Niraj Dhital

The sources of high-energy astrophysical neutrinos remain largely unknown. Multi-wavelength observational campaigns have identified a few plausible candidates, but their numbers are very few. We search for an excess of high-energy neutrino events arriving to us from the directions of blazar sources over the number we expect from the background. We generate random samples of events following the right ascension and declination distributions of the high-energy neutrino events detected by the IceCube Neutrino Observatory and count the coincidences of both the generated samples and the true observations within a 3◦ angular separation with the Fermi-LAT blazar sources. We also investigate blazars located within an angular separation smaller than the maximum positional error calculated on an event-by-event basis by incorporating the event-specific angular uncertainty in neutrino localization and analyze the characteristics of these blazars to assess their plausibility as neutrino sources. We also conduct temporal and spectral analyses of blazar γ-ray light curves within event-specific maximum angular separations from directions corresponding to the highest number of neutrino events. We find an excess of high-energy neutrino events from the directions of Fermi blazars beyond random coincidence, with a significance of 2.42 σ. Among the fifteen blazars that lie within the neutrino error regions and have a maximum number of neutrino events (six) around them, the sources 4FGL J0509.4+0542 and 4FGL J2256.7+1307 are identified as plausible high-energy neutrino source candidates.

This study examines neural responses to visual stimuli under Near and Far flanker conditions using EEG. Fifty participants (25 per condition) completed a visual task with closely or distantly positioned distractors. EEG data were analyzed using spectrograms, wavelet transformation, and neural firing rate estimation. Standard preprocessing techniques ensured data quality, and statistical tests assessed differences between conditions. Findings provide insight into how spatial stimulus configurations affect neural processing and attention.

We report the findings of analysis of X-ray flares in TXS 0506+056 using XMM-Newton data obtained from the maximum likelihood analysis. Two publicly available XMM-Newton X-ray observations for TXS 0506+056 were analyzed to study the spectrum and light curves. The spectrum curves revealed two energy bumps, with the lower energy bump at 0.5 keV and the higher energy bump at 6 keV. For observational IDs 0083960101 and 0083960201, the integrated flux for hard X-ray (2–10 keV) is 1.835 10^-12 ergs cm^-2 s^-1 and 1.813 10^-12 ergs cm^-2 s^-1 with corresponding uncertainty range of (1.754–1.913) 10^-12 ergs cm^-2 s^-1 and (1.490–3.515) 10^-12 ergs cm^-2 s^-1, respectively. The best fit models for X-ray data observations of observational IDs of 0083960101 and 0083960201 were phabs (gaussian+power-law) and Tbabs (gaussian+log-parabola) with reduced chi squared values of 1.56 and 1.05, respectively. A turning point at around 2 keV appeared in the spectrum curve, suggesting that the gaussian model only applies for soft X-ray (0.3–2 keV), while the power law and the log parabola model are the best fit models for hard X-ray (2–10 keV). Observation ID 0850780101 shows that the source TXS 0506+056 has a fractional variability of 1.4 %, while Observation ID 0850780201 shows a higher fractional variability of 3.0 % which indicates brightness varies over time. A greater disparity in the source's rise time suggests a higher degree of variability in its brightness.

This research work was carried out to analyze the X-ray flares in Blazar Mkn 421 using data from XMM-Newton observation (Observation ID: 0658801301) that lasted for 8 hours. EPIC/pn data was used for statistical analysis of the light and spectrum curve in energy ranges from 0.3 to 10.0 keV. The best fit model for the spectrum was found to be the additive model (log-parabola + black-body). The measured integrated flux in the energy range of 0.3-2 keV is 5.015x10^-10 ergs cm^-2 s^-1 with an associated uncertainty range of (5.010 – 5.020) x 10^-10 ergs cm^-2 s^-1 at a 90% confidence level. Similarly, the measured integrated flux in the energy range of 2-10 keV is 2.398 x 10^-10 ergs cm^-2 s^-1 with an associated uncertainty range of (2.392 – 2.405) x 10^-10 ergs cm^-2 s^-1 at a 90% confidence level. The fractional variability of 0.444 is relatively high, which indicates that the source is variable. The fall in count per second per energy around 2 keV in the spectrum curve suggests that the intensity of X-rays decreases in a power law manner after a strong flare at this energy. The count-rate distribution of the observation analyzed is best described by a normal distribution which suggests that the emission mechanism in the blazar is governed by additive processes.

