Oleh Petruk - Academia.edu (original) (raw)

History of Astronomy and Outreach by Oleh Petruk

Представлено розвиток астрономії у Львівському університеті за часів Австрійської імперії, Австро... more Представлено розвиток астрономії у Львівському університеті за часів Австрійської імперії, Австро-Угорської імперії та Польської республіки, а саме в період від початку XIX століття до вересня 1939 року. Описано викладання астрономії професорами математики та фізики, зусилля керівництва університету, спрямовані на створення кафедри астрономії та відродження астрономічної обсерваторії, діяльність людей, з іменами яких пов’язано відновлення підготовки фахівців-астрономів і проведення астрономічних досліджень у Львівському університеті. У додатках подано документи, листи, спогади та інші свідчення з історії астрономії в університеті Львова.

Книга «Українське небо 2» є продовженням збірника з аналогічною назвою, який вийшов 2014 року. Во... more Книга «Українське небо 2» є продовженням збірника з аналогічною назвою, який вийшов 2014 року. Вона містить наукові розвідки авторів з різних міст України та з-поза її меж. Статті описують різноманітні аспекти історії розвитку астрономічних знань та уявлень на основі матеріальної, документальної та культурної спадщини України від найдавніших часів до часу заснування перших обсерваторій у XVIII столітті. Результати досліджень виявляють тривалі традиції у використанні астрономічних знань, подають аналіз їх проявів у культурній спадщині, окреслюють картину розвитку астрономії в Україні та її зв’зок із досягненнями цієї науки у світі. Вони можуть бути використані студентами та науковцями різних галузей для розуміння стану розвитку знань та уявлень у відповідні епохи, викладачами вищих навчальних закладів та вчителями шкіл для популяризації науки та укладання програм не лише з астрономії чи інших точних дисциплін, а й, для прикладу, археології, історії України чи її культури. Для наукових працівників, докторантів, аспірантів та усіх, хто не байдужий як до науки про зорі, так і до минулого України.

Збірник містить наукові праці, присвячені різним аспектам історії астрономічних знань та уявлень ... more Збірник містить наукові праці, присвячені різним аспектам історії астрономічних знань та уявлень в Україні від найдавніших часів до кінця XVIII – початку XIX століть, коли були засновані перші в Україні спеціалізовані наукові установи – астрономічні обсерваторіі. У статтях прослідковано розвиток уявлень про Всесвіт та рух небесних тіл шляхом аналізу археологічних знахідок, предметів образотворчого та ужиткового мистецтва, народних астрономічних уявлень та власних назв, описано календарну тематику та згадки про астрономічні явища в українських літописах, представлено початки використання наукових підходів, поширення в Україні геліоцентричних ідей та долю українських вчених-астрономів, викладання астрономії у вищих навчальних закладах 17-18 століть, подано бібліографію астрономічних стародруків зі збірок України, описано заснування першої обсерваторії (Львів, 1771 р.). Автори статей – фахівці наукових установ України з Києва, Львова, Івано-Франківська, Галича й Острога.

Популярна стаття у часописі для школярів "Колосок", чч.7-8 за 2012 р.

Художній альбом, путівник

Astrophysics by Oleh Petruk

Basic steps in history of X-ray astronomy and models of the one of the brightest cosmic X-ray sou... more Basic steps in history of X-ray astronomy and models of the one of the brightest cosmic X-ray sources, supernova remnants (SNRs), are described. The model of evolution of the SNR Tycho which takes into account the nonuniform ambient medium is presented for the first time. Characteristics of the SNR are found: energy of supenova explosion E = 1050 erg, ambient proton number density around the explosion position n = 1 cm-3, shock front radius Rs(theta=0) = 2.3 pc, Rs(theta=pi) = 2.1 pc, shock front velocity Ds(0) = 2200 km/s, Ds(p) = 1900 km/s, ambient proton number density in the region of the shock front n(0) = 0.75 cm-3, n(p) = 1.36 cm-3, swept-up mass M = 1.6 Msun, distance to the SNR d = 2.4 kpc.

