83 research outputs found
Measurement of the Energy Spectrum of Ultra-High Energy Cosmic Rays using Hybrid Data of the Pierre Auger Observatory
The subject of this thesis is the measurement of the energy spectrum of ultra-high energy cosmic rays from simultaneous observation of fluorescence and surface detectors of the Pierre Auger Observatory. Extending the nominal energy range of the Pierre Auger Observatory to lower energy, the hybrid energy spectrum above 10^{18} eV is measured. It shows a significant break of the power-law behavior at 10^{18.7} eV
All sky archival search for FRB high energy counterparts with Swift and Fermi
Fast radio bursts (FRBs) are millisecond-duration radio signals from unknown
cosmic origin. Many models associate FRBs with high-energy astrophysical
objects such as magnetars. In this attempt to find counterparts to FRBs, we
explore gamma-ray bursts (GRBs) from the Swift and Fermi missions. We first
search for spatial correlations between FRB and GRB populations as a whole and
then search for a one-by-one correlation between each of the FRBs and GRBs
investigated. Temporal coincidences are not considered. To evaluate the
significance of any correlation found, we generate background realizations that
take into account instrumentally induced anisotropies in the distribution of
the sources. Neither study yields any significant counterpart detection. We
estimate that less than 4\% of the FRBs are associated with GRBs in the studied
samplesComment: Proceedings 38th International Cosmic Ray Conference (ICRC2023
On the measurement of the proton-air cross section using air shower data
The analysis of high-energy air shower data allows one to study the
proton-air cross section at energies beyond the reach of fixed target and
collider experiments. The mean depth of the first interaction point and its
fluctuations are a measure of the proton-air particle production cross section.
Since the first interaction point in air cannot be measured directly, various
methods have been developed in the past to estimate the depth of the first
interaction from air shower observables in combination with simulations. As the
simulations depend on assumptions made for hadronic particle production at
energies and phase space regions not accessible in accelerator experiments, the
derived cross sections are subject to significant systematic uncertainties. The
focus of this work is the development of an improved analysis technique that
allows a significant reduction of the model dependence of the derived cross
section at very high energy. Performing a detailed Monte Carlo study of the
potential and the limitations of different measurement methods, we quantify the
dependence of the measured cross section on the used hadronic interaction
model. Based on these results, a general improvement to the analysis methods is
proposed by introducing the actually derived cross section already in the
simulation of reference showers. The reduction of the model dependence is
demonstrated for one of the measurement methods.Comment: Accepted by NJP. To appear in the Focus Issue "High Energy Cosmic
Rays
The Cherenkov Telescope array on-site integral sensitivity: observing the Crab
The Cherenkov Telescope Array (CTA) is the future large observatory in the very high energy (VHE) domain. Operating from 20 GeV to 300 TeV, it will be composed of tens of Imaging Air Cherenkov Telescopes (IACTs) displaced in a large area of a few square kilometers in both the southern and northern hemispheres. Thanks to the wide energy coverage and the tremendous boost in effective area (10 times better than the current IACTs), for the first time a VHE observatory will be able to detect transient phenomena in short exposures. The CTA/DATA On-Site Analysis (OSA) is the system devoted to the development of dedicated pipelines and algorithms to be used at the CTA site for the reconstruction, data quality monitoring, science monitoring and realtime science alerting during observations. The minimum exposure required to issue a science alert is not a general requirement of the observatory but is a function of the astrophysical object under study, because the ability to detect a given source is determined by the integral sensitivity which, in addition to the CTA Monte Carlo simulations, providing the energy-dependent instrument response (e.g. the effective area and the background rate), requires the spectral distribution of the science target. The OSA integral sensitivity is computed here for the most studied source at Gamma-rays, the Crab Nebula, for a set of exposures ranging from 1000 seconds to 50 hours, using the full CTA Southern array. The reason for the Crab Nebula selection as the first example of OSA integral sensitivity is twofold: (i) this source is characterized by a broad spectrum covering the entire CTA energy range; (ii) it represents, at the time of writing, the standard candle in VHE and it is often used as unit for the IACTs sensitivity. The effect of different Crab Nebula emission models on the CTA integral sensitivity is evaluated, to emphasize the need for representative spectra of the CTA science targets in the evaluation of the OSA use cases. Using the most complete model as input to the OSA integral sensitivity, we obtain a significant detection of the Crab nebula (about 10% of flux) even for a 1000 second exposure, for an energy threshold less than 10 TeV
tilepy: rapid tiling strategies in mid/small FoV observatories
The challenges inherent to time-domain multi-messenger astronomy require
strategic actions so that adapted, optimized follow-up observations are
performed efficiently. In particular, poorly localized events require dedicated
tiling and/or targeted, follow-up campaigns so that the region in which the
source really is can be efficiently covered, increasing the chances to detect
the multi-wavelength counterpart. We have developed the python package "tilepy"
