Attributes of GRB Pulses: Bayesian Blocks Analysis of TTE Data; a Microburst in GRB 920229

Bayesian Blocks is a new time series algorithm for detecting localized structures (spikes or shots), revealing pulse shapes, and generally characterizing intensity variations. It maps raw counting data into a maximum likelihood piecewise constant representation of the underlying signal. This bin-free method imposes no lower limit on measurable time scales. Applied to BATSE TTE data, it reveals the shortest know burst structure -- a spike superimposed on the main burst in GRB 920229 = Trigger 1453, with rise and decay timescales ~ few 100 microseconds.Comment: 5 pages, 2 figures; presented at the 4th Huntsville Gamma-ray Burst Symposiu

GRB Spikes Could Resolve Stars

GRBs vary more rapidly than any other known cosmological phenomena. The lower limits of this variability have not yet been explored. Improvements in detectors would reveal or limit the actual rate of short GRBs. Were microsecond "spike" GRBs to exist and be detectable, they would time-resolve stellar mass objects throughout the universe by their gravitational microlensing effect. Analyzing the time structure of sufficient numbers of GRB spikes would reveal or limit $\Omega_{star}$, $\Omega_{MACHO}$, and/or $\Omega_{baryon}$.Comment: 18 pages, 2 figures, in press: ApJ (Letters

On Suggestive Correlations Between GRBs and Clusters of Galaxies

Recent claims of angular correlations between gamma-ray bursts (GRBs) and clusters of galaxies are evaluated in light of existing but previously uncorrelated GRB positional data. Additional GRB data sets we use include sub-samples of soft BATSE 3B bursts, bursts located by the Interplanetary Network (IPN), and GRBs localized by COMPTEL. We confirm a previously reported excess by Rood and Struble (1996) of the 185 rich, nearby clusters of galaxies (Abell, Corwin, and Olowin 1989, ACO) in the 1-$\sigma$ error circles of 74 BATSE 3B positions, but find a typical correlation strength of only $~$2.5-$\sigma$ for typical sub-samples. However, none of the 185 ACO clusters occur in the 1-$\sigma$ error boxes of 40 IPN GRBs or 18 COMPTEL GRBs. When all ACO clusters are correlated with BATSE 3B GRBs however, we find an increasingly strong correlation for GRBs with decreasingly small error boxes, reaching above the 3.5-$\sigma$ level. We also find a slight excess of {\it soft} BATSE GRBs near the positions of 185 rich, nearby ACO clusters, but the significance of the correlation averages only $~$2.5-$\sigma$ for sub-samples delineated by softness. We caution that the statistical significance of all these correlations is marginal, and so conclude that the excess is at best only suggestive of a physical association. Statistical fluke is still a strong possibility. BATSE could confirm or refute such correlations in a 10-year lifetime.Comment: 17 pages in LateX including 2 postcript figures. To be published in ApJ. One affiliation has been change

Limits on the cosmological abundance of supermassive compact objects from a millilensing search in gamma-ray burst data

A new search for the gravitational lens effects of a significant cosmological density of supermassive compact objects (SCOs) on gamma-ray bursts has yielded a null result. We inspected the timing data of 774 BATSE-triggered GRBs for evidence of millilensing: repeated peaks similar in light-curve shape and spectra. Our null detection leads us to conclude that, in all candidate universes simulated, $\Omega_{SCO} < 0.1$ is favored for $10^5 < M_{SCO}/M_{\odot} < 10^9$, while in some universes and mass ranges the density limits are as much as 10 times lower. Therefore, a cosmologically significant population of SCOs near globular cluster mass neither came out of the primordial universe, nor condensed at recombination.Comment: 14 pages including 3 figures, appeared 2001 January 2

Digital Narratives of COVID-19 on Twitter: From Data to Interpretation

The bilingual project Digital Narratives of COVID-19 brings together researchers, programmers, and stu- dents from the University of Miami and CONICET (Argentina). DHCovid aims to analyze and interpret Twitter data (in English and Spanish) on the SARS-CoV -2 global pandemic from the end of April 2020 to May 2021, through quantitative methods and tools used in the field of DH. This article explores the differ- ent methods and tools that the project has used, from basic search platforms and semi-automated text- mining to more complex and more or less supervised ones. The paper additionally discusses how this set of tweets was collected to study the narratives and emerging issues about the pandemic in South Florida and specific Spanish-speaking countries (Argentina, Mexico, Peru, Colombia, Ecuador, Spain). Furthermore, it presents the GitHub and Zenodo data repository as well as some of the tools developed by the project. Finally, work with data mining, frequency analysis of terms and concordances, and topic modeling will be exhibited.El proyecto bilingüe Narrativas digitales de la COVID -19 (DHCovid) reúne a participantes de la Universidad de Miami (EE. UU.) y CONICET (Argentina). Tiene como objetivo analizar e interpretar datos (en inglés y español) sobre la pandemia global de SARS-CoV-2 procedentes de Twitter desde finales de abril de 2020 hasta mayo 2021, por medio de métodos y herramientas cuantitativos utilizados en el campo de las Humanidades Digitales. Se presentarán distintos métodos y herramientas empleados, desde plataformas simples de búsqueda y minería semi- automatizada a otras más complejas y humanamente semi-supervisadas. Asimismo, se describirá cómo se ha realizado la recopilación de tweets para estudiar narrativas y temas sobre la pandemia en diversas zonas de habla hispana (Argentina, México, Perú, Colombia, Ecuador, España); donde se haya el repositorio de datos de GitHub y Zenodo así como otras herramientas desarrolladas por el proyecto. Finalmente, se exhibirá lo trabajado con minería de datos, análisis de frecuencia de términos y concordancias, y topic modeling.Universidad Nacional de La PlataAsociación Argentina de Humanidades Digitale

Correlations Between Lag, Luminosity, and Duration in Gamma-ray Burst Pulses

We derive a new peak lag vs. peak luminosity relation in gamma-ray burst (GRB) pulses. We demonstrate conclusively that GRB spectral lags are pulse rather than burst properties and show how the lag vs. luminosity relation determined from CCF measurements of burst properties is essentially just a rough measure of this newly derived relation for individual pulses. We further show that most GRB pulses have correlated properties: short-lag pulses have shorter durations, are more luminous, and are harder within a burst than long-lag pulses. We also uncover a new pulse duration vs. pulse peak luminosity relation, and indicate that long-lag pulses often precede short-lag pulses. Although most pulse behaviors are supportive of internal shocks (including long-lag pulses), we identify some pulse shapes that could result from external shocks.Comment: 14 pages, 4 figures, 1 table; accepted for publication in Astrophysical Journal Letter

LAT Onboard Science: Gamma-Ray Burst Identification

The main goal of the Large Area Telescope (LAT) onboard science program is to provide quick identification and localization of Gamma Ray Bursts (GRB) onboard the LAT for follow-up observations by other observatories. The GRB identification and localization algorithm will provide celestial coordinates with an error region that will be distributed via the Gamma ray burst Coordinate Network (GCN). We present results that show our sensitivity to bursts as characterized using Monte Carlo simulations of the GLAST observatory. We describe and characterize the method of onboard track determination and the GRB identification and localization algorithm. Onboard track determination is considerably different than in the onground case, resulting in a substantially altered point spread function. The algorithm contains tunable parameters which may be adjusted after launch when real bursts characteristics at very high energies have been identified