Search

Context. Supernova remnants (SNRs) are believed to be capable of accelerating cosmic rays (CRs) to PeV energies. SNR G106.3+2.7 is a prime PeVatron candidate. It is formed by a head region, where the pulsar J2229+6114 and its boomerang-shaped pulsar wind nebula are located, and a tail region containing SN ejecta. The lack of observed gamma ray emission from the two regions of this SNR has made it difficult to assess which region would be responsible for the PeV CRs. Aims. We aim to characterize the very-high-energy (VHE, 0.1–100 TeV) gamma ray emission from SNR G106.3+2.7 by determining the morphology and spectral energy distribution of the region. This is accomplished using 2565 days of data and improved reconstruction algorithms from the High Altitude Water Cherenkov (HAWC) Observatory. We also explore possible gamma ray production mechanisms for different energy ranges. Methods. Using a multi-source fitting procedure based on a maximum-likelihood estimation method, we evaluate the complex nature of this region. We determine the morphology, spectrum, and energy range for the source found in the region. Molecular cloud information is also used to create a template and evaluate the HAWC gamma ray spectral properties at ultra-high-energies (UHE, > 56 TeV). This will help probe the hadronic nature of the highest-energy emission from the region. Results. We resolve one extended source coincident with all other gamma ray observations of the region. The emission reaches above 100 TeV and its preferred log-parabola shape in the spectrum shows a flux peak in the TeV range. The molecular cloud template fit on the higher energy data reveals that the SNR's energy budget is fully capable of producing a purely hadronic source for UHE gamma rays. Conclusions. The HAWC observatory resolves one extended source between the head and the tail of SNR G106.3+2.7 in the VHE gamma ray regime. The template fit suggests the highest energy gamma rays could come from a hadronic origin. However, the leptonic scenario, or a combination of the two, cannot be excluded at this time. [ABSTRACT FROM AUTHOR]

Context. Recently, the Nereides nebula was discovered through deep optical emission line observations and was classified as a supernova remnant (SNR) candidate, G107.7−5.1. Aims. Since very little is known about this SNR, we have looked at several archival datasets to better understand the environment and properties of the object. Methods. We present a detailed analysis of the gamma-ray emission detected by the Fermi Large Area Telescope in the region of the nebula. A model of the nonthermal emission is presented that allows us to derive the particle distribution responsible for the gamma rays. We also use molecular gas and atomic hydrogen observations to try to constrain the source age and distance. Results. An extended (∼2°) GeV source coincident with the location of the nebula is found. The nonthermal emission has a hard spectrum and is detected up to ∼100 GeV, confirming the SNR nature of this object. The GeV properties of G107.7−5.1 are similar to those of other SNRs such as G150.3​ + ​4.5, and it likely expands in a relatively low-density medium. The Nereides nebula is one more example of a growing population of dim SNRs detected at high energies. A simple leptonic model is able to account for the gamma-ray emission. Standard SNR evolutionary models constrain the age to be in the 10 − 50 kyr range, which is consistent with estimates of the maximum particle energy obtained from GeV observations. However, more detailed observations of the source should be carried out to better understand its properties. [ABSTRACT FROM AUTHOR]

The Milky Way's Central Molecular Zone (CMZ) differs dramatically from our local solar neighbourhood, both in the extreme interstellar medium conditions it exhibits (e.g. high gas, stellar, and feedback density) and in the strong dynamics at play (e.g. due to shear and gas influx along the bar). Consequently, it is likely that there are large-scale physical structures within the CMZ that cannot form elsewhere in the Milky Way. In this paper, we present new results from the Atacama Large Millimeter/submillimeter Array (ALMA) large programme ACES (ALMA CMZ Exploration Survey) and conduct a multi-wavelength and kinematic analysis to determine the origin of the M0.8–0.2 ring, a molecular cloud with a distinct ring-like morphology. We estimate the projected inner and outer radii of the M0.8–0.2 ring to be 79″ and 154″, respectively (3.1 pc and 6.1 pc at an assumed Galactic Centre distance of 8.2 kpc) and calculate a mean gas density >104 cm−3, a mass of ~106 M⊙, and an expansion speed of ~20 km s−1, resulting in a high estimated kinetic energy (>1051 erg) and momentum (>107 M⊙ km s−1). We discuss several possible causes for the existence and expansion of the structure, including stellar feedback and large-scale dynamics. We propose that the most likely cause of the M0.8–0.2 ring is a single high-energy hypernova explosion. To viably explain the observed morphology and kinematics, such an explosion would need to have taken place inside a dense, very massive molecular cloud, the remnants of which we now see as the M0.8–0.2 ring. In this case, the structure provides an extreme example of how supernovae can affect molecular clouds. [ABSTRACT FROM AUTHOR]