Evolution of the adiabatic remnants of an aspherical supernova explosion in uniform medium is con... more Evolution of the adiabatic remnants of an aspherical supernova explosion in uniform medium is considered. Thermal X-ray emission of the remnants is investigated. It is shown that integral thermal X-ray characteristics (X-ray luminosity and spectrum) of the objects do not allow to reveal the asymmetry in the explosion of the progenitor because these characteristics are close to their Sedov counterparts. Surface distribution of the X-ray emission is sensitive to the anisotropy of the explosion and nonuniformity of interstellar medium.

Astronomy and Astrophysics

The large-scale gradient of the interstellar medium (ISM) density distribution essentially affect... more The large-scale gradient of the interstellar medium (ISM) density distribution essentially affects the evolution of Supernova remnants (SNRs). In a non-uniform ISM, the shape of SNR becomes essentially non-spherical, and distributions of gas parameters inside the remnant become strongly anisotropic. The well-known self-similar Sedov solutions may not be applied to modelling such non-spherical objects. Therefore we propose a new approximate analytical method for full hydrodynamical description of 3D point-like explosions in non-uniform media with arbitrary density distribution. On the basis of this method, we investigate the general properties of evolution of 2D non-spherical adiabatic SNRs in ISM with large-scale density gradient. It is shown that the real shape of adiabatic SNR becomes more non-spherical with age, but the visible shape remains close to spherical even for strong real asymmetry (ratio of maximal to minimal shock radii) and surface brightness contrast. It is shown als...

Large-scale gradient of the interstellar medium density distribution essentially affects the evol... more Large-scale gradient of the interstellar medium density distribution essentially affects the evolution of supernova remnants. To model this influence, a new approximate analytical method for the full hydrodynamical description of 3D point-like explosions in the non-uniform media with arbitrary density distribution is developed. General features of the evolution of the adiabatic supernova remnants in the medium with a large-scale density gradient are investigated. Real anisotropy of the remnants increases with age, but the visible shape remains close to spherical. X-ray emission characteristics from the entire SNR (luminosity, spectral index) are close to those in the spherical Sedov case with the same initial data. However, the surface distribution of the X-ray emission characteristics is very sensitive to the initial density distribution around the Supernova progenitor.

Recent nonthermal X-ray and gamma-ray observations, attributed to electron emission processes, fo... more Recent nonthermal X-ray and gamma-ray observations, attributed to electron emission processes, for the first time give an experimental confirmation that electrons are accelerated on SNR shocks up to the energy 10^{14} eV. We have no direct observational confirmations about proton acceleration by SNR. Different models of gamma-emission from SNRs predict different emission mechanisms as dominating. Only decays of neutral pion created in proton-nucleon interactions allow us to look inside the CR nuclear component acceleration processes. A new model for the thermal X-ray composites strongly suggest that thermal X-ray peak inside the radio shell of SNR tells us about entering of one part of SNR shock into a denser medium compared with other parts of the shell. This makes a TXCs promising sites for gamma-ray generation via neutral pion decays. Detailed consideration of SNR-cloud interaction allows to increase an expected proton induced gamma-ray flux from SNR at least on an order of magni...

Kinematics and Physics of Celestial Bodies

The adiabatic stage of evolution of supernova remnants (SNR) in a media with arbitrary large-scal... more The adiabatic stage of evolution of supernova remnants (SNR) in a media with arbitrary large-scale density gradient is investigated. The new approximate analytical method for calculation of a hydrodynamic model of the point asymmetric explosion in the arbitrary inhomogeneous medium is presented. The shape evolution and X-ray characteristics of nonspherical SNR are studied.

