Developing Tools for Multimessenger Gravitational Wave Astronomy

We present work in progress to craft open-sourced numerical tools that will enable the calculation of electromagnetic counterparts to gravitational waveforms: the {\tt GiRaFFE} (General Relativistic Force-Free Electrodynamics) code. {\tt GiRaFFE} numerically solves the general relativistic magnetohydrodynamics system of equations in the force-free limit, to model the magnetospheres surrounding compact binaries, in order (1) to characterize the nonlinear interaction between the source and its surrounding magnetosphere, and (2) to evaluate the electromagnetic counterparts of gravitational waves, including the production of collimated jets. We apply this code to various configurations of spinning black holes immersed in external magnetic field, in order to both test our implementation, and to explore the effect of strong gravitational field, high spins and of misalignment between the magnetic field lines an black hole spin, on the electromagnetic output and the collimation of Poynting jets. We will extend our work to collisions of black holes immersed in external magnetic field, which are prime candidates for coincident detection in both gravitational and electromagnetic spectra.Comment: 6 pages, 6 figures, MG15 proceeding

Some mathematical problems in numerical relativity

The main goal of numerical relativity is the long time simulation of highly nonlinear spacetimes that cannot be treated by perturbation theory. This involves analytic, computational and physical issues. At present, the major impasses to achieving global simulations of physical usefulness are of an analytic/computational nature. We present here some examples of how analytic insight can lend useful guidance for the improvement of numerical approaches.Comment: 17 pages, 12 graphs (eps format

Testing the well-posedness of characteristic evolution of scalar waves

Recent results have revealed a critical way in which lower order terms affect the well-posedness of the characteristic initial value problem for the scalar wave equation. The proper choice of such terms can make the Cauchy problem for scalar waves well posed even on a background spacetime with closed lightlike curves. These results provide new guidance for developing stable characteristic evolution algorithms. In this regard, we present here the finite difference version of these recent results and implement them in a stable evolution code. We describe test results which validate the code and exhibit some of the interesting features due to the lower order terms.Comment: 22 pages, 15 figures Submitted to CQ

Cauchy-Characteristic Patching with Improved Accuracy

Cauchy-characteristic extractions (CCE) avoids the errors due to extraction at finite worldtube. The Cauchy and the characteristic approaches have complementary strengths and weaknesses. Unification of the two methods is a promising way of combining the strengths of both formalisms

Steps Towards a Nonlinear Cauchy-characteristic Code Patching

Cauchy-characteristic extractions (CCE) avoids the errors due to extraction at finite worldtube. The Cauchy and the characteristic approaches have complementary strengths and weaknesses. Unification of the two methods is a promising way of combining the strengths of both formalisms

Realistic Binary Neutron Stars Collisions Simulations: Challenges and Opportunities

Since 2015, when the LIGO-Virgo collaboration announced the first simultaneous detections of gravitational waves (GW150914) until now, more than 66 gravitational wave detections were reported, but only two signals came from a binary neutron star collision, the GW170817 and GW190425 events. GW170817 was accompanied by an electromagnetic outburst manifested as a kilonova and an off-axis jet. However, no conclusive electromagnetic signature was found to come from the GW190425. Indeed, nature proves again more complicated than our models, and it is still a big question how to model kilonovae, or to understand the mechanisms driving astrophysical jets and gamma ray bursts. Not only the electromagnetic counterpart of such collisions, but also the nature of the remnant is also mostly unknown, and its investigation can give glimpses of the internal structure of neutron stars. This talk will focus on the challenges encountered endeavoring to perform numerical relativity simulations of realistic binary neutron star collisions, using open-source General-Relativistic Magnetohydrodynamic codes such as GRHydro, Spritz and IllinoisGRMHD, that run within the Einstein Toolkit software platform. We construct initial data for 6 parametrized hybrid equations of state, and add both interior magnetic field, and exterior magnetosphere, then perform simulations of BNS mergers within the mass range of the two detections. Besides addressing the problem of the reproducibility of the results, the aim of this talk is to forge a path through this complicated procedure, and make it approachable to graduate students, or researchers that just enter the field