Context. Observations of radio emission from young core-collapse supernovae (CCSNe) allow one to study the history of the pre-supernova stellar wind, trace the density structure of the ejected material, and probe the magnetohydrodynamics that describe the interaction between the two, as the forward shock expands into the circumstellar medium. The radio shell of supernova SN 1993J has been observed with very long baseline interferometry (VLBI) for ∼20 years, giving one of the most complete pictures of the evolution of a CCSN shock. However, different results about the expansion curve and properties of the radio-emitting structure have been reported by different authors, likely due to systematics in the data calibration and/or model assumptions made by each team. Aims. We aim to perform an analysis of the complete set of VLBI observations of SN 1993J that accounts for different instrumental and source-intrinsic effects, in order to retrieve robust conclusions about the shock expansion and physics in SN 1993J. Methods. We have explored the posterior probability distribution of a complete data model, using a technique based on Markov chains. Our model accounts for antenna calibration effects, as well as different kinds of radio-emission structures for the supernova. Results. The posterior parameter distributions strongly favor a spherical shell-like radio structure with a nonuniform radial intensity profile, with a broad brightness distribution that peaks close to or just above the region where the contact discontinuity is expected to be located. Regarding the shell expansion, the full dataset can be well described using one single deceleration parameter, β ∼ 0.80, being the shell outer radius R ∝ tβ. There is clear evidence of a relative widening of the shell width beyond day 2600−3300 after the explosion, which is due to an increased deceleration of the inner shell boundary. This is similar to findings previously reported by other authors. Conclusions. The radial intensity profile and the late evolution of the shell suggest a scenario in which the magnetic field is amplified mainly by the Rayleigh-Taylor instability, which emanates from the contact discontinuity. Furthermore, the increased deceleration of the inner boundary indicates that the reverse shock enters a region of the ejecta at around 3000 days, where the density distribution is substantially flatter. Such a weakening of the reverse shock can also explain the achromatic break in the radio light curves, which occurs at the same time. The deduced radial intensity distribution for SN 1993J is quite similar to that observed in the spatially well-resolved supernova remnant Cassiopeia A. [ABSTRACT FROM AUTHOR]

Aims. OB-runaway stars ejected by the binary supernova mechanism can be found near young open star clusters. In this paper, we present an OB-runaway candidate as a pre-SN binary companion to the progenitor of the pulsar PSR J2238+5903 inside the young open star cluster Berkeley 97. Methods. We tried to find a kinematic outlier based on Gaia DR3 proper motions and parallaxes to be the pre-supernova binary companion to the progenitor of the pulsar. We took the spectra of two bright early B-type stars of the cluster, determined their effective temperature and surface gravity, and updated the parameters of the cluster. Through isochrone fitting of the color-magnitude diagram of the star cluster, we identified the members and determined the stellar parameters of the runaway star. Results. Two bright members of the cluster, HD 240015 and HD 240016, are massive stars with spectral types of B0.5II and B1.5II and effective temperatures of Teff = 21 000 ± 1000 K and Teff = 24 000 ± 2000 K, respectively, as well as surface gravities of log(g[cm/s2]) = 3.0 ± 0.2. We find that Berkeley 97 is a star cluster with an age of log(age[yr]) = 7.1, an uncertainty of < 0.1 dex, and an interstellar extinction of AV = 3.1 ± 0.1 mag. The runaway star has an effective temperature of Teff = 12 250 ± 1750 K with a surface gravity of log(g[cm/s2]) = 4.38 ± 0.2 (B8V type star). By tracing back the proper motion of the runaway star, the explosion center was found for different possible pulsar ages of 10, 20, and 26.6 kyr. The pulsar moving out from the 20 kyr position must have a space velocity of ∼340 km s−1, which is consistent with the general pulsar velocity distribution. This supports the idea that the pulsar originated from the cluster as a result of a binary supernova. Despite its young age, τ < 26.6 kyr, the supernova remnant is not visible. [ABSTRACT FROM AUTHOR]

