Monte Carlo simulations of soft proton flares: testing the physics with XMM-Newton

Low energy protons (<100-300 keV) in the Van Allen belt and the outer regions can enter the field of view of X-ray focusing telescopes, interact with the Wolter-I optics, and reach the focal plane. The use of special filters protects the XMM-Newton focal plane below an altitude of 70000 km, but above this limit the effect of soft protons is still present in the form of sudden flares in the count rate of the EPIC instruments, causing the loss of large amounts of observing time. We try to characterize the input proton population and the physics interaction by simulating, using the BoGEMMS framework, the proton interaction with a simplified model of the X-ray mirror module and the focal plane, and comparing the result with a real observation. The analysis of ten orbits of observations of the EPIC/pn instrument show that the detection of flares in regions far outside the radiation belt is largely influenced by the different orientation of the Earth's magnetosphere respect with XMM-Newton's orbit, confirming the solar origin of the soft proton population. The Equator-S proton spectrum at 70000 km altitude is used for the proton population entering the optics, where a combined multiple and Firsov scattering is used as physics interaction. If the thick filter is used, the soft protons in the 30-70 keV energy range are the main contributors to the simulated spectrum below 10 keV. We are able to reproduce the proton vignetting observed in real data-sets, with a 50\% decrease from the inner to the outer region, but a maximum flux of 0.01 counts cm-2 s-1 keV-1 is obtained below 10 keV, about 5 times lower than the EPIC/MOS detection and 100 times lower than the EPIC/pn one. Given the high variability of the flare intensity, we conclude that an average spectrum, based on the analysis of a full season of soft proton events is required to compare Monte Carlo simulations with real events

Development of a Multi-component based Methodology for the Simulation of Reacting High Injection Pressure Diesel Sprays☆

Abstract Modern Diesel engines are attractive for fuel economy and performances but they are suffering from increasingly strict emission standards. Therefore the investigation of the injection and combustion processes are mandatory. This paper focuses on the development of a multi-component fuel based methodology for the simulation of non-reacting and reacting high injection pressure Diesel sprays. In multi-dimensional modeling fuels are represented predominantly by single components, such as n-Dodecane for Diesel, and this is a limitation in their ability to represent real fuels which are blends of hundreds components. This study outlines a method by which the fuel composition is represented by means of a Discrete Multi-Component (DMC) model approach in order to improve the prediction of the vaporization behavior of high injection pressure Diesel sprays. A testing blend of 6 hydrocarbons is taken into account and a reduced one is developed in order to reduce the computational cost of the CFD simulations while maintaining the advantages due to a multi-component description of the mixture. The CFD methodology is developed within Star-CD commercial code while particular care is also dedicated to the prediction of the atomization and secondary breakup processes. At the nozzle exit the atomized droplets are predicted by a primary breakup approach which is able to take into account the cavitation phenomena and the turbulent effects. The atomization model is based on a simplified approach that is able to evaluate the effects of the nozzle geometry. The preliminary investigations are performed in a constant volume vessel, validating the numerical parameters against experimental data in order to correctly reproduce spray vaporization behavior. Then, to illustrate the important differences between the vaporization characteristics of a multi-component mixture compared to a mono-component one, the CFD methodology is tested investigating the in-cylinder combustion process of a 4 cylinders, Common Rail Diesel engine of current production

An Off-Nucleus Nonstellar Black Hole in the Seyfert Galaxy NGC 5252

We report the discovery of a ultraluminous X-ray source (ULX; CXO J133815.6+043255) in NGC 5252. This ULX is an off-nuclear point-source, which is 22$^{\prime\prime}$ away from the center of NGC 5252, and has an X-ray luminosity of 1.5 $\times$ $10^{40}$erg s$^{-1}$. It is one of the rare examples of ULX, which exhibits clear counterparts in radio, optical, UV bands. Follow-up optical spectrum of the ULX shows strong emission lines. The redshift of [O III] emission line coincides with the systematic velocity of NGC 5252, suggesting the ULX is gravitationally bound to NGC 5252. The flux of [O III] appears to be correlated with both X-ray and radio luminosity in the same manner as ordinary AGNs, indicating that the [O III] emission is intrinsically associated with the ULX. Based on the multiwavelength data, we argue that the ULX is unlikely to be a background AGN. A more likely option is an accreting BH with a black hole mass of $\geq 10^4M_\odot$, which might be a stripped remnant of a merging dwarf galaxy.Comment: To appear in Ap

