Precessing warped accretion discs in X-ray binaries

We study the radiation-driven warping of accretion discs in the context of X-ray binaries. The latest evolutionary equations are adopted, which extend the classical alpha theory to time-dependent thin discs with non-linear warps. We also develop accurate, analytical expressions for the tidal torque and the radiation torque, including self-shadowing. We investigate the possible non-linear dynamics of the system within the framework of bifurcation theory. First, we re-examine the stability of an initially flat disc to the Pringle instability. Then we compute directly the branches of non-linear solutions representing steadily precessing discs. Finally, we determine the stability of the non-linear solutions. Each problem involves only ordinary differential equations, allowing a rapid, accurate and well resolved solution. We find that radiation-driven warping is probably not a common occurrence in low-mass X-ray binaries. We also find that stable, steadily precessing discs exist for a narrow range of parameters close to the stability limit. This could explain why so few systems show clear, repeatable `super-orbital' variations. The best examples of such systems, Her X-1, SS 433 and LMC X-4, all lie close to the stability limit for a reasonable choice of parameters. Systems far from the stability limit, including Cyg X-2, Cen X-3 and SMC X-1, probably experience quasi-periodic or chaotic variability as first noticed by Wijers & Pringle. We show that radiation-driven warping provides a coherent and persuasive framework but that it does not provide a generic explanation for the long-term variabilities in all X-ray binaries.Comment: 20 pages, 10 figures, to be published in MNRA

High-energy gamma-ray observations of the accreting black hole V404 Cygni during its June 2015 outburst

We report on Fermi/Large Area Telescope observations of the accreting black hole low-mass X-ray binary V404 Cygni during its outburst in June-July 2015. Detailed analyses reveal a possible excess of $\gamma$-ray emission on 26 June 2015, with a very soft spectrum above $100$ MeV, at a position consistent with the direction of V404 Cyg (within the $95\%$ confidence region and a chance probability of $4 \times 10^{-4}$). This emission cannot be associated with any previously-known Fermi source. Its temporal coincidence with the brightest radio and hard X-ray flare in the lightcurve of V404 Cyg, at the end of the main active phase of its outburst, strengthens the association with V404 Cyg. If the $\gamma$-ray emission is associated with V404 Cyg, the simultaneous detection of $511\,$keV annihilation emission by INTEGRAL requires that the high-energy $\gamma$ rays originate away from the corona, possibly in a Blandford-Znajek jet. The data give support to models involving a magnetically-arrested disk where a bright $\gamma$-ray jet can re-form after the occurrence of a major transient ejection seen in the radio.Comment: 5 pages, 3 figures, accepted for publication in MNRA

INTEGRAL observation of the high-mass X-ray transient V 0332+53 during the 2005 outburst decline

The decline of the high mass X-ray transient V 0332+53 during the Dec. 2004 to Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is shown to decrease exponentially until 2005 Feb. 10, with a decay time scale of ∼30 days above 20 keV and ∼20 days at lower energies, and to decrease linearly thereafter. The energy spectrum is well modelled throughout the decay by a power law with a folding energy of ∼7.5 keV, and with two cyclotron absorption features. The folding energy does not vary significantly over the decay, but the spectrum becomes harder with time. Most importantly, we show that the parameters describing the fundamental cyclotron line around 27 keV do vary with time: its energy and depth increase (by about 17% for the energy in ∼6 weeks), while its width decreases. These changes of the cyclotron line parameters are interpreted as resulting from a change in the extent of the cyclotron scattering region. Two quasi-periodic oscillations are also observed at various times during the observations, one at 0.05 Hz and another one near the pulsation frequency around 0.23 Hz

Hypoxia promotes chemoresistance in acute lymphoblastic leukemia cell lines by modulating death signaling pathways

