Afterglows after Swift

Since their discovery by the Beppo-SAX satellite in 1997, gamma-ray burst afterglows have attracted an ever-growing interest. They have allowed redshift measurements that have confirmed that gamma-ray bursts are located at cosmological distances. Their study covers a huge range both in time (from one minute to several months after the trigger) and energy (from the GeV to radio domains). The purpose of this review is first to give a short historical account of afterglow research and describe the main observational results with a special attention to the early afterglow revealed by Swift. We then present the standard afterglow model as it has been developed in the pre-Swift era and show how it is challenged by the recent Swift and Fermi results. We finally discuss different options (within the standard framework or implying a change of paradigm) that have been proposed to solve the current problems.Comment: 16 page

Scattered Emission from A Relativistic Outflow and Its Application to Gamma-Ray Bursts

We investigate a scenario of photons scattering by electrons within a relativistic outflow. The outflow is composed of discrete shells with different speeds. One shell emits radiation for a short duration. Some of this radiation is scattered by the shell(s) behind. We calculate in a simple two-shell model the observed scattered flux density as a function of the observed primary flux density, the normalized arrival time delay between the two emission components, the Lorentz factor ratio of the two shells and the scattering shell's optical depth. Thomson scattering in a cold shell and inverse Compton scattering in a hot shell are both considered. The results of our calculations are applied to the Gamma-Ray Bursts and the afterglows. We find that the scattered flux from a cold slower shell is small and likely to be detected only for those bursts with very weak afterglows. A hot scattering shell could give rise to a scattered emission as bright as the X-ray shallow decay component detected in many bursts, on a condition that the isotropically equivalent total energy carried by the hot electrons is large, $\sim 10^{52-56}$ erg. The scattered emission from a faster shell could appear as a late short $\gamma$-ray/MeV flash or become part of the prompt emission depending on the delay of the ejection of the shell.Comment: 13 pages, 3 figures, MNRAS in press; a short intuitive estimation is added before detailed calculations; references update

Comparative Morphology of the Penis and Clitoris in Four Species of Moles (Talpidae).

The penile and clitoral anatomy of four species of Talpid moles (broad-footed, star-nosed, hairy-tailed, and Japanese shrew moles) were investigated to define penile and clitoral anatomy and to examine the relationship of the clitoral anatomy with the presence or absence of ovotestes. The ovotestis contains ovarian tissue and glandular tissue resembling fetal testicular tissue and can produce androgens. The ovotestis is present in star-nosed and hairy-tailed moles, but not in broad-footed and Japanese shrew moles. Using histology, three-dimensional reconstruction, and morphometric analysis, sexual dimorphism was examined with regard to a nine feature masculine trait score that included perineal appendage length (prepuce), anogenital distance, and presence/absence of bone. The presence/absence of ovotestes was discordant in all four mole species for sex differentiation features. For many sex differentiation features, discordance with ovotestes was observed in at least one mole species. The degree of concordance with ovotestes was highest for hairy-tailed moles and lowest for broad-footed moles. In relationship to phylogenetic clade, sex differentiation features also did not correlate with the similarity/divergence of the features and presence/absence of ovotestes. Hairy-tailed and Japanese shrew moles reside in separated clades, but they exhibit a high degree of congruence. Broad-footed and hairy-tailed moles reside within the same clade but had one of the lowest correlations in features and presence/absence of ovotestes. Thus, phylogenetic affinity and the presence/absence of ovotestes are poor predictors for most sex differentiation features within mole external genitalia

External Validation of the “Walking Estimated Limitation Calculated by History” (WELCH) Questionnaire in Patients with Claudication