Both the lack of observation of ultra-high energy (UHE) photons and the limitations of the state-of-the-art methodology being applied for their identification motivate studies on alternative approaches to the relevant simulations and the related observational strategies. One of such new approaches is proposed in this report and it concerns new observables allowing indirect identification of UHE photons through cosmic ray phenomena composed of many spatially correlated extensive air showers or primary cosmic rays observed at one time. The study is based on simulations of interactions of UHE photons with the magnetic field of the Sun using the PRESHOWER program with some essential modifications. One of the expected results of such interactions is a generation of cosmic ray ensembles (CRE) in the form of very thin and very elongated cascades of secondary photons of energies spanning the whole cosmic ray energy spectrum. Upon entering the Earth's atmosphere, these cascades or their parts may generate uniquely characteristic walls of spatially correlated extensive air showers, and the effect is expected also in cases when primary UHE photons are not directed towards the Earth. Particle distributions in these multi-primary UHE photon footprints are expected to have thicknesses of the order of meters and elongations reaching even hundreds of millions kilometers, making them potentially observable with a global, multi-experiment approach, including re-exploring of the historical data, with the expected event rate exceeding the capabilities of even very large cosmic ray observatories. The methods described in this report allow for simulating potentially observable quantities related to CRE induced by UHE photons: densities, energy spectra and geographical orientations of particles at the top of the Earth's atmosphere.

Both the lack of observation of ultra-high energy (UHE) photons and the limitations of the state-of-the-art methodology being applied for their identification motivate studies on alternative approaches to the relevant simulations and the related observational strategies. One such new approach is proposed in this report and it concerns new observables allowing indirect identification of UHE photons through cosmic ray phenomena composed of many spatially correlated extensive air showers or primary cosmic rays observed at one time. The study is based on simulations of interactions of UHE photons with the magnetic field of the Sun using the PRESHOWER program with some essential modifications. One of the expected results of such interactions is a generation of cosmic ray ensembles (CREs) in the form of very thin and very elongated cascades of secondary photons of energies spanning the whole cosmic ray energy spectrum. Upon entering the Earth’s atmosphere, these cascades or their parts may generate uniquely characteristic walls of spatially correlated extensive air showers, and the effect is expected also in cases when primary UHE photons are not directed towards the Earth. Particle distributions in these multi-primary UHE photon footprints are expected to have thicknesses of the order of meters and elongations reaching even hundreds of millions of kilometers, making them potentially observable with a global, multi-experiment approach, including re-exploring of the historical data, with the expected event rate exceeding the capabilities of even very large cosmic ray observatories. In this report, we introduce for the first time the methods allowing for simulating the isotropic flux of UHE photons in the Sun’s vicinity. Presented methods were verified and optimised in such a way that they would successfully model the cumulative spatial distribution of secondary photons at the top of the atmosphere. The preliminary results of simulations for the UHE photon flux of energy 100 EeV demonstrate the possibility of simulating potentially observable quantities related to CRE induced by UHE photons: densities, energy spectra and geographical orientations of secondary particles at the top of the Earth’s atmosphere. A measurement of at least one of these quantities would be equivalent to a confirmation of the existence of UHE photons, which would give an insight into fundamental physics processes at unprecedentedly high energies, far beyond the reach of man-made accelerators. On the other hand, a lack of such an observation would allow for further constraining of these fundamental processes with the physically new upper limits on UHE photon fluxes after careful analysis of the technical observation ability. The novel advantage of such an approach would lay in the purely electrodynamical character of the underlying simulations which are fully independent on extrapolations of hadronic interaction models by many orders of magnitude. Such extrapolations are necessary in the UHE photon identification methods based on the analyses of properties of individual extensive air showers presently used to determine the UHE photon upper limits.

