arXiv subjects

R. Moderski

Publications and source records attributed to R. Moderski.

At least 55 records · Page 3Linked to original sources

arXiv2022

Time-resolved hadronic particle acceleration in the recurrent Nova RS Ophiuchi

Recurrent Novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to the accretion of fresh material from a binary companion. The shock generated by ejected material slamming into the companion star's wind, accelerates particles to very-high-energies. We report very-high-energy (VHE, $\gtrsim100$\,GeV) gamma rays from the recurrent nova RS\,Ophiuchi up to a month after its 2021 outburst, using the High Energy Stereoscopic System. The VHE emission has a similar temporal profile to lower-energy GeV emission, indicating a common origin, with a two-day delay in peak flux. These observations constrain models of time-dependent particle energization, favouring a hadronic emission scenario over the leptonic alternative. This confirms that shocks in dense winds provide favourable environments for efficient cosmic-ray acceleration to very-high-energies.

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arXiv2017

Control Software for the SST-1M Small-Size Telescope prototype for the Cherenkov Telescope Array

The SST-1M is a 4-m Davies--Cotton atmospheric Cherenkov telescope optimized to provide gamma-ray sensitivity above a few TeV. The SST-1M is proposed as part of the Small-Size Telescope array for the Cherenkov Telescope Array (CTA), the first prototype has already been deployed. The SST-1M control software of all subsystems (active mirror control, drive system, safety system, photo-detection plane, DigiCam, CCD cameras) and the whole telescope itself (master controller) uses the standard software design proposed for all CTA telescopes based on the ALMA Common Software (ACS) developed to control the Atacama Large Millimeter Array (ALMA). Each subsystem is represented by a separate ACS component, which handles the communication to and the operation of the subsystem. Interfacing with the actual hardware is performed via the OPC UA communication protocol, supported either natively by dedicated industrial standard servers (PLCs) or separate service applications developed to wrap lower level protocols (e.g. CAN bus, camera slow control) into OPC UA. Early operations of the telescope without the camera were already carried out. The camera is fully assembled and is capable to perform data acquisition using artificial light source.

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arXiv2017

Performance of a small size telescope (SST-1M) camera for gamma-ray astronomy with the Cherenkov Telescope Array

The foreseen implementations of the Small Size Telescopes (SST) in CTA will provide unique insights into the highest energy gamma rays offering fundamental means to discover and under- stand the sources populating the Galaxy and our local neighborhood. Aiming at such a goal, the SST-1M is one of the three different implementations that are being prototyped and tested for CTA. SST-1M is a Davies-Cotton single mirror telescope equipped with a unique camera technology based on SiPMs with demonstrated advantages over classical photomultipliers in terms of duty-cycle. In this contribution, we describe the telescope components, the camera, and the trigger and readout system. The results of the commissioning of the camera using a dedicated test setup are then presented. The performances of the camera first prototype in terms of expected trigger rates and trigger efficiencies for different night-sky background conditions are presented, and the camera response is compared to end-to-end simulations.

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arXiv2017

Development of a strategy for calibrating the novel SiPM camera of the SST-1M telescope proposed for the Cherenkov Telescope Array

CTA will comprise a sub-array of up to 70 small size telescopes (SSTs) at the southern array. The SST-1M project, a 4 m-diameter Davies Cotton telescope with 9 degrees FoV and a 1296 pixels SiPM camera, is designed to meet the requirements of the next generation ground based gamma-ray observatory CTA in the energy range above 3 TeV. Silicon photomultipliers (SiPM) cameras of gamma-ray telescopes can achieve good performance even during high night sky background conditions. Defining a fully automated calibration strategy of SiPM cameras is of great importance for large scale production validation and online calibration. The SST-1M sub-consortium developed a software compatible with CTA pipeline software (CTApipe). The calibration of the SST-1M camera is based on the Camera Test Setup (CTS), a set of LED boards mounted in front of the camera. The CTS LEDs are operated in pulsed or continuous mode to emulate signal and night sky background respectively. Continuous and pulsed light data analysis allows us to extract single pixel calibration parameters to be used during CTA operation.

