Search

The maximum energy of electrons in supernova remnant (SNR) shocks is typically limited by radiative losses, where the synchrotron cooling time equals the acceleration time. The low speed of shocks in a dense medium increases the acceleration time, leading to lower maximum electron energies and fainter X-ray emissions. However, in Kepler's SNR, an enhanced electron acceleration, which proceeds close to the Bohm limit, occurs in the north of its shell, where the shock is slowed by a dense circumstellar medium (CSM). To investigate whether this scenario still holds at smaller scales, we analyzed the temporal evolution of the X-ray synchrotron flux in filamentary structures, using the two deepest Chandra/ACIS X-ray observations, performed in 2006 and 2014. We examined spectra from different filaments, we measured their proper motion and calculated the acceleration to synchrotron time-scale ratios. The interaction with the turbulent and dense northern CSM induces competing effects on electron acceleration: on one hand, turbulence reduces the electron mean free path enhancing the acceleration efficiency, on the other hand, lower shock velocities increase the acceleration time-scale. In most filaments, these effects compensate each other, but in one region the acceleration time-scale exceeds the synchrotron time-scale, resulting in a significant decrease in nonthermal X-ray emission from 2006 to 2014, indicating fading synchrotron emission. Our findings provide a coherent understanding of the different regimes of electron acceleration observed in Kepler's SNR through various diagnostics., Comment: 11 pages, 8 figures, 3 tables, Accepted for publication in The Astrophysical Journal. arXiv admin note: text overlap with arXiv:2308.13435

By using surface brightness maps of Tycho's supernova remnant (SNR) in radio and X-rays, along with the properties of thermal and synchrotron emission, we have derived the post-shock density and magnetic field strength distributions over the projection of this remnant. Our analysis reveals a density gradient oriented towards the north-west, while the magnetic field strength gradient aligns with the Galactic plane, pointing eastward. Additionally, utilizing this magnetic field map, we have derived the spatial distributions of the cut-off frequency and maximum energy of electrons in Tycho's SNR. We further comment on the implications of these findings for interpreting the gamma-ray emission from Tycho's SNR., Comment: Accepted by Astrophysical Journal

Supernova (SN) 1987A is widely regarded as an excellent candidate for leveraging the capabilities of the freshly launched XRISM satellite. Recent researches indicate that the X-ray emission from SN 1987A will increasingly originate from its ejecta in the years to come. In a previous study, we thoroughly examined the proficiency of XRISM-Resolve in identifying signatures of shocked ejecta in SN 1987A, synthesizing the XRISM-Resolve spectrum based on a state-of-the-art magneto-hydrodynamic simulation. However, following the satellite's launch, a technical issue arose with the XRISM instrument's gate valve, which failed to open, thereby affecting observations with the Resolve spectrometer. Here, we update our analysis, reevaluating our diagnostic approach under the assumption that the gate valve remains closed. We find that, even with the reduced instrumental capabilities, it will be possible to pinpoint the ejecta contribution through the study of the line profiles in the XRISM-Resolve spectrum of SN 1987A., Comment: 4 pages, 1 figure. Updates of the results described in Sapienza et al. 2024 (http://doi.org/10.3847/2041-8213/ad16e3). Submitted for publication in Research Notes of the AAS

Based on our Chandra imaging-spectroscopic observations, we present the latest evolution of the X-ray remnant of SN 1987A. Recent changes in the electron temperatures and volume emission measures suggest that the blast wave in SN 1987A is moving out of the dense inner ring structure, also called the equatorial ring (ER). The 0.5-2.0 keV X-ray light curve shows a linearly declining trend (by $\sim$4.5 % yr$^{-1}$) between 2016 and 2020, as the blast wave heats the hitherto unknown circumstellar medium (CSM) outside the ER. While the peak X-ray emission in the latest 0.3-8.0 keV image is still within the ER, the radial expansion rate in the 3.0-8.0 keV images suggests an increasing contribution of the X-ray emission from less dense CSM since 2012, at least partly from beyond the ER. It is remarkable that, since 2020, the declining soft X-ray flux has stabilized around $\sim$7 $\times$ 10$^{-12}$ erg s$^{-1}$ cm$^{-2}$, which may signal a contribution from the reverse-shocked outer layers of ejecta as predicted by the 3-D magneto-hydrodynamic (MHD) models. In the latest ACIS spectrum of supernova remnant (SNR) 1987A in 2022 we report a significant detection of the Fe K line at $\sim$6.7 keV, which may be due to changing thermal conditions of the X-ray emitting CSM and/or the onset of reverse shock interactions with the Fe-ejecta., Comment: 19 pages, 13 figures, resubmitted to ApJ after addressing referee's comments

