We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights ...show steep power spectra dominated by slow variations on ∼100–1000 s time-scales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ∼ few × 1036 erg s−1. Some are unresolved down to a time resolution of 24 ms. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power and characteristic time-scales of the fast flares can be explained as optically thin synchrotron emission from a compact jet arising on size scales ∼140–500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong Hα emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e. red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in time-scale during the outburst.
We present cross-correlation analyses of simultaneous X-ray and near-infrared (near-IR) observations of the microquasar GRS 1915+105 during relativistic jet-producing epochs (X-ray class alpha and ...beta). While previous studies have linked the large amplitude IR flares and X-ray behaviors to jet formation in these states, our new analyses are sensitive to much lower amplitude IR variability, providing more sensitive probes of the jet formation process. The X-ray to IR cross-correlation function (CCF) shows significant correlations that vary in form between the different X-ray states. During low/hard dips in both classes, we find no significant X-ray/IR correlation. During high-variability epochs, we find consistently significant correlations in both alpha and beta classes, but with strong differences in the CCF structure. The high variability alpha CCF shows strong anti-correlation between X-ray/IR, with the X-ray preceding the IR by ~13 + or - 2 s. The high variability beta state shows a time-variable CCF structure, which is statistically significant but without a clearly consistent lag. Our simulated IR light curves, designed to match the observed CCFs, show variably flickering IR emission during the class beta high-variability epoch, while class alpha can be fit by IR flickering with frequencies in the range 0.1-0.3 Hz, strengthening ~10 s after every X-ray subflare. We interpret these features in the context of the X-ray-emitting accretion disk and IR emission from relativistic jet formation in GRS 1915+105, concluding that the CCF analysis places the origin in a synchrotron-emitting relativistic compact jet at a distance from the compact object of ~0.02 AU.
Aims. Massive B-type stars with strong magnetic fields and fast rotation are very rare and pose a mystery for theories of star formation and magnetic field evolution. Only two such stars, called σ ...Ori E analogues, were known until recently. A team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, announced the discovery of two additional rigidly rotating magnetosphere stars, HD 23478 and HD 345439. The magnetic fields in these newly discovered σ Ori E analogues have not been investigated so far. Methods. In the framework of our ESO Large Programme and one normal ESO programme, we carried out low-resolution FORS 2 spectropolarimetric observations of HD 23478 and HD 345439. Results. In the measurements of hydrogen lines, we discover a rather strong longitudinal magnetic field of up to 1.5 kG in HD 23478 and up to 1.3 kG using the entire spectrum. The analysis of HD 345439 using four subsequent spectropolarimetric subexposures does not reveal a magnetic field at a significance level of 3σ. On the other hand, individual subexposures indicate that HD 345439 may host a strong magnetic field that rapidly varies over 88 min. The fast rotation of HD 345439 is also indicated by the behaviour of several metallic and He i lines in the low-resolution FORS 2 spectra that show profile variations already on this short time-scale.
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Objective: To assess the feasibility of backward cycling for people with Parkinson’s disease. Secondary objectives were to assess changes in gait and balance following a 6-week program. Design: A ...single-group prospective pre-test, post-test study with 1-month follow-up. Subjects/Patients: Twenty-six people with Parkinson’s disease (mean age: 69 (7.74) years, gender: 83% males, time since diagnosis: 6 (4.44) years). Methods: Participants pedaled backward on a stationary bicycle for 30 minutes at moderate intensity twice a week for 6 weeks. Feasibility was assessed by acceptability, suitability, and burden. Data collected at pre- and post-intervention with 1-month follow-up included backward stepping response variables, forward/backward gait variables, Mini-Balance Evaluation Systems Test (MBT), and 6 Minute Walk Test. Results: There was a high retention rate (95.8%) and adherence rate (100%) with one adverse event and minimal burden. Significant improvements were seen in step count and excursion distance during backward stepping responses, forward and backward gait velocity, forward step length, and the Mini-BESTest. Conclusion: Backward cycling was a feasible intervention for people with Parkinson’s disease, demonstrating low burden with high retention and adherence rates, and it is a safe exercise with the potential for benefits in gait and balance variables.
The bright, erratic black hole X-ray binary GRS 1915+105 has long been a target for studies of disk instabilities, radio/infrared jets, and accretion disk winds, with implications that often apply to ...sources that do not exhibit its exotic X-ray variability. With the launch of the Neutron star Interior Composition Explorer (NICER), we have a new opportunity to study the disk wind in GRS 1915+105 and its variability on short and long timescales. Here we present our analysis of 39 NICER observations of GRS 1915+105 collected during five months of the mission data validation and verification phase, focusing on Fe xxv and Fe xxvi absorption. We report the detection of strong Fe xxvi in 32 (>80%) of these observations, with another four marginal detections; Fe xxv is less common, but both likely arise in the well-known disk wind. We explore how the properties of this wind depend on broad characteristics of the X-ray lightcurve: mean count rate, hardness ratio, and fractional rms variability. The trends with count rate and rms are consistent with an average wind column density that is fairly steady between observations but varies rapidly with the source on timescales of seconds. The line dependence on spectral hardness echoes the known behavior of disk winds in outbursts of Galactic black holes; these results clearly indicate that NICER is a powerful tool for studying black hole winds.
