The Kepler Light Curve of V344 Lyrae: Constraining the Thermal-Viscous Limit Cycle Instability

We present time dependent modeling based on the accretion disk limit cycle model for a 270 d light curve of the short period SU UMa-type dwarf nova V344 Lyr taken by Kepler. The unprecedented precision and cadence (1 minute) far surpass that generally available for long term light curves. The data encompass two superoutbursts and 17 normal (i.e., short) outbursts. The main decay of the superoutbursts is nearly perfectly exponential, decaying at a rate ~12 d/mag, while the much more rapid decays of the normal outbursts exhibit a faster-than-exponential shape. Our modeling using the basic accretion disk limit cycle can produce the main features of the V344 Lyr light curve, including the peak outburst brightness. Nevertheless there are obvious deficiencies in our model light curves: (1) The rise times we calculate, both for the normal and superoutbursts, are too fast. (2) The superoutbursts are too short. (3) The shoulders on the rise to superoutburst have more structure than the shoulder in the observed superoutburst and are too slow, comprising about a third to half of the total viscous plateau, rather than the ~10% observed. However, one of the alpha_{cold} -> alpha_{hot} interpolation schemes we investigate (one that is physically motivated) does yield longer superoutbursts with suitably short, less structured shoulders.Comment: 39 pages, 9 figures, accepted in the Astrophysical Journa

Optical properties of Ge-oxygen defect center embedded in silica films

The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick Ge-doped silica film on a pure silica substrate were investigated by looking at the emission spectra and time decay detected under synchrotron radiation excitation in the 10-300 K temperature range. This center exhibits two luminescence bands centered at 4.3eV and 3.2eV associated with its de-excitation from singlet (S1) and triplet (T1) states, respectively, that are linked by an intersystem crossing process. The comparison with results obtained from a bulk Ge-doped silica sample evidences that the efficiency of the intersystem crossing rate depends on the properties of the matrix embedding the Ge-oxygen defect centers, being more effective in the film than in the bulk counterpart.Comment: 10 pages, 3 figures, in press on J. Non cryst. solids (2007

Short gamma-ray bursts within 200 Mpc

We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14 yr of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance ≲100 Mpc and four plausible candidates in the range 100 Mpc ≲ D ≲ 200 Mpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses (⁠≲10−3M⊙⁠) of lanthanide-poor ejecta or unfavorable orientations (θ_(obs) ≳ 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is 1.3^(+1.7)_(−0.8) yr⁻¹ (68 per cent confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of ≲2.0 yr⁻¹ (90 per cent confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi

Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li

We carried out the first multi-wavelength (optical/UV and X-ray) photometric reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find that its X-ray variations are correlated with and lag the optical/UV fluctuations by 32$\pm$4 days. Based on the direction and the magnitude of the X-ray time lag, we rule out X-ray reprocessing and direct emission from a standard circular thin disk as the dominant source of its optical/UV emission. The lag magnitude also rules out an AGN disk-driven instability as the origin of ASASSN-14li and thus strongly supports the tidal disruption picture for this event and similar objects. We suggest that the majority of the optical/UV emission likely originates from debris stream self-interactions. Perturbations at the self-interaction sites produce optical/UV variability and travel down to the black hole where they modulate the X-rays. The time lag between the optical/UV and the X-rays variations thus correspond to the time taken by these fluctuations to travel from the self-interaction site to close to the black hole. We further discuss these time lags within the context of the three variants of the self-interaction model. High-cadence monitoring observations of future TDFs will be sensitive enough to detect these echoes and would allow us to establish the origin of optical/UV emission in TDFs in general.Comment: Publish in ApJ Letter

The Structure of Cooling Fronts in Accretion Disks

Recent work has shown that the speed of the cooling front in soft X-ray transients may be an important clue in understanding the nature of accretion disk viscosity. In a previous paper (Vishniac and Wheeler 1996) we derived the scaling law for the cooling front speed. Here we derive a similarity solution for the hot inner part of disks undergoing cooling. This solution is exact in the limit of a thin disk, power law opacities, and a minimum hot state column density which is an infinitesimal fraction of the maximum cold state density. For a disk of finite thickness the largest error is in the ratio of the mass flow across the cooling front to the mass flow at small radii. Comparison to the numerical simulations of Cannizzo et al. (1995) inidcates that the errors in the other parameters do not exceed $(c_{sF}/r_F\Omega_F)^q$, that is, the ratio of the sound speed at the disk midplane to its orbital velocity, evaluated at the cooling front, to the qth power. Here $q\approx 1/2$. Its precise value is determined by the relevant hot state opacity law and the functional form of the dimensionless viscosity.Comment: 13 pages, 1 figure, Astrophysical Journal (in press

Numerical simulations of the Accretion-Ejection Instability in magnetised accretion disks

The Accretion-Ejection Instability (AEI) described by Tagger & Pellat (1999) is explored numerically using a global 2d model of the inner region of a magnetised accretion disk. The disk is initially currentless but threaded by a vertical magnetic field created by external currents, and frozen in the flow. In agreement with the theory a spiral instability, similar in many ways to those observed in self-gravitating disks, develops when the magnetic field is, within a factor of a few, at equipartition with the disk thermal pressure. Perturbations in the flow build up currents and create a perturbed magnetic field within the disk. The present non-linear simulations give good evidence that such an instability can occur in the inner region of accretion disks, and generate accretion of gas and vertical magnetic flux toward the central object, if the equilibrium radial profiles of density and magnetic flux exceed a critical threshold.Comment: single tar file with GIF figure