Supernova (SN) 1987A is one of the best candidates to exploit the capabilities of the freshly launched XRISM satellite. This celestial object offers the unique opportunity to study the evolution of a SN into a young supernova remnant. To date, the X-ray emission has been dominated by the shocked circumstellar medium (CSM), with no shocked ejecta firmly detected. However, recent studies provide compelling evidence that in the forthcoming years the X-ray emission from SN 1987A will increasingly stem from the ejecta. Our aim is to assess the proficiency of XRISM-Resolve high resolution spectrometer in pinpointing signatures of the shocked ejecta in SN 1987A. Taking advantage of a self consistent state-of-art magneto-hydrodynamic simulation that describes the evolution from SN 1987A to its remnant, we synthesized the XRISM-Resolve spectrum of SN 1987A, as it would be collected in the allocated observation during the performance verification phase, which is foreseen for 2024. Our predictions clearly show the leading role of shocked ejecta in shaping the profile of the emission lines. The Doppler broadening associated with the bulk motion along the line of sight of the rapidly expanding ejecta is shown to increase the line widths well above the values observed so far. The quantitative comparison between our synthetic spectra and the XRISM spectra will enable us to establish a strong connection between the broadened line emission and the freshly shocked ejecta. This, in turn, will allow us to retrieve the ejecta dynamics and chemical composition from the X-ray emission., Comment: 9 pages, 4 figures, 1 table, Accepted for publication in The Astrophysical Journal Letters

Supernova remnants (SNRs) are the best candidates for galactic cosmic ray acceleration to relativistic energies via diffusive shock acceleration. The gamma-ray emission of SNRs can provide direct evidence of leptonic (inverse Compton and bremsstrahlung) and hadronic (proton-proton interaction and subsequently pion decay) processes. Puppis A is a ~ 4 kyr old SNR interacting with interstellar clouds which has been observed in a broad energy band, from radio to gamma-ray. We performed a morphological and spectral analysis of 14 years of observations with Fermi-LAT telescope in order to study its gamma-ray emission. We found a clear asymmetry in high-energy brightness between the eastern and western sides of the remnant, reminiscent to that observed in the X-ray emission. The eastern side, interacting with a molecular cloud, shows a spectrum which can be reproduced by a pion decay model. Moreover, we analyzed two gamma-ray sources located close to the remnant. The hardness of their spectra suggests that the gamma-ray emission can be due to particles escaping from the shock of Puppis A., Comment: Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 8 pages, 2 figures, 3 tables

The maximum energy of electrons accelerated by supernova remnants (SNR) is typically limited by radiative losses. In this scenario, the synchrotron cooling time scale is equal to the acceleration time scale. On the other hand, the low propagation speed of a shock in a dense medium is expected to result in an extended acceleration time scale, thus inducing a decrease in the maximum electron energy for a given SNR age and in the X-ray nonthermal flux. The young Kepler's SNR shows an enhanced efficiency of the acceleration process, which is close to the Bohm limit in the north of its shell, where the shock is slowed down by a dense circumstellar medium. Conversely, in the south, where no interaction with a dense medium is evident and the shock speed is high, the acceleration proceeds with a higher Bohm factor. To investigate this scenario, we studied the temporal evolution of the non-thermal emission, taking advantage of two Chandra X-ray observations of Kepler's SNR (performed in 2006 and 2014). We analyzed the spectra of different filaments both in the north and south of the shell, and measured their proper motion. We found a region with low shock velocity where we measured a significant decrease in flux from 2006 to 2014. This could be the first evidence of fading synchrotron emission in Kepler's SNR. This result suggests that under a certain threshold of shock speed the acceleration process could exit the loss-limited regime., Comment: Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 8 pages, 2 figures, 2 tables

To investigate the impact of matter mixing on the formation of molecules in the ejecta of SN 1987A, time-dependent rate equations for chemical reactions are solved for one-zone and one-dimensional ejecta models of SN 1987A. The latter models are based on the one-dimensional profiles obtained by angle-averaging of the three-dimensional hydrodynamical models (Ono et al. 2020), which effectively reflect the 3D matter mixing; the impact is demonstrated, for the first time, based on three-dimensional hydrodynamical models. The distributions of initial seed atoms and radioactive $^{56}$Ni influenced by the mixing could affect the formation of molecules. By comparing the calculations for spherical cases and for several specified directions in the bipolar-like explosions in the three-dimensional hydrodynamical models, the impact is discussed. The decay of $^{56}$Ni, practically $^{56}$Co at later phases, could heat the gas and delay the molecule formation. Additionally, Compton electrons produced by the decay could ionize atoms and molecules and could destruct molecules. Several chemical reactions involved with ions such as H$^+$ and He$^+$ could also destruct molecules. The mixing of $^{56}$Ni plays a non-negligible role in both the formation and destruction of molecules through the processes above. The destructive processes of carbon monoxide and silicon monoxide due to the decay of $^{56}$Ni generally reduce the amounts. However, if the molecule formation is sufficiently delayed under a certain condition, the decay of $^{56}$Ni could locally increase the amounts through a sequence of reactions., Comment: 85 pages, 32 figures, 8 tables; accepted for publication in ApJS

Observations collected with the Atacama Large Millimeter/submillimeter Array (ALMA) and analysis of broadband X-ray spectra have recently suggested the presence of a central compact object (CCO) in SN 1987A. However, no direct evidence of the CCO has been found yet. Here we analyze Chandra X-ray observations of SN 1987A collected in 2007 and 2018, and synthesize the 2027 Chandra and 2037 Lynx spectra of the faint inner region of SN 1987A. We estimate the temporal evolution of the upper limits of the intrinsic luminosity of the putative CCO in three epochs (2018, 2027 and 2037). We find that these upper limits are higher for higher neutron star (NS) kick velocities due to the increased absorption from the surrounding cold ejecta. We compare NS cooling models with both the intrinsic luminosity limits obtained from the X-ray spectra, and the ALMA constraints with the assumption that the observed blob of SN 1987A is primarily heated by thermal emission. We find that the synthetic Lynx spectra are crucial to constrain physical properties of the CCO, which will be confirmed by future observations in the 2040s. We draw our conclusions based on two scenarios, namely the non-detection and detection of NS by Lynx. If the NS is not detected, its kick velocity should be ~700 km/s. Furthermore, the non-detection of the NS would suggest rapid cooling processes around the age of 40 years, implying strong crust superfluidity. Conversely, in the case of NS detection, the mass of the NS envelope must be high., Comment: 37 pages, 17 figures, 6 tables, accepted for publication in ApJ