Astronomy and Astrophysics

The results of the 2D modelling of Supernova remnant (SNR) RCW86 are given. Models of this remnan... more The results of the 2D modelling of Supernova remnant (SNR) RCW86 are given. Models of this remnant, which for the first time interpret the anisotropy of surface brightness as a result of the evolution of adiabatic SNR in the interstellar medium with a large-scale gradient of density, are considered. Estimations on the basic characteristics of RCW86 and the surrounding medium which follow from these models are found. It is shown that the observed surface brightness distribution of RCW86 may be obtaned in the both proposed up till now models with different initial assumptions: one about a Supernova explosion in 185 A.D. and another about an explosion in the OB-asossiation. In order to obtain the observational contrast of surface brightness it is necessary to have a medium with the characteristic scale of nonuniformity 11 pc if the age of RCW86 is 1800 years or 20-25 pc when the SNR is distant from us on 2.8 kpc. The preshock density contrast between the southwestern and northeastern p...

Methods for estimation of different reference times which appear in the description of transition... more Methods for estimation of different reference times which appear in the description of transition of a strong adiabatic shock into the radiative era are reviewed. The need for consideration of an additional transition subphase in between the end of the adiabatic era and the beginning of the radiative ''pressure-driven snowplow'' stage for a shock running in the uniform or nonuniform medium is emphasized. This could be of importance in particular for studying the interaction of supernova remnants (SNRs) with molecular clouds and therefore for understanding the processes of the cosmic ray production in such systems. The duration of this subphase - about 70% of SNR age at its beginning - is almost independent of the density gradient for media with increasing density and is longer for higher supernova explosion energy and for smaller density in the place of explosion. It is shown as well that if the density of the ambient medium decreases then the cooling processes could...

A number of theoretical results suggest that the shape of the high-energy end of the spectrum of ... more A number of theoretical results suggest that the shape of the high-energy end of the spectrum of electrons accelerated by the shocks in supernova remnants (SNR) have to be close to the exponential one: N(E) propto exp(-(E/Emax)^a) with a approx 1. However, a fit of the observational data from SNR G347.3-0.5 requires a broadening of the electron spectrum, i.e. the value of a approx 0.5. In our report we investigate the possibility for such broadening to be a result of the shock evolution in the nonuniform interstellar medium. We check as well the possible influence of the interstellar magnetic field and the shock obliquity on such broadening. Our conclusion is that none of these possibilities is able to be responsible for the value of a

The extension of the individual particle approach of Bell to the problem of injection of electron... more The extension of the individual particle approach of Bell to the problem of injection of electrons on the nonrelativistic shocks is proposed. The basic idea of the theory is the direct relation between the injection and thermalisation of particles on the shocks. This approach has been applied to the electron injection on the shocks of supernova remnants. The estimations on the injection an thermalisation efficiences for a number of SNRs in our Galaxy based on their radio and X-ray observations are presented.

MAGIC and H.E.S.S experiments are the first to produce images of supernova remnats (SNRs) in TeV ... more MAGIC and H.E.S.S experiments are the first to produce images of supernova remnats (SNRs) in TeV gamma-rays. The gamma-radiation are produced either by electrons (due to inverse-Compton scatterings) or protons (due to pion decays). We present a method to synthesize gamma-ray images of Sedov SNRs due to hadronic emission. The model is developed in the frame of a classic approach to proton acceleration and hydrodynamics of the shocks in a uniform interstellar medium; it includes energy losses of relativistic protons due to pp interactions. Our calculations show that these losses are important only for large densities of protons as it could be in case of interactions of the supernova shock with molecular cloud. Numerical simulations are used to synthesize radial profiles of hadronic TeV gamma-rays.

The goal of the work is to find out which Supernova Remnants (SNRs) are detected be INTEGRAL sate... more The goal of the work is to find out which Supernova Remnants (SNRs) are detected be INTEGRAL satellite and what scientific results can be extracted from the public data available on these objects. We use the selection criteria for SNRs: () shell-type SNRs that have robust signatures of presence of nonthermal energetic electrons and protons, () composite-type SNRs with evidences

Популярна стаття у часописі для школярів "Колосок", чч.7-8 за 2012 р.

