Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants

The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3~PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy $\gamma$-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte--Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a $\gamma$-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 hours of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with $\mathcal{O}(100)$ hours of exposure per source.Comment: 34 pages, 16 figures, Accepted for publication in Astroparticle Physic

Influence of External Acoustic Noise οn the Operation of an Open Photoacoustic Helmholtz Cell

One of the most important problems in the design of open photoacoustic cells is appropriate attenuation of the external acoustic noise, because in the case of weak photoacoustic signals even relatively low level of such an acoustic noise can severely limit sensitivity of the setup. It is important that the mentioned filtering is not limited to the frequencies close to the light modulation frequency, but performed in the possibly widest band width, because although it is usually considered that setup sensitivity depends directly on the parameters of the final narrowband filtering and/or synchronous detection, it should be noticed that it can be also seriously affected by saturation of the signal amplifiers being overdriven by the signal components resulting from the mentioned acoustic noise. The paper describes how influence of the external acoustic noise on the operation of an open photoacoustic Helmholtz cell depends on mechanical dimensions of the cell. The results show that appropriate selection of the dimensions results in noticeable improvement of the external acoustic noise attenuation

Simultaneous multiple synchronous detection in photoacoustic measurements

Photoacoustic detection of multiple compounds can be done in at least a few ways. One of the simplest methods is performing sequential measurements at selected wavelengths at which the compounds under detection would absorb. The main disadvantage of the method is relatively long time of the measurements – proportional to the number of wavelengths at which the measurements are performed. Time of the measurements can be significantly shortened e.g. by means of a simultaneous detection at a few light wavelengths, intensity of each modulated with a different frequency. Typical approach to implementation of such a setup requires use of a corresponding number of synchronous detectors. The paper presents a solution based on a single A/D converter and programmable logic circuit that implements high precision, simultaneous, synchronous detection of a few signals of different frequencies. The discussed equipment is capable of simultaneous recording of shape of all these signals independently. Strongly reduced hardware concept results in low cost and small size of the device