arXiv subjects

M. Niechciol

Publications and source records attributed to M. Niechciol.

3 recordsLinked to original sources

arXiv2024

An improved method to search for flares from point sources of ultra-high-energy photons

Flares produced by certain classes of astrophysical objects may be sources of some ultra-high-energy particles, which, if they are photons, would group into clusters of events correlated in space and time. Identification of such clustering in cosmic-ray data would provide important evidence for possible existence of ultra-high-energy (UHE) photons and could potentially help identify their sources. We present an analysis method to search for space-time clustering of ultra-high-energy extensive air showers, namely the stacking method, which combines a time-clustering algorithm with an unbinned likelihood study. In addition, to enhance the capability to discriminate between signal (photon-initiated events) and background (hadron-initiated) events, we apply a photon tag. This involves using relevant probability distribution functions to classify each event as more likely to be either a photon or a hadron. We demonstrate that the stacking method can effectively distinguish between events initiated by photons and those initiated by hadrons (background). The number of photon events in a data sample, as well as the flare(s) duration can also be retrieved correctly. The stacking method with a photon tag requires only a few events to identify a photon flare. This method can be used to search for the cosmic ray sources and/or improve limits on the fluxes of UHE photons.

astro-ph.HE↗

arXiv2017

Improved bound on isotropic Lorentz violation in the photon sector from extensive air showers

Cosmic rays have extremely high particle energies (up to $10^{20} \; \text{eV}$) and can be used to search for violations of Lorentz invariance. We consider isotropic nonbirefringent Lorentz violation in the photon sector for the case of a photon velocity larger than the maximum attainable velocity of the standard fermions. Up to now, Earth-based bounds on this type of Lorentz violation have been determined from observations of TeV gamma rays. Here, we elaborate on a novel approach to test Lorentz invariance with greatly improved sensitivity. This approach is based on investigating extensive air showers which are induced by cosmic-ray particles in the Earth's atmosphere. We study the impact of two Lorentz-violating decay processes on the longitudinal development of air showers, notably the atmospheric depth of the shower maximum $X_\text{max}$. Specifically, the two Lorentz-violating decay processes considered are photon decay into an electron-positron pair and modified neutral-pion decay into two photons. We use Monte Carlo simulations performed with the CONEX code which was extended to include these two Lorentz-violating decay processes at a magnitude allowed by the best previous Earth-based bound. Compared to standard physics, these Lorentz-violating decay processes reduce the average $X_\text{max}$ for showers with primary energies above $10^{18}\;\text{eV}$ by an amount that is significantly larger than the average resolution of current air shower experiments. Comparing the simulations of the average $X_\text{max}$ to observations, new Earth-based bounds on this type of Lorentz violation are obtained, which are better than the previous bounds by more than three orders of magnitude. Prospects of further studies are also discussed.

hep-ph↗

arXiv2017

$F_γ$: a new observable for photon-hadron discrimination in hybrid air shower events

To search for ultra-high-energy photons in primary cosmic rays, air shower observables are needed that allow a good separation between primary photons and primary hadrons. We present a new observable, $F_γ$, which can be extracted from ground-array data in hybrid events, where simultaneous measurements of the longitudinal and the lateral shower profile are performed. The observable is based on a template fit to the lateral distribution measured by the ground array with the template taking into account the complementary information from the measurement of the longitudinal profile, i.e. the primary energy and the geometry of the shower. $F_γ$ shows a very good photon-hadron separation, which is even superior to the separation given by the well-known $X_\text{max}$ observable (the atmospheric depth of the shower maximum). At energies around $1\,\text{EeV}$ ($10\,\text{EeV}$), $F_γ$ provides a background rejection better than $97.8\,\%$ ($99.9\,\%$) at a signal efficiency of $50\,\%$. Advantages of the observable $F_γ$ are its technical stability with respect to irregularities in the ground array (i.e. missing or temporarily non-operating stations) and that it can be applied over the full energy range accessible to the air shower detector, down to its threshold energy. Furthermore, $F_γ$ complements nicely to $X_\text{max}$ such that both observables can well be combined to achieve an even better discrimination power, exploiting the rich information available in hybrid events.

astro-ph.HE↗