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Gabrijela Zaharijas, Collaboration Fermi LAT, Collaboration LIGO, 2016, original scientific article

Abstract: The Fermi Large Area Telescope (LAT) has an instantaneous field of view (FoV) covering ~1 5 of the sky and it completes a survey of the entire sky in high-energy gamma-rays every 3 hr. It enables searches for transient phenomena over timescales from milliseconds to years. Among these phenomena could be electromagnetic counterparts to gravitational wave (GW) sources. In this paper, we present a detailed study of the LAT observations relevant to Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914, which is the first direct detection of gravitational waves and has been interpreted as being due to the coalescence of two stellar-mass black holes. The localization region for GW150914 was outside the LAT FoV at the time of the GW signal. However, as part of routine survey observations, the LAT observed the entire LIGO localization region within ∼70 minutes of the trigger and thus enabled a comprehensive search for a γ-ray counterpart to GW150914. The study of the LAT data presented here did not find any potential counterparts to GW150914, but it did provide limits on the presence of a transient counterpart above 100 MeV on timescales of hours to days over the entire GW150914 localization region.
Found in: ključnih besedah
Keywords: gravitational waves, gamma rays
Published: 20.06.2016; Views: 3323; Downloads: 0
.pdf Fulltext (2,04 MB)

Detection of gravitational waves
Gregor Mrak, 2016, undergraduate thesis

Abstract: This report mainly focuses on the first two detections of gravitational waves (GW). At the beginning of the thesis the historical background of GW explorations is discussed by pointing out some arguments and researchers that were essential for the progress. Continuing with the derivation based on the theory of general relativity, in order to express where certain properties derive. In the main part of the report, the subject of interest becomes Laser interferometer gravitational-wave observatory (LIGO), beginning with the problems occurring on the way to detection, describing different noise sources one by one. After pointing out the problems, solutions are discussed, namely the technological advances made to lower the background noise as much as possible. The chapter (4) points out different parts of the detector which are implemented to produce a clearer signal. As only physical noise reduction methods are not enough, digital signal processing algorithms are mentioned as well which are used to analyze the data. Subsequently the required theoretical knowledge is given, so the main part ends with the analysis of actual data taken from LIGO’s public release for both GW150914 and GW151226 events (first and second official detections). In the conclusion of the report a brief descriptions of various detectors besides Ligo are given and some insight of the future detectors that are planned to be built.
Found in: ključnih besedah
Keywords: Gravitational waves, Ligo, Binary black hole merger, gravitational wave interferometry
Published: 27.09.2016; Views: 5295; Downloads: 265
.pdf Fulltext (3,27 MB)

Search for UHE neutrinos – in coincidence with LIGO GW150914 event – with the Pierre Auger Observatory
Lili Yang, 2016, published scientific conference contribution abstract

Abstract: The first gravitational wave transient GW150914 was observed by Advanced LIGO on September 14th, 2015 at 09:50:45 Universal Time. In addition to follow-up electromagnetic observations, the detection of neutrinos will probe deeply and more on the nature of astrophysical sources, especially in the ultra-high energy regime. Neutrinos in the EeV energy range were searched in data collected at the surface detector of the Pierre Auger Observatory within ± 500 s and 1 day after the GW150914 event. No neutrino candidates were found. Based on this non-observation, we derive the first and only one neutrino fluence upper limit at EeV energies for this event at 90% CL, and report constraints on existence of accretion disk around mergers.
Found in: ključnih besedah
Keywords: gravitational waves, neutrinos, black hole physics
Published: 06.12.2016; Views: 3490; Downloads: 0
.pdf Fulltext (627,39 KB)

Lidar measurements of Bora wind effects on aerosol loading
Maruška Mole, Longlong Wang, Samo Stanič, Klemen Bergant, William Eichinger, Francisco Ocaña, Benedikt Strajnar, Primož Škraba, Marko Vučković, William Willis, 2017, original scientific article