The SDSS III APOGEE survey recently identified two new a Ori E type candidates, HD 345439 and HD 23478, which are a rare subset of rapidly rotating massive stars whose large (kGauss) magnetic fields ...confine circumstellar material around these systems. Our analysis of multi-epoch photometric observations of HD 345439 from the Kilodegree Extremely Little Telescope, Wide Angle Search for Planets, and ASAS surveys reveals the presence of a ~0.7701 day period in each data set, suggesting the system is among the faster known sigma Ori E analogs. We also see clear evidence that the strength of Halpha, HI Brackett series lines, and He I lines also vary on a ~0.7701 day period from our analysis of multi-epoch, multi-wavelength spectroscopic monitoring of the system from the APO 3.5 m telescope. We trace the evolution of select emission line profiles in the system, and observe coherent line profile variability in both optical and infrared H I lines, as expected for rigidly rotating magnetosphere stars. We also analyze the evolution of the H I Br-11 line strength and line profile in multi-epoch observations of HD 23478 from the SDSS-III APOGEE instrument. The observed periodic behavior is consistent with that recently reported by Sikora and collaborators in optical spectra.
Objectives: Glioblastomas are aggressive primary brain cancers that are characterized by extensive infiltration into the brain and are highly resistant to treatment. Through mathematical modelling, ...we model the process of invasion and predict the relative importance of mechanisms contributing to malignant invasion. Clinically, we predict patterns of tumour recurrence following various modes of therapeutic intervention.
Materials and methods: Our mathematical model uses a realistic three‐dimensional brain geometry and considers migrating and proliferating cells as separate classes. Several mechanisms for infiltrative migration are considered. Methods are developed for simulating surgical resection, radiotherapy and chemotherapy.
Results: The model provides clinically realistic predictions of tumour growth and recurrence following therapeutic intervention. Specific results include (i) invasiveness is governed largely by the ability of glioblastoma cells to degrade and migrate through the extracellular matrix and the ability of single migrating cells to form colonies; (ii) tumours originating deeper in the brain generally grow more quickly than those of superficial origin; (iii) upon surgery, the margins and geometry of resection significantly determine the extent and pattern of postoperative recurrence; (iv) radiotherapy works synergistically with greater resection margins to reduce recurrence; (v) simulations in both two‐ and three‐dimensional geometries give qualitatively similar results; and (vi) in an actual clinical case comprising several surgical interventions, the model provides good qualitative agreement between the simulated and observed course of the disease.
Conclusions: The model provides a useful initial framework by which biological mechanisms of invasion and efficacy of potential treatment regimens may be assessed.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
We present an extinction map of the inner ∼15′ by 16′ of the Galactic center (GC) with map pixels measuring 5″ × 5″ using integrated light color measurements in the near- and mid-infrared. ...We use a variant of the Rayleigh–Jeans color excess (RJCE) method first described by Majewski et al. as the basis of our work, although we have approached our problem with a Bayesian mindset and dispensed with point-source photometry in favor of surface photometry, turning the challenge of the extremely crowded field at the GC into an advantage. Our results show that extinction at the GC is not inconsistent with a single power-law coefficient,
β
= 2.03 ± 0.06, and compare our results with those using the red clump (RC) point-source photometry method of extinction estimation. We find that our measurement of
β
and its apparent lack of spatial variation are in agreement with prior studies, despite the bimodal distribution of values in our extinction map at the GC with peaks at 5 and 7.5 mag. This bimodal nature of extinction is likely due to the infrared dark clouds that obscure portions of the inner GC field. We present our extinction law and map of the GC region using the point-source catalog of infrared sources compiled by DeWitt et al. The dereddening is limited by the error in the extinction measurement (typically 0.6 mag), which is affected by the size of our map pixels and is not fine-grained enough to separate out the multiple stellar populations present toward the GC.
We analyzed multiwavelength observations of the previously identified Galactic center X-ray binary CXO 174528.79-290942.8 (XID 6592) and determine that the near-infrared counterpart is a red ...supergiant based on its spectrum and luminosity. Scutum X-1 is the only previously known X-ray binary with a red supergiant donor star and closely resembles XID 6592 in terms of X-ray luminosity (LX), absolute magnitude, and IR variability (LIR,var), supporting the conclusion that XID 6592 contains a red supergiant donor star. The XID 6592 infrared counterpart shows variability of ∼0.5 mag in the Wide-field Infrared Survey Explorer-1 band (3.4 m) on timescales of a few hours. Other infrared data sets also show large-amplitude variability from this source at earlier epochs but do not show significant variability in recent data. We do not expect red supergiants to vary by ∼50% in luminosity over these short timescales, indicating that the variability should be powered by the compact object. However, the X-ray luminosity of this system is typically ∼1000× less than the variable luminosity in the infrared and falls below the Chandra detection limit. While X-ray reprocessing can produce large-amplitude fast infrared variability, it typically requires LIR,var to do so, indicating that another process must be at work. We suggest that this system may be a supergiant fast X-ray transient (SFXT), and that a large (∼1038 ergs s−1), fast (102-4 s) X-ray flare could explain the rapid IR variability and lack of a long-lasting X-ray outburst detection. SFXTs are normally associated with blue supergiant companions, so if confirmed, XID 6592 would be the first red supergiant SFXT, as well as the second X-ray red supergiant binary.
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