ГАММА-ВИПРОМІНЮВАННЯ ТЕВНОГО ДІАПАЗОНУ ВІД ЗАЛИШКУ НАДНОВОЇ ВІТРИЛА

When a star dies, it leaves a mark on its surrounding environment. The energy from the supernova explosion forms an expanding shock wave that interacts with interstellar and circumstellar material, creating what we know as a supernova remnant (SNR). If the original star has a mass that is greater than or equal to 8 solar masses, this can also lead to the formation of a rapidly rotating neutron star called a pulsar. As these objects evolve, they interact with the surrounding environment, producing non-thermal and thermal emission. For an SNR, its non-thermal emission arises from a population of relativistic particles being accelerated at the shock front of the SNR, while its thermal emission arises from the shock front heating ejecta and and swept-up interstellar medium to X-ray emitting temperatures. For pulsars, their non-thermal emission arises from relativistic particles being accelerated at the termination shock of a pulsar wind. These particles interact with surrounding magnetic fields and ambient photon fields producing synchrotron and inverse Compton emission which we observe as a pulsar wind nebula (PWN), while its thermal emission arises from the surface of the neutron star. These properties of SNRs and pulsars provide a unique window into studying the acceleration, injection, propagation and interaction of highly energetic particles called cosmic rays with the interstellar medium. In addition, they providing information about the evolution, and dynamics of these objects; properties of the shock fronts; details about the original progenitor star; and the impact that these objects have on their surroundings. The research presented here focuses on analysing the intimate connection between cosmic rays, the non-thermal emission arising from SNRs interacting with molecular clouds, and pulsar wind nebulae; as well as analysing the observational and evolutionary properties of these objects. In this thesis we model the propagation of cosmic rays through the Galaxy in an attempt to characterise a standard cosmic ray background with uncertainties, to reveal the origin of the cosmic ray electron positron anomaly. Furthermore, we analyse the gamma-ray emission from SNRs Kes 79 and MSH 11-61A, which are known to be interacting with molecular clouds, as well as the non-thermal X-ray emission arising from the PWN of PSR J1741-2054. We find that the emission from both SNRs most likely arises from the decay of neutral pions that resulted from the interaction of relativistic ions which are accelerated at the shock-front of a SNR, with ambient material. For PSR J1741-2054, we characterise the properties, minimum magnetic field and minimum energy of the particle population that produces the observed diffuse synchrotron emission that surrounds and trails the pulsar. In addition, we characterise the X-ray emission arising from Kes 79, MSH 11-61A and PSR J1741-2054, in an attempt to shed light on the origin and nature of these objects and their emission. Using X-ray data from XMM-Newton and Suzaku respectively, we probe the temperature, ionisation state, and elemental abundance of the shocked gas of each SNR. This allows us to determine their evolutionary properties, properties of the shock, and mass of the original progenitor; and constrain the density of the X-ray emitting plasma. Using Chandra, we determined the temperature of PSR J1741-2054, as well as characterised its proper motion, velocity, direction of motion, and presence of small scale structure immediately surrounding the pulsar.

The non-thermal supernova remnant RX J1713.7-3946 (G347.3-0.5) has recently been shown to be a site of cosmic ray (CR) electron acceleration to TeV energies (Muraishi et al. 2000). Here we present evidence that this remnant is also accelerating CR nuclei. Such nuclei can interact with ambient interstellar gas to produce high energy gamma-rays via the decay of neutral pions. We associate the unidentified EGRET GeV gamma- ray source 3EG J1714-3857 with a massive (~3*10 5 Mo) and dense (~500 nucleons cm -3) molecular cloud interacting with RX J1713.7-3946. Direct evidence for such interaction is provided by observations of the lowest two rotational transitions of CO in the cloud; as in other clear cases of interaction, the CO(J=2-1)/CO(J=1-0) ratio is significantly enhanced. Since the cloud is of low radio and X-ray brightness, CR electrons cannot be responsible for the bulk of its GeV emission there. A picture thus emerges where both electrons and nuclei are being accelerated by the SNR: whereas the CR electrons dominate the local non-thermal radio, X-ray and TeV emission, the shock accelerated CR protons and ions (hadrons) are revealed through their interactions in the adjacent massive cloud. Such a scenario had been anticipated by Aharonian, Drury and Volk (1994).