Abstract: The Vipava valley in Slovenia is well known for the appearance of strong, gusty North-East Bora winds, which occur as a result of air flows over an adjacent orographic barrier. There are three revealing wind directions within the valley which were found to give rise to specific types of atmospheric structures. These structures were investigated using a Mie scattering lidar operating at 1064 nm, which provided high temporal and spatial resolution backscatter data on aerosols, which were used as tracers for atmospheric flows. Wind properties were monitored at the bottom of the valley and at the rim of the barrier using two ultrasonic anemometers. Twelve time periods between February and April 2015 were selected when lidar data was available. The periods were classified according to the wind speed and direction and investigated in terms of appearance of atmospheric structures. In two periods with strong or moderate Bora, periodic atmospheric structures in the lidar data were observed at heights above the mountain barrier and are believed to be Kelvin–Helmholtz waves, induced by wind shear. No temporal correlation was found between these structures and wind gusts at the ground level. The influence of the wind on the height of the planetary boundary layer was studied as well. In periods with low wind speeds, the vertical evolution of the planetary boundary layer was found to be governed by solar radiation and clouds. In periods with strong or moderate Bora wind, convection within the planetary boundary layer was found to be much weaker due to strong turbulence close to the ground, which inhibited mixing through the entire layer.
Found in: ključnih besedah
Keywords: Downslope wind Lidar observations Kelvin–Helmholtz waves Bora
Published: 06.01.2017; Views: 3737; Downloads: 0
.pdf Fulltext (3,02 MB)

New Frontiers in Black Hole Astrophysics
2017, proceedings of peer-reviewed scientific conference contributions (international and foreign conferences)

Found in: ključnih besedah
Keywords: astronomy, black holes, active galactic nuclei, gamma ray bursts, tidal disruption events, gravitational waves
Published: 17.08.2017; Views: 2616; Downloads: 0
.pdf Fulltext (106,73 KB)

Search for UHE neutrinos in coincidence with LIGO GW150914 event with the Pierre Auger Observatory
Lili Yang, 2017, published scientific conference contribution

Found in: ključnih besedah
Keywords: astronomy, gravitational waves, Pierre Auger observatory
Published: 17.08.2017; Views: 2547; Downloads: 0
.pdf Fulltext (447,07 KB)

Study of the properties of air flow over orographic barrier
Maruška Mole, 2017, doctoral dissertation

Abstract: Earth’s atmosphere is a complex system. All weather phenomena take place in its lowest layer, the troposphere, which is strongly influenced by human activities and the underlying surface orography. A good example of the influence the orography has on the behavior of air flows is the appearance of strong north-east downslope wind in Vipava valley, called Bora. Numerical models used to analyze flows in complex terrain need meteorological data both for setting the initial conditions and the verification of modeling results. Obtaining spatial distributions of meteorological observables can be challenging, especially in the case of strong winds, such as Bora, where traditional methods may be inadequate due to prohibitive wind speeds. In most cases, vertical properties of the atmosphere can be obtained using remote sensing techniques. Contrary to vertical profile measurements with traditional methods, remote sensing techniques do not require the measuring device to be placed within the flow and are therefore more appropriate for measurements in severe weather conditions such as strong winds. The aim of this thesis is a detailed analysis of wind and tropospheric structure properties in and above the Vipava valley in a variety of typical atmospheric conditions, including strong wind events. It employs a combination of high resolution wind and lidar data in addition to standard meteorological measurements. In Ajdovščina, there are four predominant wind directions, two of them directly connected to Bora. In the case of Bora, periodicity analysis of wind data from Ajdovščina yielded a range of possible wind gust periods between 1 and 7 minutes. The periods were not stable, with the periodogram less noisy for stable wind directions. Wavelike structures were found to be present in the troposphere in half of the investigated cases, regardless of the presence of Bora. In statically stable conditions, gravity waves propagated throughout the planetary boundary layer (PBL). In the case of Bora, the PBL experienced oscillations with periods between 1 and 2 minutes. A shear layer was present above the PBL, causing Kelvin-Helmholtz waves at its boundaries with periods ranging from 3 to 6 minutes. In some cases, periodic structures were observed above the shear layer as well, which were found to have longer periods than those within the PBL.
Found in: ključnih besedah
Keywords: remote sensing, Vipava valley, wind properties, Bora, wind gusts, wind periodicity, tropospheric structures, Kelvin-Helmholtz waves
Published: 18.09.2017; Views: 4367; Downloads: 133
.pdf Fulltext (45,11 MB)

Fermi -LAT Observations of LIGO / Virgo Event GW170817
Gabrijela Zaharijas, 2018, original scientific article

Found in: ključnih besedah
Keywords: gamma-ray burst, gamma rays, gravitational waves
Published: 23.08.2018; Views: 2132; Downloads: 0
.pdf Fulltext (5,09 MB)

A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary
Tanja Petrushevska, 2018, original scientific article

Abstract: Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.
Found in: ključnih besedah
Keywords: supernova, neutron stars, gravitational waves
Published: 12.10.2018; Views: 2052; Downloads: 0
.pdf Fulltext (3,36 MB)

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