We present the discovery of possibly the youngest Galactic supernova remnant (SNR) with associated pulsar-wind nebula (PWN), which we name Perun (G329.9−0.5). Perun was serendipitously discovered in the Australian Square Kilometre Array Pathfinder–Evolutionary Map of the Universe survey at 943 MHz, and subsequent follow-up observations were conducted with the Australia Telescope Compact Array observatory at 5500 and 9000 MHz. We combine these with additional radio observations from the MeerKAT, Molonglo Observatory Synthesis Telescope, and Murchison Widefield Array telescopes, infrared (IR) observations from the SpitzerSpace Telescope , and X-ray observations from the Chandra X-ray observatory to perform a multifrequency analysis. The radio morphology shows a small angular size shell (D  = 70 arcsec) with a luminous, central PWN. We measure a total spectral index of |$\alpha = -0.49\pm 0.05$|⁠ , which should be typical for a young, composite SNR. Crucial evidence for Perun's SNR classification comes from the detection of linear fractional polarization at radio frequencies of |$\sim$| 7 per cent–10 per cent with both radial and tangential orientations, similar to the young SNR G1.9+0.3. We use data from the Southern Galactic Plane Survey to perform an H  i analysis and estimate a favoured distance range of 6–9 kpc, and thus a favoured age range of |$\sim$| 70–500 yr. We find no high-energy emission in Fermi- Large Area Telescope data. We detect Perun's outer shell in 24  |$\mu$| m indicating the possible presence of [O  iv ] and [Fe  iii ] emission, also typical for young SNRs. Overall, these observations and analysis confirm Perun as a young, Galactic SNR with a prominent PWN. [ABSTRACT FROM AUTHOR]

We report new radio timing solutions from a 3-yr observing campaign conducted with the MeerKAT and Murriyang telescopes for nine Small Magellanic Cloud pulsars, increasing the number of characterized rotation-powered extragalactic pulsars by 40 per cent. We can infer from our determined parameters that the pulsars are seemingly all isolated, that six are ordinary pulsars, and that three of the recent MeerKAT discoveries have a young characteristic age of under 100 kyr and have undergone a spin-up glitch. Two of the sources, PSRs J0040 |$-$| 7337 and J0048 |$-$| 7317, are energetic young pulsars with spin-down luminosities of the order of 10 |$^{36}$|  erg s |$^{-1}$|⁠. They both experienced a large glitch, with a change in frequency of about 30  |$\mu$| Hz, and a frequency derivative change of order |$-10^{-14}$|  Hz s |$^{-1}$|⁠. These glitches, the inferred glitch rate, and the properties of these pulsars (including potentially high inter-glitch braking indices) suggest these neutron stars might be Vela-like repeating glitchers and should be closely monitored in the future. The position and energetics of PSR J0048 |$-$| 7317 confirm it is powering a new pulsar wind nebula (PWN) detected as a radio continuum source; and similarly the association of PSR J0040 |$-$| 7337 with the PWN of supernova remnant (SNR) DEM S5 (for which we present a new Chandra image) is strengthened. Finally, PSR J0040 |$-$| 7335 is also contained within the same SNR but is a chance superposition. It has also been seen to glitch with a change of frequency of |$10^{-2}$|   |$\mu$| Hz. This work more than doubles the characterized population of SMC radio pulsars. [ABSTRACT FROM AUTHOR]

