To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Semiconductors CulnSe2 (CIS) and alloys of Cu(ln,Ga)Se2 (CIGS) are often used as the light absorbing layer in thin film photovoltaic devices. These polycrystalline materials reach good conversion efficiencies despite the presence of grain boundaries, which can degrade device performance. Grain properties such as size distribution and orientation can be characterized using electron backscatter diffraction (EBSD). The EBSD method has been used extensively to determine texture and recrystallization in metal forming processes but to a lesser extent for characterization of CIGS thin film properties. This article describes measurements of grain properties for CIGS thin films grown under different reaction conditions.
This paper presents experimental results on the synthesis of boron rich diamond-like carbon phases (BCx) obtained by high pressure sintering (s-BCx) and pulsed laser deposition (PLD-BCx). It has been shown that sintering of a mixture of a powder of micro-diamonds with a powder of boron in the toroid type high pressure device leads to the creation of s-BCx phase with a low resistivity, and high elastic moduli. The PLD-BCx film found to be rigid with the resistivity as low as that of best conductive boron–doped diamond films. It indicates that the presence of B atoms in a laser plasma leads to the formation of sp3 bonds in the material in the process of chemical sputtering. The combination of unique characteristics can be achieved by changing the ratio B/C.
Gamma-ray observations for Supernova remnant (SNR)-molecular cloud (MC) association systems play an important role in the research on the acceleration and propagation of cosmic-ray protons. Through the analysis of 5.6 years of Fermi-Large Area Telescope observation data, here we report on the detection of a gamma-ray emission source near the SNR Kesteven 41 with a significance of 24σ in 0.2–300 GeV. The best-fit location of the gamma-ray source is consistent with the MC with which the SNR interacts. Several hypotheses including both leptonic and hadronic scenarios are considered to investigate the origin of these gamma-rays. The gamma-ray emission can be naturally explained by the decay of neutral pions produced via the collision between high energy protons accelerated by the shock of Kesteven 41 and the adjacent MC. The electron energy budget would be too high for the SNR if the gamma-rays were produced via inverse Compton (IC) scattering off the Cosmic Microwave Background (CMB) photons.
We report detections of thermal X-ray line emission and proper motions in the supernova remnant (SNR) RX J1713.7-3946, the prototype of the small class of synchrotron dominated SNRs. Based on deep XMM-Newton observations, we find clear line features including Ne Lyα, Mg Heα, and Si Heα from the central portion of the remnant. The metal abundance ratios suggest that the thermal emission originates from core-collapse SN ejecta arising from a relatively low-mass (≲20 M⊙) progenitor. In addition, using XMM-Newton observations on a 13 yr time interval, we have measured expansion in the southeastern rim to be ~0.75″ yr−1 or ~3500 km s−1 at a distance of 1 kpc. Given this, we derive an upstream density to be ~0.01 cm−3, compatible with the lack of thermal X-rays from the shocked ambient medium. We also estimate the age of the remnant to be ~1200–1600 yr, roughly consistent with the idea that RX J1713.7-3946 is the remnant of SN 393.
In the framework of the Sardinia Radio Telescope (SRT) Early Science Program, we obtained single-dish high-resolution imaging of the Supernova Remnants IC443 and W44 at 7 GHz. By coupling them with SRT 1.5 GHz maps, we provided spatially-resolved spectral measurements that are highlighting a spread in spectral slope distribution. The observed features range from flat or slightly inverted spectra corresponding to bright radio limbs and filaments, to relatively steep spectra in fainter radio regions. Different theoretical possibilities explaining the above challenging findings are discussed. In particular, we exclude that the observed region-dependent wide spread in spectral slope distribution could be related to absorption processes. Our high-frequency results can be directly related to distinct electron populations in the SNRs including secondary hadronic electrons and resulting from different shocks conditions and/or undergoing different cooling processes. Integrated fluxes associated with the whole SNRs obtained by SRT in comparison with previous results in the literature support the evidence for a slight spectral steepening above 1 GHz for both sources, which could be related to primary electrons or more likely secondary hadronic electrons cut-offs.
In an aspherical supernova explosion, shock emergence is not simultaneous and non-radial flows develop near the stellar surface. Oblique shock breakouts tend to be easily developed in compact progenitors like stripped-envelop core collapse supernovae. According to Matzner et al. (2013), non-spherical explosions develop non-radial flows that alters the observable emission and radiation of a supernova explosion. These flows can limit ejecta speed, change the distribution of matter and heat of the ejecta, suppress the breakout flash, and most importantly engender collisions outside the star. We construct a global numerical FLASH hydrodynamic simulation in a two dimensional spherical coordinate, focusing on the non-relativistic, adiabatic limit in a polytropic envelope to see how these fundamental differences affect the early light curve of core-collapse SNe.