Supernova remnants (SNRs), the products of stellar explosions, are powerful astrophysical laboratories, which allow us to study the physics of collisionless shocks, thanks to their bright electromagnetic emission. Blast wave shocks generated by supernovae (SNe) provide us with an observational window to study extreme conditions, characterized by high Mach (and Alfvenic Mach) numbers, together with powerful nonthermal processes. In collisionless shocks, temperature equilibration between different species may not be reached at the shock front. In this framework, different particle species might be heated at different temperatures (depending on their mass) in the post-shock medium of SNRs. SNRs are also characterized by a broadband nonthermal emission stemming at the shock front as a result of nonthermal populations of leptons and hadrons. These particles, known as cosmic rays, are accelerated up to ultrarelativistic energies via diffusive shock acceleration. If SNRs lose a significant fraction of their ram energy to accelerate cosmic rays, the shock dynamics should be altered with respect to the adiabatic case. This shock modification should result in an increase of the total shock compression ratio with respect to the Rankine-Hugoniot value of 4. Here I show that the combination of X-ray high resolution spectroscopy (to measure ion temperatures) and moderate resolution spectroscopy (for a detailed diagnostic of the post-shock density) can be exploited to study both the heating mechanism and the particle acceleration in collisionless shocks. I report on new results in the temperatures measured for different ion species in the remnant of SN 1987A. I also discuss evidence of shock modification recently obtained in the remnant of SN 1006 a. D., where the shock compression ratio increases significantly as the angle between the shock velocity and the ambient magnetic field is reduced., Comment: Author's preprint. Accepted for publication in Plasma Physics and Controlled Fusion after minor revisions

The origin of cosmic rays is a pivotal open issue of high-energy astrophysics. Supernova remnants are strong candidates to be the Galactic factory of cosmic rays, their blast waves being powerful particle accelerators. However, supernova remnants can power the observed flux of cosmic rays only if they transfer a significant fraction of their kinetic energy to the accelerated particles, but conclusive evidence for such efficient acceleration is still lacking. In this scenario, the shock energy channeled to cosmic rays should induce a higher post-shock density than that predicted by standard shock conditions. Here we show this effect, and probe its dependence on the orientation of the ambient magnetic field, by analyzing deep X-ray observations of the Galactic remnant of SN 1006. By comparing our results with state-of-the-art models, we conclude that SN 1006 is an efficient source of cosmic rays and obtain an observational support for the quasi-parallel acceleration mechanism., Comment: Published in Nature Communications. The published version of the paper, including supplementary material, is freely available online here https://doi.org/10.1038/s41467-022-32781-4 or as a PDF here https://www.nature.com/articles/s41467-022-32781-4.pdf

Synchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high energy electrons accelerated at the shock front and the acceleration process. We performed a spatially resolved spectral analysis of NuSTAR and XMM-Newton observations of the young Kepler's SNR, aiming to study in detail its non-thermal emission in hard X-rays. We selected a set of regions all around the rim of the shell and extracted the corresponding spectra. The spectra were analyzed by adopting a model of synchrotron radiation in the loss-limited regime, to constrain the dependence of the cutoff energy of the synchrotron radiation on the shock velocity. We identify two different regimes of particle acceleration, characterized by different Bohm factors. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with dense CSM. Our results suggest an enhanced efficiency of the acceleration process in regions where the shock-CSM interaction generates an amplified and turbulent magnetic field. By combining hard X-ray spectra with radio and $\gamma-$ray observations of Kepler's SNR, we modelled the spectral energy distribution. In the light of our results we propose that the observed $\gamma-$ray emission is mainly hadronic, and originates in the northern part of the shell., Comment: 16 pages, 7 figures, 5 tables, Accepted for publication in ApJ

Since the day of its explosion, supernova (SN) 1987A has been closely monitored to study its evolution and to detect its central compact relic. In fact, the formation of a neutron star is strongly supported by the detection of neutrinos from the SN. However, besides the detection in the Atacama Large Millimeter/submillimeter Array (ALMA) data of a feature that is compatible with the emission arising from a proto-pulsar wind nebula (PWN), the only hint for the existence of such elusive compact object is provided by the detection of hard emission in NuSTAR data up to ~ 20 keV. We report on the simultaneous analysis of multi-epoch observations of SN 1987A performed with Chandra, XMM-Newton and NuSTAR. We also compare the observations with a state-of-the-art 3D magnetohydrodynamic (MHD) simulation of SN 1987A. A heavily absorbed power-law, consistent with the emission from a PWN embedded in the heart of SN 1987A, is needed to properly describe the high-energy part of the observed spectra. The spectral parameters of the best-fit power-law are in agreement with the previous estimate, and exclude diffusive shock acceleration as a possible mechanism responsible for the observed non-thermal emission. The information extracted from our analysis are used to infer the physical characteristics of the pulsar and the broad-band emission of its nebula, in agreement with the ALMA data. Analysis of the synthetic spectra also show that, in the near future, the main contribution to Fe K emission line will originate in the outermost shocked ejecta of SN 1987A., Comment: Accepted for publication in ApJ

