Early afterglow, magnetized central engine, and a quasi-universal jet configuration for long GRBs

Two separate topics are discussed. (1) We describe the classifications of the long GRB early afterglow lightcurves within the framework of the fireball shock model, focusing on the interplay between the reverse and forward shock emission components. We will also provide evidence that the central engine of at least two bursts are entrained with strong magnetic fields, and discuss the implications of this result for our understanding of the GRB phenomenon; (2) We argue that the current gamma-ray burst (GRB) and X-ray flash (XRF) data are consistent with a picture that all GRB-XRF jets are structured and quasi-universal, with a typical Gaussian-like jet structure.Comment: 5 pages, 8 figures, to appear in the Proceedings of Santa Fe GRB Conference (talk by Zhang at the meeting

The SOS Pilot Study: a RCT of routine oxygen supplementation early after acute stroke—effect on recovery of neurological function at one week

Mild hypoxia is common after stroke and associated with poor long-term outcome. Oxygen supplementation could prevent hypoxia and improve recovery. A previous study of routine oxygen supplementation showed no significant benefit at 7 and 12 months. This pilot study reports the effects of routine oxygen supplementation for 72 hours on oxygen saturation and neurological outcomes at 1 week after a stroke

Light-Driven Nanoscale Vectorial Currents

Controlled charge flows are fundamental to many areas of science and technology, serving as carriers of energy and information, as probes of material properties and dynamics, and as a means of revealing or even inducing broken symmetries. Emerging methods for light-based current control offer promising routes beyond the speed and adaptability limitations of conventional voltage-driven systems. However, optical manipulation of currents at nanometer spatial scales remains a basic challenge and a key step toward scalable optoelectronic systems and local probes. Here, we introduce vectorial optoelectronic metasurfaces as a new class of metamaterial in which ultrafast charge flows are driven by light pulses, with actively-tunable directionality and arbitrary patterning down to sub-diffractive nanometer scales. In the prototypical metasurfaces studied herein, asymmetric plasmonic nanoantennas locally induce directional, linear current responses within underlying graphene. Nanoscale unit cell symmetries are read out via polarization- and wavelength-sensitive currents and emitted terahertz (THz) radiation. Global vectorial current distributions are revealed by spatial mapping of the THz field polarization, also demonstrating the direct generation of elusive broadband THz vector beams. We show that a detailed interplay between electrodynamic, thermodynamic, and hydrodynamic degrees of freedom gives rise to these currents through rapidly-evolving nanoscale forces and charge flows under extreme spatial and temporal localization. These results set the stage for versatile patterning and optical control over nanoscale currents in materials diagnostics, nano-magnetism, microelectronics, and ultrafast information science

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.Comment: 14 pages including 3 figure

Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs

(Abridged) The two high-redshift gamma-ray bursts, GRB 080913 at z=6.7 and GRB 090423 at z=8.3, recently detected by Swift appear as intrinsically short, hard GRBs. They could have been recognized by BATSE as short/hard GRBs should they have occurred at z <= 1. We perform a more thorough investigation on two physically distinct types (Type I/II) of cosmological GRBs and their observational characteristics. We reiterate the definitions of Type I/II GRBs and review the observational criteria and their physical motivations. Contrary to the traditional approach of assigning the physical category based on the gamma-ray properties (duration, hardness, and spectral lag), we take an alternative approach to define the Type I and Type II Gold Samples using several criteria that are more directly related to the GRB progenitors, and study the properties of the two Gold Samples and compare them with the traditional long/soft and short/hard samples. We find that the Type II Gold Sample reasonably tracks the long/soft population, although it includes several intrinsically short (shorter than 1s in the rest frame) GRBs. The Type I Gold Sample only has 5 GRBs, 4 of which are not strictly short but have extended emission. Other short/hard GRBs detected in the Swift era represent the BATSE short/hard sample well, but it is unclear whether all of them belong to Type I. We suggest that some (probably even most) high-luminosity short/hard GRBs instead belong to Type II. We suggest that GRB 080913 and GRB 090423 are more likely Type II events. We re-emphasize the importance of invoking multiple observational criteria, and cautiously propose an operational procedure to infer the physical origin of a given GRB with available multiple observational criteria, with various caveats laid out.Comment: 32 pages, ApJ, in press. The strengths and weaknesses of physical classification and its relation to phenomenological classification are fully discussed in a newly added section 3. Discussions on GRBs 090423, 090426, and 090510 are include

Astrophysics with the Laser Interferometer Space Antenna

Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy as it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and other space-based instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed: ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or intermediate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help make progress in the different areas. New research avenues that LISA itself, or its joint exploitation with studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe

AI is a viable alternative to high throughput screening: a 318-target study

: High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that our AtomNet® convolutional neural network successfully finds novel hits across every major therapeutic area and protein class. We address historical limitations of computational screening by demonstrating success for target proteins without known binders, high-quality X-ray crystal structures, or manual cherry-picking of compounds. We show that the molecules selected by the AtomNet® model are novel drug-like scaffolds rather than minor modifications to known bioactive compounds. Our empirical results suggest that computational methods can substantially replace HTS as the first step of small-molecule drug discovery