Nuclear lamins are the main components of the nuclear lamina at the nuclear periphery, providing mechanical support to the nucleus. However, recent findings suggest that lamins also reside in the ...nuclear interior, as a distinct and dynamic pool with critical roles in transcriptional regulation. In our work we found a functional and evolutionary conserved crosstalk between Lamin A/C and the Polycomb group (PcG) of proteins, this being required for the maintenance of the PcG repressive functions. Indeed, Lamin A/C knock-down causes PcG foci dispersion and defects in PcG-mediated higher order structures, thereby leading to impaired PcG mediated transcriptional repression. By using ad-hoc algorithms for image analysis and PLA approaches we hereby show that PcG proteins are preferentially located in the nuclear interior where they interact with nucleoplasmic Lamin A/C. Taken together, our findings suggest that nuclear components, such as Lamin A/C, functionally interact with epigenetic factors to ensure the correct transcriptional program maintenance.
GRB080319B reached fifth optical magnitude during the burst prompt emission. Thanks to the Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES) rapid response mode, we ...observed its afterglow just 8m:30s after the gamma-ray burst (GRB) onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise (S/N), high-resolution spectrum of a GRB afterglow ever (S/N per resolution element ~50). The spectrum is rich of absorption features belonging to the main system at z = 0.937, divided in at least six components spanning a total velocity range of 100 km s-1. The VLT/UVES observations caught the absorbing gas in a highly excited state, producing the strongest Fe II fine structure lines ever observed in a GRB. A few hours later, the optical depth of these lines was reduced by a factor of 4-20, and the optical/UV flux by a factor of ~60. This proves that the excitation of the observed fine structure lines is due to 'pumping' by the GRB UV photons. A comparison of the observed ratio between the number of photons absorbed by the excited state and those in the Fe II ground state suggests that the six absorbers are ~2-6 kpc from the GRB site, with component I ~ 3 times closer to the GRB site than components III-VI. Component I is characterized also by the lack of Mg I absorption, unlike all other components. This may be both due to a closer distance and a lower density, suggesting a structured interstellar matter in this galaxy complex.
Context.New information on short/hard gamma-ray bursts (GRBs) is being gathered thanks to the discovery of their optical and X-ray afterglows. However, some key aspects are still poorly understood, ...including the collimation level of the outflow, the duration of the central engine activity, and the properties of the progenitor systems. Aims.We want to constrain the physical properties of the short GRB 050724 and of its host galaxy, and make some inferences on the global short GRB population. Methods.We present optical observations of the afterglow of GRB 050724 and of its host galaxy, significantly expanding the existing dataset for this event. We compare our results with models, complementing them with available measurements from the literature. We study the afterglow light curve and spectrum including X-ray data. We also present observations of the host galaxy. Results.The observed optical emission was likely related to the large flare observed in the X-ray light curve. The apparent steep decay was therefore not due to the jet effect. Available data are indeed consistent with low collimation, in turn implying a large energy release, comparable to that of long GRBs. The flare properties also constrain the internal shock mechanism, requiring a large Lorentz factor contrast between the colliding shells. This implies that the central engine was active at late times, rather than ejecting all shells simultaneously. The host galaxy has red colors and no ongoing star formation, consistent with previous findings on this GRB. However, it is not a pure elliptical, and has some faint spiral structure. Conclusions.GRB 050724 provides the most compelling case for association between a short burst and a galaxy with old stellar population. It thus plays a pivotal role in constraining progenitors models, which should allow for long delays between birth and explosion.
Abstract-We introduce the spike-and-slab group lasso (SSGL) for Bayesian estimation and variable selection in linear regression with grouped variables. We further extend the SSGL to sparse ...generalized additive models (GAMs), thereby introducing the first nonparametric variant of the spike-and-slab lasso methodology. Our model simultaneously performs group selection and estimation, while our fully Bayes treatment of the mixture proportion allows for model complexity control and automatic self-adaptivity to different levels of sparsity. We develop theory to uniquely characterize the global posterior mode under the SSGL and introduce a highly efficient block coordinate ascent algorithm for maximum a posteriori estimation. We further employ de-biasing methods to provide uncertainty quantification of our estimates. Thus, implementation of our model avoids the computational intensiveness of Markov chain Monte Carlo in high dimensions. We derive posterior concentration rates for both grouped linear regression and sparse GAMs when the number of covariates grows at nearly exponential rate with sample size. Finally, we illustrate our methodology through extensive simulations and data analysis.
Supplementary materials
for this article are available online.
