Abstract
Aerosol levels influence the wavelength dependent transmission properties of the atmosphere. Variations in aerosol levels therefore affect the amount of Cherenkov light from air-showers that ...can reach an atmospheric Cherenkov detector. As the amount of detected Cherenkov light is directly related to a primary shower particle’s energy, deviations between actual and assumed atmospheric transmission properties yield errors in reconstructed particle energies as well as energy axes of instrument response functions. In this work, a scheme is presented to assess this influence and potentially reduce related errors in the air-shower reconstruction. The proposed scheme relies on estimations or measurements of the aerosol optical depth and atmospheric density profile which are then used in radiative transfer simulations to generate atmospheric transmission profiles. As the scheme furthermore uses detector specific quantum efficiencies and generalised shower evolution models, it does not rely on detailed Monte Carlo simulations for the different atmospheric conditions but only on the transmission profile which the initial shower reconstruction algorithm is based on. The approach is derived and presented on the example of the H.E.S.S. experiment which employs imaging atmospheric Cherenkov telescopes in the Khomas Highland of Namibia to detect gamma rays in the GeV to TeV energy range.
Ground based γ-ray observations with Imaging Atmospheric Cherenkov Telescopes (IACTs) play a significant role in the discovery of very high energy (E > 100 GeV) γ-ray emitters. The analysis of IACT ...data demands a highly efficient background rejection technique, as well as methods to accurately determine the position of its source in the sky and the energy of the recorded γ-ray. We present results for background rejection and signal direction reconstruction from first studies of a novel data analysis scheme for IACT measurements. The new analysis is based on a set of Convolutional Neural Networks (CNNs) applied to images from the four H.E.S.S. phase-I telescopes. As the H.E.S.S. cameras pixels are arranged in a hexagonal array, we demonstrate two ways to use such image data to train CNNs: by resampling the images to a square grid and by applying modified convolution kernels that conserve the hexagonal grid properties.
The networks were trained on sets of Monte-Carlo simulated events and tested on both simulations and measured data from the H.E.S.S. array. A comparison between the CNN analysis to current state-of-the-art algorithms reveals a clear improvement in background rejection performance. When applied to H.E.S.S. observation data, the CNN direction reconstruction performs at a similar level as traditional methods. These results serve as a proof-of-concept for the application of CNNs to the analysis of events recorded by IACTs.
Observations of astrophysical transients have brought many novel discoveries and provided new insights into the physical processes at work under extreme conditions in the Universe. Multi-wavelength ...and multi-messenger observations of variable objects require dedicated procedures and follow-up systems capable of digesting and reacting to external alerts to execute coordinated follow-up campaigns. The main functions of such follow-up systems are the processing, filtering, and ranking of the incoming alerts, the fully automated rapid execution of the observations according to an observation strategy tailored to the instrument, and real-time data analysis with feedback to the operators and other instruments. The High Energy Stereoscopic System (H.E.S.S.) has been searching for transient phenomena since its inauguration in 2003. In this paper, we describe the transients follow-up system of H.E.S.S. which became operational in 2016. The system allows H.E.S.S. to conduct a more versatile, optimised, and largely autonomous transient follow-up programme, combining all major functionalities in one systematic approach. We describe the design, central functionalities, and interfaces of the follow-up system in general and its three main components in detail: the Target of Opportunity (ToO) alert system, the data acquisition and central control system, and the real-time analysis. We highlight architectural decisions and features that enable fully automatic ToO follow-up and indicate key performance metrics of the subsystems. We discuss the system's capabilities and highlight the need for a fine-tuned interplay of the different subsystems in order to react quickly and reliably. Lessons learnt from the development, integration, and operation of the follow-up system are reviewed in light of new and large science infrastructures and associated challenges in this exciting new era of inter-operable astronomy.
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new ...observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, i.e., the Inner Galaxy Survey, at very high energies (& GSIM;100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section (sigma v). Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach (sigma v) values of 3.7 x 10-26 cm3 s-1 for 1.5 TeV DM mass in the W+W- annihilation channel, and 1.2 x 10-26 cm3 s-1 for 0.7 TeV DM mass in the tau+tau- annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based gamma-ray observations thus probe (sigma v) values expected from thermal-relic annihilating TeV DM particles.
Abstract
Magnetic fields in galaxies and galaxy clusters are believed to be the result of the amplification of intergalactic seed fields during the formation of large-scale structures in the ...universe. However, the origin, strength, and morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower limits on (or indirect detection of) the IGMF can be obtained from observations of high-energy gamma rays from distant blazars. Gamma rays interact with the extragalactic background light to produce electron−positron pairs, which can subsequently initiate electromagnetic cascades. The gamma-ray signature of the cascade depends on the IGMF since it deflects the pairs. Here we report on a new search for this cascade emission using a combined data set from the Fermi Large Area Telescope and the High Energy Stereoscopic System. Using state-of-the-art Monte Carlo predictions for the cascade signal, our results place a lower limit on the IGMF of
B
> 7.1 × 10
−16
G for a coherence length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed. This improves on previous lower limits by a factor of 2. For longer duty cycles of 10
4
(10
7
) yr, IGMF strengths below 1.8 × 10
−14
G (3.9 × 10
−14
G) are excluded, which rules out specific models for IGMF generation in the early universe.