Художній альбом, путівник

Astronomy and Astrophysics

Kinematics and Physics of Celestial Bodies

Astronomy and Astrophysics

Proceedings of the International Astronomical Union, 2013

ABSTRACT We investigate the role played by initial clumping of ejecta and by efficient accelerati... more ABSTRACT We investigate the role played by initial clumping of ejecta and by efficient acceleration of cosmic rays (CRs) in determining the density structure of the post-shock region of a Type Ia supernova remnant (SNR) through detailed 3D MHD modeling. Our model describes the expansion of a SNR through a magnetized interstellar medium (ISM), including the initial clumping of ejecta and the effects on shock dynamics due to back-reaction of accelerated CRs. The model predictions are compared to the observations of SN 1006. We found that the back-reaction of accelerated CRs alone cannot reproduce the observed separation between the forward shock (FS) and the contact discontinuity (CD) unless the energy losses through CR acceleration and escape are very large and independent of the obliquity angle. On the contrary, the clumping of ejecta can naturally reproduce the observed small separation and the occurrence of protrusions observed in SN 1006, even without the need of accelerated CRs. We conclude that FS-CD separation is a probe of the ejecta structure at the time of explosion rather than a probe of the efficiency of CR acceleration in young SNRs.

Kinematics and Physics of Celestial Bodies, 2007

A model is proposed for the nonthermal synchrotron emission from supernova remnants in the unifor... more A model is proposed for the nonthermal synchrotron emission from supernova remnants in the uniform interstellar medium. Some characteristics of nonthermal and thermal emission (luminosity and surface brightness distribution) are compared. The conditions when the nonthermal component can be prominent in the X-ray spectrum are specified. We point out some observational tests which will allow a number of parameters characterizing the cosmic ray injection on supernova remnant shocks to be estimated. The cases when electron radiation losses may be neglected are considered.

Kinematics and Physics of Celestial Bodies, 2008

We present a model which describes the evolution of the energy spectrum of relativistic electrons... more We present a model which describes the evolution of the energy spectrum of relativistic electrons in supernova remnants, with radiation losses of electrons taken into account. The model can be used to calculate the synchrotron X-ray emission from supernova remnants in the uniform interstellar medium and in the uniform interstellar magnetic field. The importance of various factors in the variations of spatial distributions of nonthermal electrons and their synchrotron emissive capacity is demonstrated. We analyze the errors which arise in the magnetic field strength when it is estimated with the use of the models which ignore the detailed pattern of the evolution of the magnetic field and the electron spectrum behind the shock front in the remnant. The evolution of synchrotron emission spectrum and the ratio between the synchrotron radio and X-ray fluxes from supernova remnants are calculated.

Kinematics and Physics of Celestial Bodies, 2007

ABSTRACT We propose an approximate analytical approach to the problem of the transition of supern... more ABSTRACT We propose an approximate analytical approach to the problem of the transition of supernova remnants from the adiabatic stage of their evolution to the radiative one. Contrary to the traditional notion, this process turns out to last for a quite long time which is commensurable with the duration of the adiabatic stage. We calculate some parameters of the thermal X-ray radiation of supernova remnants.

Condensed Matter Physics, 1998

We examine the hypothesis that some supernova remnants (SNRs) may be responsible for some unident... more We examine the hypothesis that some supernova remnants (SNRs) may be responsible for some unidentified γ-ray sources detected by EGRET instrument aboard the Compton Gamma Ray Observatory. If this is the case, γ-rays are produced via pion production and decay from direct inelastic collisions of accelerated by SNR shock wave ultrarelativistic protons with target protons of the interstellar medium. We develop a 3-D hydrodynamical model of SNR IC 443 as a possible cosmic γ-ray source 2EG J0618+2234. The derived parameters of IC 443: the explosion energy E o = 2.7 · 10 50 erg, the initial hydrogen number density n(0) = 0.21 cm −3 , the mean radius R = 9.6 pc and the age t = 4500 yr result in too low γ-ray flux, mainly because of the low explosion energy. Therefore, we investigate in detail the hydrodynamics of IC 443 interaction with a nearby massive molecular cloud and show that the reverse shock wave considerably increases the cosmic ray density in the interaction region. Meantime, the Rayleigh-Taylor instability of contact discontinuity between the SNR and the cloud provides an effective mixing of the containing cosmic ray plasma and the cloud material. We show that the resulting γ-ray flux is consistent with the observational data.