The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection does not involve any a priori considerations, and its search strategy encompasses both spatial and temporal correlations, on different scales. Here we search for time clustering of the cosmic ray events collected with a small sea-level extensive air shower array at the University of Adelaide. The array consists of seven one-square-metre scintillators enclosing an area of 10 m × 19 m. It has a threshold energy ~0.1 PeV, and records cosmic ray showers at a rate of ~6 mHz. We have examined event arrival times over a period of over 2.5 years in two equipment configurations (without and with GPS timing), recording ~300 k events and ~100 k events. We determined the event time spacing distributions between individual events and the distributions of time periods which contained specific numbers of multiple events. We find that the overall time distributions are as expected for random events. The distribution which was chosen a priori for particular study was for time periods covering five events (four spacings). Overall, these distributions fit closely with expectation, but there are two outliers of short burst periods in data for each configuration. One of these outliers contains eight events within 48 s. The physical characteristics of the array will be discussed together with the analysis procedure, including a comparison between the observed time distributions and expectation based on randomly arriving events.

The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a newly formed, global collaboration dedicated to observing and studying cosmic rays (CR) and cosmic-ray ensembles (CRE): groups of at least two CR with a common primary interaction vertex or the same parent particle. The CREDO program embraces testing known CR and CRE scenarios, and preparing to observe unexpected physics, it is also suitable for multi-messenger and multi-mission applications. Perfectly matched to CREDO capabilities, CRE could be formed both within classical models (e.g., as products of photon–photon interactions), and exotic scenarios (e.g., as results of decay of Super-Heavy Dark Matter particles). Their fronts might be significantly extended in space and time, and they might include cosmic rays of energies spanning the whole cosmic-ray energy spectrum, with a footprint composed of at least two extensive air showers with correlated arrival directions and arrival times. As the CRE are predominantly expected to be spread over large areas and, due to the expected wide energy range of the contributing particles, such a CRE detection might only be feasible when using all available cosmic-ray infrastructure collectively, i.e., as a globally extended network of detectors. Thus, with this review article, the CREDO Collaboration invites the astroparticle physics community to actively join or to contribute to the research dedicated to CRE and, in particular, to pool together cosmic-ray data to support specific CRE detection strategies.

The Cosmic Ray Extremely Distributed Observatory (CREDO) is a newly formed, global collaboration dedicated to observing and studying cosmic rays (CR) and cosmic ray ensembles (CRE): groups of a minimum of two CR with a common primary interaction vertex or the same parent particle. The CREDO program embraces testing known CR and CRE scenarios, and preparing to observe unexpected physics, it is also suitable for multi-messenger and multi-mission applications. Perfectly matched to CREDO capabilities, CRE could be formed both within classical models (e.g. as products of photon-photon interactions), and exotic scenarios (e.g. as results of decay of Super Heavy Dark Matter particles), their fronts might be significantly extended in space and time, and they might include cosmic rays of energies spanning the whole cosmic ray energy spectrum. CRE are expected to be partially observable on Earth even if the initiating interaction or process occurs as far as ~1 Gpc away. They would have a footprint composed of at least two extensive air showers with correlated arrival directions and arrival times. Since CRE are mostly expected to be spread over large areas and, because of the expected wide energy range of the contributing particles, CRE detection might only be feasible when using available cosmic ray infrastructure collectively, i.e. as a globally extended network of detectors. Thus, with this review article, the CREDO Collaboration invites the astroparticle physics community to actively join or to contribute to the research dedicated to CRE, and in particular to share any cosmic ray data useful for the specific CRE detection strategies.

The Pierre Auger Observatory has been very successful in determining many aspects of the highest-energy cosmic rays including, among others, the flux suppression at energies above 4 × 10¹⁹ eV, stringent upper limits on photon and neutrino fluxes at ultra-high energies and an unexpected evolution of the mass composition with energy. We expect an extension of the frontiers of our knowledge on these aspects from a major upgrade of the Observatory. The upgrade, known as AugerPrime, will include an addition of a 4 m² Surface Scintillator Detector atop each water-Cherenkov station of the Surface array. The new detectors will provide us with an unprecedented opportunity to perform a complementary measurement of the shower particles and thus determine the primary mass composition with good accuracy on an event-by-event basis. AugerPrime will also include an upgrade of electronics, installation of the AMIGA Underground Muon Detector and a change of observation mode of the Fluorescence Detector, which will increase its current duty cycle by about 50%. Current status of the upgrade with the main focus on the Surface Scintillator Detectors will be presented, following a brief description of the physics motivation for the upgrade.