Institute of Accelerating Systems and Applications

ABSTRACT The first four all-sky surveys with eROSITA the soft X-ray instrument on board the Spektrum–Roentgen–Gamma (SRG) satellite revealed a new X-ray source, eRASSU J012422.9–724248, in the Magellanic Bridge, near the Eastern Wing of the Small Magellanic Cloud (SMC). We performed a broad-band timing and spectral analysis using the optical and X-ray data of eRASSU J012422.9–724248. Using the X-ray observations with eROSITA, Swift, NuSTAR and optical data from the optical Gravitational Lensing Experiment (OGLE) and the Las Cumbres Observatory (LCO), we confirm the nature of eRASSU J012422.9–724248as a Be/X-ray binary (BeXRB) pulsar in the Magellanic Bridge. The position is coincident with that of an early-type star (OGLE ID SMC732.10.7). We detect the spin period at 341.71 s in NuSTAR data and infer a period of 63.65 d from the 15 yr monitoring with OGLE, that we interpret as the orbital period of the system. A tentative CRSF at $\sim$12.3 keV is identified in NuSTAR spectra with $\sim 1.8\sigma$. The source appears to show a persistent X-ray luminosity and an optical magnitude transition on the long timescale. We propose eRASSU J012422.9–724248is a new member of the class of persistent BeXRBs.

Motivated by the need for more accurate radiation environment modelling, this study focuses on identifying and analyzing the drivers behind the sub-relativistic electron flux variations in the inner magnetosphere. We utilize electron flux data between 1 and 500 keV from the Hope and MagEIS instruments on board the RBSP satellites, as well as from the FEEPS instruments on board the MMS spacecrafts, along with solar wind parameters and geomagnetic indices obtained from the OmniWeb2 and SuperMag data services. We calculate the correlation coefficients between these parameters and electron flux. Our analysis shows that substorm activity is a crucial driver of the source electron population (10 - 100 keV), while also showing that seed electrons (100 - 400 keV) are not purely driven by substorm events, but also from enhanced convection/inward diffusion. By introducing time lags, we observed a delayed response of electron flux to changes in geospace conditions, and we identified specific time lag periods where the correlation is maximum. This work contributes to our broader understanding of the outer belt sub-relativistic electron dynamics, and forms the basis for future research.

Context.Very high-energy (VHE,E > 100 GeV) observations of the blazar Mrk 501 with MAGIC in 2014 provided evidence for an unusual narrow spectral feature at about 3 TeV during an extreme X-ray flaring activity. The one-zone synchrotron-self Compton scenario, widely used in blazar broadband spectral modeling, fails to explain the narrow TeV component.Aims.Motivated by this rare observation, we propose an alternative model for the production of narrow features in the VHE spectra of flaring blazars. These spectral features may result from the decay of neutral pions (π0bumps) that are in turn produced via interactions of protons (of tens of TeV energy) with energetic photons, whose density increases during hard X-ray flares.Methods.We explored the conditions needed for the emergence of narrowπ0bumps in VHE blazar spectra during X-ray flares reaching synchrotron energies ∼100 keV using time-dependent radiative transfer calculations. We focused on high-synchrotron peaked (HSP) blazars, which comprise the majority of VHE-detected extragalactic sources.Results.We find that synchrotron-dominated flares with peak energies ≳100 keV can be ideal periods for the search ofπ0bumps in the VHE spectra of HSP blazars. The flaring region is optically thin to photopion production, its energy content is dominated by the relativistic proton population, and the inferred jet power is highly super-Eddington. Application of the model to the spectral energy distribution of Mrk 501 on MJD 56857.98 shows that the VHE spectrum of the flare is described well by the sum of a synchrotron self-Compton (SSC) component and a distinctπ0bump centered at 3 TeV. Spectral fitting of simulated SSC+π0spectra for the Cherenkov Telescope Array (CTA) show that aπ0bump could be detected at a 5σsignificance level with a 30-min exposure.Conclusions.A harder VHEγ-ray spectrum than the usual SSC prediction or, more occasionally, a distinct narrow bump at VHE energies during hard X-ray flares, can be suggestive of a relativistic hadronic component in blazar jets that otherwise would remain hidden. The production of narrow features or spectral hardenings due toπ0decay in the VHE spectra of blazars is testable with the advent of CTA.