Approximate analytical method for modelling of the radiative blast waves from the spherical point... more Approximate analytical method for modelling of the radiative blast waves from the spherical point explosion in nonuniform medium with isotropical density distribution is presented. Comparison of the method with few known results of numerical calculations shows that the accuracy of the method is high enough to use it in physical applications.

Cornell University - arXiv, Feb 4, 2000

Approximations of the Sedov self-similar solution for a strong point explosion in a medium with t... more Approximations of the Sedov self-similar solution for a strong point explosion in a medium with the power-law density distribution ρ o ∝ r −m are reviewed and their accuracy are analyzed. Taylor approximation is extended to cases m = 0. Two approximations of the solution are presented in the Lagrangian coordinates for spherical, cylindrical and plane geometry. These approximations may be used for the investigation of the ionization structure of the adiabatic flow, i.e., inside adiabatic supernova remnants.

Cornell University - arXiv, Oct 17, 2016

List of contributions from the Cherenkov Telescope Array (CTA) Consortium presented at the 6th In... more List of contributions from the Cherenkov Telescope Array (CTA) Consortium presented at the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg, Germany.

arXiv: Astrophysics, Apr 4, 2006

Methods for estimation of different reference times which appear in the description of transition... more Methods for estimation of different reference times which appear in the description of transition of a strong adiabatic shock into the radiative era are reviewed. The need for consideration of an additional transition subphase in between the end of the adiabatic era and the beginning of the radiative "pressure-driven snowplow" stage for a shock running in the uniform or nonuniform medium is emphasized. This could be of importance in particular for studying of the interaction of supernova remnants (SNRs) with molecular clouds and therefore for understanding the processes of the cosmic ray production in such systems. The duration of this subphase-about 70% of SNR age at its beginning-is almost independent of the density gradient for media with increasing density and is longer for higher supernova explosion energy and for smaller density in the place of explosion. It is shown as well that if the density of the ambient medium decreases then the cooling processes could differ from the commonly accepted scenario of the "thin dense radiative shell" formation. This property should be studied in the future because it is important for models of nonspherical SNRs which could be only partially radiative.

Monthly Notices of the Royal Astronomical Society, 2021

Supernova remnants (SNRs) can be rich sources of information on the parent SN (supernova) explosi... more Supernova remnants (SNRs) can be rich sources of information on the parent SN (supernova) explosion. Thus, investigating the transition from the phase of SN to that of SNR can be crucial to link these two phases of evolution. Here, we aim to study the early development of SNR in more detail, paying the major attention to the transition from the early expansion stage to the Sedov stage and the role played by magnetic field in this transition. To this end, spherical magnetohydrodynamic simulations of SNRs have been performed to study the evolution of magnetic field in young SNRs and explore a sequence of the SNR evolutionary stages in the pre-radiative epoch. Remnants of three supernova types are considered, namely, SNIa, SNIc, and SNIIP, that covers a wide space of parameters relevant for SNRs. Changes in global characteristics and development of spatial distributions are analysed. It is shown that the radial component of magnetic field rapidly drops downstream of the forward shock. ...