International audienceBackground: Several studies show that bone marrow (BM) microenvironment and hypoxia condition can promote the survival of leukemic cells and induce resistance to anti-leukemic drugs. However, the molecular mechanism for chemoresistance by hypoxia is not fully understood.Methods: In the present study, we investigated the effect of hypoxia on resistance to two therapies, methotrexate (MTX) and prednisolone (PRD), in two cell models for acute lymphoblastic leukemia (ALL). To look for an implication of hypoxia in chemoresistance, cell viability, total cell density and cell proliferation were analyzed. Survival and death signaling pathways were also screened by "reverse phase protein array" (RPPA) and western blotting experiments conducted on selected proteins to confirm the results.Results: We found that hypoxia promotes chemoresistance in both ALL cell lines. The induction of drug-resistance by hypoxia was not associated with an increase in total cell density nor an increase in cell proliferation. Using RPPA, we show that chemoresistance induced by hypoxia was mediated through an alteration of cell death signaling pathways. This protective effect of hypoxia seems to occur via a decrease in pro-apoptotic proteins and an increase in anti-apoptotic proteins. The results were confirmed by immunoblotting. Indeed, hypoxia is able to modulate the expression of anti-apoptotic proteins independently of chemotherapy while a pro-apoptotic signal induced by a chemotherapy is not modulated by hypoxia.Conclusions: Hypoxia is a factor in leukemia cell resistance and for two conventional chemotherapies modulates cell death signaling pathways without affecting total cell density or cell proliferation

Optical and Infrared Light Curves of the Eclipsing X-ray Binary V395 Car = 2S 0921-630

We present results of optical and infrared photometric monitoring of the eclipsing low-mass X-ray binary V395 Car (2S 0921-630). Our observations reveal a clear, repeating orbital modulation with an amplitude of about one magnitude in B, and V and a little less in J. Combining our data with archival observations spanning about 20 years, we derive an updated ephemeris with orbital period 9.0026+/-0.0001d. We attribute the modulation to a combination of the changing aspect of the irradiated face of the companion star and eclipses of the accretion disk around the neutron star. Both appear to be necessary as a secondary eclipse of the companion star is clearly seen. We model the B, V, and J lightcurves using a simple model of an accretion disk and companion star and find a good fit is possible for binary inclinations of 82.2+/-1.0 degrees. We estimate the irradiating luminosity to be about 8x10^35 erg/s, in good agreement with X-ray constraints.Comment: 6 pages, accepted for publication in MNRA

What Role for Angiogenesis in Childhood Acute Lymphoblastic Leukaemia?

The role of angiogenesis in acute leukaemia has been discussed since the cloning of the gene of vascular endothelial growth factor (VEGF) from the acute myelogenous leukemia cell line (HL60) and, thereafter, when the first studies reported increased bone marrow vascularity and elevation of angiogenic cytokines in acute lymphoblastic leukaemia (ALL). VEGF and basic fibroblast growth factor (bFGF) are the major proangiogenic cytokines that have been studied, and evaluation of their prognostic impact in childhood ALL has been reported in several studies, though with controversial results. The antiangiogenic response, contributing to the angiogenic balance, has scarcely been reported. The origin of the factors, their prognostic value, and their relevance as good markers of what really happens in the bone marrow are discussed in this paper. The place of antiangiogenic drugs in ALL has to be defined in the global treatment strategy

Dependent patients discharged home from PRM departments: relevant indicators

OBJECTIVE: To evaluate simple, measurable indicators of optimal organizational procedures for the hospital-to-home discharge of dependent patients.MATERIAL AND METHOD: All the general practitioners (GPs) in the Maine-et-Loire county of France were sent a questionnaire asking them to rank the three main criteria (from the most important to the least significant) from a list of 14. We analyzed the median ranking for each item and identified the most important items in terms of their relative frequency. RESULTS: The response rate was 10.77% (104 out of 966). Four criteria had a median score over 9: contact with the GP prior to discharge, informing the GP of the discharge date, training for the patient and his/her family in activities of daily living and providing a list of people to be contacted in the event of a problem at home. Respite hospitalization (in the event of difficulties at home) was cited as one of the three most relevant criteria. DISCUSSION-CONCLUSION: The criteria highlighted by the GPs were not highly specific for the discharge of a dependent patient. However, it would be interesting to extend this study by interviewing other stakeholders and determining whether these criteria indeed improve the organization of hospital-to-home discharge

Pulsed high energy gamma-rays from thermal populations in the current sheets of pulsar winds