Based on observations with the $Chandra$ X-ray Observatory, we present the latest spectral evolution of the X-ray remnant of SN 1987A (SNR 1987A). We present a high-resolution spectroscopic analysis using our new deep ($\sim$312 ks) $Chandra$ HETG observation taken in March 2018, as well as archival $Chandra$ gratings spectroscopic data taken in 2004, 2007, and 2011 with similarly deep exposures ($\sim$170 - 350 ks). We perform detailed spectral model fits to quantify changing plasma conditions over the last 14 years. Recent changes in electron temperatures and volume emission measures suggest that the shocks moving through the inner ring have started interacting with less dense circumstellar material, probably beyond the inner ring. We find significant changes in the X-ray line flux ratios (among H- and He-like Si and Mg ions) in 2018, consistent with changes in the thermal conditions of the X-ray emitting plasma that we infer based on the broadband spectral analysis. Post-shock electron temperatures suggested by line flux ratios are in the range $\sim$0.8 - 2.5 keV as of 2018. We do not yet observe any evidence of substantial abundance enhancement, suggesting that the X-ray emission component from the reverse-shocked metal-rich ejecta is not yet significant in the observed X-ray spectrum., Comment: Accepted for publication by ApJ. 23 pages, 14 figures, and 3 tables

The Vela supernova remnant (SNR) shows several ejecta fragments protruding beyond the forward shock (shrapnel). Recent studies have revealed high Si abundance in two 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. We analyzed an XMM-Newton observation of a bright clump, behind shrapnel G, which lies along the direction connecting 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. We produced background-corrected and adaptively-smoothed count-rate images and median photon energy maps, and performed a spatially resolved spectral analysis. We identified two structures with different physical properties. The first one is remarkably elongated along the direction connecting 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 G. The second structure, running along the southeast-northwest direction, has a higher temperature and appears like 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. We obtained a thorough description of the tail of Shrapnel G. In addition we discovered a coherent and very extended feature 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., Comment: 10 pages, 13 figures, Accepted to A&A

Since the day of its explosion, SN 1987A (SN87A) was closely monitored with the aim to study its evolution and to detect its central compact relic. The detection of neutrinos from the supernova strongly supports the formation of a neutron star (NS). However, the constant and fruitless search for this object has led to different hypotheses on its nature. Up to date, the detection in the ALMA data of a feature somehow compatible with the emission arising from a proto Pulsar Wind Nebula (PWN) is the only hint of the existence of such elusive compact object. Here we tackle this 33-years old issue by analyzing archived observations of SN87A performed Chandra and NuSTAR in different years. We firmly detect nonthermal emission in the $10-20$ kev energy band, due to synchrotron radiation. The possible physical mechanism powering such emission is twofold: diffusive shock acceleration (DSA) or emission arising from an absorbed PWN. By relating a state-of-the-art magneto-hydrodynamic simulation of SN87A to the actual data, we reconstruct the absorption pattern of the PWN embedded in the remnant and surrounded by cold ejecta. We found that, even though the DSA scenario cannot be firmly excluded, the most likely scenario that well explains the data is the PWN emission., Comment: Accepted for publication in ApJ Letters

The aim of this work is to bridge the gap between CC SNe and their remnants by investigating how post-explosion anisotropies in the ejecta influence the structure and chemical properties of the remnant at later times. We performed three-dimensional magneto-hydrodynamical simulations starting soon after the SN event and following the evolution of the system in the circumstellar medium (consisting of the wind of the stellar progenitor), for 5000 years, obtaining the physical scenario of a SNR. Here we focused the analysis on the case of a progenitor red supergiant of 19.8 M_sun. We also investigated how a post-explosion large-scale anisotropy in the SN affects the ejecta distribution and the matter mixing of heavy elements in the remnant, during the first 5000 years of evolution. In the case of a spherically symmetric SN explosion without large-scale anisotropies, the remnant roughly keeps memory of the original onion-like layering of ejecta soon after the SN event. Nevertheless, as the reverse shock hits the ejecta, the element distribution departs from a homologous expansion, because of the slowing down of the outermost ejecta layers due to interaction with the reverse shock. In the case of a large-scale anisotropy developed after the SN, we found that the chemical stratification in the ejecta can be strongly modified and the original onion-like layering is not preserved. The anisotropy may cause spatial inversion of ejecta layers, for instance leading to Fe/Si-rich ejecta outside the O shell, and may determine the formation of Fe/Si-rich jet-like features that may protrude the remnant outline. The level of matter mixing and the properties of the jet-like feature are sensitive to the initial physical (density and velocity) and geometrical (size and position) initial characteristics of the anisotropy., Comment: 16 pages, 14 figures, accepted to A&A