The two-component jet of GRB 080413B Filgas, R.; Krühler, T.; Greiner, J. ...
Astronomy and astrophysics (Berlin),
02/2011, Letnik:
526
Journal Article
Recenzirano
Odprti dostop
Aims. The quick and precise localization of GRBs by the Swift telescope allows the early evolution of the afterglow light curve to be captured by ground-based telescopes. With GROND measurements we ...can investigate the optical/near-infrared light curve of the afterglow of gamma-ray burst 080413B in the context of late rebrightening. Methods. Multi-wavelength follow-up observations were performed on the afterglow of GRB 080413B. X-ray emission was detected by the X-ray telescope onboard the Swift satellite and obtained from the public archive. Optical and near-infrared photometry was performed with the seven-channel imager GROND mounted at the MPG/ESO 2.2 m telescope and additionally with the REM telescope, both in La Silla, Chile. The light curve model was constructed using the obtained broad-band data. Results. The broad-band light curve of the afterglow of GRB 080413B is well fitted with an on-axis two-component jet model. The narrow ultra-relativistic jet is responsible for the initial decay, while the rise of the moderately relativistic wider jet near its deceleration time is the cause of the rebrightening of the light curve. The later evolution of the optical/NIR light curve is then dominated by the wide component, the signature of which is almost negligible in the X-ray wavelengths. These components have opening angles of θn ~ 1.7° and θw ~ 9°, and Lorentz factors of Γn > 188 and Γw ~ 18.5. We calculated the beaming-corrected energy release to be Eγ = 7.9 × 1048 erg.
Context. Our knowledge of the intrinsic properties of short duration Gamma-Ray Bursts has relied, so far, only upon a few cases for which the estimate of the distance and an extended, multiwavelength ...monitoring of the afterglow have been obtained. Aims. We carried out multiwavelength observations of the short GRB 061201 aimed at estimating its distance and studying its properties. Methods.We performed a spectral and timing analysis of the prompt and afterglow emission and discuss the results in the context of the standard fireball model. Results. A clear temporal break was observed in the X-ray light curve about 40 min after the burst trigger. We find that the spectral and timing behaviour of the X-ray afterglow is consistent with a jet origin of the observed break, although the optical data can not definitively confirm this and other scenarios are possible. No underlying host galaxy down to R ~ 26 mag was found after fading of the optical afterglow. Thus, no secure redshift could be measured for this burst. The nearest galaxy is at $z = 0.111$ and shows evidence of star formation activity. We discuss the association of GRB 061201 with this galaxy and with the ACO S 995 galaxy cluster, from which the source is at an angular distance of 17'' and 8.5', respectively. We also test the association with a possible undetected, positionally consistent galaxy at z ~ 1. In all these cases, in the jet interpretation, we find a jet opening angle of 1–2 degrees.
Direct laser acceleration (DLA) of electrons in a plasma of near-critical electron density (NCD) and the associated synchrotron-like radiation are discussed for moderate relativistic laser intensity ...(normalized laser amplitude a0 ≤ 4.3) and ps length pulse. This regime is typical of kJ PW-class laser facilities designed for high-energy-density (HED) research. In experiments at the PHELIX facility, it has been demonstrated that interaction of a 1019 W/cm2 sub-ps laser pulse with a sub-mm length NCD plasma results in the generation of high-current well-directed super-ponderomotive electrons with an effective temperature ten times higher than the ponderomotive potential Rosmej et al., Plasma Phys. Controlled Fusion 62, 115024 (2020). Three-dimensional particle-in-cell simulations provide good agreement with the measured electron energy distribution and are used in the current work to study synchrotron radiation from the DLA-accelerated electrons. The resulting x-ray spectrum with a critical energy of 5 keV reveals an ultrahigh photon number of 7 × 1011 in the 1–30 keV photon energy range at the focused laser energy of 20 J. Numerical simulations of betatron x-ray phase contrast imaging based on the DLA process for the parameters of a PHELIX laser are presented. The results are of interest for applications in HED experiments, which require a ps x-ray pulse and a high photon flux.
A developing application of laser-driven currents is the generation of magnetic fields of picosecond–nanosecond duration with magnitudes exceeding
$B=10~\text{T}$
. Single-loop and helical coil ...targets can direct laser-driven discharge currents along wires to generate spatially uniform, quasi-static magnetic fields on the millimetre scale. Here, we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter. Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target. Using this dual-axis platform for proton deflectometry, robust measurements can be made of the evolution of magnetic fields in a capacitor coil target.
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