arXiv subjects

Roger Clay

Publications and source records attributed to Roger Clay.

7 recordsLinked to original sources

arXiv2025

The 2025 June 01 Forbush Decrease measured over a range of primary cosmic ray energies

The 2025 June 01 Forbush Decrease in the terrestrial ground-level flux of cosmic ray secondaries was recorded by many cosmic ray systems. This was the deepest such decrease, from the quiescent value of the flux, which has been observed in the past two decades. It resulted from a complex series of solar events, none of which on its own reached the most extreme level. The extreme depth of this Decrease has enabled measurements of the flux reduction to be made, which would normally be severely limited by particle counting statistics. In particular, here we examine the Decrease phenomenon over a primary cosmic ray energy range which is rarely accessible, due to the low flux of high energy cosmic rays. This work considers data mainly from a muon telescope system which can respond to both unaccompanied muons and small cosmic ray air showers, providing data from GeV to mid-TeV energies, where the Forbush Decrease ceases to be statistically observable. This paper examines the depth of the flux Decrease, as a fraction below its quiescent value, over that primary energy range. The progressive development of internal time structure in the flux through the seven days of the phenomenon is also demonstrated.

astro-ph.HE↗

arXiv2025

The Large Magellanic Cloud as a source of the highest energy cosmic rays

The Pierre Auger Observatory has published properties of the 100 highest-energy cosmic ray events (to energies above 100 EeV) which it recorded over a 17 year period. We have examined the directional properties of these events and have taken particular note of the most energetically extreme events. We find that the most energetic events have directions which are grouped in a non-random way at the 1\% level. There is an apparent clustering in a limited region of the sky. Close to that direction is found Centaurus A, which has long been considered as a source of such particles, but we also note that a close-by dwarf galaxy, the Large Magellanic Cloud (LMC) is closer in angular terms. We examine the possibility that the LMC might be a source of observed cosmic rays at the highest energies.

astro-ph.HE↗

arXiv2022

Advancing the Landscape of Multimessenger Science in the Next Decade

The last decade has brought about a profound transformation in multimessenger science. Ten years ago, facilities had been built or were under construction that would eventually discover the nature of objects in our universe could be detected through multiple messengers. Nonetheless, multimessenger science was hardly more than a dream. The rewards for our foresight were finally realized through IceCube's discovery of the diffuse astrophysical neutrino flux, the first observation of gravitational waves by LIGO, and the first joint detections in gravitational waves and photons and in neutrinos and photons. Today we live in the dawn of the multimessenger era. The successes of the multimessenger campaigns of the last decade have pushed multimessenger science to the forefront of priority science areas in both the particle physics and the astrophysics communities. Multimessenger science provides new methods of testing fundamental theories about the nature of matter and energy, particularly in conditions that are not reproducible on Earth. This white paper will present the science and facilities that will provide opportunities for the particle physics community renew its commitment and maintain its leadership in multimessenger science.

astro-ph.HE↗

arXiv2015

Connections: the relationships between Neolithic and Bronze Age Megalithic Astronomy in Britain

It has already been empirically verified that for many Bronze Age monuments erected in Scotland between 1400-900 BC, there was a concerted effort on behalf of the builders to align their monuments to astronomical bodies on the horizon. It has also been found that there are two common sets of complex landscape and astronomical patternings, combining specific horizon qualities, like distance and elevation, with the rising and setting points of particular astronomical phenomena. However, it has only been very recently demonstrated by us that that the visible astronomical-landscape variables found at Bronze Age sites on the inner isles and mainland of western Scotland were first established nearly two millennia earlier, with the erection of the mooted first standing-stone 'great circles' in Britain: Callanish and Stenness of Scotland (see G. Higginbottom and R. Clay, The Origins of Standing Stone Astronomy in Britain submitted to Journal of Archaeological Science & available on ArXiv). In the current paper we demonstrate the connection between all of these monuments and the large Late Neolithic circles south of Scotland, namely those of Castlerigg and Swinside in Cumbria, England.