Observations of SNRs in X-ray and gamma-ray bands promise to contribute with important informatio... more Observations of SNRs in X-ray and gamma-ray bands promise to contribute with important information in our understanding of the kinematics of charged particles and magnetic fields in the vicinity of strong non-relativistic shocks and, therefore, on the nature of galactic cosmic rays. Here we investigate the origin of non-thermal X-ray and gamma-ray emission from SN 1006 through accurate MHD modeling

Journal of Cosmology and Astroparticle Physics, 2021

High-energy gamma rays are promising tools to constrain or reveal the nature of dark matter, in p... more High-energy gamma rays are promising tools to constrain or reveal the nature of dark matter, in particular Weakly Interacting Massive Particles. Being well into its pre-construction phase, the Cherenkov Telescope Array (CTA) will soon probe the sky in the 20 GeV-300 TeV energy range. Thanks to its improved energy and angular resolutions as well as significantly larger effective area when compared to the current generation of Cherenkov telescopes, CTA is expected to probe heavier dark matter, with unprecedented sensitivity, reaching the thermal annihilation cross-section at 1 TeV. This talk will summarise the planned dark matter search strategies with CTA, focusing on the signal from the Galactic centre. As observed with the Fermi LAT at lower energies, this region is rather complex and CTA will be the first ground-based observatory sensitive to the large scale diffuse astrophysical emission from that region. We report on the collaboration effort to study the impact of such extended astrophysical backgrounds on the dark matter search, based on Fermi-LAT data in order to guide our observational strategies, taking into account various sources of systematic uncertainty.

Proceedings of the 15th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG15), Mar 26, 2020

We perform three-dimensional (3D) hydrodynamical/magnetohydrodynamical (MHD) simulations of core-... more We perform three-dimensional (3D) hydrodynamical/magnetohydrodynamical (MHD) simulations of core-collapse supernovae focusing on Supernova (SN) 1987A up to 50 yr after the explosion. As the initial conditions of the simulations, two blue supergiant (BSG) progenitors, one based on a single star evolution and the other based on a binary merger scenario, are used. Based on the results of hydrodynamical simulations, X-ray light curves and images are modeled. Additionally, from the results of the hydrodynamical simulations up to about 1 day, the molecule formation in the ejecta is calculated. The results show that an aspherical explosion model with the binary merger progenitor model consistently reproduces the mass distribution of 56 Ni as a function of the line of sight velocity corresponding to observed [Fe II] lines in SN 1987A and the X-ray light curves. Obtained spatial distributions of CO and SiO molecules show a qualitatively similar feature as ones recently observed by Atacama Large Millimeter/submillimeter Array (ALMA).

Astronomy & Astrophysics, 2020

Context.Massive stars end their lives in catastrophic supernova (SN) explosions. Key information ... more Context.Massive stars end their lives in catastrophic supernova (SN) explosions. Key information on the explosion processes and on the progenitor stars can be extracted from observations of supernova remnants (SNRs), which are the outcome of SNe. Deciphering these observations, however, is challenging because of the complex morphology of SNRs.Aims.We aim to link the dynamical and radiative properties of the remnant of SN 1987A to the geometrical and physical characteristics of the parent aspherical SN explosion and to the internal structure of its progenitor star.Methods.We performed comprehensive three-dimensional hydrodynamic simulations which describe the long-term evolution of SN 1987A from the onset of the SN to the full-fledged remnant at the age of 50 years, accounting for the pre-SN structure of the progenitor star. The simulations include all physical processes relevant for the complex phases of SN evolution and for the interaction of the SNR with the highly inhomogeneous a...

Nature Astronomy, 2019

Astrophysical shocks at all scales, from those in the heliosphere up to the cosmological shock wa... more Astrophysical shocks at all scales, from those in the heliosphere up to the cosmological shock waves, are typically "collisionless", because the thickness of their jump region is much shorter than the collisional mean free path. Across these jumps, electrons, protons, and ions are expected to be heated at different temperatures. Supernova remnants (SNRs) are ideal targets to study collisionless processes because of their bright post-shock emission and fast shocks. Although optical observations of Balmer-dominated shocks in young SNRs showed that the post-shock proton temperature is higher than the electron temperature, the actual dependence of the post-shock temperature on the particle mass is still widely debated 1. We tackle