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arXiv2016

The Single Mirror Small Sized Telescope For The Cherenkov Telescope Array

The Small Size Telescope with Single Mirror (SST-1M) is one of the proposed types of Small Size Telescopes (SST) for the Cherenkov Telescope Array (CTA). About 70 SST telescopes will be part the CTA southern array which will also include Medium Sized Telescopes (MST) in its threshold configuration. Optimized for the detection of gamma rays in the energy range from 5 TeV to 300 TeV, the SST-1M uses a Davies-Cotton optics with a 4 m dish diameter with a field of view of 9 degrees. The Cherenkov light resulting from the interaction of the gamma-rays in the atmosphere is focused onto a 88 cm side-to-side hexagonal photo-detection plane. The latter is composed of 1296 hollow light guides coupled to large area hexagonal silicon photomultipliers (SiPM). The SiPM readout is fully digital readout as for the trigger system. The compact and lightweight design of the SST-1M camera offers very high performance ideal for gamma-ray observation requirement. In this contribution, the concept, design, performance and status of the first telescope prototype are presented.

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arXiv2015

N_H - N_HI correlation in Gigahertz-peaked-spectrum galaxies

With the Westerbork Synthesis Radio Telescope, we performed HI observations of a sample of known X-ray emitting Gigahertz-peaked-spectrum galaxies with compact-symmetric-object morphology (GPS/CSOs) that lacked an HI absorption detection. We combined radio and X-ray data of the full sample of X-ray emitting GPS/CSOs and found a significant, positive correlation between the column densities of the total and neutral hydrogen ($N_{\rm H}$ and $N_{\rm HI}$, respectively). Using a Bayesian approach, we simultaneously quantified the parameters of the $N_{\rm H} - N_{\rm HI}$ relation and the intrinsic spread of the data set. For a specific subset of our sample, we found $N_{\rm H} \propto N_{\rm HI}^b$, with $b=0.93^{+0.49}_{-0.33}$, and $σ_{int} (N_{\rm H})= 1.27^{+1.30}_{-0.40}$. The $N_{\rm H} - N_{\rm HI}$ correlation suggests a connection between the physical properties of the radio and X-ray absorbing gas.

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arXiv2015

Prototype of the SST-1M Telescope Structure for the Cherenkov Telescope Array

A single-mirror small-size (SST-1M) Davies-Cotton telescope with a dish diameter of 4 m has been built by a consortium of Polish and Swiss institutions as a prototype for one of the proposed small-size telescopes for the southern observatory of the Cherenkov Telescope Array (CTA). The design represents a very simple, reliable, and cheap solution. The mechanical structure prototype with its drive system is now being tested at the Institute of Nuclear Physics PAS in Krakow. Here we present the design of the prototype and results of the performance tests of the structure and the drive and control system.

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arXiv2015

Using muon rings for the optical throughput calibration of the SST-1M prototype for the Cherenkov Telescope Array

Imaging Atmospheric Cherenkov Telescopes (IACTs) are ground-based instruments devoted to the study of very high energy gamma-rays coming from space. The detection technique consists of observing images created by the Cherenkov light emitted when gamma rays, or more generally cosmic rays, propagate through the atmosphere. While in the case of protons or gamma-rays the images present a filled and more or less elongated shape, energetic muons penetrating the atmosphere are visualised as characteristic circular rings or arcs. A relatively simple analysis of the ring images allows the reconstruction of all the relevant parameters of the detected muons, such as the energy, the impact parameter, and the incoming direction, with the final aim to use them to calibrate the total optical throughput of the given IACT telescope. We present the results of preliminary studies on the use of images created by muons as optical throughput calibrators of the single mirror small size telescope prototype SST-1M proposed for the Cherenkov Telescope Array.