We present a spatially resolved study of the kinematical properties of known supernova remnants (SNRs) in the nearest galaxies of the SIGNALS survey, namely NGC 6822 (one object) and M33 (163 objects), based on data obtained with the SITELLE imaging Fourier transform spectrometer at the Canada–France–Hawaii Telescope. The purpose of this paper is to provide a better scheme of identification for extragalactic SNRs and, in particular, to distinguish between H  ii regions and SNRs. For that we have used diagrams which involve both the [S  ii ]/H |$\alpha$| ratio and the velocity dispersion (⁠|$\sigma$|⁠). We also introduce a new parameter, |$\xi = {[\rm S\, {\small II}] \over H\alpha } \times \sigma$|⁠ , which enhances still the contrast between SNRs and the rest of the ionized gas. More than 90 per cent of the SNRs in our entire sample show an integrated [S  ii ]/H |$\alpha$| ratio larger than the canonical value (0.4). 86 per cent of the SNRs present in our field show a significant velocity dispersion. The spectral resolution of our observations allows us to observe the complex velocity structure of some SNRs. [ABSTRACT FROM AUTHOR]

Context. We present multi-wavelength observations of the Galactic supernova remnant (SNR) HB9 and the H II region G159.2+3.3 apparently projected nearby, in order to study their properties and potential physical connections. Aims. Confirming the physical connections between SNRs and H II regions is crucial to understanding their origin and interactions with the environment. Optical emission lines are powerful tools with which to measure the physical, chemical, and dynamical properties of the ionised gas, so could further help us to confirm such physical connections. Methods. We present new optical narrow-band images of G159.2+3.3, as well as long-slit medium-resolution optical spectroscopy of both G159.2+3.3 and the SNR HB9 projected nearby. We compared these new data to archival multi-wavelength data to study the properties of the multi-phase interstellar medium in and around these two objects. Results. HB9 is bright in γ-rays, but the γ-ray morphology is centrally filled and most of it is not clearly associated with the surrounding molecular clouds. There is a weak apparent connection of HB9 to the infrared bright enclosing shell of G159.2+3.3 in the γ-ray. The diffuse Balmer line has an almost identical morphology to the radio emission in G159.2+3.3, indicating they are both thermal in origin. Using medium-band high-resolution optical spectra from selected regions of the southeast (SE) shell of HB9 and G159.2+3.3, we found the radial velocity dispersion of HB9 along the slit to be significantly higher than the full width at half maximum of the lines. In contrast, these two values are both smaller and comparable to each other in G159.2+3.3. This indicates that the gas in HB9 may have additional global motion triggered by the SNR shock. The [N II] λ6583 Å/Hα line ratio of both objects can be interpreted with photo-ionisation by hot stars or low-velocity shocks, except for the post-shock region in the SE shell of HB9, where the elevated [N II]/Hα line ratio suggests a contribution from shock ionisation. The measured electron density from the [S II] 6716/6730 line ratio is significantly lower in the brighter G159.2+3.3 compared to the SE shell of HB9. Conclusions. Our density estimate suggests that G159.2+3.3, although appearing brighter and more compact, is likely located at a much larger distance than HB9, so the two objects have no physical connections, unless the shock compressed gas in HB9 has a significantly lower filling factor. [ABSTRACT FROM AUTHOR]

Context. Supernova remnants (SNRs) carry vast amounts of mechanical and radiative energy that heavily influence the structural, dynamical, and chemical evolution of galaxies. To this day, more than 300 SNRs have been discovered in the Milky Way, exhibiting a wide variety of observational features. However, existing classification schemes are mainly based on their radio morphology. Aims. In this work, we introduce a novel unsupervised deep learning pipeline to analyse a representative subsample of the Galactic SNR population (~50% of the total) with the aim of finding a connection between their multi-wavelength features and their physical properties. Methods. The pipeline involves two stages: (1) a representation learning stage, consisting of a convolutional autoencoder that feeds on imagery from infrared and radio continuum surveys (WISE 22 μm, Hi-GAL 70 μm and SMGPS 30 cm) and produces a compact representation in a lower-dimensionality latent space; and (2) a clustering stage that seeks meaningful clusters in the latent space that can be linked to the physical properties of the SNRs and their surroundings. Results. Our results suggest that this approach, when combined with an intermediate uniform manifold approximation and projection (UMAP) reprojection of the autoencoded embeddings into a more clusterable manifold, enables us to find reliable clusters. Despite a large number of sources being classified as outliers, most clusters relate to the presence of distinctive features, such as the distribution of infrared emission, the presence of radio shells and pulsar wind nebulae, and the existence of dust filaments. [ABSTRACT FROM AUTHOR]