We present single-dish imaging of the well-known Supernova Remnants (SNRs) IC443 and W44 at 1.5 GHz and 7 GHz with the recently commissioned 64-m diameter Sardinia Radio Telescope (SRT). Our images were obtained through on-the-fly mapping techniques, providing antenna beam oversampling, automatic baseline subtraction and radio-frequency interference removal. It results in high-quality maps of the SNRs at 7 GHz, which are usually lacking and not easily achievable through interferometry at this frequency due to the very large SNR structures. SRT continuum maps of our targets are consistent with VLA maps carried out at lower frequencies (at 324 MHz and 1.4 GHz), providing a view of the complex filamentary morphology. New estimates of the total flux density are given within 3% and 5% error at 1.5 GHz and 7 GHz respectively, in addition to flux measurements in different regions of the SNRs.
In their final stages, massive stars can show large eruptions which can resemble core-collapse IIn SNe. Here we present SN 2015bh in NGC 2770, a IIn/impostor, where archival data show variabilities for at least 21 years before the main event in 2015. Serendipitous spectra during an outburst are the only SN progenitor spectra available since SN 1987A and show an LBV with a fast, dense outflow. Analogues to SN 2015bh are SN 2009ip and SNhunt 248 while the SN 2000ch impostor could be equivalent to the outburst phase of SN 2015bh. It is currently unclear whether SN 2015bh (and SN 2009ip) were final core-collapse events. Alternatively, they might be large outbursts shedding the outer envelope and creating a Wolf-Rayet star in only a matter of decades. Future large-scale high-cadence surveys such as LSST will detect many more of these events and allow us a unique insight into the largely unknown late stages of massive stellar evolution.
We investigate the relation between the emission properties of supernova shock breakout in the circumstellar matter (CSM) and the behavior of the shock. Using a Monte-Carlo method, we examine how the light curve and spectrum depends on the asphericity of the shock and bulk-Compton scattering, and compare the results with the observed properties of X-ray outburst (XRO) 080109/SN 2008D. We found that the rise and decay time of the X-ray light curve do not significantly depend on the degree of shock asphericity and the viewing angle in a steady and spherically symmetric CSM. The observed X-light curve and spectrum of XRO 080109 can be reproduced by considering the shock with a radial velocity of 60% of the speed of light, and the wind mass loss rate is about 5 × 10−4M⊙.
We carried out high resolution simulations of weakly-magnetized core-collapse supernovae in two-dimensional axisymmetry in order to see the influence of the magnetic field and rotation on the explosion. We found that the magnetic field amplified by magnetorotational instability (MRI) has a great positive impact on the explosion by enhancing the neutrino heating, provided that the progenitor has large angular momentum close to the highest value found in stellar evolution calculations. We also found that even for progenitors neither involving strong magnetic flux nor large angular momentum, the magnetic field is greatly amplified by the convection aand rotation, and this leads to the boost of the explosion again by enhancing the neutrino heating.
Gamma ray lines are expected to be emitted as part of the afterglow of supernova explosions, because radioactive decay of freshly synthesised nuclei occurs. Significant radioactive gamma ray line emission is expected from 56Ni and 44Ti decay on time scales of the initial explosion (56Ni, τ ~days) and the young supernova remnant (44Ti,τ ~90 years). Less specific, and rather informative for the supernova population as a whole, are lessons from longer lived isotopes such as 26Al and 60Fe. From isotopes of elements heavier than iron group elements, any interesting gamma-ray line emission is too faint to be observable. Measurements with space-based gamma-ray telescopes have obtained interesting gamma ray line emissions from two core collapse events, Cas A and SN1987A, and one thermonuclear event, SN2014J. We discuss INTEGRAL data from all above isotopes, including all line and continuum signatures from these two objects, and the surveys for more supernovae, that have been performed by gamma ray spectrometry. Our objective here is to illustrate what can be learned from gamma-ray line emission properties about the explosions and their astrophysics.
We investigate the supernova remnant (SNR) 3C 397 and its neighboring pulsar PSR J1906+0722 in high energy gamma rays by using nearly six years of archival data of Large Area Telescope on board Fermi Gamma Ray Space Telescope (Fermi-LAT). The off-pulse analysis of gamma-ray flux from the location of PSR J1906+0722 reveals an excess emission which is found to be very close to the radio location of 3C 397. Here, we present the preliminary results of this gamma-ray analysis of 3C 397 and PSR J1906+0722.
Observing the supernovae (SNe) associated to the different types of gamma-ray bursts (GRBs) is one of the few means to study their progenitors. In the past years, it has become clear that GRB-like events are more heterogeneous than previously thought. There is a marked difference between long GRBs, which are produced by the collapse of very massive stars and are normally associated with broad-lined type Ic SNe, and short bursts, which occur when two compact objects merge and that, at least in some cases, can produce an associated kilonova. Moreover, the SNe associated with different sub-types of long GRBs are also seen to differ, especially those associated with ultra-long duration GRBs. To address this issue in a systematic way we started an observing programme in 2010 at the 10.4m GTC telescope. Here we present some results of our programme, including the detection of 12 new GRB-SNe. Highlights of our sample are the discovery of the first spectroscopic SN associated with a highly energetic (Eγ, iso ~ 1054 erg) “cosmological” burst (GRB 130427A), the study of the SN associated with a shock-breakout GRB (GRB 140606B) and the SN associated with the peculiar ultra-long GRB 101225A at z = 0.85. The sample includes also the follow-up of several short GRBs in search for kilonovae emission (GRB 130603B and GRB 160821B are important examples). Amongst our latest results we present the photometric and spectroscopic observations of the SNe associated with GRB 150818A and GRB 161219B.