Context. Jets from supermassive black holes at the centers of active galaxies are the most powerful and persistent sources of electromagnetic radiation in the Universe. To infer the physical conditions in the otherwise out-of-reach regions of extragalactic jets, we usually rely on fitting their spectral energy distributions (SEDs). The calculation of radiative models for the jet’s non-thermal emission usually relies on numerical solvers of coupled partial differential equations. Aims. In this work, we use machine learning to tackle the problem of high computational complexity to significantly reduce the SED model evaluation time, which is necessary for SED fittings carried out with Bayesian inference methods. Methods. We computed the SEDs based on the synchrotron self-Compton model for blazar emission using the radiation code ATHEvA. We used them to train neural networks (NNs) to explore whether they can replace the original code, which is computationally expensive. Results. We find that a NN with gated recurrent unit neurons (GRUN) can effectively replace the ATHEvA leptonic code for this application, while it can be efficiently coupled with Markov chain Monte Carlo (MCMC) and nested sampling algorithms for fitting purposes. We demonstrate this approach through an application to simulated data sets, as well as a subsequent application to observational data. Conclusions. We present a proof-of-concept application of NNs to blazar science as the first step in a list of future applications involving hadronic processes and even larger parameter spaces. We offer this tool to the community through a public repository.

The REINFORCE project engages and supports citizens to cooperate with researchers and actively contribute to the development of new knowledge for the needs of science and society. The overall aim is to bridge the gap between them, and reinforce society’s science capital. Within this context, the demonstrator titled “New Particle Search at CERN” will engage citizen-scientists in searches for new elementary particles produced in the high-energy proton-proton collisions at the LHC. To make this possible, the demonstrator adopts a three-stage architecture. The first two stages use simulated data from the ATLAS detector to train citizens, but also to allow for a quantitative assessment of their performance and a comparison with machine learning algorithms. The third stage, on the other hand, uses real data from the ATLAS Open-Data subset, providing two research paths: (a) study of Higgs boson decays to two photons, one of which could be converted to an electron-positron pair by interaction with detector material, and (b) search for yet undiscovered long-lived particles predicted by certain theories Beyond-the-Standard-Model.

Besides the noiseless extraction of the energy deposited in the absorber, an ideal event reconstruction in a Compton-Camera system requires the accurate determination of both interaction points in the scatterer and absorber. Limited energy and spatial resolution of the system combined with other misidentification effects leads frequently to the acceptance of faulty events, which affect the quality of the reconstructed image. Based on GEANT4/GATE simulation studies, a filtering procedure to eliminate energy and spatially unbalanced events is proposed in the current work. Attention has been paid to exclude from the coincidence selection procedure events that alternate the normal interaction sequence in the scatterer-absorber subsystems or violate total energy sum rules. Following the proposed filtering approach, volume effects traced back to the angular acceptance of a two-stage Compton-Camera system are systematically investigated and a normalization-correction technique to improve the performance of the system for phantoms with out-of-plane sources is presented.

A recently installed polarized electron source will allow internal target experiments to be performed with polarized electrons at the NIKHEF Internal Target Hall, lb measure the longitudinal component of the polarization vector of the stored electron beam, a Polarimeter based on spin-dependent Compton scattering has been developed and successfully commissioned

A progress report on the architectural design and implementation of the Control System for the Racetrack Microtron at the Institute of Accelerating Systems and Applications (IASA) in Athens, Greece is presented. The Control System for the IASA CW Microtron is being developed on the Experimental Physics and Industrial Control System (EPICS) environment. Since top priority for this project is the construction and commissioning of the Mcrotron's injector, emphasis is being given to the definition and refinement of the Control Architecture and its realization for the injector. The experience gained from the Control System at the injector will guide the further development of the Control System for the entire Microtron.

Abstract We investigate the response of the outer Van Allen belt electrons to various types of solar wind and magnetospheric disturbances. We use electron phase space density calculations as well as concurrent Pc5 and chorus wave activity observations in the outer belt during the Van Allen Probes era to compare 20 electron enhancement and 8 depletion events. Results indicate that the combined effect of magnetopause shadowing and outward diffusion driven by Pc5 waves is present in both groups of events. Furthermore, in the case of enhancement events, the synergy of enhanced seed population levels and chorus activity—due to the enhanced substorm activity—can effectively replenish the losses of relativistic electrons, while inward diffusion can further accelerate them.