Resolved Ultraviolet Spectroscopy of the SW Sex Star DW UMa: Confirmation of a Hidden White Dwarf and the UV Counterpart to Phase 0.5 Absorption Events

We present time-resolved, ultraviolet (UV) spectroscopy of the SW Sex star DW UMa in the high state. We confirm that, shortward of 1500 Å, the high-state, UV continuum level is lower than the white dwarf (WD)-dominated low-state level. We also do not see the WD contact phases in the high state eclipse light curves. These results confirm our earlier finding that the WD in this system is hidden from view in the high state. Based on this, we caution that eclipse mapping of high-inclination SW Sex stars in the high state may yield incorrect or misleading results. In the context of DW UMa, we demonstrate explicitly that distance estimates obtained by recent eclipse mapping studies cannot be reconciled with the WD-dominated low-state spectrum. We also show that the fluxes of the UV emission lines in the high state drop near orbital phase 0.5. This is the first detection of a UV counterpart to the class-defining phase 0.5 absorption seen in the optical emission lines of SW Sex stars.

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arXiv2004

Correlated X-ray and Optical Variability in X-ray Binaries

It has long been known that X-ray and optical/UV variability in active X-ray binaries is sometimes correlated. The expectation has been that this arises from rapid reprocessing of X-rays into longer wavelength photons, and hence that the lags between the bandpasses can be used to reconstruct an echo-map of the binary, revealing the geometry and spatial scale of reprocessing sites. I will review how this can be done, what can be learned, and what progress has been made with real data. In addition, an interesting twist to the story has emerged in the form of correlated variability that does not seem associated with reprocessing. This extends to very short timescales, includes quasi-periodic behavior, and may be associated with optical synchrotron emission from a jet. Finally, contrary to expectations we have recently discovered that similar correlations are seen even in an ostensibly `quiescent' object allowing similar analyses of reprocessing effects.

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