arXiv subjects

L. Lisalda

Publications and source records attributed to L. Lisalda.

6 recordsLinked to original sources

arXiv2026

Trigger system for the Payload for Ultrahigh Energy Observations (PUEO) balloon-borne neutrino detector

The Payload for Ultrahigh Energy Observations (PUEO) is a NASA balloon-borne instrument for the detection of ultra-high energy (UHE) neutrinos with energies above $10^{17.5}~\textrm{eV}$ via either the Askaryan effect or geomagnetic emissions from an upward-going air shower. The main instrument trigger system for PUEO is a fully digital supersample rate beamformer based on 24 Xilinx Radio Frequency System-on-a-Chip (RFSoC) digitizers sampling 192 channels operating at $3~\textrm{GSa/s}$ and a system clock frequency of $375~\textrm{MHz}$. The trigger implements frequency band conditioning, dynamic radio-frequency interference (RFI) rejection, and matched filtering, with significant emphasis on optimization to reduce both the power and resource usage while maintaining sensitivity. The system implements 48 total synthetic antenna beams with up to 8 antennas each, covering a $\sim25^\circ$ range in zenith and $\sim60^\circ$ range in azimuth. Preflight testing demonstrated a trigger performance of a minimum signal-to-noise ratio (SNR) of $\sim1.5$ using simulated signals while consuming between $5-7~\textrm{W}$ in the trigger logic.

astro-ph.IM↗

arXiv2025

IXPE Observations of the Blazar Mrk 501 in 2022: A Multiwavelength View

The blazar Markarian 501 (Mrk 501) was observed on three occasions over a 4-month period between 2022 March and 2022 July with the Imaging X-ray Polarimetry Explorer (IXPE). In this paper, we report for the first time on the third IXPE observation, performed between 2022 July 9 and 12, during which IXPE detected a linear polarization degree of $\Pi_X=6\pm2$ per cent at a polarization angle, measured east of north, of $\Psi_X=143^\circ\pm11^\circ$ within the 2-8 keV X-ray band. The X-ray polarization angle and degree during this observation are consistent with those obtained during the first two observations. The chromaticity of the polarization across radio, optical, and X-ray bands is likewise consistent with the result from the simultaneous campaigns during the first two observations. Furthermore, we present two types of models to explain the observed spectral energy distributions (SEDs) and energy-resolved polarization: a synchrotron self-Compton model with an anisotropic magnetic field probability distribution in the emitting volume, as well as an energy-stratified shock model. Our results support both the shock scenario as well as support that small levels of magnetic field anisotropy can explain the observed polarization.

astro-ph.HE↗

arXiv2024

Systematic effects on a Compton polarimeter at the focus of an X-ray mirror

XL-Calibur is a balloon-borne Compton polarimeter for X-rays in the $\sim$15-80 keV range. Using an X-ray mirror with a 12 m focal length for collecting photons onto a beryllium scattering rod surrounded by CZT detectors, a minimum-detectable polarization as low as $\sim$3% is expected during a 24-hour on-target observation of a 1 Crab source at 45$^{\circ}$ elevation. Systematic effects alter the reconstructed polarization as the mirror focal spot moves across the beryllium scatterer, due to pointing offsets, mechanical misalignment or deformation of the carbon-fiber truss supporting the mirror and the polarimeter. Unaddressed, this can give rise to a spurious polarization signal for an unpolarized flux, or a change in reconstructed polarization fraction and angle for a polarized flux. Using bench-marked Monte-Carlo simulations and an accurate mirror point-spread function characterized at synchrotron beam-lines, systematic effects are quantified, and mitigation strategies discussed. By recalculating the scattering site for a shifted beam, systematic errors can be reduced from several tens of percent to the few-percent level for any shift within the scattering element. The treatment of these systematic effects will be important for any polarimetric instrument where a focused X-ray beam is impinging on a scattering element surrounded by counting detectors.

astro-ph.IM↗

arXiv2022

The design and performance of the XL-Calibur anticoincidence shield

The XL-Calibur balloon-borne hard X-ray polarimetry mission comprises a Compton-scattering polarimeter placed at the focal point of an X-ray mirror. The polarimeter is housed within a BGO anticoincidence shield, which is needed to mitigate the considerable background radiation present at the observation altitude of ~40 km. This paper details the design, construction and testing of the anticoincidence shield, as well as the performance measured during the week-long maiden flight from Esrange Space Centre to the Canadian Northwest Territories in July 2022. The in-flight performance of the shield followed design expectations, with a veto threshold <100 keV and a measured background rate of ~0.5 Hz (20-40 keV). This is compatible with the scientific goals of the mission, where %-level minimum detectable polarisation is sought for a Hz-level source rate.

astro-ph.IM↗

arXiv2020

XL-Calibur -- a second-generation balloon-borne hard X-ray polarimetry mission

XL-Calibur is a hard X-ray (15-80 keV) polarimetry mission operating from a stabilised balloon-borne platform in the stratosphere. It builds on heritage from the X-Calibur mission, which observed the accreting neutron star GX 301-2 from Antarctica, between December 29th 2018 and January 1st 2019. The XL-Calibur design incorporates an X-ray mirror, which focusses X-rays onto a polarimeter comprising a beryllium rod surrounded by Cadmium Zinc Telluride (CZT) detectors. The polarimeter is housed in an anticoincidence shield to mitigate background from particles present in the stratosphere. The mirror and polarimeter-shield assembly are mounted at opposite ends of a 12 m long lightweight truss, which is pointed with arcsecond precision by WASP - the Wallops Arc Second Pointer. The XL-Calibur mission will achieve a substantially improved sensitivity over X-Calibur by using a larger effective area X-ray mirror, reducing background through thinner CZT detectors, and improved anticoincidence shielding. When observing a 1 Crab source for $t_{\rm day}$ days, the Minimum Detectable Polarisation (at 99% confidence level) is $\sim$2$\%\cdot t_{\rm day}^{-1/2}$. The energy resolution at 40 keV is $\sim$5.9 keV. The aim of this paper is to describe the design and performance of the XL-Calibur mission, as well as the foreseen science programme.

astro-ph.IM↗

arXiv2020

Observations of a GX 301-2 Apastron Flare with the X-Calibur Hard X-Ray Polarimeter Supported by NICER, the Swift XRT and BAT, and Fermi GBM

The accretion-powered X-ray pulsar GX 301-2 was observed with the balloon-borne X-Calibur hard X-ray polarimeter during late December 2018, with contiguous observations by the NICER X-ray telescope, the Swift X-ray Telescope and Burst Alert Telescope, and the Fermi Gamma-ray Burst Monitor spanning several months. The observations detected the pulsar in a rare apastron flaring state coinciding with a significant spin-up of the pulsar discovered with the Fermi GBM. The X-Calibur, NICER, and Swift observations reveal a pulse profile strongly dominated by one main peak, and the NICER and Swift data show strong variation of the profile from pulse to pulse. The X-Calibur observations constrain for the first time the linear polarization of the 15-35 keV emission from a highly magnetized accreting neutron star, indicating a polarization degree of (27+38-27)% (90% confidence limit) averaged over all pulse phases. We discuss the spin-up and the X-ray spectral and polarimetric results in the context of theoretical predictions. We conclude with a discussion of the scientific potential of future observations of highly magnetized neutron stars with the more sensitive follow-up mission XL-Calibur.

astro-ph.HE↗