Context. More than one hundred GeV pulsars have been detected up to now by the LAT telescope on the Fermi gamma-ray observatory, showing peak energies around a few GeV. Current modelling proposes that the high energy emission comes from outer magnetospheric gaps, however radiation from the equatorial current sheet which separates the two magnetic hemispheres outside the light cylinder has also been investigated. Aims. In this paper we discuss the region right outside the light cylinder, or "near wind" zone. We investigate the possibility that synchrotron radiation emitted by thermal populations in the equatorial current sheet of the pulsar wind in this region can explain the lightcurves and spectra observed by Fermi/LAT. Methods. We use analytical estimates as well as detailed numerical computation to calculate the gamma-ray luminosities, lightcurves and spectra of gamma-ray pulsars. Results. Many of the characteristics of the gamma-ray pulsars observed by Fermi/LAT can be reproduced by our model, most notably the position of these objects in the P - Pdot diagram, and the range of gamma-ray luminosities. A testable result is a sub-exponential cutoff with an index b = 0.35. We also predict the existence of a population of pulsars with cutoff energies in the MeV range. These have systematically lower spindown luminosities than the Fermi/LAT detected pulsars. Conclusions. It is possible for relativistic populations of electrons and positrons in the current sheet of a pulsar's wind right outside the light cylinder to emit synchrotron radiation that peaks in the sub-GeV to GeV regime, with gamma-ray efficiencies similar to those observed for the Fermi/LAT pulsars.Comment: 13 pages, submitted to A&

Effectiveness of three treatment strategies on occupational limitations and quality of life for patients with non-specific chronic low back pain: Is a multidisciplinary approach the key feature to success: study protocol for a randomized controlled trial

BACKGROUND: Chronic low back pain (cLBP) is a significant public health problem, being the primary cause of work absenteeism, as well as affecting sufferers\u27 quality of life, in industrialized society. International guidelines recommend intensive multidisciplinary approaches for patients with cLBP. However, these costly and time-consuming programs can only be offered to a minority of the most heavily affected patients and therefore do not seem likely to respond to public health requirements. Lighter programs may be an alternative to full time hospital-based programs with valuable results in terms of disability and occupational activity for cLBP patients. It is therefore important to define both what the determining components of management to improve activity restriction are and how to treat a larger number of patients more effectively at a lower cost. The aim of this study is to compare three programs with various levels of intensity and multidisciplinary. METHODS/DESIGN: This paper describes the protocol for a prospective, randomized, controlled, clinical trial in working aged patients with cLBP. Three treatment strategies are compared: (1) intensive and multidisciplinary program conducted in a rehabilitation center; (2) less intensive outpatient program conducted by a private physiotherapist; (3) mixed strategy combining the same out program with a multidisciplinary intervention. The primary outcome of the trial is the impact of the mixed strategy on being able to work compared to hospital centered-program and out program. The secondary outcome is the impact of the mixed strategy on quality of life and social ability compared to the two others programs. The intervention part of the trial programs will take 5 weeks and observational follow-up will take 12 months. The sample size will be 180 participants (60 for each arm). The project has been approved by the Ethical Committee of Angers Hospital, France. DISCUSSION: On the hypothesis that a multidisciplinary approach is the key feature to programs success in reducing social and occupational impairment in cLBP patients, we suggest that it is possible to achieve the same results with less intensive strategies if a multidisciplinary approach is maintained. TRIAL REGISTRATION: Current Controlled Trials NCT02030171

Gamma-ray binaries

Recent observations have shown that some compact stellar binaries radiate the highest energy light in the universe. The challenge has been to determine the nature of the compact object and whether the very high energy gamma-rays are ultimately powered by pulsar winds or relativistic jets. Multiwavelength observations have shown that one of the three gamma-ray binaries known so far, PSR B1259-63, is a neutron star binary and that the very energetic gamma-rays from this source and from another gamma-ray binary, LS I +61 303, may be produced by the interaction of pulsar winds with the wind from the companion star. At this time it is an open question whether the third gamma-ray binary, LS 5039, is also powered by a pulsar wind or a microquasar jet, where relativistic particles in collimated jets would boost the energy of the wind from the stellar companion to TeV energies.Comment: 4 pages, 3 figures. Invited talk to appear in Proceedings of the conference "The Multi-Messenger Approach to High-Energy Gamma-ray Sources", Barcelona, 4-7 July 200