Accretion dynamics in neutron star black hole binaries

We perform three-dimensional, Newtonian hydrodynamic simulations with a nuclear equation of state to investigate the accretion dynamics in neutron star black hole systems. We find as a general result that non-spinning donor stars yield larger circularization radii than corotating donors. Therefore, the matter from a neutron star without spin will more likely settle into an accretion disk outside the Schwarzschild radius. With the used stiff equation of state we find it hard to form an accretion disk that is promising to launch a gamma-ray burst. In all relevant cases the core of the neutron star survives and keeps orbiting the black hole as a mini neutron star for the rest of the simulation time (up to several hundred dynamical neutron star times scales). The existence of this mini neutron star leaves a clear imprint on the gravitational wave signal which thus can be used to probe the physics at supra-nuclear densities.Comment: submitted to MNRAS, 23 pages, 16 figure

Three Types of Cooling Superfluid Neutron Stars: Theory and Observations

Cooling of neutron stars (NSs) with the cores composed of neutrons, protons, and electrons is simulated assuming $^1$S$_0$ pairing of neutrons in the NS crust, and also $^1$S$_0$ pairing of protons and weak $^3$P$_2$ pairing of neutrons in the NS core, and using realistic density profiles of the superfluid critical temperatures $T_{\rm c}(\rho)$. The theoretical cooling models of isolated middle-aged NSs can be divided into three main types. (I) {\it Low-mass}, {\it slowly cooling} NSs where the direct Urca process of neutrino emission is either forbidden or almost fully suppressed by the proton superfluidity. (II) {\it Medium-mass} NSs which show {\it moderate} cooling via the direct Urca process suppressed by the proton superfluidity. (III) {\it Massive} NSs which show {\it fast} cooling via the direct Urca process weakly suppressed by superfluidity. Confronting the theory with observations we treat RX J0822--43, PSR 1055--52 and RX J1856--3754 as slowly cooling NSs. To explain these sufficiently warm sources we need a density profile $T_{\rm c}(\rho)$ in the crust with a rather high and flat maximum and sharp wings. We treat 1E 1207--52, RX J0002+62, PSR 0656+14, Vela, and Geminga as moderately cooling NSs. We can determine their masses for a given model of proton superfluidity, $T_{\rm cp}(\rho)$, and the equation of state in the NS core. No rapidly cooling NS has been observed so far.Comment: 12 pages, 10 figures, Astron. Astrophys., submitte

Computation of Neutron Star Structure Using Modern Equation of State

Using the modern equations of state derived from microscopic calculations, we have calculated the neutron star structure. For the neutron star, we have obtained a minimum mass about $0.1 {\rm M_{\odot}}$ which is nearly independent of the equation of state, and a maximum mass between $1.47 {\rm M_{\odot}}$ and $1.98 {\rm M_{\odot}}$ which is strongly dependent on the equation of state. It is shown that among the equations of state of neutron star matter which we have used, the stiffest one leads to higher maximum mass and radius and lower central density. It is seen that the given maximum mass for the Reid-93 equation of state shows a good consistency with the accurate observations of radio pulsars. We have indicated that the thickness of neutron star crust is very small compared to the predicted neutron star radius.Comment: 16 pages, 6 figure

Cooling of Akmal-Pandharipande-Ravenhall neutron star models

We study the cooling of superfluid neutron stars whose cores consist of nucleon matter with the Akmal-Pandharipande-Ravenhall equation of state. This equation of state opens the powerful direct Urca process of neutrino emission in the interior of most massive neutron stars. Extending our previous studies (Gusakov et al. 2004a, Kaminker et al. 2005), we employ phenomenological density-dependent critical temperatures T_{cp}(\rho) of strong singlet-state proton pairing (with the maximum T_{cp}^{max} \sim 7e9 K in the outer stellar core) and T_{cnt}(\rho) of moderate triplet-state neutron pairing (with the maximum T_{cnt}^{max} \sim 6e8 K in the inner core). Choosing properly the position of T_{cnt}^{max} we can obtain a representative class of massive neutron stars whose cooling is intermediate between the cooling enhanced by the neutrino emission due to Cooper pairing of neutrons in the absence of the direct Urca process and the very fast cooling provided by the direct Urca process non-suppressed by superfluidity.Comment: 9 pages, 6 figures; accepted for publication in MNRA

The effects of r-process heating on fall-back accretion in compact object mergers

We explore the effects of r-process nucleosynthesis on fall-back accretion in neutron star(NS)-NS and black hole-NS mergers, and the resulting implications for short-duration gamma-ray bursts (GRBs). Though dynamically important, the energy released during the r-process is not yet taken into account in merger simulations. We use a nuclear reaction network to calculate the heating (due to beta-decays and nuclear fission) experienced by material on the marginally-bound orbits nominally responsible for late-time fall-back. Since matter with longer orbital periods t_orb experiences lower densities, for longer periods of time, the total r-process heating rises rapidly with t_orb, such that material with t_orb > 1 seconds can become completely unbound. Thus, r-process heating fundamentally changes the canonical prediction of an uninterrupted power-law decline in the fall-back rate dM/dt at late times. When the timescale for r-process to complete is > 1 second, the heating produces a complete cut-off in fall-back accretion after ~ 1 second; if robust, this would imply that fall-back accretion cannot explain the late-time X-ray flaring observed following some short GRBs. However, for a narrow, but physically plausible, range of parameters, fall-back accretion can resume after ~ 10 s, despite having been strongly suppressed for ~ 1-10 s after the merger. This suggests the intriguing possibility that the gap observed between the prompt and extended emission in short GRBs is a manifestation of r-process heating.Comment: 7 pages; 4 figures; submitted to MNRA