ObjectiveTo externally validate the recently proposed “Walking Estimated Limitation Calculated by History” (WELCH) questionnaire.MethodsA prospective study was performed on 450 new patients referred to our laboratory for treadmill testing (constant load 3.2 km/h and 10% slope for 15 minutes and then incremental increases). Results are presented as mean ± SD or median [25th–75th percentiles] or number (percentage). An ankle brachial index <0.90 defined the presence of peripheral artery disease (PAD). Typical “vascular-type claudication” is a lower-limb pain or discomfort that is absent at rest, appears at exercise, forces stopping, and disappears within 10 minutes of exercise stopping. The Spearman r coefficient of correlation between maximal walking time (MWT) on treadmill and WELCH scores was calculated for patients with (PAD+) or without (PAD−) PAD, and reporting typical vascular-type claudication (VTC+) or not (VTC−).ResultsThe WELCH score was obtained in all included patients. The number (%) of patients with a WELCH score <25 was 37 (54%), 198 (65%), 14 (44%), and 18 (38%), and the Spearman correlation coefficient between WELCH score and treadmill MWT was 0.588, 0.609, 0.581, and 0.591 in the VTC−/PAD+, VTC+/PAD+, VTC−/PAD−, and VTC+/PAD− groups respectively (all p < .001). In PAD+/VTC+ patients, the WELCH positive predictive value for the inability to walk for 5 minutes on the treadmill was 79%.ConclusionThe WELCH score correlates moderately with treadmill-walking capacity in patients with or without PAD, and with or without typical VTC. It appears to be a simple to complete and easily scored instrument to help clinicians standardise the subjective estimation of walking capacity in their patients

Comparison between classical potentials and ab initio for silicon under large shear

The homogeneous shear of the {111} planes along the direction of bulk silicon has been investigated using ab initio techniques, to better understand the strain properties of both shuffle and glide set planes. Similar calculations have been done with three empirical potentials, Stillinger-Weber, Tersoff and EDIP, in order to find the one giving the best results under large shear strains. The generalized stacking fault energies have also been calculated with these potentials to complement this study. It turns out that the Stillinger-Weber potential better reproduces the ab initio results, for the smoothness and the amplitude of the energy variation as well as the localization of shear in the shuffle set

The Microchannel X-ray Telescope on Board the SVOM Satellite

We present the Micro-channel X-ray Telescope (MXT), a new narrow-field (about 1{\deg}) telescope that will be flying on the Sino-French SVOM mission dedicated to Gamma-Ray Burst science, scheduled for launch in 2021. MXT is based on square micro pore optics (MPOs), coupled with a low noise CCD. The optics are based on a "Lobster Eye" design, while the CCD is a focal plane detector similar to the type developed for the seven eROSITA telescopes. MXT is a compact and light (<35 kg) telescope with a 1 m focal length, and it will provide an effective area of about 45 cmsq on axis at 1 keV. The MXT PSF is expected to be better than 4.2 arc min (FWHM) ensuring a localization accuracy of the afterglows of the SVOM GRBs to better than 1 arc min (90\% c.l. with no systematics) provided MXT data are collected within 5 minutes after the trigger. The MXT sensitivity will be adequate to detect the afterglows for almost all the SVOM GRBs as well as to perform observations of non-GRB astrophysical objects. These performances are fully adapted to the SVOM science goals, and prove that small and light telescopes can be used for future small X-ray missions.Comment: 6 pages, 6 figures, proceedings of the conference "Swift: 10 years of Discovery", Rome, December 2-5, 2014. To be published by Po

Temperature dependence of current density and admittance in metal-insulator-semiconductor junctions with molecular insulator

