Very Early Optical Afterglows of Gamma-Ray Bursts: Evidence for Relative Paucity of Detection

Very early observations with the Swift satellite of gamma-ray burst (GRB) afterglows reveal that the optical component is not detected in a large number of cases. This is in contrast to the bright optical flashes previously discovered in some GRBs (e.g. GRB 990123 and GRB 021211). Comparisons of the X-ray afterglow flux to the optical afterglow flux and prompt gamma-ray fluence is used to quantify the seemingly deficient optical, and in some cases X-ray, light at these early epochs. This comparison reveals that some of these bursts appear to have higher than normal gamma-ray efficiencies. We discuss possible mechanisms and their feasibility for explaining the apparent lack of early optical emission. The mechanisms considered include: foreground extinction, circumburst absorption, Ly-alpha blanketing and absorption due to high redshift, low density environments, rapid temporal decay, and intrinsic weakness of the reverse shock. Of these, foreground extinction, circumburst absorption, and high redshift provide the best explanations for most of the non-detections in our sample. There is tentative evidence of suppression of the strong reverse shock emission. This could be because of a Poynting-flux-dominated flow or a pure non-relativistic hydrodynamical reverse shock.Comment: 22 pages, 5 figures. Accepted for publication in Ap

Colliding Worlds: Asteroid research and the legitimization of war in space

Accepted versio

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Observing strain localisation processes in bio-cemented sand using x-ray imaging

International audienceIn-situ x-ray tomography has been used to follow deformation processes in 3D during two triaxial compression tests, one on a specimen of bio-cemented Ottawa 50-70 sand and the other on a specimen of the non-cemented sand. The global stress-strain responses show that the bio-cementation process increases the shear strength (peak deviator stress is approximately doubled), and causes the material to exhibit a linear behaviour up until peak, as well as increasing the dila-tancy angle. The residual strength of the two samples is very close at large strain. Quantitative 3D digital image analysis (porosity, cement-density and strain field measurements), reveals that a dilatant shear band gradually develops pre-peak in the reference material. The cemented sample however undergoes an abrupt change of deformation mechanism at peak stress: from homogeneous deformation to localised dilatant shearing, which is associated with a local loss of cementation

The fall and recovery of the Tagish Lake meteorite

The Tagish Lake C2 (ungrouped) carbonaceous chondrite fall of January 18, 2000, delivered 10 kg of one of the most primitive and physically weak meteorites yet studied. In this paper, we report the detailed circumstances of the fall and the recovery of all documented Tagish Lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide. Nearly 1 kg of "pristine" meteorites were collected one week after the fall before new snow covered the strewnfield; the majority of the recovered mass was collected during the spring melt. Ground eyewitnesses and a variety of instrument-recorded observations of the Tagish Lake fireball provide a refined estimate of the fireball trajectory. From its calculated orbit and its similarity to the remotely sensed properties of the D- and P-class asteroids, the Tagish Lake carbonaceous chondrite apparently represents these outer belt asteroids. The cosmogenic nuclide results and modeled production indicate a prefall radius of 2.1-2.4 m (corresponding to 60-90 tons) consistent with the observed fireball energy release. The bulk oxygen-isotope compositions plot just below the terrestrial fractionation line (TFL), following a trend similar to the CM meteorite mixing line. The bulk density of the Tagish Lake material (1.64 +/- 0.02 g/cm^3) is the same, within uncertainty, as the total bulk densities of several C-class and especially D- and P-class asteroids. The high microporosity of Tagish Lake samples (~40%) provides an obvious candidate material for the composition of low bulk density primitive asteroids.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Very early optical afterglows of gamma-ray bursts: evidence for relative paucity of detection,”

ABSTRACT Very early observations with the Swift satellite of -ray burst (GRB) afterglows reveal that the optical component is not detected in a large number of cases. This is in contrast to the bright optical flashes previously discovered in some GRBs (e.g., GRB 990123 and GRB 021211). Comparisons of the X-ray afterglow flux to the optical afterglow flux and prompt -ray fluence is used to quantify the seemingly deficient optical, and in some cases X-ray, light at these early epochs. This comparison reveals that some of these bursts appear to have higher than normal -ray efficiencies. We discuss possible mechanisms and their feasibility for explaining the apparent lack of early optical emission. The mechanisms considered include, foreground extinction, circumburst absorption, Ly blanketing and absorption due to high-redshift, low-density environments, rapid temporal decay, and intrinsic weakness of the reverse shock. Of these, foreground extinction, circumburst absorption, and high redshift provide the best explanations for most of the nondetections in our sample. There is tentative evidence of suppression of the strong reverse shock emission. This could be because of a Poynting flux-dominated flow or a pure nonrelativistic hydrodynamic reverse shock