Spectral analysis of X-ray emission from ejecta in supernova remnants (SNRs) is hampered by the low spectral resolution of CCD cameras, which creates a degeneracy between the best-fit values of abundances and emission measure. The combined contribution of shocked ambient medium and ejecta to the X-ray emission complicates the determination of the ejecta mass and chemical composition, leading to big uncertainties in mass estimates and it can introduce a bias in the comparison between the observed ejecta composition and the yields predicted by explosive nucleosynthesis. We explore the capabilities of present and future spectral instruments with the aim of identifying a spectral feature which may allow us to discriminate between metal-rich and pure-metal plasmas in X-ray spectra of SNRs. We studied the behavior of the most common X-ray emission processes of an optically thin plasma in the high-abundance regime. We investigated spectral features of bremsstrahlung, radiative recombination continua (RRC) and line emission, by exploring a wide range of chemical abundances, temperatures and ionization parameters. We synthesized X-ray spectra from a 3D hydrodynamic (HD) simulation of Cas A, by using the response matrix from the Chandra/ACIS-S CCD detector and that of the XRISM/Resolve X-ray calorimeter. We found that a bright RRC shows up when the plasma is made of pure-metal ejecta, and a high spectral resolution is needed to identify this ejecta signature. We verified the applicability of our novel diagnostic tool and we propose a promising target for the future detection of such spectral feature: the southeastern Fe-rich clump of Cas A. While there is no way to unambiguously reveal pure-metal ejecta emission with CCD detectors, X-ray calorimeters will be able to pinpoint the presence of pure-metal RRC and to recover correctly absolute mass and the chemical composition of the ejecta., Comment: 13 pages, 12 figures, accepted for publication in A&A

Recent X-ray studies revealed over-ionized recombining plasmas (RPs) in a dozen mixed-morphology (MM) supernova remnants (SNRs). However, the physical process of the over-ionization has not been fully understood yet. Here we report on spatially resolved spectroscopy of X-ray emission from W44, one of the over-ionized MM-SNRs, using XMM-Newton data from deep observations, aiming to clarify the physical origin of the over-ionization. We find that combination of low electron temperature and low recombination timescale is achieved in the region interacting with dense molecular clouds. Moreover, a clear anti-correlation between the electron temperature and the recombining timescale is obtained from each of the regions with and without the molecular clouds. The results are well explained if the plasma was over-ionized by rapid cooling through thermal conduction with the dense clouds hit by the blast wave of W44. Given that a few other over-ionized SNRs show evidence for adiabatic expansion as the major driver of the rapid cooling, our new result indicates that both processes can contribute to over-ionization in SNRs, with the dominant channel depending on the evolutionary stage., Comment: 10 pages, 7 figures Accepted for publication in ApJ

We perform three-dimensional hydrodynamic simulations of aspherical core-collapse supernovae focusing on the matter mixing in SN 1987A. The impacts of four progenitor (pre-supernova) models and parameterized aspherical explosions are investigated. The four pre-supernova models include a blue supergiant (BSG) model based on a slow merger scenario developed recently for the progenitor of SN 1987A (Urushibata et al. 2018). The others are a BSG model based on a single star evolution and two red supergiant (RSG) models. Among the investigated explosion (simulation) models, a model with the binary merger progenitor model and with an asymmetric bipolar-like explosion, which invokes a jetlike explosion, best reproduces constraints on the mass of high velocity $^{56}$Ni, as inferred from the observed [Fe II] line profiles. The advantage of the binary merger progenitor model for the matter mixing is the flat and less extended $\rho \,r^3$ profile of the C+O core and the helium layer, which may be characterized by the small helium core mass. From the best explosion model, the direction of the bipolar explosion axis (the strongest explosion direction), the neutron star (NS) kick velocity, and its direction are predicted. Other related implications and future prospects are also given., Comment: Accepted for publication in The Astrophysical Journal, 62 pages, 26 figures, 3 tables

Magnetars are regarded as the most magnetized neutron stars in the Universe. Aiming to unveil what kinds of stars and supernovae can create magnetars, we have performed a state-of-the-art spatially resolved spectroscopic X-ray study of the supernova remnants (SNRs) Kes 73, RCW 103, and N49, which host magnetars 1E 1841-045, 1E 161348-5055, and SGR 0526-66, respectively. The three SNRs are O- and Ne-enhanced and are evolving in the interstellar medium with densities of >1--2 cm$^{-3}$. The metal composition and dense environment indicate that the progenitor stars are not very massive. The progenitor masses of the three magnetars are constrained to be < 20 Msun (11--15 Msun for Kes 73, < 13 Msun for RCW 103, and ~13 --17 Msun for N49). Our study suggests that magnetars are not necessarily made from very massive stars, but originate from stars that span a large mass range. The explosion energies of the three SNRs range from $10^{50}$ erg to ~2$\times 10^{51}$ erg, further refuting that the SNRs are energized by rapidly rotating (millisecond) pulsars. We report that RCW 103 is produced by a weak supernova explosion with significant fallback, as such an explosion explains the low explosion energy (~$10^{50}$ erg), small observed metal masses ($M_{\rm O}\sim 4\times 10^{-2}$ Msun and $M_{\rm Ne}\sim 6\times 10^{-3}$ Msun), and sub-solar abundances of heavier elements such as Si and S. Our study supports the fossil field origin as an important channel to produce magnetars, given the normal mass range ($M_{\rm ZAMS} < 20$ Msun) of the progenitor stars, the low-to-normal explosion energy of the SNRs, and the fact that the fraction of SNRs hosting magnetars is consistent with the magnetic OB stars with high fields., Comment: 13 pages, 8 figures, published in A&A

