Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

A further search on waves generated by solar energetic protons

It has been suggested that in the interplanetary medium Alfven waves may be significantly amplified or damped during large solar proton events. This implies the increase or decrease of the ambient magnetic fluctuations in concurrence with the presence of the streaming particles, that we have analysed in a first study at times of eight proton events observed by Hellos spacecraft (Valdes-Galicia and Alexander, 1997). However, it is not possible with interplanetary magnetic field measurements only to distinguish between waves moving away or towards the Sun in the frame of reference of the spacecraft. Plasma data for these eight events have now been made available to us and hence the energetic content of inward and outward propagating waves may be found, which is an important aid in our search for signatures left by the energetic protons. In the present work we incorporate the new information into the analyses of those events that in our first study showed more favourable evidence and therefore try to give a more definite answer as to whether it might be observed. The new results do not reinforce the evidence of our previous work, as they seem to be mildly consistent with the presence of the proton self-generated waves in just one of the three cases studied

Calibration and monitoring of water Cherenkov detectors with stopping and crossing muons

The Auger Observatory water Cherenkov detectors (WCD) will require that the initial calibration and subsequent monitoring of each of the WCDs be done in a remote way. We present a method to perform these tasks based on the detection of muons decaying inside the detectors and the application of adequate selection cuts. This technique may be complemented with another based on muons crossing the WCDs, Samples of decaying and crossing muon events were obtained with a WCD prototype to demonstrate the viability of the techniques. Three clear peaks of PMT charge distributions were identified. All of them are useful for calibration and monitoring of WCDs: one for stopping muons, one for decay electrons and one for crossing muons. The mean value of the peak found in the decay-electron charge distribution is 0.18 times the corresponding value for vertically crossing muon

The Pierre Auger Observatory scaler mode for the study of solar activity modulation of galactic cosmic rays

Since data-taking began in January 2004, the Pierre Auger Observatory has been recording the count rates of low energy secondary cosmic ray particles for the self-calibration of the ground detectors of its surface detector array. After correcting for atmospheric effects, modulations of galactic cosmic rays due to solar activity and transient events are observed. Temporal variations related with the activity of the heliosphere can be determined with high accuracy due to the high total count rates. In this study, the available data are presented together with an analysis focused on the observation of Forbush decreases, where a strong correlation with neutron monitor data is found.Comision Nacional de Energia Atomica, ArgentinaFundacion AntorchasGobierno De La Provincia de Mendoza, Municipalidad de Malargue, ArgentinaNDM HoldingsValle Las Lenas, ArgentinaAustralian Research Council (ARC)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Financiadora de Estudos e Projetos (FINEP)Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Ministério da Ciência, Tecnologia e Inovação do Brasil (MCTI)Academy of Sciences of the Czech Republic (AVCR) [AV0Z10100502] [AV0Z10100522] [GAAV KJB300100801] [KJB100100904] [MSMT-CR LA08016] [LC527] [1M06002] [MSM0021620859]Centre National de la Recherche Scientifique (CNRS), Centre de Calcul IN2P3/CNRSConseil Regional Ile-de-France, Departement Physique Nucleaire et Corpusculaire [PNC-IN2P3/CNRS]Departement Sciences de l`Univers (SDU-INSU/CNRS), FranceBundesministerium fur Bildung und Forschung (BMBF)Deutsche Forschungsgemeinschaft (DFG)Finanzministerium Baden-WurttembergHelmholtz-Gemeinschaft Deutscher Forschungszentren (HGF)Ministerium fur Wissenschaft und Forschung, Nordrhein-Westfalen, GermanyMinisterium fur Wissenschaft, Forschung und Kunst, Baden-Wurttemberg, GermanyIstituto Nazionale di Fisica Nucleare (INFN)Istituto Nazionale di Astrofisica (INAF)Ministero dell Istruzione, dell Universita e della Ricerca (MIUR), ItalyConsejo Nacional de Ciencia y Tecnologia (CONACYT), MexicoMinisterie van Onderwijs, Cultuur en Wetenschap, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)Stichting voor Fundamenteel Onderzoek der Materie (FOM), NetherlandsMinistry of Science and Higher Education, Poland [1 P03 D 014 30] [N N202 207238]Fundacao para a Ciencia e a Tecnologia (FCT), PortugalMinistry for Higher Education, Science, and Technology, Slovenian Research Agency, SloveniaComunidad de Madrid, SpainConsejeria de Educacion de la Comunidad de Castilla La ManchaFondo Europeo de Desarrollo Regional (FEDER)Ministerio de Ciencia e Innovacion, Consolider-Ingenio, SpainGeneralitat ValencianaJunta de AndaluciaXunta de Galicia, SpainScience and Technology Facilities Council, United KingdomU.S. Department of Energy (DOE) [DE-AC02-07CH11359] [DE-FR02-04ER41300]National Science Foundation (NSF) [0450696]Grainger Foundation USAALFA-EC / HELENEuropean Union [MEIF-CT-2005-025057] [PIEF-GA-2008-220240]United Nations Educational, Scientific and Cultural Organization (UNESCO

The rapid atmospheric monitoring system of the Pierre Auger Observatory

The Pierre Auger Observatory is a facility built to detect air showers produced by cosmic rays above 1017 eV. During clear nights with a low illuminated moon fraction, the UV fluorescence light produced by air showers is recorded by optical telescopes at the Observatory. To correct the observations for variations in atmospheric conditions, atmospheric monitoring is performed at regular intervals ranging from several minutes (for cloud identification) to several hours (for aerosol conditions) to several days (for vertical profiles of temperature, pressure, and humidity). In 2009, the monitoring program was upgraded to allow for additional targeted measurements of atmospheric conditions shortly after the detection of air showers of special interest, e. g., showers produced by very high-energy cosmic rays or showers with atypical longitudinal profiles. The former events are of particular importance for the determination of the energy scale of the Observatory, and the latter are characteristic of unusual air shower physics or exotic primary particle types. The purpose of targeted (or "rapid") monitoring is to improve the resolution of the atmospheric measurements for such events. In this paper, we report on the implementation of the rapid monitoring program and its current status. The rapid monitoring data have been analyzed and applied to the reconstruction of air showers of high interest, and indicate that the air fluorescence measurements affected by clouds and aerosols are effectively corrected using measurements from the regular atmospheric monitoring program. We find that the rapid monitoring program has potential for supporting dedicated physics analyses beyond the standard event reconstruction. </p

Search for a correlation between the UHECRs measured by the Pierre Auger Observatory and the Telescope Array and the neutrino candidate events from IceCube

We have conducted three searches for correlations between ultra-high energy cosmic rays detected by the Telescope Array and the Pierre Auger Observatory, and high-energy neutrino candidate events from IceCube. Two cross-correlation analyses with UHECRs are done: one with 39 cascades from the IceCube `high-energy starting events' sample and the other with 16 high-energy `track events'. The angular separation between the arrival directions of neutrinos and UHECRs is scanned over. The same events are also used in a separate search using a maximum likelihood approach, after the neutrino arrival directions are stacked. To estimate the significance we assume UHECR magnetic deflections to be inversely proportional to their energy, with values 3◦, 6◦ and 9◦ at 100 EeV to allow for the uncertainties on the magnetic field strength and UHECR charge. A similar analysis is performed on stacked UHECR arrival directions and the IceCube sample of through-going muon track events which were optimized for neutrino point-source searches

Introducing the CTA concept

The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project