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arXiv2015

Software design for the control system for Small-Size Telescopes with single-mirror of the Cherenkov Telescope Array

The Small-Size Telescope with single-mirror (SST-1M) is a 4 m Davies-Cotton telescope and is among the proposed telescope designs for the Cherenkov Telescope Array (CTA). It is conceived to provide the high-energy ($>$ few TeV) coverage. The SST-1M contains proven technology for the telescope structure and innovative electronics and photosensors for the camera. Its design is meant to be simple, low-budget and easy-to-build industrially. Each device subsystem of an SST-1M telescope is made visible to CTA through a dedicated industrial standard server. The software is being developed in collaboration with the CTA Medium-Size Telescopes to ensure compatibility and uniformity of the array control. Early operations of the SST-1M prototype will be performed with a subset of the CTA central array control system based on the Alma Common Software (ACS). The triggered event data are time stamped, formatted and finally transmitted to the CTA data acquisition. The software system developed to control the devices of an SST-1M telescope is described, as well as the interface between the telescope abstraction to the CTA central control and the data acquisition system.

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arXiv2015

Development of the optical system for the SST-1M telescope of the Cherenkov Telescope Array observatory

The prototype of a Davies-Cotton small size telescope (SST-1M) has been designed and developed by a consortium of Polish and Swiss institutions and proposed for the Cherenkov Telescope Array (CTA) observatory. The main purpose of the optical system is to focus the Cherenkov light emitted by extensive air showers in the atmosphere onto the focal plane detectors. The main component of the system is a dish consisting of 18 hexagonal mirrors with a total effective collection area of 6.47 m2 (including the shadowing and estimated mirror reflectivity). Such a solution was chosen taking into account the analysis of the Cherenkov light propagation and based on optical simulations. The proper curvature and stability of the dish is ensured by the mirror alignment system and the isostatic interface to the telescope structure. Here we present the design of the optical subsystem together with the performance measurements of its components.

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arXiv2015

Camera calibration strategy of the SST-1M prototype of the Cherenokov Telescope Array

The SST-1M telescope is one of the prototypes under construction proposed to be part of the future Cherenkov Telescope Array. It uses a standard Davis-Cotton design for the optics and telescope structure, with a dish diameter of 4 meters and a large field-of-view of 9 degrees. The innovative camera design is composed of a photo-detection plane with 1296 pixels including entrance window, light concentrators, Silicon Photomultipliers (SiPMs), and pre-amplifier stages together with a fully digital readout and trigger electronics, DigiCam. In this contribution we give a general description of the analysis chain designed for the SST-1M prototype. In particular we focus on the calibration strategy used to convert the SiPM signals registered by DigiCam to the quantities needed for Cherenkov image analysis. The calibration is based on an online feedback system to stabilize the gain of the SiPMs, as well as dedicated events (dark count, pedestal, and light flasher events) to be taken during the normal operation of the prototype.

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arXiv2015

The SST-1M camera for the Cherenkov Telescope Array

The prototype camera of the single-mirror Small Size Telescopes (SST-1M) proposed for the Cherenkov Telescope Array (CTA) project has been designed to be very compact and to deliver high performance over thirty years of operation. The camera is composed of an hexagonal photo-detection plane made of custom designed large area hexagonal silicon photomultipliers and a high throughput, highly configurable, fully digital readout and trigger system (DigiCam). The camera will be installed on the telescope structure at the H. Niewodnicza{ń}ski institute of Nuclear Physics in Krakow in fall 2015. In this contribution, we review the steps that led to the development of the innovative photo-detection plane and readout electronics, and we describe the test and calibration strategy adopted.

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arXiv2015

Performance of the SST-1M telescope for the Cherenkov Telescope Array observatory

The single mirror small-size telescope (SST-1M) is one of the telescope projects being proposed for the Cherenkov Telescope Array observatory by a sub-consortium of Polish and Swiss institutions. The SST-1M prototype structure is currently being constructed at the Institute of Nuclear Physics in Cracow, Poland, while the camera will be assembled at the University of Geneva, Switzerland. This prototype enables measurements of parameters having a decisive influence on the telescope performance. We present results of numerical simulations of the SST-1M performance based on such measurements. The telescope effective area, the expected trigger rates and the optical point spread function are calculated.

