Multi-Wavelength Observations of Short-Duration Gamma-Ray Bursts: Recent Results

The number of detections as well as significantly deep non-detections of optical/NIR afterglows of Type I (short-duration population) Gamma-Ray Bursts (GRBs) has become large enough that statistically meaningful samples can now be constructed. I present within some recent results on the luminosity distribution of Type I GRB afterglows in comparison to those of Type II GRBs (collapsar population), the issue of the existence of jet breaks in Type I GRB afterglows, and the discovery of dark Type I GRBs.Comment: 10 pages, 3 figures, based on an invited talk, to appear in the proceedings of the Gamma-Ray Burst Symposium 2012- IAA-CSIC - Marbella, editors: Castro-Tirado, A. J., Gorosabel, J. and Park, I. H; v2: accepted, slightly expanded, minor changes after referee repor

Afterglows of Gamma-Ray Bursts: Short vs. Long GRBs

We compiled a large sample of Swift-era photometric data on long (Type II) and short (Type I) GRB afterglows. We compare the luminosity and energetics of the different samples to each other and to the afterglows of the pre-Swift era. Here, we present the first results of these studies.Comment: Conference Proceedings, "Gamma-Ray Bursts 2007", Santa Fe, shortened poster presentation; 4 pages, 3 figures; for full updated papers, go here to arXiv:0712.2186 and also here to arXiv:0804.195

Impact of Bayesian weighting in a probabilistic nowcasting from INCA and C-LAEF

Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019

The afterglows of swift-era short and long gamma-ray bursts

The phenomenon of Gamma-Ray Bursts (GRBs) has been a great mystery since their discovery four decades ago. Even today, over a decade into the "afterglow age", many questions are still unanswered. The canonical picture which satisfies most of the data is that GRBs are produced when a massive celestial body (either a post-main sequence star or merging compact objects) at cosmological distances collapses to a rapidly rotating compact object (a black hole, for example) which launches ultra-relativistic polar jets. The internal dissipation of energy within the jets leads to collimated non-thermal high-energy emission (the actual GRB), whereas shocks created from the interactions of the jets with the interstellar medium create a long-lasting fading afterglow. The collected physical processes describing this emission are called the standard fireball model. GRBs have been found to be the most luminous electromagnetic sources in the universe for short time periods. In this Thesis, I present my study of the afterglows of Type I (not associated with massive star formation, probably due to the merger of compact objects) and Type II (associated with massive star formation, the late optical emission includes a component due to a Type Ic supernova with high expansions speeds) GRBs, and compare them with each other, especially in terms of host-galaxy dust extinction and the luminosity distribution. To accomplish this, I have collected the largest sample of photometric afterglow data available worldwide, and from this, selected GRBs with data sufficient for a more detailed analysis.Das Phänomen der Gammastrahlenausbrüche (Gamma-Ray Bursts, GRBs) war auch lange nach ihrer Entdeckung vor über vier Jahrzehnten ein großes Rätsel. Selbst heute, über ein Jahrzehnt seit Beginn der "Ära der Nachglühen" (engl.: Afterglows) sind noch viele Fragen unbeantwortet. Das akzeptierte Bild, welches einen Großteil der Daten erklären kann ist, dass GRBs erzeugt werden, wenn ein massereicher Himmelskörper (entweder ein Stern, der die Hauptreihe verlassen hat, oder miteinander verschmelzende kompakte Objekte) in kosmologischer Distanz zu einem schnell rotierenden Objekt kollabiert (z.B. ein Schwarzes Loch), welches ultrarelativistische Materieauswürfe ("Jets") entlang der Polachse ausschleudert. Die interne Dissipation von Energie in dem Jet führt zu kollimierter nicht-thermischer Strahlung bei hohen Energien (der GRB), während Schockfronten, die bei der Interaktion des Jets mit der interstellaren Materie erzeugt werden, zu einem langlebigen abklingenden Afterglow führen. Die gesammelten physikalischen Prozesse, die die GRB-Emission beschreiben, werden als das Standard-Feuerballmodell bezeichnet. GRBs sind für kurze Zeiträume nachweislich die leuchtkräftigsten elektromagnetischen Quellen des Universums. In dieser Dissertation präsentiere ich meine Untersuchungen zu den Afterglows von Typ I (nicht mit massereicher Sternentstehung verknüpft, vermutlich durch die Verschmelzung kompakter Objekte ausgelöst) und Typ II (mit massereicher Sternentstehung verknüpft, die optische Emission zu späten Zeiten enthält eine Komponente, die einer Typ Ic Supernova mit hoher Ausbreitungsgeschwindigkeit zuzuschreiben ist) GRBs, und vergleiche sie miteinander, insbesondere, was die Extinktion durch Staub in den Muttergalaxien sowie die Leuchtkraftverteilung angeht. Um dies zu ermöglichen, habe ich das weltweit größte Archiv an photometrischen Daten zu Afterglows zusammengestellt und habe aus diesem GRBs selektiert, die ausreichende Daten für eine weitergehende Analyse boten

Gamma-Ray Burst/Supernova Associations: Energy Partition and the Case of a Magnetar Central Engine