Search for Gravitational Waves from Intermediate Mass Binary Black Holes

We present the results of a weakly modeled burst search for gravitational waves from mergers of non-spinning intermediate mass black holes (IMBH) in the total mass range 100-450 solar Mass and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the IMBH mergers as a function of the component masses. In the most efficiently detected bin centered on 88 + 88 solar Mass , for non-spinning sources, the rate density upper limit is 0.13 per Mpc(exp 3) per Myr at the 90% confidence level

522. Targeting FVIII-Expression To Liver Sinusoidal Cells By Lentiviral Vectors Corrects the Bleeding Phenotype in Hemophilia A Overcoming Immunological Responses

Hemophilia A (HA) is an X-linked bleeding disorder due to mutations in clotting factor (F) VIII gene. To date the treatment for preventing major bleeding episodes is represented by replacement therapy with recombinant or plasma-derived FVIII. The two major concerns are high cost and development of FVIII neutralizing antibodies in 20-30% of patients.Several studies on gene transfer by direct injection of LV for HA have been recently published. Many efforts were focused on the improvement of LV, to obtain a selective targeting of transgene expression, or on the production of several bioengineered FVIII, in order to overcome some of the issues related to FVIII expression in HA animal models. However, in most cases, the immune responses associated with FVIII remain the major obstacle.We prepared LVs containing the B-domain deleted (BDD) hFVIII under the control of PGK, VEC or CD11b promoters with or without the addition of the miRTs used for initial GFP expression studies, and we then injected HA mice with 109 TU/mouse of these LVs (3 mice for LV PGK-hFVIII ±42; 4-9 mice for the other vectors) and assessed FVIII activity by aPTT assay.All mice injected with LV-VEC-hFVIII ± miRTs and LV-CD11b-hFVIII ± miRTs showed a FVIII activity between 3.5 and 5% one week after injection, while HA mice injected with LV-PGK-hFVIII± 42 showed a FVIII activity £1%. Moreover, starting from 2 weeks after LVs injection we evaluated the presence of anti-FVIII antibodies by a direct ELISA. We detected the presence of anti-FVIII antibodies in the plasma of mice injected with LV-PGK-hFVIII±miRT-142 1 month after LV injection. Interestingly, the antibody titer was significantly lower in mice injected with LV-PGK-hFVIII-miRT-142-3p. In all mice injected with LV-VEC-hFVIII±miRT-122-142-3pwe detected hFVIII activity by aPTT assay up to 52 weeks after injection without production of anti-FVIII antibodies. HA mice injected LV-CD11b-hFVIII±miRT-126 showed hFVIII activity up to 52 w as well; interestingly, 60% of mice injected with LV-CD11b-hFVIII produced anti-FVIII antibodies 10-16 weeks after LV injection, while no anti-FVIII antibodies were detected in plasma of injected mice with LV-CD11b-hFVIII-miRT-126.Genomic analysis on liver samples from mice 24 w after injection of LV-VEC-hFVIII±miRT-122-142-3p and LV-CD11b-hFVIII±miRT-126 demonstrated the presence of LV sequence integrated in the genome of injected mice. Immunofluorescence on liver sections showed that LSECs and KCs were positive for hFVIII. Next, to assess whether EC, in particular LSECs, are able to induce immunotolerance, we immunized mice with Refacto. Mice producing anti-FVIII Ab were then injected with 109 TU of LV-VEC-hFVIII-miRT-122-142-3p. We detected hFVIII activity in all injected mice and, noteworthy, antibody titer decreased over time in the plasma of these mice.In conclusion, LV expressing FVIII under the control of VEC or CD11b promoters combined with miRTs combinations were able to overcome FVIII off-target expression limiting immune responses and providing phenotypic correction in treated HA mice with FVIII expression by sinusoidal cells

16s rrna sequencing analysis of the gut microbiota in broiler chickens prophylactically administered with antimicrobial agents

In poultry production, gut microbiota (GM) plays a pivotal role and influences different host functions related to the efficiency of production performances. Antimicrobial (AM) use is one of the main factors affecting GM composition and functions. Although several studies have focused their attention on the role of AMs as growth promoters in the modulation of GM in broilers, the consequences of higher AM concentrations administered during prophylactic treatments need to be better elucidated. For this purpose, 16S rRNA gene sequencing was performed to evaluate the impact of different prophylactic AM protocols on the composition and diversity of the broiler GM. Diversity analysis has shown that AM treatment significantly affects alpha diversity in ileum and beta diversity in both ileum and caecum. In ileal samples, the Enterobacteriaceae family has been shown to be particularly affected by AM treatments. AMs have been demonstrated to affect GM composition in broiler. These findings indicate that withdrawal periods were not enough for the restoral of the original GM. Further studies are needed for a better elucidation of the negative effects caused by an altered GM in broilers

The impact of viscosity on the morphology of gaseous flows in semidetached binary systems

Results of 3D gas dynamical simulation of mass transfer in binaries are presented for systems with various values of viscosity. Analysis of obtained solutions shows that in the systems with low value of viscosity the flow structure is qualitatively similar to one for systems with high viscosity. Presented calculations confirm that there is no shock interaction between the stream from L1 and the forming accretion disk (`hot spot') at any value of viscosity.Comment: LaTeX, 18 pages, 15 eps-figures, Astron. Reports, in pres