arXiv subjects

Alasdair Gent

Publications and source records attributed to Alasdair Gent.

5 recordsLinked to original sources

arXiv2026

Design and Performance of the Upgraded Prototype Schwarzschild-Couder Telescope Camera Module

The Cherenkov Telescope Array Observatory (CTAO) is a ground-based observatory that will improve upon the sensitivities of the current generation of very-high-energy gamma-ray instruments. The Schwarzschild-Couder Telescope (SCT) is a dual-mirror candidate design for a CTAO Medium-Sized Telescope (MST). The prototype Schwarzschild-Couder Telescope (pSCT) was inaugurated in 2019 at Fred Lawrence Whipple Observatory (FLWO) in Arizona and observed significant gamma-ray emission from the Crab Nebula with a partially populated camera. The pSCT camera is currently being upgraded to fully instrument the focal plane with 11,328 silicon photomultiplier (SiPM) pixels split between 177 camera modules. Additionally, the modules will feature upgraded electronics designed to reduce electronics crosstalk and noise. A module calibration procedure has been developed using a preproduction test module. Following this calibration procedure, performance testing shows that the upgrade module has low noise, minimal electronics crosstalk, and excellent charge resolution. After calibration and optimization, the 177 production modules will be installed in the pSCT camera for commissioning. This will be followed by observations of known VHE gamma-ray sources for camera performance validation.

astro-ph.IM↗

arXiv2026

Learning a Continuous Sepsis Severity Score Without Hour-by-Hour Supervision: A Two-Site Retrospective Study

Currently used sepsis severity indices rely on fixed variables and weights established decades ago, which are coarsely discretized and calibrated to a cohort that no longer reflects contemporary critical care. No alternative learned directly from patient trajectories is in routine use. We conducted a retrospective two-cohort study on a total of 29,116 and 7,691 adult patients meeting Sepsis-3 criteria from two hospital systems in Massachusetts and Georgie, respectively. We developed a sepsis index using 43 routinely charted variables over a 72-hour treatment window. Unlike previous studies, we use mortality as a treatment-level ranking signal rather than a per-state target, allowing credit to be redistributed non-uniformly across timesteps. Evaluation was done on a permanent 20% test holdout, using clinical vignettes and Spearman correlation. Uncertainty intervals were obtained by bootstrap resampling of whole patients. Under this ranking scheme, non-survivors scored 1.19-1.64 points higher than survivors on a 0-10 scale within all strata of baseline SOFA-2, with similar results stratifying within lactate, mean arterial pressure (MAP), and creatinine. Within-patient change in the index correlated with change in lactate (Spearman rho = 0.39; n = 1,854). Similar, weaker correlations were found for MAP and creatinine. On a cohort level, cross-institutional agreement measured by Spearman correlation between models trained on different sites, were 70-77% of same-site correlation. External within-patient correlations were 0.54 and 0.59 against ceilings of 0.92 and 0.90. Our index also correlated with established indices, while null controls stayed near zero. Our index demonstrated hourly prognostic information that meaningfully separates patient outcomes and is consistent with clinical expectation, indicating potential as a decision support tool complementing clinical judgement.

cs.AI↗

arXiv2022

Design and Performance of the Prototype Schwarzschild-Couder Telescope Camera

The prototype Schwarzschild-Couder Telescope (pSCT) is a candidate for a medium-sized telescope in the Cherenkov Telescope Array. The pSCT is based on a novel dual mirror optics design which reduces the plate scale and allows for the use of silicon photomultipliers as photodetectors. The prototype pSCT camera currently has only the central sector instrumented with 25 camera modules (1600 pixels), providing a 2.68$^{\circ}$ field of view (FoV). The camera electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application specific integrated circuits. Field programmable gate arrays sample incoming signals at a gigasample per second. A single backplane provides camera-wide triggers. An upgrade of the pSCT camera is in progress, which will fully populate the focal plane. This will increase the number of pixels to 11,328, the number of backplanes to 9, and the FoV to 8.04$^{\circ}$. Here we give a detailed description of the pSCT camera, including the basic concept, mechanical design, detectors, electronics, current status and first light.

astro-ph.IM↗

arXiv2021

Robust constraints on Lorentz Invariance Violation from H.E.S.S., MAGIC and VERITAS data combination

Gamma-Ray bursts, flaring active galactic nuclei and pulsars are distant and energetic astrophysical sources, detected up to tens of TeV with Imaging Atmospheric Cherenkov Telescopes (IACTs). Due to their high variability, they are the most suitable sources for energy-dependent time-delay searches related to Lorentz Invariance Violation (LIV) predicted by some Quantum Gravity (QG) models. However, these studies require large datasets. A working group between the three major IACTs ground experiments - H.E.S.S., MAGIC and VERITAS - has been formed to address this issue and combine for the first time all the relevant data collected by the three experiments in a joint analysis. This proceeding will review the new standard combination method. The likelihood technique used to deal with data from different source types and instruments will be presented, as well as the way systematic uncertainties are taken into account. The method has been developed and tested using simulations based on published source observations from the three experiments. From these simulations, the performance of the method will be assessed and new light will be shed on time delays dependencies with redshift.

astro-ph.HE↗

arXiv2021

A Search for TeV Gamma-ray Emission from Pulsar Tails by VERITAS

We report on the search for very-high-energy gamma-ray emission from the regions around three nearby supersonic pulsars (PSR B0355+54, PSR J0357+3205 and PSR J1740+1000) that exhibit long X-ray tails. To date there is no clear detection of TeV emission from any pulsar tail that is prominent in X-ray or radio. We provide upper limits on the TeV flux, and luminosity, and also compare these limits with other pulsar wind nebulae detected in X-rays and the tail emission model predictions. We find that at least one of the three tails is likely to be detected in observations that are a factor of 2-3 more sensitive. The analysis presented here also has implications for deriving the properties of pulsar tails, for those pulsars whose tails could be detected in TeV.

astro-ph.HE↗