High-Energy Spectra of Active Galactic Nuclei. II. Absorption in Seyfert Galaxies

Absorption by cold material in a large sample of active galaxies has been analyzed in order to study statistically the behavior of absorbed sources. The analysis indicates that on the basis of the column density alone, sources can be divided into low-absorption ([NH/NHGal] ? 50) and high-absorption ([NH/NHGal] ? 50) objects. While the second group consists mostly of narrow emission line galaxies (Seyfert galaxies of type 1.9-2), the first group is less homogenous, being formed by a mixture of broad and narrow emission line objects (Seyfert 1-2 galaxies). A study of the distribution of the column density values by means of bootstrap analysis confirms the reality of this effect. One group consisting of optically selected objects is well explained within the unified theory as nuclei obscured by a molecular torus. The second group made up of X-ray- and IRAS-selected objects is more difficult to define: in these sources the absorption is underestimated owing to difficulties (1) in fitting complex absorption spectra or (2) in measuring NH values in Compton-thick sources or the absorption has a different origin than in the torus. Possible correlations of absorption with X-ray luminosity, axial ratio, and Balmer decrement have also been investigated. Previous suggestions that lower luminosity AGNs tend to be more highly absorbed than those with higher luminosity are not confirmed by the present data; neither is any evidence for a correlation of NH with axial ratio (b/a) found except for a preference of Seyfert 1-1.5 galaxies to be in face-on galaxies. While some sources (Seyfert 1-1.5 galaxies and low-absorption objects) have X-ray absorption compatible with Balmer decrement, high-absorption objects have column densities much higher than predicted from optical observations. These results are in agreement with the unified theory since the torus parameters are expected to be independent of luminosity, its orientation should be random with respect to the host galaxy, and its location should be in between the broad- and narrow-line regions. A study of the NH variability indicates that in a large fraction (70%) of the sources for which the analysis could be done, NH varies on timescales from months to years. In Seyfert 1-1.5 galaxies, the variability is associated with a region in or near the broad-line region and is explained in terms of partial covering and/or warm absorption models. In Seyfert 2 galaxies, the only variability observed is that associated with narrow emission line galaxies. The study of the column density distributions indicates that Seyfert 1-1.5 galaxies are characterized by NH = 18+9?7 ? 1021 atoms cm-2. Seyfert 1.9-2 galaxies have instead NH = 96+54?35 ? 1021 atoms cm-2 and a larger dispersion; if this group is divided into low- and high-absorption objects, NH = 14.5+7.2?5.3 ? 1021 atoms cm-2 and NH = 132.8+80.1?52.6 ? 1021 atoms cm-2, respectively, are obtained. The observed dispersion in each group is consistent with being entirely due to column density variability

The ICT monitoring system of the ASTRI SST-2M prototype proposed for the Cherenkov Telescope Array

