Angular momentum losses and the orbital period distribution of cataclysmic variables below the period gap: effects of circumbinary disks

The population synthesis of cataclysmic variables below the period is investigated. A grid of detailed binary evolutionary sequences has been calculated and included in the simulations to take account of additional angular momentum losses beyond that associated with gravitational radiation and mass loss, due to nova outbursts, from the system. As a specific example, we consider the effect of a circumbinary disk to gain insight into the ingredients necessary to reproduce the observed orbital period distribution. The resulting distributions show that the period minimum lies at about 80 minutes with the number of systems monotonically increasing with increasing orbital period to a maximum near 90 minutes. There is no evidence for an accumulation of systems at the period minimum which is a common feature of simulations in which only gravitational radiation losses are considered. The period distribution is found to be fairly flat for orbital periods ranging from about 85 to 120 minutes. The steepness of the lower edge of the period gap can be reproduced, for example, by an input of systems at periods near 2.25 hrs due to a flow of cataclysmic variable binary systems from orbital periods longer than 2.75 hrs. The good agreement with the cumulated distribution function of observed systems within the framework of our model indicates that the angular momentum loss by a circumbinary disk or a mechanism which mimics its features coupled with a weighting factor to account for selection effects in the discovery of such systems and a flow of systems from above the period gap to below the period gap are important ingredients for understanding the overall period distribution of cataclysmic variable binary systems.Comment: Accepted for publication in Ap

An approach for the estimation of the aggregated photovoltaic power generated in several European countries from meteorological data

Classical approaches to the calculation of the photovoltaic (PV) power generated in a region from meteorological data require the knowledge of the detailed characteristics of the plants, which are most often not publicly available. An approach is proposed with the objective to obtain the best possible assessment of power generated in any region without having to collect detailed information on PV plants. The proposed approach is based on a model of PV plant coupled with a statistical distribution of the prominent characteristics of the configuration of the plant and is tested over Europe. The generated PV power is first calculated for each of the plant configurations frequently found in a given region and then aggregated taking into account the probability of occurrence of each configuration. A statistical distribution has been constructed from detailed information obtained for several thousands of PV plants representing approximately 2 % of the total number of PV plants in Germany and was then adapted to other European countries by taking into account changes in the optimal PV tilt angle as a function of the latitude and meteorological conditions. The model has been run with bias-adjusted ERA-interim data as meteorological inputs. The results have been compared to estimates of the total PV power generated in two countries: France and Germany, as provided by the corresponding transmission system operators. Relative RMSE of 4.2 and 3.8 % and relative biases of −2.4 and 0.1 % were found with three-hourly data for France and Germany. A validation against estimates of the country-wide PV-power generation provided by the ENTSO-E for 16 European countries has also been conducted. This evaluation is made difficult by the uncertainty on the installed capacity corresponding to the ENTSO-E data but it nevertheless allows demonstrating that the model output and TSO data are highly correlated in most countries. Given the simplicity of the proposed approach these results are very encouraging. The approach is particularly suited to climatic timescales, both historical and future climates, as demonstrated here

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

A Spectacular VHE Gamma-Ray Outburst from PKS 2155-304 in 2006

Since 2002 the VHE (>100 GeV) gamma-ray flux of the high-frequency peaked BL Lac PKS 2155-304 has been monitored with the High Energy Stereoscopic System (HESS). An extreme gamma-ray outburst was detected in the early hours of July 28, 2006 (MJD 53944). The average flux above 200 GeV observed during this outburst is ~7 times the flux observed from the Crab Nebula above the same threshold. Peak fluxes are measured with one-minute time scale resolution at more than twice this average value. Variability is seen up to ~600 s in the Fourier power spectrum, and well-resolved bursts varying on time scales of ~200 seconds are observed. There are no strong indications for spectral variability within the data. Assuming the emission region has a size comparable to the Schwarzschild radius of a ~10^9 solar mass black hole, Doppler factors greater than 100 are required to accommodate the observed variability time scales.Comment: 4 pages, 3 figures; To appear in the Proceedings of the 30th ICRC (Merida, Mexico

Extreme Blazars Studied with Fermi-LAT and Suzaku: 1ES 0347-121 and Blazar Candidate HESS J1943+213

We report on our study of high-energy properties of two peculiar TeV emitters: the "extreme blazar" 1ES 0347-121 and the "extreme blazar candidate" HESS J1943+213 located near the Galactic Plane. Both objects are characterized by quiescent synchrotron emission with flat spectra extending up to the hard X-ray range, and both were reported to be missing GeV counterparts in the Fermi-LAT 2-year Source Catalog. We analyze a 4.5 year accumulation of the Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as well as in improved upper limits for HESS J1943+213. We also present the analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray spectrum is well represented by a single power law extending up to 25 keV with photon index 2.00+/-0.02 and a moderate absorption in excess of the Galactic value, in agreement with previous X-ray observations. No short-term X-ray variability was found over the 80 ks duration of the Suzaku exposure. Under the blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121 and HESS J1943+213, and derived constraints on the intergalactic magnetic field strength and source energetics. We conclude that although the classification of HESS J1943+213 has not yet been determined, the blazar hypothesis remains the most plausible option, since in particular the broad-band spectra of the two analyzed sources along with the source model parameters closely resemble each other, and the newly available WISE and UKIDSS data for HESS J1943+213 are consistent with the presence of an elliptical host at the distance of approximately ~600 Mpc.Comment: 10 pages, 7 figures, 3 tables. Accepted by Ap

