The outburst radial velocity curve of X-Ray Nova Scorpii 1994 (=GRO J1655--40)

We present a reanalysis of the outburst radial velocity data for X-Ray Nova Scorpii 1994. Using a model based on X-ray heating of the secondary star we suggest a more realistic treatment of the radial velocity data. Solutions are obtained in the (K_2,q) plane which, when combined with the published value for the binary mass ratio and inclination, constrain the mass of the black hole to within the region 4.1<M_1<6.6 Msun (90 per cent confidence), which is significantly lower than the value obtained by Orosz & Bailyn (1997). This reduced lower bound for the black hole mass together with the high space velocity of the system is consistent with the idea that it was formed by the post-supernova collapse of a neutron star.Comment: Accepted for MNRAS, 4 pages Latex, 4 figure

Inclination Effects and Beaming in Black Hole X-ray Binaries

We investigate the dependence of observational properties of black hole X-ray binaries on the inclination angle i of their orbits. We find the following: (1) Transient black hole binaries show no trend in their quiescent X-ray luminosities as a function of i, suggesting that the radiation is not significantly beamed. This is consistent with emission from an accretion disk. If the X-rays are from a jet, then the Lorentz factor gamma of the jet is less than 1.24 at the 90% confidence level. (2) The X-ray binary 4U1543-47 with i of order 21 degrees has a surprisingly strong fluorescent iron line in the high soft state. Quantifying an earlier argument by Park et al. (2004), we conclude that if the continuum X-ray emission in this source is from a jet, then gamma < 1.04. (3) None of the known binaries has cos i 75 degrees. This fact, plus the lack of eclipses among the 20 black hole binaries in our sample, strongly suggests at the 99.5% confidence level that systems with large inclination angles are hidden from view. The obscuration could be the result of disk flaring, as suggested by Milgrom (1978) for neutron star X-ray binaries. (4) Transient black hole binaries with i ~ 70-75 degrees have significantly more complex X-ray light curves than systems with i < 65 degrees. This may be the result of variable obscuration and/or variable height above the disk of the radiating gas.Comment: 26 pages, to appear in The Astrophysical Journal, vol. 624, May 1, 200

HST/STIS UV Spectroscopy of Two Quiescent X-ray Novae: A0620-00 and Centaurus X-4

In 1998 we made UV spectroscopic observations with HST/STIS of A0620-00 and Cen X-4, which are two X-ray novae (aka soft X-ray transients). These binary systems are similar in all respects except that the former contains a black hole and the latter contains a neutron star. A UV spectrum (1700-3100A) is presented for the quiescent state of each system in the context of previously published UV/optical and X-ray data. The non-stellar, continuum spectrum of black hole A0620-00 has a prominent UV/optical peak centered at about 3500A. In contrast the spectrum of neutron-star Cen X-4 lacks a peak and rises steadily with frequency over the entire UV/optical band. In the optical, the two systems are comparably luminous. However, black hole A0620-00 is about 6 times less luminous at 1700A, and about 40 times less luminous in the X-ray band. The broadband spectrum of A0620-00 is discussed in terms of the advection-dominated accretion flow model.Comment: 18 pages including 4 figures; tentatively scheduled for the March 10, 2000 issue of ApJ; minor revision

Near-Infrared Light Curves of the Black Hole Binary A0620-00

We measured the near-infrared orbital light curve of the black hole binary A0620-00 in 1995 and 1996. The light curves show an asymmetric, double-humped modulation with extra emission in the peak at orbital phase 0.75. There were no significant changes in the shape of the light curve over the one-year observation period. There were no sharp dips in the light curves nor reversals of the asymmetry between the two peaks as seen in earlier observations. The light curves are well fit by models incorporating ellipsoidal variations from the mass-losing K-type star plus a beamed bright spot on the accretion disk around the compact star. The long-term stability of the light curve shape rules out superhumps and star spots as sources of asymmetry when we observed A0620-00. The ellipsoidal variations yield a lower limit i >= 38 deg on the orbital inclination. The light curves show no eclipse features, which places an upper limit i <= 75 deg. This range of inclinations constrains the mass of the compact object to 3.3 < M_1 < 13.6 Msun. The light curves do not further constrain the orbital inclination because the contribution of the accretion disk to the observed flux is unknown. We argue that a previous attempt to measure the near-infrared flux from the accretion disk using the dilution of the 12CO(2,0) bandhead in the spectrum of the K star is not reliable because the band strength depends strongly on surface gravity.Comment: Accepted for publication in the Astronomical Journal. 17 pages, 4 figures. Prepared using AASTEX V. 5.