Astronomy & Astrophysics, 2019

Aims. We investigate the role played by a pre-supernova (SN) ambient magnetic field in the dynami... more Aims. We investigate the role played by a pre-supernova (SN) ambient magnetic field in the dynamics of the expanding remnant of SN 1987A, and the origin and evolution of the radio emission from the remnant, in particular during the interaction of the blast wave with the nebula surrounding the SN. Methods. We modeled the evolution of SN 1987A from the breakout of the shock wave at the stellar surface to the expansion of its remnant through the surrounding nebula using three-dimensional magnetohydrodynamic simulations. The model considers the radiative cooling, the deviations from equilibrium of ionization, the deviation from temperature-equilibration between electrons and ions, and a plausible configuration of the pre-SN ambient magnetic field. We explore the strengths of the pre-SN magnetic field ranging between 1 and 100 μG at the inner edge of the nebula and we assume an average field strength at the stellar surface B0 ≈ 3 kG. From the simulations, we synthesize the thermal X-ray ...

Monthly Notices of the Royal Astronomical Society, 2018

The main characteristics in the radio continuum spectra of Supernova Remnants (SNRs) result from ... more The main characteristics in the radio continuum spectra of Supernova Remnants (SNRs) result from simple synchrotron emission. In addition, electron acceleration mechanisms can shape the spectra in specific ways, especially at high radio frequencies. These features are connected to the age and the peculiar conditions of the local interstellar medium interacting with the SNR. Whereas the bulk radio emission is expected at up to 20-50 GHz, sensitive high-resolution images of SNRs above 10 GHz are lacking and are not easily achievable, especially in the confused regions of the Galactic Plane. In the framework of the early science observations with the Sardinia Radio Telescope in February-March 2016, we obtained highresolution images of SNRs Tycho, W44, and IC443 that provided accurate integrated flux density measurements at 21.4 GHz: 8.8 ± 0.9 Jy for Tycho, 25 ± 3 Jy for W44, and 66 ± 7 Jy for IC443. We coupled the SRT measurements with radio data available in the literature in order to characterize the integrated and spatially resolved spectra of these SNRs, and to find significant frequency-and region-dependent spectral slope variations. For the first time, we provide direct evidence of a spectral break in the radio spectral energy distribution of W44 at an exponential cutoff frequency of 15 ± 2 GHz. This result constrains the maximum energy of the accelerated electrons in the range 6-13 GeV, in agreement with predictions indirectly derived from AGILE and Fermi-LAT gamma-ray observations. With regard to IC443, our results confirm the noticeable presence of a bump in the integrated spectrum around 20-70 GHz that could result from a spinning dust emission mechanism.

The Astrophysical Journal, 2017

We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7−3946... more We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7−3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very-high-energy (VHE) gamma rays. Special attention is paid to explore possible spatial (anti-)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/Hi emission. We present a series of simulated images of RX J1713.7−3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the non-thermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and Hi observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic vs leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.

Monthly Notices of the Royal Astronomical Society, 2016

The maps of intensity and polarization of the radio synchrotron emission from shell-type supernov... more The maps of intensity and polarization of the radio synchrotron emission from shell-type supernova remnants (SNRs) contain a considerable amount of information, although of not easy interpretation. With the aim of deriving constraints on the 3D spatial distribution of the emissivity, as well as on the structure of both ordered and random magnetic fields (MFs), we present here a scheme to model maps of the emission and polarization in SNRs. We first generalize the classical treatment of the synchrotron emission to the case in which the MF is composed of an ordered MF plus an isotropic random component, with arbitrary relative strengths. For a power-law particle energy distribution, we derive analytic formulae that formally resemble those for the classical case. We also treat the shock compression of a fully random upstream field and we predict that the polarization fraction in this case should be higher than typically measured in SNRs. We implement the above treatment into a code, which simulates the observed polarized emission of an emitting shell, taking into account also the effect of the internal Faraday rotation. Finally, we show simulated maps for different orientations with respect to the observer, levels of the turbulent MF component, Faraday rotation levels, distributions of the emissivity (either barrel-shaped or limited to polar caps) and geometries for the ordered MF component (either tangential to the shell or radial). Their analysis allows us to outline properties useful for the interpretation of radio intensity and polarization maps.