Supernova remnants act as particle accelerators, providing the cosmic-ray protons that permeate the interstellar medium and initiate the ion–molecule reactions that drive interstellar chemistry. Enhanced fluxes of cosmic-ray protons in close proximity to supernova remnants have been inferred from observations tracing particle interactions with nearby molecular gas. Here I present observations of and CO absorption, molecules that serve as tracers of the cosmic-ray ionization rate and gas density, respectively, in sight lines toward the W28 and Vela supernova remnants. Cosmic-ray ionization rates inferred from these observations range from about 2 to 10 times the average value in Galactic diffuse clouds (∼3 × 10−16 s−1), suggesting that the gas being probed is experiencing an elevated particle flux. While it is difficult to constrain the line-of-sight locations of the absorbing gas with respect to the supernova remnants, these results are consistent with a scenario where cosmic rays are diffusing away from the acceleration site and producing enhanced ionization rates in the surrounding medium.

\n Supernova remnants (SNRs) are widely considered to be sites of Galactic cosmic ray (CR) acceleration. Vela is one of the Galactic composite SNRs closest to Earth accompanied by the Vela pulsar and its pulsar wind nebula (PWN) Vela X. The Vela SNR is one of the most studied remnants and it benefits from precise estimates of various physical parameters such as distance and age. Therefore, it is a perfect object for a detailed study of physical processes in SNRs. The Vela SNR expands into the highly inhomogeneous cloudy interstellar medium (ISM) and its dynamics are determined by the heating and evaporation of ISM clouds. It features an asymmetrical X-ray morphology, which is explained by the expansion into two media with different densities. This could occur if the progenitor of the Vela SNR exploded close to the edge of the stellar wind bubble of the nearby Wolf-Rayet star γ2 Velorum causing one part of the remnant to expand into the bubble. The interaction of the ejecta and the main shock of the remnant with ISM clouds causes formation of secondary shocks at which additional particle acceleration takes place. This may lead to the almost uniform distribution of relativistic particles inside the remnant. We calculate the synchrotron radio emission within the framework of the new hydrodynamical model that assumes the supernova explosion at the edge of the stellar wind bubble. The simulated radio emission agrees well with both the total radio flux from the remnant and the complicated radio morphology of the source.\n

An X-ray investigation of crab-like supernova remnants

Gamma-ray signatures of cosmic ray acceleration, propagation, and confinement in the era of CTA

Gamma-ray emission from molecular clouds: A probe of cosmic-ray origin and propagation

Context. The Vela supernova remnant (SNR) shows several ejecta fragments (or shrapnel) protruding beyond the forward shock, which are most likely relics of anisotropies that developed during the supernova (SN) explosion. Recent studies have revealed high Si abundance in two shrapnel (shrapnel A and G), located in opposite directions with respect to the SNR center. This suggests the possible existence of a Si-rich jet-counterjet structure, similar to that observed in the SNR Cassiopea A. Aims. We analyzed an XMM-Newton observation of a bright clump, behind shrapnel G, which lies along the direction connecting shrapnel A and G. The aim is to study the physical and chemical properties of this clump to ascertain whether it is part of this putative jet-like structure. Methods. We produced background-corrected and adaptively-smoothed count-rate images and median photon energy maps, and performed a spatially resolved spectral analysis. Results. We identified two structures with different physical properties. The first one is remarkably elongated along the direction connecting shrapnel A and G. Its X-ray spectrum is much softer than that of the other two shrapnel, to the point of hindering the determination of the Si abundance; however, its physical and chemical properties are consistent with those of shrapnel A and shrapnel G. The second structure, running along the southeast-northwest direction, has a higher temperature and appears similar to a thin filament. By analyzing the ROSAT data, we have found that this filament is part of a very large and coherent structure that we identified in the western rim of the shell. Conclusions. We obtained a thorough description of the collimated, jet-like tail of shrapnel G in Vela SNR. In addition we discovered a coherent and very extended feature roughly perpendicular to the jet-like structure that we interpret as a signature of an earlier interaction of the remnant with the stellar wind of its progenitor star. The peculiar Ne/O ratio we found in the wind residual may be suggestive of a Wolf-Rayet progenitor for Vela SNR, though further analysis is required to address this point.