We search for an indirect signal of dark matter through very high-energy γ rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would ...produce Standard Model particles in the final state such as γ rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well-measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the five-telescopes of the high energy stereoscopic system observed the dwarf irregular galaxy WLM for 18 hours. We present the first analysis based on data obtained from an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation ⟨ σv ⟩ as a function of the dark matter particle mass for various continuum channels, as well as the prompt γγ emission. For the τ+ τ− channel, the limits reach a ⟨ σv ⟩ value of about 4 × 10−22 cm3 s−1 for a dark matter particle mass of 1 TeV. For the prompt γγ channel, the upper limit reaches a ⟨ σv ⟩ value of about 5 × 10−24 cm3 s−1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200, with respect to previous results for the dwarf irregular galaxies for TeV dark matter search.
Dwarf spheroidal galaxy satellites of the Milky Way are prime targets for indirect detection of dark matter with gamma rays due to their proximity, high dark matter content, and absence of nonthermal ...emission processes. Recently, the Dark Energy Survey (DES) revealed the existence of new ultrafaint dwarf spheroidal galaxies in the southern-hemisphere sky, therefore ideally located for ground-based observations with the imaging atmospheric Cherenkov telescope array H.E.S.S. We present a search for very-high-energy ( E ≳ 100 GeV ) gamma-ray emission using H.E.S.S. observations carried out recently towards Reticulum II, Tucana II, Tucana III, Tucana IV, and Grus II satellites. No significant very-high-energy gamma-ray excess is found from the observations on any individual object nor in the combined analysis of all the datasets. Using the most recent modeling of the dark matter distribution in the dwarf galaxy halo, we compute for the first time on DES satellites individual and combined constraints from Cherenkov telescope observations on the annihilation cross section of dark matter particles in the form of Weakly Interacting Massive Particles. The combined 95% C.L. observed upper limits reach ⟨ σ v ⟩ ≃ 1 × 10−23 cm3 s−1 in the W+W− channel and 4 × 10−26 cm3 s−1 in the γ γ channels for a dark matter mass of 1.5 TeV. The H.E.S.S. constraints well complement the results from Fermi-LAT, HAWC, MAGIC, and VERITAS and are currently the most stringent in the γγ channels in the multi-GeV/multi-TeV mass range.
Significant adverse events (AE) during cancer therapy disrupt treatment and escalate to emergency admissions. Approaches to improve the timeliness and accuracy of AE reporting may improve safety and ...reduce health service costs. Reporting AE via patient reported outcomes (PROs), can improve clinician–patient communication and making data available to clinicians in ‘real-time’ using electronic PROs (ePROs) could potentially transform clinical practice by providing easily accessible records to guide treatment decisions. This manuscript describes the development of eRAPID (electronic patient self-Reporting of Adverse-events: Patient Information and aDvice) is a National Institute for Health Research-funded programme, a system for patients to self-report and manage AE online during and after cancer treatment.
A multidisciplinary team of IT experts, staff and patients developed using agile principles a secure web application interface (QStore) between an existing online questionnaire builder (QTool) displaying real-time ePRO data to clinicians in the electronic patient record at Leeds Teaching Hospitals NHS Trust. Hierarchical algorithms were developed corresponding to Common Terminology Criteria for Adverse Events grading using the QTool question dependency function. Patient advocates (N = 9), patients (N = 13), and staff (N = 19) usability tested the system reporting combinations of AE.
The eRAPID system allows patients to report AE from home on PC, tablet or any web enabled device securely during treatment. The system generates immediate self-management advice for low or moderate AE and for severe AE advice to contact the hospital immediately. Clinicians can view patient AE data in the electronic patient record and receive email notifications when patients report severe AE.
Evaluation of the system in a randomised controlled trial in breast, gynaecological and colorectal cancer patients undergoing systemic therapy is currently underway. To adapt eRAPID for different treatment groups, pilot studies are being undertaken with patients receiving pelvic radiotherapy and upper gastrointestinal surgery.
ISRCTN88520246.
Observations of astrophysical transients have brought many novel discoveries and provided new insights into physical processes at work under extreme conditions in the Universe. Multi-wavelength and ...multi-messenger observations of variable objects require dedicated procedures and follow-up systems capable of digesting and reacting to external alerts to execute coordinated follow-up campaigns. The main functions of such follow-up systems are the processing, filtering, and ranking of the incoming alerts, the fully automated rapid execution of the observations according to an observation strategy tailored to the instrument, and real-time data analysis with feedback to the operators and other instruments. H.E.S.S. has been searching for transient phenomena since its inauguration in 2003. In this paper, we describe the transients follow-up system of H.E.S.S. which became operational in 2016. The system allows H.E.S.S. to conduct a more versatile, optimised, and largely autonomous transient follow-up program, combining all major functionalities in one systematic approach. We describe the design, central functionalities, and interfaces of the follow-up system in general and its three main components in detail: the Target of Opportunity (ToO) alert system, the data acquisition and central control system, and the real-time analysis. We highlight architectural decisions and features that enable fully automatic ToO follow-up and indicate key performance metrics of the sub-systems. We discuss the system's capabilities and highlight the need for a fine-tuned interplay of the different sub-systems in order to react quickly and reliably. Lessons learned from the development, integration, and operation of the follow-up system are reviewed in light of new and large science infrastructures and associated challenges in this exciting new era of inter-operable astronomy.
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