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. We tackle this longstanding issue through the analysis of deep multi-epoch and high-resolution observations of the youngest nearby supernova remnant, SN 1987A, made with the Chandra X-ray telescope. We introduce a novel data analysis method by studying the observed spectra in close comparison with a dedicated full 3-D hydrodynamic simulation. The simulation is able to reproduce self-consistently the whole broadening of the spectral lines of many ions altogether. We can therefore measure the post shock temperature of protons and selected ions through comparison of the model with observations. We have obtained information about the heating processes in collisional shocks by finding that the ion to proton temperature ratio is always significantly higher than one and increases linearly with the ion mass for a wide range of masses and shock parameters., Comment: The final version of this manuscript (including Methods) is published in Nature Astronomy and is publicly available at this link: https://rdcu.be/bhO7Z

We present ~400ks NuSTAR observations of the northeast (NE) and southwest (SW) non-thermal limbs of the Galactic SNR SN1006. We discovered three sources with X-ray emission detected at >50keV. Two of them are identified as background AGN. We extract the NuSTAR spectra from a few regions along the non-thermal limbs and jointly analyze them with the XMM-Newton spectra and the radio data. The broad-band radio/X-ray spectra can be well described with a synchrotron emission model from a single population of CR electrons with a power law energy distribution and an exponential cutoff. The power law index of the electron particle distribution function (PDF) is ~1.88-1.95 for both the NE and SW limbs, and we do not find significant evidence for a variation of this index at different energy (curvature). There are significant spatial variations of the synchrotron emission parameters. The highest energy electrons are accelerated in regions with the lowest expansion velocity, which is opposite to what has been found in the Tycho's SNR. In addition to a gradual steepening of synchrotron emission from the center of the non-thermal limbs to larger azimuthal angles, we also find that both the emission spectrum and the PDF are significantly flatter in three regions in the SW limb where the shock encounters higher density ambient medium. The NE limb also shows significantly higher cutoff energy in the PDF than the SW limb. By comparing with the roughly symmetric TeV emission and largely asymmetric GeV emission from the two non-thermal limbs, we conclude that the asymmetry in the ambient medium and magnetic fields may have largely modified the acceleration and emission of CR leptons., Comment: 21 pages, 14 figures, 7 tables, ApJ in press

IC443 is a supernova remnant located in a quite complex environment since it interacts with nearby clouds. Indications for the presence of overionized plasma have been found though the possible physical causes of overionization are still debated. Moreover, because of its peculiar position and proper motion, it is not clear if the pulsar wind nebula (PWN) within the remnant is the relic of the IC443 progenitor star or just a rambling one seen in projection on the remnant. Here we address the study of IC443 plasma in order to clarify the relationship PWN-remnant, the presence of overionization and the origin of the latter. We analyzed two \emph{XMM-Newton} observations producing background-subtracted, vignetting-corrected and mosaicked images in two different energy bands and we performed a spatially resolved spectral analysis of the X-ray emission. We identified an elongated (jet-like) structure with Mg-rich plasma in overionization. The head of the jet is interacting with a molecular cloud and the jet is aligned with the position of the PWN at the instant of the supernova explosion. Interestingly, the direction of the jet of ejecta is somehow consistent with the direction of the PWN jet. Our discovery of a jet of ejecta in IC443 enlarge the sample of core-collapse SNRs with collimated ejecta structures. IC443's jet is the first one which shows overionized plasma, possibly associated with the adiabatic expansion of ejecta. The match between the jet's direction and the original position of the PWN strongly supports the association between the neutron star and IC443., Comment: Accepted for publication in A&A

Molecular clouds are predicted to emit nonthermal X-rays when they are close to particle-accelerating supernova remnants (SNRs), and the hard X-ray source AX J1714.1-3912, near the SNR RX J1713.7-3946, has long been considered a candidate for diffuse nonthermal emission associated with cosmic rays diffusing from the remnant to a closeby molecular cloud. We aim at ascertaining the nature of this source by analyzing two dedicated X-ray observations performed with Suzaku and Chandra. We extracted images from the data in various energy bands, spectra, and light curves and studied the long-term evolution of the X-ray emission on the basis of the ~4.5 yr time separation between the two observations. We found that there is no diffuse emission associated with AX J1714.1-3912, which is instead the point-like source CXOU J171343.9-391205. We discovered rapid time variability (timescale ~1 ks), together with a high intrinsic absorption and a hard nonthermal spectrum (power law with photon index Gamma~1.4). We also found that the X-ray flux of the source drops down by 1-2 orders of magnitude on a timescale of a few years. Our results suggest a possible association between AX J1714.1-3912 and a previously unknown supergiant fast X-ray transient, although further follow-up observations are necessary to prove this association definitively., Comment: Accepted for publication in Astronomy & Astrophysics. The new version includes a note after acceptance

The supernova remnant SN 1006 is a source of high-energy particles and its southwestern limb is interacting with a dense ambient cloud, thus being a promising region for gamma-ray hadronic emission. We aim at describing the physics and the nonthermal emission associated with the shock-cloud interaction to derive the physical parameters of the cloud (poorly constrained by the data analysis), to ascertain the origin of the observed spatial variations in the spectral properties of the X-ray synchrotron emission, and to predict spectral and morphological features of the resulting gamma-ray emission. We performed 3-D magnetohydrodynamic simulations modeling the evolution of SN 1006 and its interaction with the ambient cloud, and explored different model setups. By applying the REMLIGHT code on the model results, we synthesized the synchrotron X-ray emission, and compared it with actual observations, to constrain the parameters of the model. We also synthesized the leptonic and hadronic gamma-ray emission from the models, deriving constraints on the energy content of the hadrons accelerated at the southwestern limb. We found that the impact of the SN 1006 shock front with a uniform cloud with density 0.5 cm^-3 can explain the observed morphology, the azimuthal variations of the cutoff frequency of the X-ray synchrotron emission, and the shock proper motion in the interaction region. Our results show that the current upper limit for the total hadronic energy in the southwestern limb is 2.5e49 erg., Comment: Accepted for publication in A&A