Context. Supernova remnants are known to accelerate cosmic rays on account of their nonthermal emission of radio waves, X-rays, and gamma rays. Although there are many models for the acceleration of cosmic rays in supernova remnants, the escape of cosmic rays from these sources has not yet been adequately studied. Aims. We aim to use our time-dependent acceleration code RATPaC to study the acceleration of cosmic rays and their escape in post-adiabatic supernova remnants and calculate the subsequent gamma-ray emission from inverse-Compton scattering and Pion decay. Methods. We performed spherically symmetric 1D simulations in which we simultaneously solved the transport equations for cosmic rays, magnetic turbulence, and the hydrodynamical flow of the thermal plasma in a volume large enough to keep all cosmic rays in the simulation. The transport equations for cosmic rays and magnetic turbulence were coupled via the cosmic-ray gradient and the spatial diffusion coefficient of the cosmic rays, while the cosmic-ray feedback onto the shock structure can be ignored. Our simulations span 100 000 years, thus covering the free-expansion, the Sedov–Taylor, and the beginning of the post-adiabatic phase of the remnant’s evolution. Results. At later stages of the evolution, cosmic rays over a wide range of energy can reside outside of the remnant, creating spectra that are softer than predicted by standard diffusive shock acceleration, and feature breaks in the 10 − 100 GeV-range. The total spectrum of cosmic rays released into the interstellar medium has a spectral index of s ≈ 2.4 above roughly 10 GeV which is close to that required by Galactic propagation models. We further find the gamma-ray luminosity to peak around an age of 4000 years for inverse-Compton-dominated high-energy emission. Remnants expanding in low-density media generally emit more inverse-Compton radiation, matching the fact that the brightest known supernova remnants – RCW86, Vela Jr., HESS J1731−347 and RX J1713.7−3946 – are all expanding in low density environments.

Molecular clouds interacting with supernova remnants may be subject to a greatly enhanced irradiation by cosmic rays produced at the shocked interface between the ejecta and the molecular gas. Over the past decade, broad-band observations have provided important clues about these relativistic particles and indicate that they may dominate over the locally observed cosmic-ray population by a significant amount. In this paper, we estimate the enhancement and find that the cosmic ray energy density can be up to $\sim$1000 times larger in the molecular cloud than in the field. This enhancement can last for a few Myr and leads to a corresponding increase in the ionization fraction, which has important consequences for star formation. Ionization fractions in] molecular cloud cores determine, in part, the rate of ambipolar diffusion, an important process in core formation and pre-collapse evolution. Ionization fractions in newly formed circumstellar disks affect the magneto-rotational instability mechanism, which in turn affects the rate of disk accretion. As estimated here, the increased ionization acts to increase the ambipolar diffusion time by a factor of $\sim30$ and thereby suppresses star formation. In contrast, the increased ionization fraction reduces the sizes of dead zones in accretion disks (by up to an order of magnitude) and thus increases disk accretion rates (by a comparable factor).

Supernova remnant (SNR) RX J0852.0-4622 is one of the youngest and is most likely the closest among known galactic supernova remnants (SNRs). It was detected in X-rays, the 44Ti gamma-line, and radio. We obtain and analyze medium-resolution spectra of 14 stars in the direction towards the SNR RX J0852.0-4622 in an attempt to detect broad absorption lines of unshocked ejecta against background stars. Spectral synthesis is performed for all the stars in the wavelength range of 3740-4020AA to extract the broad absorption lines of Ca II related to the SNR RX J0852.0-4622. We do not detect any broad absorption line and place a 3-sigma upper limit on the relative depths of <0.04 for the broad Ca II absorption produced by the SNR. We detect narrow low and high velocity absorption components of Ca II. High velocity |V(LSR)|=100-140 km/s components are attributed to radiative shocks in clouds engulfed by the old Vela SNR. The upper limit to the absorption line strength combined with the width and flux of the 44Ti gamma-ray line 1.16 MeV lead us to conclude that SNR RX J0852.0-4622 was probably produced by an energetic SN Ic explosion.

We present the results of an optical search for supernova remnants (SNRs) in the spiral galaxies NGC 5204, NGC 5585, NGC 6946, M81, and M101. Using the criterion that emission nebulae with [S II]/Hα ≥ 0.45 are identified as SNRs, we found three SNRs in NGC 5204, five in NGC 5585, 27 in NGC 6946, 41 in M81, and 93 in M101. Including the 35 SNRs recently detected in NGC 2403 by Matonick et al., we have doubled the current number of galaxies that have been well searched for SNRs and increased the number of known extragalactic SNRs by about 50%. Since no SNRs were detected inside H II regions and because our optical search appears biased against detecting large, faint SNRs, we estimate that there could be 4 times more SNRs in each of our target galaxies than we detected. Statistical analysis of the spatial distribution of detected SNRs indicates that those in NGC 2403, M81, and M101 are associated with star-forming regions (e.g., H II regions, spiral arms, and molecular clouds), suggesting that a significant fraction of the detected SNRs are the result of SN II or SN Ib/c explosions. Thirty-one SNRs found in these six galaxies have estimated diameters greater than 100 pc, which is larger than is possible for a single SNR in an interstellar medium of density ~0.1-1 cm-3. Such objects are probably combinations of multiple SNRs and massive stellar winds. We present an overview of extragalactic SNR searches, combining our SNR samples with published results of optical SNR searches in the Large and Small Magellanic Clouds and in M31, M33, NGC 300, and NGC 7793 to create an ensemble of 12 SNR samples. From these data, we find that an important selection effect is the apparent trend for higher L(Hα)mode with increasing galaxy distance because intrinsically fainter SNRs are more difficult to detect in more distant galaxies. In addition, several physical trends were found in the SNR ensemble, including a constant value of Dmode ≈ 40 pc for the SNR samples in these galaxies, suggesting that a significant fraction of the detected SNRs are in a similar evolutionary stage.