Availability of Supervised Exercise Programs and the Role of Structured Home-based Exercise in Peripheral Arterial Disease

AbstractObjectivesThe effectiveness of supervised exercise programs (SEPs) for the management of peripheral arterial disease (PAD) can be hampered by low accessibility and poor compliance. The current international availability and use of SEPs was evaluated and the evidence on alternative approaches such as structured, home-based exercise programs (HEPs) was reviewed.Methods-materialsInternational survey on SEP availability among vascular surgeons using an online questionnaire. A systematic review on structured-HEPs effectiveness was also performed.ResultsA total of 378 responses were collected from 43 countries, with the majority (95%) from Europe. Only 30.4% of the participants had access to SEPs and within this group there was significant heterogeneity on the way SEPs were implemented. This systematic review identified 12 studies on the effectiveness of HEPs. In 3 studies SEPs were superior to HEPs in improving functional capacity or equivalent in improving quality of life (QoL). HEPs significantly improved most of the functional capacity and QoL markers when compared to the “go home and walk” advice and baseline measurements.ConclusionsSEPs remain an underutilized tool despite recommendations. Structured HEPs may be effective and can be useful alternatives when SEPs are not available. Further research is warranted to establish cost-effectiveness

Validation of a New Duplex Derived Haemodynamic Effectiveness Score, the Saphenous Treatment Score, in Quantifying Varicose Vein Treatments

AbstractObjectivesTo evaluate a duplex-derived score for varicose vein treatments using numerical values of haemodynamic effectiveness.DesignThe saphenous treatment score (STS) was developed prospectively to compare the effect of endovenous treatments on reflux within saphenous segments.PatientsSixty-six patients were randomised to endovenous laser ablation (EVLA) or ultrasound-guided foam sclerotherapy (UGFS) to the great saphenous vein (GSV).MethodsAssessments included the Aberdeen varicose vein severity score (AVVSS), the venous clinical severity score (VCSS), the venous filling index (VFI) and the STS.ResultsA mean STS of 5.70 decreased to 3.30, P < .0005, post-treatment. The median (IQR) AVVSS, VCSS and VFI (ml/sec) decreased from 21.52(15.48) to 18.86(11.27), P = .14, from 6(4) to 3(4), P < .0005 and from 7.1(6.9) to 1.9(.9) P < .0005, respectively. In 15 patients requiring additional UGFS the mean STS values decreased from 5.8 to 4.13 and then to 2.6 P < .0005, respectively. The individual above and below knee mean treatment differences in STS on 38 EVLA and 28 UGFS patients were 1.92 and .87 (EVLA) compared to 1.57and .29 (UGFS) P = .001, respectively.ConclusionsThe STS has been shown to grade the haemodynamic effects of different treatments as well as ongoing treatments on the GSV

Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter

The bulk viscosity of the neutron star matter due to the direct Urca processes involving nucleons, electrons and muons is studied taking into account possible superfluidity of nucleons in the neutron star cores. The cases of singlet-state pairing or triplet-state pairing (without and with nodes of the superfluid gap at the Fermi surface) of nucleons are considered. It is shown that the superfluidity may strongly reduce the bulk viscosity. The practical expressions for the superfluid reduction factors are obtained. For illustration, the bulk viscosity is calculated for two models of dense matter composed of neutrons, protons,electrons and muons. The presence of muons affects the bulk viscosity due to the direct Urca reactions involving electrons and produces additional comparable contribution due to the direct Urca reactions involving muons. The results can be useful for studying damping of vibrations of neutron stars with superfluid cores.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy and Astrophysic

Nucleon Superfluidity vs Observations of Cooling Neutron Stars

Cooling simulations of neutron stars (NSs) are performed assuming that stellar cores consist of neutrons, protons and electrons and using realistic density profiles of superfluid critical temperatures $T_{cn}(\rho)$ and $T_{cp}(\rho)$ of neutrons and protons. Taking a suitable profile of $T_{cp}(\rho)$ with maximum $\sim 5 \times 10^9$ K one can obtain smooth transition from slow to rapid cooling with increasing stellar mass. Adopting the same profile one can explain the majority of observations of thermal emission from isolated middle--aged NSs by cooling of NSs with different masses either with no neutron superfluidity in the cores or with a weak superfluidity, $T_{cn} < 10^8$ K. The required masses range from $\sim 1.2 M_\odot$ for (young and hot) RX J0822-43 and (old and warm) PSR 1055-52 and RX J1856-3754 to $\approx 1.45 M_\odot$ for the (colder) Geminga and Vela pulsars. Observations constrain the $T_{cn}(\rho)$ and $T_{cp}(\rho)$ profiles with respect to the threshold density of direct Urca process and maximum central density of NSs.Comment: 4 pages, 2 figures, AA Letters, accepte