Broad and Luminous [OIII] and [NII] in Globular Cluster ULXs

We consider an accretion-disc origin for the broad and luminous forbidden-line emission observed in ultraluminous X-ray (ULX) sources CXOJ033831.8-352604 and XMMU 122939.7+075333 in globular clusters hosted by elliptical galaxies NGC 1399 and NGC 4472, respectively. We will refer to the latter by the globular cluster name RZ2109. The first has strong [OIII] and [NII], the second only [OIII]. Both H$\alpha$ and H$\beta$ are very weak or undetected in both objects. We assume that the large line widths are due to Keplerian rotation around a compact object and derive expressions for maximum line luminosities. These idealized models require central masses $\gtrsim100$ and \gtrsim30000\Msun for CXOJ033831.8-352604 and RZ2109, respectively. An independent, bootstrap argument for the total disc mass yields, for both systems, M_{\mathrm{disc}}\gtrsim10^{-4}\Msun for a purely metallic disc (and two orders of magnitude larger for solar metallicities). If Roche-lobe overflow is implicated, viscous time-scales are $\gtrsim300$ yr. Standard disc theory then offers another limit on the central masses. Lobe radii for a \sim1\Msun donor are $\gtrsim10^{13}$ cm. We therefore rule out Roche-lobe overflow of a white dwarf in both systems. Red giants could fill the necessary lobes. Whether they are too metal-poor to produce the strong forbidden lines without strong hydrogen emission is unclear.Comment: Accepted to MNRAS Letters, 5 pages, 6 figure

The origin and fate of short-period low-mass black-hole binaries

We present results of a population synthesis study for semidetached short orbital period binaries which contain low-mass(<1.5 Msun) donors and black hole (>4 Msun) accretors. Evolution of these binaries is determined by nuclear evolution of the donors and/or orbital angular momentum loss due to magnetic braking by the stellar wind of the donors and gravitational wave radiation. According to our model, the estimated total number of this type of black-hole binaries in the Galaxy is about 10000. If the magnetic braking is described by the Verbunt & Zwaan formula, the model predicts around 3000 transient systems with periods >2 hours and around 300 luminous stable systems with periods between 3 and 8 hours. Several dozens of these bright systems should be above the RXTE ASM sensitivity limit. The absence of such systems implies that angular momentum losses are reduced by a factor more than 2 with respect to the Verbunt & Zwaan prescription. We show that it is unlikely that the transient behaviour of black-hole short-period X-ray binaries is explained by the evolved nature of the stellar companion. A substantial fraction of black-hole binaries with periods >3 hours could be faint with truncated, stable cold accretion discs as proposed by Menou et al. Most of the semidetached black-hole binaries are expected to have periods shorter than ~2 hours. Properties of such, still to be observed, very small mass-ratio (q<0.02) binaries are different from those of their longer period cousins.Comment: 13 pages, 6 figures, accepted for publication in A&

XMM-Newton Observations of the Ultraluminous Nuclear X-ray Source in M33

We present observations with XMM-Newton of M33 X-8, the ultraluminous X-ray source (L_{0.5-10 keV} ~ 2x10^39 erg/s) closest to the centre of the galaxy. The best-fit model is similar to the typical model of Galactic black holes in very high state. Comparison with previous observations indicates that the source is still in a very high state after about 20 years of observations. No state transition has been observed even during the present set of XMM-Newton observations. We estimate the lower limit of the mass of the black hole >6 M_sun, but with proper parameters taking into account different effects, the best estimate becomes 12 M_sun. Our analysis favours the hypothesis that M33 X-8 is a stellar mass black hole candidate, in agreement with the findings of other authors. In addition, we propose a different model where the high luminosity of the source is likely to be due to orientation effects of the accretion disc and anisotropies in the Comptonized emission.Comment: 9 pages, 5 figures. Accepted for publication on A&A Main Journal. A bug in the introduction has been corrected (a citation

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

Return to work of 87 severely impaired low back pain patients two years after a program of intensive functional restoration

Return to work is the main long-term objective of rehabilitation programs for patients with chronic low back pain (LBP).Objectives Evaluation of work status and number of sick leaves in 87 severely impaired LBP patients 2 years after a functional restoration program. Patients and methods Open prospective study. Population: 87 chronic LBP patients. Intervention: multidisciplinary functional restoration program. Ergonomic advice on the workplace was performed for 53 patients. Outcome: work status and number of sick leaves due to LBP. Results The characteristics of the 26 patients lost to follow-up did not differ significantly from the rest of the population before the program. In the 61 remaining patients, 48 (78%) were at work at 2 years, 43 full-time and 22 at the same job. Nineteen worked in a different environment. Sick leaves were reduced by 60% compared to the 2 years prior to the program: 128 days (± 200 days) versus 329 days (± 179 days); p &lt; 0.005. Conclusion Sick leaves remained significantly reduced and the number of workers who were at work significantly increased at 2 years after an intensive program