In the framework of the international Cherenkov Telescope Array (CTA) observatory, the Italian National Institute for Astrophysics (INAF) has developed a dual mirror, small sized, telescope prototype (ASTRI SST-2M), installed in Italy at the INAF observing station located at Serra La Nave, Mt. Etna. The ASTRI SST-2M prototype is the basis of the ASTRI telescopes that will form the mini-array proposed to be installed at the CTA southern site during its preproduction phase. This contribution presents the solutions implemented to realize the monitoring system for the Information and Communication Technology (ICT) infrastructure of the ASTRI SST-2M prototype. The ASTRI ICT monitoring system has been implemented by integrating traditional tools used in computer centers, with specific custom tools which interface via Open Platform Communication Unified Architecture (OPC UA) to the Alma Common Software (ACS) that is used to operate the ASTRI SST-2M prototype. The traditional monitoring tools are based on Simple Network Management Protocol (SNMP) and commercial solutions and features embedded in the devices themselves. They generate alerts by email and SMS. The specific custom tools convert the SNMP protocol into the OPC UA protocol and implement an OPC UA server. The server interacts with an OPC UA client implemented in an ACS component that, through the ACS Notification Channel, sends monitor data and alerts to the central console of the ASTRI SST-2M prototype. The same approach has been proposed also for the monitoring of the CTA onsite ICT infrastructures. <P /

UVC-Mirror for effective pathogens inactivation in air ducts

Improving the air quality of indoor environments (IAQ) is of utmost importance to safeguard public health as people spend about 80–90% of their time indoor. Efficient Ultraviolet germicidal irradiation (UVGI) system represents a strategic and sustainable solution to protect from recurrent and new airborne pathogens. Here, we present a new approach to design highly efficient UVGI systems, which can be installed in existing Air Treatment Units (ATU) plants with minimal effort. The increased efficiency relies on the concept of an optical cavity, thanks to its shape and source position. The internal volume consists of a highly reflective cavity illuminated with UV-C lamps. Optical simulations permitted the variation of the parameters to maximize the internal irradiance and, thus, the performance. The sanitation efficacy of the system was assessed on a full-scale pilot system. Tests were carried out under normal operating conditions against various microorganisms showed an inactivation rate of > 99%. The benefits of such systems are triple and encompass economic, environmental, and societal aspects. Since the system requires little energy to operate, its application for air disinfection may yield significant energy savings and ensure a balance between energy sustainability and good IAQ

The Camera Server of the ASTRI SST-2M Telescopes Proposed for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) project is an international initiative to build the next generation of ground-based very high energy gamma-ray instrument . Three classes of telescopes with different mirror size will cover the full energy range from tens of GeV up to hundreds of TeV. The full sky coverage will be assured by two arrays, with one site located in each of the northern and southern hemispheres. In the current design scenario, the southern hemisphere array of CTA will include seventy small size telescopes (SST, 4m diameter) covering the highest energy region. Their implementation includes proposed intermediate steps with the development of mini-arrays of telescope precursors like the ASTRI mini-array, led by the Italian National Institute for Astrophysics (INAF) in synergy with the Universidade de Sao Paulo (Brazil) and the North-West University (South Africa). The ASTRI mini-array will be composed of nine telescope units (ASTRI SST-2M) based on double-mirror configuration whose end-to-end prototype has been installed on Mt. Etna (Italy) and is currently undergoing engineering tests. In the ASTRI SST-2M prototype, operating in single telescope configuration, the basic camera server software is being deployed and tested; it acquires the data sent by the camera back end electronics as a continuous stream of packets. In near real time, the bulk data of a given run are stored in one raw file. In parallel they are sorted by data type, converted to FITS format and stored in one file for data type. Upon closure, each file is transferred to the on-site archive. In addition, the quick look component allows the operator to display the camera data during the acquisition. This contribution presents how the camera server software of the prototype is being upgraded in order to fulfil the mini-array requirements, where it will be deployed on the camera server of each ASTRI SST-2M telescope. Particular emphasis will be devoted to the most challenging requirements that are related to the stereoscopy, when two or more telescopes have triggered simultaneously. To handle stereoscopy, each camera server has also to: (i) get the timestamp information from the clock distribution and trigger time stamping system, and associate it to the related camera event; (ii) get from the software array trigger the timestamp which passed the stereo trigger criteria; and (iii) forward to the array data acquisition system the stereo trigger events, according to the required data format and communication protocol