Supernova feedback injects energy and turbulence into the interstellar medium (ISM) in galaxies, influences the process of star formation, and is essential to understanding the formation and evolution of galaxies. In this paper we present the largest extragalactic survey of supernova remnant (SNR) candidates in nearby star-forming galaxies using exquisite spectroscopic maps from MUSE. Supernova remnants (SNRs) exhibit distinctive emission-line ratios and kinematic signatures, which are apparent in optical spectroscopy. Using optical integral field spectra from the PHANGS–MUSE project, we identified SNRs in 19 nearby galaxies at ~100 pc scales. We used five different optical diagnostics: (1) line ratio maps of [S II]/Hα (2) line ratio maps of [O I]/Hα (3) velocity dispersion map of the gas; and (4) and (5) two line ratio diagnostic diagrams from Baldwin, Phillips & Terlevich (BPT) diagrams to identify and distinguish SNRs from other nebulae. Given that our SNRs are seen in projection against H II regions and diffuse ionized gas, in our line ratio maps we used a novel technique to search for objects with [S II]/Hα or [O I]/Hα in excess of what is expected at fixed Hα surface brightness within photoionized gas. In total, we identified 2233 objects using at least one of our diagnostics, and defined a subsample of 1166 high-confidence SNRs that were detected with at least two diagnostics. The line ratios of these SNRs agree well with the MAPPINGS shock models, and we validate our technique using the well-studied nearby galaxy M83, where all the SNRs we found are also identified in literature catalogs, and we recovered 51% of the known SNRs. The remaining 1067 objects in our sample were detected with only one diagnostic, and we classified them as SNR candidates. We find that ~35% of all our objects overlap with the boundaries of H II regions from literature catalogs, highlighting the importance of using indicators beyond line intensity morphology to select SNRs. We find that the [O I]/Hα line ratio is responsible for selecting the most objects (1368; 61%); however, only half are classified as SNRs, demonstrating how the use of multiple diagnostics is key to increasing our sample size and improving our confidence in our SNR classifications. [ABSTRACT FROM AUTHOR]

Context. In spite of their key role in galaxy evolution and several decades of observational efforts, the census of supernova remnants (SNRs) in our Galaxy remains incomplete. Theoretical predictions based on the local supernova rate estimate the expected number of SNRs in the Galaxy to be ≳1000. By contrast, the number of detected SNRs amounts to about 300. High-resolution, wide-area radio surveys at low frequencies are ideal tools with which to find missing SNRs, given the prominence of these sources at low radio frequencies. Aims. We aim to find missing SNRs using proprietary data from the LOFAR Two-Metre Sky Survey (LoTSS) at 144 MHz. Methods. We used LoTSS total intensity maps of two Galactic regions, one with 39° < l < 66° and |b| < 2.5°, and the other with 145° < l < 150° and |b| < 3°, in addition to mid-infrared (MIR) data from the Wide-field Infrared Survey Explorer (WISE) all-sky survey to search for SNR candidates. Results. We report the discovery of 14 new SNR candidates selected on the basis of their morphology at 144 MHz and a lack of MIR emission. We also follow up on 24 previously reported SNR candidates, inferring their spectral index between the LoTSS frequency (144 MHz) and the frequency at which they were reported. We confirm that 6 of these 24 sources have a non-thermal spectral index, whereas another 4 have a thermal index and are thus rejected as SNR candidates; our study is inconclusive regarding the remaining 14 sources. The majority of the new SNR candidates are small in angular size (<20') and have low surface brightness at 1 GHz (≲10−21 W m−2 Hz−1 sr−1). Additionally, most of them are located in a Galactic region with 39° < l < 60° and |b| < 2.5°. Conclusions. The high resolution and sensitivity of LoTSS observations has resulted in the detection of 14 new SNR candidates. In order to unambiguously confirm the SNR nature of these candidates, follow-up X-ray observations are required with facilities such as eROSITA. [ABSTRACT FROM AUTHOR]