Etiology of burns in different climate conditions

Introducere. Arsurile termice devin evenimente din ce în ce mai frecvente în lumea contemporană. Diversitatea agenţilor termici lezionali, geografia și circumstanţele de producere, demografia victimelor necesită o sistematizare prin prisma mai multor parametri. Cunoașterea aspectelor menţionate permite o estimare mai reală a riscurilor, o alocare mai raţională a resurselor și o organizare mai bună a asistenţei medicale urgente, a serviciului de situaţii excepţionale, precum și a reabilitării victimelor. Material și metode. A fost sistematizată cazuistica arsurilor termice pe un număr de 1840 de pacienţi din trei zone climaterice (tropicală, subtropicală și continentală) prin prisma repartizării pe sexe, grupurilor de vârstă, circumstanţelor de producere și agenţilor termici lezionali. Statistică descriptivă. Rezultate. Din punct de vedere a agentului termic lezional, se constată diferenţe semnificative în cauzele, locul producerii și repartizarea pe sexe a cazurilor de combustii. Cunoașterea particularităţilor cazuisticii regionale permite o planificare și organizare mai bună a serviciilor de asistenţă medicală urgentă și specializată și celor de situaţii excepţionale. Concluzii. Repartizarea pe sexe a pacienţilor arși, cât și proporţia copiilor afectaţi de combustii (toate cauzele fiind însumate), este similară pe mapamond, indiferent de zona climaterică studiată. Cazurile de combustii se întâlnesc de două ori mai frecvent în zona tropicală (în majoritate – tentative suicidare prin autocombustie la tinere de 14-35 de ani, aflate în stare de afect sau de depresie), decât în zona continentală.Introduction. Nowadays burns become more and more frequent in our contemporary world. The variety of lesional thermal agents, geography and circumstances of occurrence, victims’ demography need a multi-parameter systematization. Knowing the above-mentioned aspects make it possible to estimate better the risks, to gestionate financial resources and better organize the first medical aid, exceptional situations’ service, as well as victims’ rehabilitation. Material and methods. A number of 1840 patients with thermal burns from 3 climate zones (tropical, subtropical and continental), taking in consideration their gender repartition, age groups, circumstances of occurrence and lesional thermal agents. Descriptive statistics. Results. Analysing the lesional thermic agent we notice significant differences in the cause, place of occurrence and gender repartition of burn cases. Knowing particularities of regional casuistry offers a chance to better plan and organize first medical aid, specialized medical assistance and the service of exceptional situations. Conclusions. Gender repartition of patients with burns as well as the proportion of affected children (with all causes included) is similar worldwide, regardless of climate zone studied. Combustion cases are twice more frequent in the tropical zone than in the continental zone (the majority of cases are suicide attempts through auto combustion in young women, 14-35 years, with depression or in an affective state)

Adding Light to the Gravitational Waves on the Null Cone

Recent interesting astrophysical observations point towards a multi-messenger, multi-wavelength approach to understanding strong gravitational sources, like compact stars or black hole collisions, supernovae explosions, or even the big bang. Gravitational radiation is properly defined only at future null infinity, but usually is estimated at a finite radius, and then extrapolated. Our group developed a characteristic waveform extraction tool, implemented in an open source code, which computes the gravitational waves infinitely far from their source, in terms of compactified null cones, by numerically solving Einstein equation in Bondi space-time coordinates. The goal is extend the capabilities of the code, by solving Einstein-Maxwell\u27s equations together with the Maxwell\u27s equations, to obtain the energy radiated asymptotically at infinity, both in gravitational and electromagnetic waves. The purpose is to analytically derive and numerically calculate both the gravitational waves and the electromagnetic counterparts at infinity, in this characteristic framework. The method is to treat the source of gravitational and electromagnetic radiation as a black box, and therefore the code will be very flexible, with potentially large applicability

Towards Improved Accuracy of Gravitational Waves Extraction

Results in developing two new methods to improve the accuracy of waveform extraction using characteristic evolution. Numerical method: circular boundaries, with angular dissipation in the characteristic code. Geometric method: computation of Weyl tensor component Y4 at null infinity, in a conformally compactified treatment. Comparison and calibration in tests problems based upon linearized waves