Based on the XMM-Newton large program on SN1006 and our newly developed spatially resolved spectroscopy tools (Paper~I), we study the thermal emission from ISM and ejecta of SN1006 by analyzing the spectra extracted from 583 tessellated regions dominated by thermal emission. With some key improvements in spectral analysis as compared to Paper~I, we obtain much better spectral fitting results with less residuals. The spatial distributions of the thermal and ionization states of the ISM and ejecta show different features, which are consistent with a scenario that the ISM (ejecta) is heated and ionized by the forward (reverse) shock propagating outward (inward). Different elements have different spatial distributions and origins, with Ne mostly from the ISM, Si and S from the ejecta, and O and Mg from both ISM and ejecta. Fe L-shell lines are only detected in a small shell-like region SE to the center of SN1006, indicating that most of the Fe-rich ejecta has not yet or just recently been reached by the reverse shock. The overall ejecta abundance patterns for most of the heavy elements, except for Fe and sometimes S, are consistent with typical Type~Ia SN products. The NW half of the SNR interior probably represents a region with turbulently mixed ISM and ejecta, so has enhanced emission from O, Mg, Si, S, lower ejecta temperature, and a large diversity of ionization age. In addition to the asymmetric ISM distribution, an asymmetric explosion of the progenitor star is also needed to explain the asymmetric ejecta distribution., Comment: 9 pages, 7 figures, 1 table, MNRAS in press

We present an X-ray analysis of the central region of supernova remnant (SNR) G332.5-5.6 through an exhaustive analysis of XMM-Netwon observations with complementary infrared observations. We characterize and discuss the origin of the observed X-ray morphology, which presents a peculiar plane edge over the west side of the central region. The morphology and spectral properties of the X-ray supernova remnant were studied using a single full frame XMM-Newton observation in the 0.3 to 10.0 keV energy band. Archival infrared WISE observations at 8, 12 and 24 \mu m were also used to investigate the properties of the source and its surroundings at different wavelengths. The results show that the extended X-ray emission is predominantly soft (0.3-1.2 keV) and peaks around 0.5 keV, which shows that it is an extremely soft SNR. X-ray emission correlates very well with central regions of bright radio emission. On the west side the radio/X-ray emission displays a plane-like feature with a terminal wall where strong infrared emission is detected. Our spatially resolved X-ray spectral analysis confirms that the emission is dominated by weak atomic emission lines of N, O, Ne, and Fe, all of them undetected in previous X-ray studies. These characteristics suggest that the X-ray emission is originated in an optically thin thermal plasma, whose radiation is well fitted by a non-equilibrium ionization collisional plasma (VNEI) X-ray emission model. Our study favors a scenario where G332.5-5.6 is expanding in a medium with an abrupt density change (the wall), likely a dense infrared emitting region of dust on the western side of the source., Comment: 7 pages, 5 figures and 2 tables. Accepted for publication in A&A

Based on our newly developed methods and the XMM-Newton large program of SN1006, we extract and analyze the spectra from 3596 tessellated regions of this SNR each with 0.3-8 keV counts $>10^4$. For the first time, we map out multiple physical parameters, such as the temperature ($kT$), electron density ($n_e$), ionization parameter ($n_et$), ionization age ($t_{ion}$), metal abundances, as well as the radio-to-X-ray slope ($\alpha$) and cutoff frequency ($\nu_{cutoff}$) of the synchrotron emission. We construct probability distribution functions of $kT$ and $n_et$, and model them with several Gaussians, in order to characterize the average thermal and ionization states of such an extended source. We construct equivalent width (EW) maps based on continuum interpolation with the spectral model of each regions. We then compare the EW maps of OVII, OVIII, OVII K$\delta-\zeta$, Ne, Mg, SiXIII, SiXIV, and S lines constructed with this method to those constructed with linear interpolation. We further extract spectra from larger regions to confirm the features revealed by parameter and EW maps, which are often not directly detectable on X-ray intensity images. For example, O abundance is consistent with solar across the SNR, except for a low-abundance hole in the center. This "O Hole" has enhanced OVII K$\delta-\zeta$ and Fe emissions, indicating recently reverse shocked ejecta, but also has the highest $n_et$, indicating forward shocked ISM. Therefore, a multi-temperature model is needed to decompose these components. The asymmetric metal distributions suggest there is either an asymmetric explosion of the SN or an asymmetric distribution of the ISM., Comment: 25 pages, 18 figures, 4 tables, MNRAS, in press

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics., Comment: Submitted in response to the call for White Papers for the definition of the L2 and L3 missions in the ESA Science program. More information: http://www.the-athena-x-ray-observatory.eu/. 19 pages, 12 figures, 4 tables