The favored progenitor model for Gamma-ray Bursts (GRBs) with Supernova (SN) association is the core collapse of massive stars. One possible outcome of such a collapse is a rapidly spinning, strongly magnetized neutron star ( magnetar ). We systematically analyze the multi-wavelength data of GRB/SN associations detected by several instruments before 2017 June. Twenty GRB/SN systems have been confirmed via direct spectroscopic evidence or a clear light curve bump, as well as some spectroscopic evidence resembling a GRB-SN. We derive/collect the basic physical parameters of the GRBs and the SNe, and look for correlations among these parameters. We find that the peak brightness, 56Ni mass, and explosion energy of SNe associated with GRBs are statistically higher than other Type Ib/c SNe. A statistically significant relation between the peak energy of GRBs and the peak brightness of their associated SNe is confirmed. No significant correlations are found between the GRB energies (either isotropic or beaming-corrected) and the supernova energy. We investigate the energy partition within these systems and find that the beaming-corrected GRB energy of most systems is smaller than the SN energy, with less than 30% of the total energy distributed in the relativistic jet. The total energy of the systems is typically smaller than the maximum available energy of a millisecond magnetar (2 × 1052 erg), especially if aspherical SN explosions are considered. The data are consistent with—although not proof of—the hypothesis that most, but not all, GRB/SN systems are powered by millisecond magnetars

Price Markups, Innovation, and Productivity: Evidence from Germany. Bertelsmann Stiftung July 2020.

Productivity is seen as a driving force behind economic growth and an indicator of a society’s material wellbeing. Over the past decades, however, many industrialized countries have experienced declining productivity growth and an expansion of the productivity differential. Possible explanations range from declining investment in R & D to structural changes to more services and increased measurement errors due to increasing digitalization. In this report, we study the role that a firm’s competitive environment plays for its own productivity development. Is an increase in industry concentration – and the expected decrease in competition – associated with lower productivity? And what is the underlying driving force of this effect? Our findings of relatively strong direct effects of price markups (in comparison to the innovation-centered indirect effects) in all sectors but services highlight the potential for a well-tailored competition policy approach in society’s effort to tackle the productivity slowdown. This is particularly true for the trade sector, where the effect of competition on R & D and innovation is of limited significance for the determination of firm-level productivity. For services, on the other hand, the interdependence of competition and innovation in their effect on productivity must be taken into account as the indirect effect partially offsets the direct effect of competition on productivity. Considering one without the other will be misguiding

On the impact of machine learning for nowcasting applications

Póster presentado en: 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019

GRB 180325A: dust grain-size distribution and interstellar iron nanoparticles contribution

We modelled dust grain-size distributions for carbonaceous and silicates dust, as well as for free-flying iron nanoparticles in the environment of a $\gamma$-ray burst (GRB) afterglow, GRB 180325A. This GRB, at $z=2.2486$, has an unambiguous detection of the 2175 \r{A} extinction feature with $R_V=4.58$ and $A_V=1.58$. In addition to silicates, polycyclic aromatic hydrocarbons (PAH), and graphite, we used iron nanoparticles grain-size distributions for the first time to model the observed extinction curve of GRB 180325A. We fit the observed extinction for four model permutations, using 232 sets of silicates, graphite, carbon abundance in hydrocarbon molecules ($b_C$), and fraction of iron abundance in free-flying nanoparticles ($b_{\text{Fe}}$). These four different permutations were chosen to test iron nanoparticles significance and carbon abundance in hydrocarbons. Our results indicate that iron nanoparticles contribution is insignificant and there is a degeneracy of carbon abundances, with the range $(0.0 \leq b_C \leq 0.7)\times10^{-5}$ providing the best-fit to the observed extinction curve of GRB 180325A. We therefore favour the simplest model of silicates and polycyclic aromatic hydrocarbons. The silicates are dominant and contribute to the entire wavelength range of the GRB extinction curve while graphite contributes towards both the 2175 \r{A} bump and the UV extinction. The afterglow peak luminosity ($1.5\times10^{51}$ ergs/s) indicates dust destruction may have taken place. We conclude that further investigations into other potential contributors of extinction are warranted, particularly for steep UV extinction.Comment: 13 pages, 7 figures, accepted for publication in MNRA

Inhomogeneous Jets from Neutron Star Mergers: One Jet to Rule them all

Using the resultant profiles from 3D hydrodynamic simulations of relativistic jets interacting with neutron star merger wind ejecta, we show how the inhomogeneity of energy and velocity {across the jet surface profile} can alter the observed afterglow lightcurve. We find that the peak afterglow flux depends sensitively on the observer's line-of-sight, not only via the jet inclination but also through the jet rotation: for an observer viewing the afterglow within the GRB-bright jet core, we find a peak flux variability on the order $<0.5$ dex through rotational orientation and $<1.3$ dex for the polar inclination. An observed afterglow's peak flux can be used to infer the jet kinetic energy, and where a top-hat jet is assumed, we find the range of inferred jet kinetic energies for our various model afterglow lightcurves (with fixed model parameters), covers $\sim 1/3$ of the observed short GRB population. Additionally, we present an analytic jet structure function that includes physically motivated parameter uncertainties due to variability through the rotation of the source. % An approximation for the change in collimation due to the merger ejecta mass is included and we show that by considering the observed range of merger ejecta masses from short GRB kilonova candidates, a population of merger jets with a fixed intrinsic jet energy is capable of explaining the observed broad diversity seen in short GRB afterglows.Comment: 21 pages, 8 figure