Measures of Health-Related Quality of Life Outcomes in Pediatric Neurosurgery: Literature Review

Background Improving value in healthcare means optimizing outcomes and minimizing costs. The emerging pay-for-performance era requires understanding of the effect of healthcare services on health-related quality of life (HRQoL). Pediatric and surgical subspecialties have yet to fully integrate HRQoL measures into practice. The present study reviewed and characterized the HRQoL outcome measures across various pediatric neurosurgical diagnoses. Methods A literature review was performed by searching PubMed and Google Scholar with search terms such as “health-related quality of life” and “pediatric neurosurgery” and then including the specific pathologies for which a HRQoL instrument was found (e.g., “health-related quality of life” plus “epilepsy”). Each measurement was evaluated by content and purpose, relative strengths and weaknesses, and validity. Results We reviewed 68 reports. Epilepsy, brain tumor, cerebral palsy, spina bifida, hydrocephalus, and scoliosis were diagnoses found in reported studies that had used disease-specific HRQoL instruments. Information using general HRQoL instruments was also reported. Internal, test–retest, and/or interrater reliability varied across the instruments, as did face, content, concurrent, and/or construct validity. Few instruments were tested enough for robust reliability and validity. Significant variability was found in the usage of these instruments in clinical studies within pediatric neurosurgery. Conclusions The HRQoL instruments used in pediatric neurosurgery are currently without standardized guidelines and thus exhibit high variability in use. Clinicians should support the development and application of these methods to optimize these instruments, promote standardization of research, improve performance measures to reflect clinically modifiable and meaningful outcomes, and, ultimately, lead the national discussion in healthcare quality and patient-centered care

Time-resolved optical/near-IR polarimetry of V404 Cyg during its 2015 outburst

We present optical and near-IR linear polarimetry of V404 Cyg during its 2015 outburst and in quiescence. We obtained time resolved r'-band polarimetry when the source was in outburst, near-IR polarimetry when the source was near quiescence and multiple wave-band optical polarimetry later in quiescence. The optical to near-IR linear polarization spectrum can be described by interstellar dust and an intrinsic variable component. The intrinsic optical polarization, detected during the rise of one of the brightest flares of the outburst, is variable, peaking at 4.5 per cent and decaying to 3.5 per cent. We present several arguments that favour a synchrotron jet origin to this variable polarization, with the optical emission originating close to the jet base. The polarization flare occurs during the initial rise of a major radio flare event that peaks later, and is consistent with a classically evolving synchrotron flare from an ejection event. We conclude that the optical polarization flare represents a jet launching event; the birth of a major ejection. For this event we measure a rather stable polarization position angle of -9 degrees E of N, implying that the magnetic field near the base of the jet is approximately perpendicular to the jet axis. This may be due to the compression of magnetic field lines in shocks in the accelerated plasma, resulting in a partially ordered transverse field that have now been seen during the 2015 outburst. We also find that this ejection occurred at a similar stage in the repetitive cycles of flares.Comment: 9 pages, 5 figures, accepted for publication by MNRA

On the bolometric quiescent luminosity and luminosity swing of black hole candidate and neutron star low mass X-ray transients

Low mass X-ray transients (LMXRTs) hosting black hole candidates (BHCs) display on average a factor of ~100 larger swing in the minimum (quiescent) to maximum (outburst) X-ray luminosity than neutron stars (NSs), despite the fact that the swing in the mass inflow rate is likely in the same range. Advection dominated accretion flows (ADAFs) were proposed to interpret such a difference. The residual optical/UV emission of quiescent LMXRTs, after subtraction of the companion star spectrum, is produced by synchrotron radiation in the (latest version) of ADAF and therefore is part of the ADAF's luminosity budget. We demonstrate that, once the residual optical/UV emission is taken into account, the bolometric luminosity swing of BHCs is consistent with that of NSs. We explore here an alternative scenario to ADAFs in which very little mass accretion onto the collapsed star takes place in the quiescence intervals. The residual optical/UV emission of BHCs are expected to derive from the energy released by the matter transferred from the companion star at radii comparable to the circularisation radius. The quiescent X-ray luminosity originates either from accretion onto the BH at very low rates and/or from coronal activity in the companion star or in the outer disk. For comparably small mass inflow rates, the NSs in these systems are likely in the radio pulsar regime. In the interaction of the radio pulsar relativistic wind with matter transferred from the companion star, a shock forms, the power law-like emission of which powers both the harder X-ray emission and most of the residual optical/UV. The soft, thermal-like X-ray component may arise from the cooling of the NS surface. This scenario matches well both the X-ray and bolometric luminosity swing of LMXRTs. (ABRIDGED).Comment: 13 pages (including 2 postscript figures - use emulateapj macro). Accepted for publication in Ap

Optical and near-infrared observations of the microquasar V4641 Sagittarii during the 1999 September outburst

We present photometric and spectroscopic optical and near-infrared (NIR) observations (Based on observations collected at the European Southern Observatory, Chile (ESO ID 63.H-0493 and 64.H-0382)) taken during the outburst of the microquasar V4641 Sgr = SAX J1819.3-2525 (in'tzand et al., 2000) in September 1999. We observed an increase in the J-Ks colour between 5 and 8 days after the outburst, which we interpret as likely evidence for the presence of dust around the source. We also observed an extraordinarily strong, broad and variable H_alpha line, with a velocity width of 4560 km/s suggesting the presence of a high-velocity outflow component. We constrain the distance of the system between 3 and 8 kpc, locating it further away than previously derived from radio observations (Hjellming et al., 2000), but consistent with Orosz et al. (2001). We then discuss the nature of this system, showing that the companion star is either a B3-A2 main sequence star, or a B3-A2 sub-giant crossing the Hertzsprung gap. The system is therefore an Intermediate or High Mass X-ray Binary System (IMXB or HMXB). The distance derived by these optical/NIR observations implies that the jets observed by Hjellming et al. (2000) would then exhibit apparent velocities of ~ 10 c. We finally discuss the possibility of an interaction between the jets and surroundings of the source, and also of this source being a ``microblazar''.Comment: 7 pages, 6 figures, accepted for publication in MNRA