International audienceElectrical transport in ultrathin Metal-insulator-semiconductor (MIS) tunnel junctions is analyzed using the temperature dependence of current density and admittance characteristics, as illustrated by Hg//C12H25 - n Si junctions incorporating n-alkyl molecular layers (1.45 nm thick) covalently bonded to Si(111). The voltage partition is obtained from J(V, T) characteristics, over eight decades in current. In the low forward bias regime (0.2-0.4 V) governed by thermionic emission, the observed linear T-dependence of the effective barrier height, qΦEFF(T) = qΦB+(kT)β0dT, provides the tunnel barrier attenuation, exp(-β0dT), with β0= 0.93 Å−1 and the thermionic emission barrier height, ΦB = 0.53 eV. In the high-forward-bias regime (0.5-2.0 V), the bias dependence of the tunnel barrier transparency, approximated by a modified Simmons model for a rectangular tunnel barrier, provides the tunnel barrier height, ΦT = 0.5 eV; the fitted prefactor value, G0 = 10−10 Ω−1, is four decades smaller than the theoretical Simmons prefactor for MIM structures. The density distribution of defects localized at the C12H25 - n Si interface is deduced from admittance data (low-high frequency method) and from a simulation of the response time τR(V) using Gomila's model for a non equilibrium tunnel junction. The low density of electrically active defects near mid-gap (DS < 2 × 1011 eV−1.cm−2) indicates a good passivation of dangling bonds at the dodecyl - n Si (111) interface

Was the "naked burst" GRB 050421 really naked ?

A few long gamma-ray bursts such as GRB 050421 show no afterglow emission beyond the usual initial steep decay phase. It has been suggested that these events correspond to "naked" bursts that occur in a very low density environment. We reconsider this possibility in the context of various scenarios for the origin of the afterglow. In the standard model where the afterglow results from the forward shock as well as in the alternative model where the afterglow comes from the reverse shock, we aim to obtain constraints on the density of the environment, the microphysics parameters, or the Lorentz factor of the ejecta, which are imposed by the absence of a detected afterglow. For the two models we compute the afterglow evolution for different values of the external density (uniform or wind medium) and various burst parameters. We then compare our results to the Swift data of GRB 050421, which is the best example of a long burst without afterglow. In the standard model we show that consistency with the data imposes that the external density does not exceed 1E-5 cm-3 or that the microphysics parameters are very small with epsilon_e <~ 1E-2 and epsilon_B <~ 1E-4. If the afterglow is caused by the reverse shock, we find that its contribution can be strongly reduced if the central source has mainly emitted fast-moving material (with less than 10 - 30 % of the kinetic energy at Gamma<100 and was located in a dense environment. The two considered scenarios therefore lead to opposite constraints on the circumburst medium. The high-density environment, favored by the reverse shock model, better corresponds to what is expected if the burst progenitor was a massive star.Comment: 6 pages, 3 figures, 1 table, to appear in A&

GRB 050713A: High Energy Observations of the GRB Prompt and Afterglow Emission

Swift discovered GRB 050713A and slewed promptly to begin observing with its narrow field instruments 72.6 seconds after the burst onset, while the prompt gamma-ray emission was still detectable in the BAT. Simultaneous emission from two flares is detected in the BAT and XRT. This burst marks just the second time that the BAT and XRT have simultaneously detected emission from a burst and the first time that both instruments have produced a well sampled, simultaneous dataset covering multiple X-ray flares. The temporal rise and decay parameters of the flares are consistent with the internal shock mechanism. In addition to the Swift coverage of GRB 050713A, we report on the Konus-Wind (K-W) detection of the prompt emission in the energy range 18-1150 keV, an upper limiting GeV measurement of the prompt emission made by the MAGIC imaging atmospheric Cherenkov telescope and XMM-Newton observations of the afterglow. Simultaneous observation between Swift XRT and XMM-Newton produce consistent results, showing a break in the lightcurve at T+~15ks. Together, these four observatories provide unusually broad spectral coverage of the prompt emission and detailed X-ray follow-up of the afterglow for two weeks after the burst trigger. Simultaneous spectral fits of K-W with BAT and BAT with XRT data indicate that an absorbed broken powerlaw is often a better fit to GRB flares than a simple absorbed powerlaw. These spectral results together with the rapid temporal rise and decay of the flares suggest that flares are produced in internal shocks due to late time central engine activity.Comment: 22 pages, 6 tables, 10 figures; Submitted to the Astrophysical Journa