G326.3-1.8 (also known as MSH 15-56) has been detected in radio as a middle-aged composite supernova remnant (SNR) consisting of a SNR shell and a pulsar wind nebula (PWN) which has been crushed by the reverse shock. With the recent Fermi-LAT data release Pass 8 providing increased acceptance and angular resolution, we investigate the morphology of this SNR to disentangle the PWN from the SNR contributions and understand the nature of the γ-ray emission. We thus perform a morphological and spectral analysis from 300 MeV to 300 GeV which highlights the contributions from these two components. The simplest interpretation is hadronic emission from the SNR and harder leptonic emission from the PWN.
Recent direct measurements of cosmic-ray (CR) light nuclei (protons, helium, and lithium) by AMS-02 have shown that the flux of each element has an unexpected hard component above ~300~GeV, and that the spectral indices of those components are almost the same (~2.5). This implies that there should be primary sources that produces CR lithium nuclei, which have been believed to be produced via spallation of heavier nuclei in the ISM (secondary origin). We propose the nearby Type Ia supernova following a nova eruption from a white dwarf as the origin of CR Li.
The Cosmic Ray (CR) physics has entered a new era driven by high precision measurements coming from direct detection (especially AMS-02 and PAMELA) and also from gamma-ray observations (Fermi-LAT). In this review we focus our attention on how such data impact the understanding of the supernova remnant paradigm for the origin of CRs. In particular we discuss advancement in the field concerning the three main stages of the CR life: the acceleration process, the escape from the sources and the propagation throughout the Galaxy. We show how the new data reveal a phenomenology richest than previously thought that could even challenge the current understanding of CR origin.
Core-collapse supernova explosions are driven by a central engine that converts a small fraction of the gravitational binding energy released during core collapse to outgoing kinetic energy. The suspected mode for this energy conversion is the neutrino mechanism, where a fraction of the neutrinos emitted from the newly formed protoneutron star are absorbed by and heat the matter behind the supernova shock. Accurate neutrino-matter interaction terms are crucial for simulating these explosions. In this proceedings for IAUS 331, SN 1987A, 30 years later, we explore several corrections to the neutrino-nucleon scattering opacity and demonstrate the effect on the dynamics of the core-collapse supernova central engine via two dimensional neutrino-radiation-hydrodynamics simulations. Our results reveal that the explosion properties are sensitive to corrections to the neutral-current scattering cross section at the 10-20% level, but only for densities at or above ~1012 g cm−3.
Reliable distances to Galactic Supernova remnants (SNRs) are essential to constrain parameters that reveal the evolutional process of SNRs. We carry out a project to measure SNRs’ distances in the first quadrant of the Galaxy. In this project, red clump stars (RCS) are used as standard candle to build the optical extinction (AV)-(D) distance relation in each direction of extinction-known SNRs. Here, G5.7-0.01, G54.1+0.3 and G78.2+2.1 are taken as typical examples. We obtain the distance of 3−0.3+0.4 kpc for G5.7-0.01, the lower limit of 5.8 kpc for G54.1+0.3, the upper limit of 2 kpc for G5.7-0.01. The results are consistent with distances from kinematic measurements. Hence, we highlight the RCS method can independently trace the distance to the SNRs.
Recently, first neutrino-driven supernova explosions have been obtained in 3D, self-consistent, first-principle simulations, these models are still not always exploding robustly and, in general, the explosions are not sufficiently energetic. To constrain the explosion mechanism, and the related uncertainties, it is thus very helpful to consider observational constraints: pulsar kicks, progenitor association and supernova remnants (SNR). Recent observations of asymmetries in the supernova ejecta of Cas A are very promising, to compare to long-term simulations of the explosion. In addition 3D observations of SN87A are becoming more constraining on the geometry of the ejected material during the explosion. In this talk I will discuss our efforts to model the late time evolution of a 3D supernova explosion, where we include the effects of beta decay, which inflates the structures rich in 56Ni. The structures we find in the simulations depend on the quantities plotted.
Supernova remnants are the site of a number of physical processes (shock-heating, non-equilibrium ionization, hydrodynamic instabilities, particle acceleration, magnetic field amplification). Their related emission processes provide us with a large set of observational data. Supernova remnants result from the interaction of high-velocity material ejected by the supernova explosion with the medium surrounding the progenitor star. This interaction gives rise to a double-shock structure that lasts for hundreds of years, with a forward shock and a reverse shock compressing and heating to tens million of degrees the surrounding medium and the ejecta, respectively. It is mostly in this phase that young supernova remnants provide information on their explosion mechanism through spectro-imaging observations of the ejected nucleosynthesis products and their dynamics, notably in the X-ray domain. I will review these observations and their implications for our current understanding of the dynamics of supernova remnants. I will conclude on the prospects with future facilities.