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arXiv2015

DigiCam - Fully Digital Compact Read-out and Trigger Electronics for the SST-1M Telescope proposed for the Cherenkov Telescope Array

The SST-1M is one of three prototype small-sized telescope designs proposed for the Cherenkov Telescope Array, and is built by a consortium of Polish and Swiss institutions. The SST-1M will operate with DigiCam - an innovative, compact camera with fully digital read-out and trigger electronics. A high level of integration will be achieved by massively deploying state-of-the-art multi-gigabit transmission channels, beginning from the ADC flash converters, through the internal data and trigger signals transmission over backplanes and cables, to the camera's server link. Such an approach makes it possible to design the camera to fit the size and weight requirements of the SST-1M exactly, and provide low power consumption, high reliability and long lifetime. The structure of the digital electronics will be presented, along with main physical building blocks and the internal architecture of FPGA functional subsystems.

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arXiv2013

4 m Davies-Cotton telescope for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the next generation very high energy gamma-ray observatory. It will consist of three classes of telescopes, of large, medium and small sizes. The small telescopes, of 4 m diameter, will be dedicated to the observations of the highest energy gamma-rays, above several TeV. We present the technical characteristics of a single mirror, 4 m diameter, Davies-Cotton telescope for the CTA and the performance of the sub-array consisting of the telescopes of this type. The telescope will be equipped with a fully digital camera based on custom made, hexagonal Geiger-mode avalanche photodiodes. The development of cameras based on such devices is an RnD since traditionally photomultipliers are used. The photodiodes are now being characterized at various institutions of the CTA Consortium. Glass mirrors will be used, although an alternative is being considered: composite mirrors that could be adopted if they meet the project requirements. We present a design of the telescope structure, its components and results of the numerical simulations of the telescope performance.

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arXiv2013

Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in very-high-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as sub-sets) and smaller-scale simulations dedicated to individual aspects were carried out and are on-going. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the on-going new round of MC simulations.

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arXiv2012

New constraints on primordial black holes abundance from femtolensing of gamma-ray bursts

The abundance of primordial black holes is currently significantly constrained in a wide range of masses. The weakest limits are established for the small mass objects, where the small intensity of the associated physical phenomenon provides a challenge for current experiments. We used gamma- ray bursts with known redshifts detected by the Fermi Gamma-ray Burst Monitor (GBM) to search for the femtolensing effects caused by compact objects. The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 \times 10^{17} - 10^{20} g do not constitute a major fraction of dark matter.

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arXiv2011

Fermi Large Area Telescope Observations of the Active Galaxy 4C +55.17: Steady, Hard Gamma-Ray Emission and its Implications

We report Fermi/LAT observations and broad-band spectral modeling of the radio-loud active galaxy 4C +55.17 (z=0.896), formally classified as a flat-spectrum radio quasar. Using 19 months of all-sky survey Fermi/LAT data, we detect a gamma-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of gamma-ray variability in the source over its observed history. We illustrate the implications of these results in two different domains. First, we investigate the origin of the steady gamma-ray emission, where we re-examine the common classification of 4C +55.17 as a quasar-hosted blazar and consider instead its possible nature as a young radio source. We analyze and compare constraints on the source physical parameters in both blazar and young radio source scenarios by means of a detailed multiwavelength analysis and theoretical modeling of its broad-band spectrum. Secondly, we show that the gamma-ray spectrum may be formally extrapolated into the very-high energy (VHE; >= 100 GeV) range at a flux level detectable by the current generation of ground-based Cherenkov telescopes. This enables us to place constraints on models of extragalactic background light (EBL) within LAT energies and features the source as a promising candidate for VHE studies of the Universe at an unprecedented redshift of z=0.896.

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