Detailed investigations of PMTs in optical sensors for neutrino telescopes such as IceCube Upgrade

Photomultiplier tubes (PMTs) are a central component of neutrino telescopes such as IceCube and KM3NeT, and an accurate understanding and measurement of their properties is indispensable for improvements of these experiments. In this contribution we focus on a detailed investigation of the photocathode and the dynode system and their influence on the performance of the PMT. Three methods are used for the investigation. Ellipsometry measurements of the photocathode analyze its optical properties in terms of absorption probability and refractive index. Scans of the photocathode in single photon illumination probe performance differences along the photocathode surface. Systematic deviations in the resulting amplifications are compared to electric field and electron tracing simulations through the dynode system to understand the measured values. The goal is an extensive understanding of efficiency, amplification, and timing as functions of wavelength and impact point as well as angle.Comment: Presented at the 38th International Cosmic Ray Conference (ICRC2023). See arXiv:2307.13047 for all IceCube contribution

A Parsec-Scale Study of the 5/15 GHz Spectral Indices of the Compact Radio Sources in M82

Observations of the starburst galaxy, M82, have been made with the VLA in its A-configuration at 15 GHz and MERLIN at 5 GHz enabling a spectral analysis of the compact radio structure on a scale of < 0.1'' (1.6 pc). Crucial to these observations was the inclusion of the Pie Town VLBA antenna, which increased the resolution of the VLA observations by a factor of ~2. A number of the weaker sources are shown to have thermal spectra and are identified as HII regions with emission measures ~10^7 cm^-6 pc. Some of the sources appear to be optically thick at 5 GHz implying even higher emission measures of ~10^8 cm^-6 pc. The number of compact radio sources in M82 whose origin has been determined is now 46, of which 30 are supernova related and the remaining 16 are HII regions. An additional 15 sources are noted, but have yet to be identified, meaning that the total number of compact sources in M82 is at least 61. Also, it is shown that the distribution of HII regions is correlated with the large-scale ionised gas distribution, but is different from the distribution of supernova remnants. In addition, the brightest HII region at (B1950) 09h 51m 42.21s +69 54' 59.2'' shows a spectral index gradient across its resolved structure which we attribute to the source becoming optically thick towards its centre.Comment: Accepted for publication in MNRAS. 15 pages, 9 figure

Rayleigh Scattering in Rare Gas Liquids

The Rayleigh scattering length has been calculated for rare-gas liquids in the ultraviolet for the frequencies at which they luminesce. The calculations are based on the measured dielectric constants in the gas phase, except in the case of xenon for which measurements are available in the liquid. The scattering length mayplace constraints on the design of some large-scale detectors, using uv luminescence, being proposed to observe solar neutrinos and dark matter. Rayleigh scattering in mixtures of rare-gas mixtures is also discussed.Comment: 8 pages, 4 tables; This version corrects erratum in table and has expanded discussion in Section II. Accepred for publication in NIM

Index of refraction, Rayleigh scattering length, and Sellmeier coefficients in solid and liquid argon and xenon

Large liquid argon detectors have become widely used in low rate experiments, including dark matter and neutrino research. However, the optical properties of liquid argon are not well understood at the large scales relevant for current and near-future detectors.The index of refraction of liquid argon at the scin- tillation wavelength has not been measured, and current Rayleigh scattering length calculations disagree with measurements. Furthermore, the Rayleigh scattering length and index of refraction of solid argon and solid xenon at their scintillation wavelengths have not been previously measured or calculated. We introduce a new calculation using existing data in liquid and solid argon and xenon to extrapolate the optical properties at the scintillation wavelengths using the Sellmeier dispersion relationship.Comment: 11 pages, 4 figure

ISOCAM view of the starburst galaxies M82, NGC253, and NGC1808

We present results of mid-infrared 5.0-16.5 micron spectrophotometric imaging of the starburst galaxies M82, NGC253, and NGC1808 from the ISOCAM instrument on board the Infrared Space Observatory. The mid-infrared spectra of the three galaxies are very similar in terms of features present. The > 11 micron continuum attributed to very small dust grains (VSGs) exhibits a large spread in intensity relative to the short-wavelength emission. We find that the 15 micron dust continuum flux density correlates well with the fine-structure [ArII] 6.99 micron line flux and thus provides a good quantitative indicator of the level of star formation activity. By contrast, the 5-11 micron region dominated by emission from polycyclic aromatic hydrocarbons (PAHs) has a nearly invariant shape. Variations in the relative intensities of the PAH features are nevertheless observed, at the 20%-100% level. We illustrate extinction effects on the shape of the mid-infrared spectrum of obscured starbursts, emphasizing the differences depending on the applicable extinction law and the consequences for the interpretation of PAH ratios and extinction estimates. The relative spatial distributions of the PAH, VSG, and [ArII] 6.99 micron emission between the three galaxies exhibit remarkable differences. The < 1 kpc size of the mid-infrared source is much smaller than the optical extent of our sample galaxies and 70%-100% of the IRAS 12 micron flux is recovered within the ISOCAM < 1.5 arcmin squared field of view, indicating that the nuclear starburst dominates the total mid-infrared emission while diffuse light from quiescent disk star formation contributes little.Comment: 25 pages, 12 figures, accepted for publication in Astronomy and Astrophysics; Figs. 3, 4, 5, 6, 7, 9, 10, 12 appear after Sect.

A mid-infrared spectroscopic survey of starburst galaxies: excitation and abundances

We present spectroscopy of MIR emission lines in twelve starburst regions, located in eleven starburst galaxies, for which a significant number of lines between 2.38 and 45micron were observed with the ISO Short Wavelength Spectrometer, with the intention of providing a reference resource for MIR spectra of starburst galaxies. The observation apertures were centred on actively star forming regions, including those which are inaccessible at optical wavelengths due to high levels of obscuration. We use this data set, which includes fine structure and hydrogen recombination lines, to investigate excitation and to derive gas phase abundances of neon, argon, and sulphur of the starburst galaxies. The derived Ne abundances span approximately an order of magnitude, up to values of ~3 times solar. The excitation ratios measured from the Ne and Ar lines correlate well with each other (positively) and with abundances (negatively). Both in excitation and abundance, a separation of objects with visible Wolf-Rayet features (high excitation, low abundance) is noted from those without (low excitation, high abundance). For a given abundance, the starbursts are of relatively lower excitation than a comparative sample of HII regions, possibly due to ageing stellar populations. By considering the abundance ratios of S with Ne and Ar we find that, in our higher metallicity systems, S is relatively underabundant by a factor of ~3. We discuss the origin of this deficit and favour depletion of S onto dust grains as a likely explanation. This weakness of the MIR fine structure lines of S has ramifications for future infrared missions such as SIRTF and Herschel since it indicates that the S lines are less favourable tracers of star formation than is suggested by nebular models which do not consider this effect.Comment: 20 pages, 23 figures, Accepted for publication in A&