Optical Bumps in Cosmological GRBs as Supernovae

From both photometric and broadband spectral monitoring of gamma-ray burst (GRB) lightcurve ``bumps,'' particularly in GRB 011121, a strong case grew for a supernova (SN) origin. The GRB-SN connection was finally solidified beyond a reasonable doubt with the discovery that the bump in GRB 030329 was spectroscopically similar to a bright Type Ic SN. In light of this result, I redress the previous SN bump claims and conclude that 1) the distribution of GRB-SN bump peak magnitudes is consistent with the local Type Ibc SNe peak distribution and suggest that 2) the late-time bumps in all long-duration GRBs are likely supernovae.Comment: 5 pages, 2 figures. To be published in Proc. IAU Colloquium #192 ``Supernovae (10 years of SN1993J),'' held 22-26 April 2003, Valencia, Spain. Editors: J.M. Marcaide and K.W. Weiler. Uses svmult.cl

Cosmological distance indicators

We review three distance measurement techniques beyond the local universe: (1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and (3) HI intensity mapping. We describe the principles and theory behind each method, the ingredients needed for measuring such distances, the current observational results, and future prospects. Time delays from strongly lensed quasars currently provide constraints on $H_0$ with < 4% uncertainty, and with 1% within reach from ongoing surveys and efforts. Recent exciting discoveries of strongly lensed supernovae hold great promise for time-delay cosmography. BAO features have been detected in redshift surveys up to z <~ 0.8 with galaxies and z ~ 2 with Ly-$\alpha$ forest, providing precise distance measurements and $H_0$ with < 2% uncertainty in flat $\Lambda$CDM. Future BAO surveys will probe the distance scale with percent-level precision. HI intensity mapping has great potential to map BAO distances at z ~ 0.8 and beyond with precisions of a few percent. The next years ahead will be exciting as various cosmological probes reach 1% uncertainty in determining $H_0$, to assess the current tension in $H_0$ measurements that could indicate new physics.Comment: Review article accepted for publication in Space Science Reviews (Springer), 45 pages, 10 figures. Chapter of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Ag

Magnetic Braking in Differentially Rotating, Relativistic Stars

We study the magnetic braking and viscous damping of differential rotation in incompressible, uniform density stars in general relativity. Differentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars. The remnant of a binary neutron star merger or supernova core collapse may produce such a "hypermassive" neutron star. Although a hypermassive neutron star may be stable on a dynamical timescale, magnetic braking and viscous damping of differential rotation will ultimately alter the equilibrium structure, possibly leading to delayed catastrophic collapse. Here we consider the slow-rotation, weak-magnetic field limit in which E_rot << E_mag << W, where E_rot is the rotational kinetic energy, E_mag is the magnetic energy, and W is the gravitational binding energy of the star. We assume the system to be axisymmetric and solve the MHD equations in both Newtonian gravitation and general relativity. Toroidal magnetic fields are generated whenever the angular velocity varies along the initial poloidal field lines. We find that the toroidal fields and angular velocities oscillate independently along each poloidal field line, which enables us to transform the original 2+1 equations into 1+1 form and solve them along each field line independently. The incoherent oscillations on different field lines stir up turbulent-like motion in tens of Alfven timescales ("phase mixing"). In the presence of viscosity, the stars eventually are driven to uniform rotation, with the energy contained in the initial differential rotation going into heat. Our evolution calculations serve as qualitative guides and benchmarks for future, more realistic MHD simulations in full 3+1 general relativity.Comment: 26 pages, 27 graphs, 1 table, accepted for publication by Phys. Rev.

Same data, different conclusions: Radical dispersion in empirical results when independent analysts operationalize and test the same hypothesis

In this crowdsourced initiative, independent analysts used the same dataset to test two hypotheses regarding the effects of scientists’ gender and professional status on verbosity during group meetings. Not only the analytic approach but also the operationalizations of key variables were left unconstrained and up to individual analysts. For instance, analysts could choose to operationalize status as job title, institutional ranking, citation counts, or some combination. To maximize transparency regarding the process by which analytic choices are made, the analysts used a platform we developed called DataExplained to justify both preferred and rejected analytic paths in real time. Analyses lacking sufficient detail, reproducible code, or with statistical errors were excluded, resulting in 29 analyses in the final sample. Researchers reported radically different analyses and dispersed empirical outcomes, in a number of cases obtaining significant effects in opposite directions for the same research question. A Boba multiverse analysis demonstrates that decisions about how to operationalize variables explain variability in outcomes above and beyond statistical choices (e.g., covariates). Subjective researcher decisions play a critical role in driving the reported empirical results, underscoring the need for open data, systematic robustness checks, and transparency regarding both analytic paths taken and not taken. Implications for organizations and leaders, whose decision making relies in part on scientific findings, consulting reports, and internal analyses by data scientists, are discussed

On the validity of the rotor model in the odd-Z nucleide 171LU

A metallic thulium target is irradiated with 28 MeV α-particles to produce the 169Tm(α, 2 n) 171Lu reaction. The excitation functions for the observed γ-rays and the angular distributions of these γ-rays are studied. A search is made for isomeric transitions with half-lives longer than 10 ns. The 137.05 keV γ-ray depopulating the 1/2+ [411] state into the 1/2- [541] level is found to have a half-life of 33 ± 8 ns. No other delayed transitions are observed. Rotational bands built on the 1/2+ [411], 5/2+ [402], 7/2+ [404] (ground state), 1/2- [541] and 9/2- [514] intrinsic states are observed. The properties of these bands are examined with respect to deviations from the rotor model. There is some evidence for the existence of coupling terms having Δ K = 2 and it is necessary to allow for a variable moment of inertia in order to explain the available data. As usual the assumption of independent quasiparticle motion overestimates the effect of the Coriolis force.Une cible métallique de thulium est irradiée par des particules α de 28 MeV pour produire la réaction 169Tm(α, 2 n) 171Lu. Les fonctions d'excitation et les distributions angulaires des rayonnements γ émis sont étudiées. Une recherche des transitions isomériques dont la durée de vie est supérieure à 10 ns a été effectuée. La transition de 137,05 keV qui dépeuple l'état 1/2+ [411] vers le niveau 1/2- [541] a une durée de vie de 33 ± 8 ns. Aucune autre transition retardée n'a pu être mise en évidence. Les bandes de rotations construites sur les états intrinsèques 1/2+ [411], 5/2 + [402], 7/2+ [404] (état fondamental), 1/2- [541] et 9/2- [514] ont été observées. Les propriétés de ces bandes sont analysées par rapport au modèle du rotor. Il est possible de mettre en évidence des termes de couplage avec ΔK = 2 et nécessaire de faire varier le moment d'inertie pour expliquer les données disponibles. L'hypothèse du mouvement de quasi particule indépendance surestime l'effet de la force de Coriolis

NIVEAUX DE SPINS ELEVES OBTENUS PAR REACTIONS (α, 2nγ)

Par réactions (α, 2nγ) sur des cibles de Tm et Lu on excite les niveaux de 171Lu et 177Ta. Les différentes bandes de rotation sont identifiées.By means of (α, 2nγ) reactions on Tm and Lu targets the levels of 171Lu and 171Ta are excited. Assignments have been made for the rotational bands