We studied the X-ray and optical absorption properties of 13 gamma-ray burst (GRB) afterglows observed by BeppoSAX. We found that X-ray absorption in addition to the Galactic one along the line of ...sight is highly statistically significant in the two cases with the best statistics (probability >99.9%). In three other cases the presence of X-ray absorption is marginally significant (probability approx97%). Measured rest-frame equivalent column densities of hydrogen, N sub(H), range from 0.1 x 10 super(22) to 10.0 x 10 super(22) cm super(-2) (at 90% confidence level) assuming a solar metal abundance. X-ray absorption may be common, although the quality of present data does not allow us to reach a firm conclusion. We found that the rest-frame column densities derived from XMM and Chandra data as quoted in the literature are in good agreement with the BeppoSAX estimated rest-frame N sub(H) range, supporting our result. For the same GRB afterglow sample we evaluated the rest-frame visual extinction A sub(Vr). We fitted the optical-NIR afterglow photometry with a power-law model corrected at short wavelengths by four different extinction curves. By comparing X-ray absorptions and optical extinction, we found that if a Galactic- like dust grain size distribution is assumed, a dust-to-gas ratio lower than the one observed in the Galaxy is required by the data. A dust-to-gas ratio approx1/10 that of the Galactic one, as in the Small Magellanic Cloud (SMC) environment, has been tested using the SMC extinction curve, which produces good agreement between the best-fit N sub(H) and A sub(Vr). We note, however, that the best-fit N sub(H) values have been obtained by assuming solar metal abundances, while the metallicity of the SMC ISM is approximage the solar one (Pei 1992). If such low metallicity were assumed, the best-fit N sub(H) values would be higher by a factor of approx7, providing a significant increase of the Chi super(2). Alternative scenarios to explain simultaneously the optical and X-ray data involve dust with grain size distributions biased toward large grains. Possible mechanisms that can bring about such a grain size distribution are discussed.
Abstract
We report the results of deep optical follow-up surveys of the first two gravitational-wave sources, GW150914 and GW151226, done by the GRAvitational Wave Inaf TeAm Collaboration (GRAWITA). ...The VLT Survey Telescope (VST) responded promptly to the gravitational wave alerts sent by the LIGO and Virgo Collaborations, monitoring a region of 90 and 72 deg2 for GW150914 and GW151226, respectively, and repeated the observations over nearly two months. Both surveys reached an average limiting magnitude of about 21 in the r band. The paper describes the VST observational strategy and two independent procedures developed to search for transient counterpart candidates in multi-epoch VST images. Several transients have been discovered but no candidates are recognized to be related to the gravitational wave events. Interestingly, among many contaminant supernovae, we find a possible correlation between the supernova VSTJ57.77559-59.13990 and GRB 150827A detected by Fermi-GBM. The detection efficiency of VST observations for different types of electromagnetic counterparts of gravitational wave events is evaluated for the present and future follow-up surveys.
Laser–plasma interaction (LPI) at intensities
$10^{15}{-}10^{16}~\text{W}\cdot \text{cm}^{-2}$
is dominated by parametric instabilities which can be responsible for a significant amount of ...non-collisional absorption and generate large fluxes of high-energy nonthermal electrons. Such a regime is of paramount importance for inertial confinement fusion (ICF) and in particular for the shock ignition scheme. In this paper we report on an experiment carried out at the Prague Asterix Laser System (PALS) facility to investigate the extent and time history of stimulated Raman scattering (SRS) and two-plasmon decay (TPD) instabilities, driven by the interaction of an infrared laser pulse at an intensity
${\sim}1.2\times 10^{16}~\text{W}\cdot \text{cm}^{-2}$
with a
${\sim}100~\unicodeSTIX{x03BC}\text{m}$
scalelength plasma produced from irradiation of a flat plastic target. The laser pulse duration (300 ps) and the high value of plasma temperature (
${\sim}4~\text{keV}$
) expected from hydrodynamic simulations make these results interesting for a deeper understanding of LPI in shock ignition conditions. Experimental results show that absolute TPD/SRS, driven at a quarter of the critical density, and convective SRS, driven at lower plasma densities, are well separated in time, with absolute instabilities driven at early times of interaction and convective backward SRS emerging at the laser peak and persisting all over the tail of the pulse. Side-scattering SRS, driven at low plasma densities, is also clearly observed. Experimental results are compared to fully kinetic large-scale, two-dimensional simulations. Particle-in-cell results, beyond reproducing the framework delineated by the experimental measurements, reveal the importance of filamentation instability in ruling the onset of SRS and stimulated Brillouin scattering instabilities and confirm the crucial role of collisionless absorption in the LPI energy balance.
SUMMARY
Regulation of the immune response directed against Leishmania is critical for the establishment of effective control of the disease. It is likely that some types of immune responses directed ...against Leishmania can lead to more severe clinical forms of leishmaniasis causing a poor control of the pathogen and/or pathology, while others lead to resolution of the infection with little pathology as in cutaneous leishmaniasis. To gain a better understanding of the possible role that subpopulations of T cells, and their associated cytokines have on disease progression and/or protective immune responses to L. braziliensis infection, a detailed study of the frequency of activated and memory T cells, as well as antigen specific, cytokine producing T cells was carried out. Following the determination of cytokine producing mononuclear cell populations in response to total Leishmania antigen (SLA), and to the recombinant antigen LACK, correlation analysis were performed between specific cytokine producing populations to identify models for cellular mechanisms of immunoregulation in human cutaneous leishmaniasis. These studies have shown: (1) a positive correlation between ex vivo CD45RO frequencies and antigen specific cytokine (IFN‐gamma or IL‐10) producing cells; (2) a negative correlation between ex vivo CD69 expression and the frequency of IFN‐gamma producing cells; (3) a positive correlation amongst SLA specific, IFN‐gamma or TNF‐alpha and IL‐10 producing lymphocytes with one another; and (4) a higher frequency of IL‐10 producing, parasite specific (anti‐SLA or anti‐LACK), lymphocytes are correlated with a lower frequency of TNF‐alpha producing monocytes, demonstrating an antigen specific delivery of IL‐10 inducing negative regulation of monocyte activity.
Summary
Leishmaniasis is caused by infection with the protozoan parasite, Leishmania, that parasitizes human cells, and the cellular immune response is essential for controlling infection. In order ...to measure the host T cell response to Leishmania infection, we have measured the expansion, activation state and functional potential of specific T cells as identified by their T cell receptor Vβ region expression. In a group of cutaneous leishmaniasis (CL) patients, we evaluated these characteristics in nine different T cell subpopulations as identified by their Vβ region expression, before and after specific Leishmania antigen stimulation. Our results show: (1) an increase in CD4+ T cells expressing Vβ 5·2 and Vβ 24 in CL compared to controls; (2) a Leishmania antigen‐induced increase in CD4+ T cells expressing Vβ 5·2, 11, 12 and 17; (3) a profile of previous activation of CD4+ Vβ 5·2‐, 11‐ and 24‐positive T cells, with higher expression of CD45RO, HLA‐DR, interferon‐γ, tumour necrosis factor‐α and interleukin‐10 compared to other Vβ‐expressing subpopulations; (4) a positive correlation between higher frequencies of CD4+Vβ5·2+ T cells and larger lesions; and (5) biased homing of CD4+ T cells expressing Vβ 5·2 to the lesion site. Given that CL disease involves a level of pathology (ulcerated lesions) and is often followed by long‐lived protection and cure, the identification of specific subpopulations active in this form of disease could allow for the discovery of immunodominant Leishmania antigens important for triggering efficient host responses against the parasite, or identify cell populations most involved in pathology.
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