to rapidly derive the observation scheduling of large uncertainty localization
events by small/mid-FoV instruments. We will describe several mature follow-up
scheduling strategies. These range from an option to use of low-resolution
grids, to the full integration of sky regions and targeted observations using
galaxy catalogs. The algorithms consider the visibility constraints of
customisable observatories and allow to schedule observations in both
astronomical darkness and in moonlight conditions. Developed initially to
provide a rapid response to gravitational wave (GW) alerts by Imaging
Atmospheric Cherenkov Telescopes (IACTs), they have been proven successful, as
shown by the GW follow-up during O2 and O3 with the H.E.S.S. telescopes, and
particularly in the follow-up of GW170817, the first binary neutron star (BNS)
merger ever detected. Here we will present a generalisation of these rapid
strategies to other alerts showing large uncertainties in the localization,
like Gamma-Ray Burst (GRB) alerts from Fermi-GBM. We will also demonstrate the
flexibility of {\it tilepy} in scheduling observations for a large variety of
observatories. We will conclude by describing the latest developments of these
algorithms that are able to derive optimised follow-up schedules across
multiple observatories and networks of telescopes.Comment: Proceedings 38th International Cosmic Ray Conference (ICRC2023
Astro-COLIBRI: An Advanced Platform for Real-Time Multi-Messenger Astrophysics
Observations of transient phenomena like Gamma-Ray Bursts (GRBs), Fast Radio
Bursts (FRBs), stellar flares and explosions (novae and supernovae), combined
with the detection of novel cosmic messengers like high-energy neutrinos and
gravitational waves has revolutionized astrophysics over the last years. The
discovery potential of both ulti-messenger and multi-wavelength follow-up
observations as well as serendipitous observations could be maximized with a
novel tool which allows for quickly acquiring an overview over relevant
information associated with each new detection. Here we present Astro-COLIBRI,
a novel and comprehensive platform for this challenge.
Astro-COLIBRI's architecture comprises a public RESTful API, real-time
databases, a cloud-based alert system and a website as well as apps for iOS and
Android as clients for users. Astro-COLIBRI evaluates incoming messages of
astronomical observations from all available alert streams in real time,
filters them by user specified criteria and puts them into their MWL and MM
context. The clients provide a graphical representation with an easy to grasp
summary of the relevant data to allow for the fast identification of
interesting phenomena, provides an assessment of observing conditions at a
large selection of observatories around the world, and much more.
Here the key features of Astro-COLIBRI are presented. We outline the
architecture, summarize the used data resources, and provide examples for
applications and use cases. Focussing on the high-energy domain, we'll discuss
the use of the platform in searches for high-energy gamma-ray counterparts to
high-energy neutrinos, gamma-ray bursts and gravitational waves.Comment: Proceedings 38th International Cosmic Ray Conference (ICRC2023
Citizen Science Time Domain Astronomy with Astro-COLIBRI
Astro-COLIBRI is an innovative tool designed for professional astronomers to
facilitate the study of transient astronomical events. Transient events - such
as supernovae, gamma-ray bursts and stellar mergers - are fleeting cataclysmic
phenomena that can offer profound insights into the most violent processes in
the universe. Revealing their secrets requires rapid and precise observations:
Astro-COLIBRI alerts its users of new transient discoveries from observatories
all over the world in real-time. The platform also provides observers the
details they need to make follow-up observations.
Some of the transient phenomena available through Astro-COLIBRI are
accessible by amateur astronomers and citizen scientists. A subset of the
features dedicated to this growing group of users are highlighted here. They
include the possibility of receiving only alerts on very bright events, the
possibility of defining custom observer locations, as well as the calculation
of optimized observation plans for searches for optical counterparts to
gravitational wave events.Comment: Proceedings Atelier Pro-AM Gemini, Journ\'ees SF2A 2023. arXiv admin
note: text overlap with arXiv:2308.0704
H.E.S.S. realtime follow-ups of IceCube high-energy neutrino alerts
The evidence for multi-messenger photon and neutrino emission from the blazar
TXS 0506+056 has demonstrated the importance of realtime follow-up of neutrino
events by various ground- and space-based facilities. The effort of H.E.S.S.
and other experiments in coordinating observations to obtain quasi-simultaneous
multiwavelength flux and spectrum measurements has been critical in measuring
the chance coincidence with the high-energy neutrino event IC-170922A and
constraining theoretical models. For about a decade, the H.E.S.S. transient
program has included a search for gamma-ray emission associated with
high-energy neutrino alerts, looking for gamma-ray activity from known sources
and newly detected emitters consistent with the neutrino location. In this
contribution, we present an overview of follow-up activities for realtime
neutrino alerts with H.E.S.S. in 2021 and 2022. Our analysis includes both
public IceCube neutrino alerts and alerts exchanged as part of a joint
H.E.S.S.-IceCube program. We focus on interesting coincidences observed with
gamma-ray sources, particularly highlighting the significant detection of PKS
0625-35, an AGN previously detected by H.E.S.S., and three IceCube neutrinos.Comment: Presented at the 38th International Cosmic Ray Conference (ICRC2023).
See arXiv:2307.13047 for all IceCube contribution
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