Aims: We want to probe the physics of fast collision-less shocks in supernova remnants. In particular, we are interested in the non-equilibration of temperatures and particle acceleration. Specifically, we aim to measure the oxygen temperature with regards to the electron temperature. In addition, we search for synchrotron emission in the northwestern thermal rim. Methods: This study is part of a dedicated deep observational project of SN 1006 using XMM-Newton, which provides us with currently the best resolution spectra of the bright northwestern oxygen knot. We aim to use the reflection grating spectrometer to measure the thermal broadening of the O vii line triplet by convolving the emission profile of the remnant with the response matrix. Results: The line broadening was measured to be {\sigma}_e = 2.4 \pm 0.3 eV, corresponding to an oxygen temperature of 275$^{+72}_{-63}$ keV. From the EPIC spectra we obtain an electron temperature of 1.35 \pm 0.10 keV. The difference in temperature between the species provides further evidence of non-equilibration of temperatures in a shock. In addition, we find evidence for a bow shock that emits X-ray synchrotron radiation, which is at odds with the general idea that due to the magnetic field orientation only in the NE and SW region X-ray synchrotron radiation should be emitted. We find an unusual H{\alpha} and X-ray synchrotron geometry, in that the H{\alpha} emission peaks downstream of the synchrotron emission. This may be an indication for a peculiar H{\alpha} shock, in which the density is lower and neutral fraction are higher than in other supernova remnants, resulting in a peak in H{\alpha} emission further downstream of the shock., Comment: 6 pages, 7 figures. Accepted for publication in A&A

Mixed-morphology SNRs are characterized by a shell-like radio emission, a centrally peaked X-ray morphology, and by interaction with molecular clouds. Many models have been proposed to explain these peculiar remnants, but their physical origin is still unclear. The recent discovery of over-ionized (i. e. recombining) ejecta in 3 mixed-morphology SNRs has dramatically challenged all the previous models and opened up new, unexpected scenarios. I review the main properties of these remnants and their peculiar X-ray spectral properties. I also discuss the hydrodynamic model developed to explain the presence of over-ionized ejecta in W49B and present a list of open issues that still need to be clarified., Comment: Invited review for Cosmic rays and their interstellar medium environment (CRISM-2011). To be published in a special issue of Memorie della Societa' Astronomica Italiana

Vela X is a large, 3x2 degrees, radio-emitting pulsar wind nebula (PWN) powered by the Vela pulsar in the Vela supernova remnant. Using four Suzaku/XIS observations pointed just outside Vela X, we find hard X-ray emission extending throughout the fields of view. The hard X-ray spectra are well represented by a power-law. The photon index is measured to be constant at Gamma~2.4, similar to that of the southern outer part of Vela X. The power-law flux decreases with increasing distance from the pulsar. These properties lead us to propose that the hard X-ray emission is associated with the Vela PWN. The larger X-ray extension found in this work strongly suggests that distinct populations relativistic electrons form the X-ray PWN and Vela X, as was recently inferred from multiwavelength spectral modeling of Vela X., Comment: 18 pages, 7 figures, accepted for publication in PASJ (Suzaku Special Issue)

W49B is a mixed-morphology supernova remnant with thermal X-ray emission dominated by the ejecta. In this remnant, the presence of overionized plasma has been directly established, with information about its spatial structure. However, the physical origin of the overionized plasma in W49B has not yet been understood. We investigate this intriguing issue through a 2D hydrodynamic model that takes into account, for the first time, the mixing of ejecta with the inhomogeneous circumstellar and interstellar medium, the thermal conduction, the radiative losses from optically thin plasma, and the deviations from equilibrium of ionization induced by plasma dynamics. The model was set up on the basis of the observational results. We found that the thermal conduction plays an important role in the evolution of W49B, in- ducing the evaporation of the circumstellar ring-like cloud (whose presence has been deduced from previous observations) that mingles with the surrounding hot medium, cooling down the shocked plasma, and pushes the ejecta backwards to the center of the remnant, forming there a jet-like structure. During the evolution, a large region of overionized plasma forms within the remnant. The overionized plasma originates from the rapid cooling of the hot plasma originally heated by the shock reflected from the dense ring-like cloud. In particular, we found two different ways for the rapid cooling of plasma to appear: i) the mixing of relatively cold and dense material evaporated from the ring with the hot shocked plasma and ii) the rapid adiabatic expansion of the ejecta. The spatial distribution of the radiative recombination continuum predicted by the numerical model is in good agreement with that observed., Comment: 7 pages, 5 figures, MNRAS in press

The Cygnus Loop is interacting with a protrusion of the cavity wall in its eastern edge (the XA region), where the X-ray emission is very bright. The complexity of the environment and the non-linear physical processes of the shock-cloud interaction make the origin of the X-ray emission still not well understood. Our purpose is to understand the physical origin of the X-ray emission in the XA region, addressing, in particular, the role of thermal conduction in the interaction process. We analyzed two XMM-Newton data sets, performing image analysis and spatially resolved spectral analysis on a set of homogeneous regions. We applied a recently developed diagnostic tool to compare spectral analysis results with predictions of theoretical models, and to estimate the efficiency of thermal conduction on the X-ray emitting shocked plasma. We found that the inhomogeneous cavity wall contains both large clumps (the protrusion) and small isolated clumps with different densities. A large indentation bent over to the south is detected. The abundance of the surrounding ISM is ~0.2 times solar value. We confirmed the important role of thermal conduction in the evolution of X-ray emitting plasma during shock-cloud interaction., Comment: 7 pages, 5 figures, MNRAS in press