physics.hist-ph↗

arXiv2014

Origins of Megalithic Astronomy in Britain

By c. 3000 BC, in the late Neolithic, there had been a significant change in the way people materialized their cosmology across Scotland with the introduction of free-standing stones. These were erected almost until the end of the Bronze Age (Burl 2000, 1993). Significantly, a series of astronomical patternings have been empirically verified for many Bronze Age monuments that were erected between 1400-900 BC (Higginbottom et 14 al. 2013, 2003, 2001, 2000). Further, two series of complex landscape patternings associated with the same monuments and their orientations have been identified (Higginbottom et al. 2013 & Higginbottom 'in preparation' - Bronze Age megalithic monuments on the isle of Mull). However, when and where these patterns were first associated with standing-stone structures was unknown. Through innovative statistics and software we show that visible astronomical-landscape variables found at Bronze Age sites on the inner isles and mainland of western Scotland were actually first established nearly two millennia earlier, with the erection of the first 'great circles' in Britain: Callanish on the Isle of Lewis and Stenness on the Isle of Orkney. In particular, we introduce our new statistical test that enables the quantitative determination of astronomical connections of stone circles. It is seen that, whilst different standing-stone monuments were created over time (Burl 2000, 1993; 22 Higginbottom et al. 2013; Sheridan & Brophy 2012) with a mixture of landscape variables (Higginbottom et al. 2013), there are nevertheless highly relevant aspects that remained unchanged through these years. This suggests that there is some continuity of this cosmological system through time, despite the various radical material and social changes that occurred from the late Neolithic to the Late Bronze Age (Lynch 2000; Mullin 26 2001; Owoc 2001).

physics.hist-ph↗

arXiv2007

Exploring the High-Energy Cosmic Ray Spectrum with a Toy Model of Cosmic Ray Diffusion

We introduce a static toy model of the cosmic ray (CR) universe in which cosmic ray propagation is taken to be diffusive and cosmic ray sources are distributed randomly with a density the same as that of local L* galaxies, $5 \times 10^{-3}$ Mpc$^{-3}$. These sources "fire" at random times through the history of the universe but with a set expectation time for the period between bursts. Our toy model model captures much of the essential CR physics despite its simplicity and, moreover, broadly reproduces CR phenomenology for reasonable parameter values and without extreme fine-tuning. Using this model we investigate -- and find tenable -- the idea that the Milky Way may itself be a typical high-energy cosmic ray source. We also consider the possible phenomenological implications of the magnetic CR horizon for the overall cosmic ray spectrum observed at Earth. Finally, we show that anisotropy studies should most profitably focus on cosmic rays detected at energies above the so-called GZK cut-off, $\sim 6 \times 10^{19}$ eV.

astro-ph↗

arXiv2003

The Anisotropy Search Program For the Pierre Auger Observatory

The Pierre Auger Southern Observatory in Argentina has begun taking data as it is being developed up to a final enclosed area of 3000 square kilometres. A key aspect of the project is to provide information on the origin of the highest energy cosmic rays through understanding the arrival directions of those particles. To avoid claims of a spurious anisotropy detection because trials have not been properly accounted, the Auger Collaboration has agreed 'a priori' to the analysis prescription presented here. It specifies the following: 1. The accumulation time for the (future) data set to be analyzed. 2. The anisotropy 'targets', each assigned a chance probability level. 3. The analysis procedure for each trial. A positive result will be claimed for any target search only if its chance probability is less than its assigned level. The levels are chosen so that the total chance probability for one or more positive results is 0.001. Exploratory searches beyond this prescription will be encouraged, but the Auger Collaboration will not assign any confidence level to anisotropies that may be discovered that way. Any such discovery would identify a good target for a prescription to be used with a subsequent Auger data set.

astro-ph↗