Since the discovery of cosmic rays (CRs) over a century ago, their origin remains an open question. Galactic CRs with energy up to the knee (1015 eV) are considered to originate from supernova remnants, but this scenario has recently been questioned due to lack of TeV γ-ray counterparts in many cases. Extragalactic CRs, on the other hand, are thought to be associated with accelerated particles in the relativistic jets launched by supermassive accreting black holes at the centre of galaxies. Scaled down versions of such jets have been detected in X-ray binaries hosting a stellar black hole (BHXBs). In this work, we investigate the possibility that the smaller scale jets in transient outbursts of low-mass BHXBs could be sources of Galactic CRs. To better test this scenario, we model the entire electromagnetic spectrum of such sources focusing on the potential TeV regime, using the ‘canonical’ low-mass BHXB GX 339–4 as a benchmark. Taking into account both the leptonic radiative processes and the γ-rays produced via neutral pion decay from inelastic hadronic interactions, we predict the GeV and TeV γ-ray spectrum of GX 339–4 using lower frequency emission as constraints. Based on this test-case of GX 339–4, we investigate whether other, nearby low-mass BHXBs could be detected by the next-generation very-high-energy γ-ray facility the Cherenkov Telescope Array, which would establish them as additional and numerous potential sources of CRs in the Galaxy.

CONTEXT: Supernova Remnants (SNRs) are considered as the primary sources of galactic cosmic rays (CRs), where CRs are assumed to be accelerated by diffusive shock acceleration (DSA) mechanism. The SNR shocks expand in the complex ambient environment, particularly in the core-collapse scenarios as those SNRs evolve inside wind-blown bubbles created by the mass-loss of massive stars. Therefore, the evolution of core-collapse SNRs, as well as CRs acceleration is expected to be considerably different from SNR evolution in a uniform environment. AIM: The aim is to observe the influence of different ambient medium of core-collapse SNR shock on the particle spectra. Furthermore, the interactions of SNR shock with fluctuations in density within the wind-blown bubble generate several transmitted and reflected shocks. So, the impact of SNR shock interactions with different discontinuities, on particle spectra, and finally the effect on emission from the remnant are also the areas of focus. Methods. The hydrodynamic structures of wind-blown bubbles at pre-supernova stages formed by $20M_{\odot}$, $35M_{\odot}$, and $60M_{\odot}$ stars have been used to create the ambient environment for SNRs. Evolution of those stars through different stages from Zero Age Main Sequence (ZAMS) to the pre-supernova stage, results into formation of structurally different wind bubbles. Then, the transport equation for cosmic rays, and hydrodynamic equations have been solved simultaneously in 1-D spherical symmetry. RESULT: The modifications in particle spectra depend on the hydrodynamics and magnetic field structure of SNR ambient medium. We have obtained softer spectra with spectra index close to 2.5 originated during SNR interaction with hot wind bubble and further, magnetic field structure effectively influences the emission morphology of SNR as it governs the transportation of particles.

RX J1713.7–3946 is a unique supernova remnant (SNR) emitting very high energy \(\gamma \)-rays and X-rays, which are likely emitted by cosmic ray particles accelerated in the SNR via diffusive shock acceleration. It has been suggested that the SNR’s shockwave interacts with the dense gas clumps around the SNR, affecting the synchrotron X-ray radiation and cosmic ray acceleration. However, to date, there has not been a quantitative study to clarify the connection among the X-rays, gas clumps, and accelerated cosmic ray electrons. In this Chapter, we show a strong connection between synchrotron X-rays and the surrounding gas distribution by comparing the spatial distribution among CO, HI, and X-rays over the entire SNR. The present work is aimed at better understanding the SNR shock interstellar gas interaction and thereby establishing the origin of the distribution of the synchrotron X-rays in the SNR RX J1713.7–3946.