Astronomy & Astrophysics, 2017

The acceleration times of the highest-energy particles, which emit gamma-rays in young and middle... more The acceleration times of the highest-energy particles, which emit gamma-rays in young and middle-age supernova remnants (SNRs), are comparable with SNR age. If the number of particles starting acceleration was varying during early times after the supernova explosion then this variation should be reflected in the shape of the gamma-ray spectrum. We use the solution of the non-stationary equation for particle acceleration in order to analyse this effect. As a test case, we apply our method to describe gamma-rays from IC 443. As a proxy of the IC 443 parent supernova we consider SN1987A. First, we infer the time dependence of injection efficiency from evolution of the radio spectral index in SN1987A. Then, we use the inferred injection behaviour to fit the gamma-ray spectrum of IC 443. We show that the break in the proton spectrum needed to explain the gamma-ray emission is a natural consequence of the early variation of the cosmic ray injection, and that the very-high-energy gamma rays originate from particles which began acceleration during the first months after the supernova explosion. We conclude that the shape of the gamma-ray spectrum observed today in SNRs critically depends on the time variation of the cosmic ray injection process in the immediate post-explosion phases. With the same model, we also estimate the future possibility of detecting gamma-rays from SN 1987A.

Monthly Notices of the Royal Astronomical Society, 2015

Gamma-rays from hadronic collisions are expected from supernova remnants (SNRs) located near mole... more Gamma-rays from hadronic collisions are expected from supernova remnants (SNRs) located near molecular clouds. The temperature of the shock interacting with the dense environment quickly reaches 10 5 K. Radiative losses of plasma become essential in the evolution of SNRs. They decrease the thermal pressure and essentially increase the density behind the shock. The presence of an ambient magnetic field may alter the behaviour of the post-adiabatic SNRs considerably compared with the hydrodynamic scenario. In the present article, magnetohydrodynamic simulations of radiative shocks in a magnetic field are performed. High plasma compression due to radiative losses also results in a prominent increase in the strength of the tangential component of magnetic field behind the shock and a decrease of the parallel one. If the strength of the tangential field before the shock is higher than about 3 μG, it prevents formation of a very dense thin shell. The higher the strength of the tangential magnetic field, the larger the thickness and the lower the maximum density in the radiative shell. The parallel magnetic field does not affect the distribution of the hydrodynamic parameters behind the shock. There are almost independent channels of energy transformations: radiative losses are due to thermal energy, magnetic energy increases come from reducing the kinetic energy. The large density and high strength of the perpendicular magnetic field in the radiative shells of SNRs should result in a considerable increase of the hadronic gamma-ray flux compared with the leptonic one.

Monthly Notices of the Royal Astronomical Society, 2016

Three approaches are considered to solve the equation which describes the timedependent diffusive... more Three approaches are considered to solve the equation which describes the timedependent diffusive shock acceleration of test particles at the non-relativistic shocks. At first, the solution of Drury (1983) for the particle distribution function at the shock is generalized to any relation between the acceleration timescales upstream and downstream and for the time-dependent injection efficiency. Three alternative solutions for the spatial dependence of the distribution function are derived. Then, the two other approaches to solve the time-dependent equation are presented, one of which does not require the Laplace transform. At the end, our more general solution is discussed, with a particular attention to the time-dependent injection in supernova remnants. It is shown that, comparing to the case with the dominant upstream acceleration timescale , the maximum momentum of accelerated particles shifts toward the smaller momenta with increase of the downstream acceleration timescale. The timedependent injection affects the shape of the particle spectrum. In particular, i) the power-law index is not solely determined by the shock compression, in contrast to the stationary solution; ii) the larger the injection efficiency during the first decades after the supernova explosion, the harder the particle spectrum around the high-energy cutoff at the later times. This is important, in particular, for interpretation of the radio and gamma-ray observations of supernova remnants, as demonstrated on a number of examples.

Journal of Physical Studies, 2006