Context. Energy and momentum feedback from stars is a key element in models of galaxy formation and interstellar medium (ISM) dynamics, but resolving the relevant length scales in order to directly include this feedback remains beyond the reach of current-generation simulations. Aims. We aim to constrain the energy feedback of winds, photoionisation, and supernovae (SNe) from massive stars. Methods. We measure the thermal and kinetic energy imparted to the ISM on various length scales, which we calculate from high-resolution 1D radiation-hydrodynamics simulations. Our grid of simulations covers a broad range of densities, metallicities, and state-of-the-art evolutionary models of single and binary stars. Results. A single star or binary system can carve a cavity of tens of parsecs (pc) in size into the surrounding medium. During the pre-SN phase, post-main sequence stellar winds and photoionisation dominate. While SN explosions dominate the total energy budget, the pre-SN feedback is of great importance by reducing the circumstellar gas density and delaying the onset of radiative losses in the SN remnant. Contrary to expectations, the metallicity dependence of the stellar wind has little effect on the cumulative energy imparted by feedback to the ISM; the only requirement is the existence of a sufficient level of pre-SN radiative and mechanical feedback. The ambient medium density determines how much and when feedback energy reaches distances of ≳10–20 pc and affects the division between kinetic and thermal feedback. Conclusions. Our results can be used as a subgrid model for feedback in large-scale simulations of galaxies. The results reinforce that the uncertain mapping of stellar evolution sequences to SN explosion energy is very important for determining the overall feedback energy from a stellar population. [ABSTRACT FROM AUTHOR]

Aims. G321.3–3.9 was first identified as a partial shell at radio frequencies a few decades ago. Although it continued to be observed, no additional studies were undertaken until recently. Methods. In this paper, we present results from a large selection of radio and X-ray data that cover the position of G321.3–3.9. We confirmed G321.3–3.9 as a new supernova remnant (SNR) using data collected by several radio surveys, spanning a frequency range from 200 to 2300 MHz. Stacked eROSITA data from four consecutive all-sky surveys (eRASS:4) provide spectro-imaging information in the energy band 0.2–8.0 keV. Results. G321.3–3.9 has an elliptical shape with major and minor axes of approximately 1.°7 × 1.°1. From CHIPASS and S-PASS data, we calculate a spectral index α = −0.8 ± 0.2, consistent with synchrotron emission from an expanding shell in the radiative phase. The eROSITA data show an X-ray diffuse structure filling almost the entire radio shell. Based on our spectral analysis, we found the temperature to be approximately 0.6 keV and the column absorption density about 1021 cm−2. Comparing this absorption density to optical extinction maps, we estimated the distance to fall within the range of (1.0–1.7) kpc, considering the 1σ uncertainty range. [ABSTRACT FROM AUTHOR]

Recent measurements of the cosmic-ray electron plus positron spectrum in several experiments have confirmed the presence of a break at ∼1 TeV. The origin of the break is still not clearly understood. In this work, we explored different possibilities for the origin, which include an electron source spectrum with a broken power law, a power law with an exponential or super-exponential cutoff, and the absence of potential nearby cosmic-ray sources. Based on the observed electron plus positron data from the DAMPE and the H.E.S.S experiments, and considering supernova remnants as the main sources of cosmic rays in the Galaxy, we find statistical evidence in favor of the scenario with a broken power-law source spectrum, with the best-fit source parameters obtained as Γ = 2.39 for the source spectral index, E0 ≈ 1.6 TeV for the break energy, and f = 1.59 × 1048 ergs for the amount of supernova kinetic energy injected into cosmic-ray electrons. This power-law break in the spectrum has been predicted for electrons confined inside supernova remnants after acceleration via diffusive shock acceleration process, and also indicated by the multi-wavelength study of supernova remnants. All of this evidence shows that the observed spectral break provides a strong indication of a direct link between cosmic-ray electrons and their sources. Our findings further show that electrons must undergo spectral changes while escaping the source region in order to reconcile the difference between the spectral index of electrons observed inside supernova remnants and that obtained from Galactic cosmic-ray propagation studies. [ABSTRACT FROM AUTHOR]

JWST /NIRCam obtained high angular resolution (0.05–0.1 arcsec), deep near-infrared 1–5  |$\mu$| m imaging of Supernova (SN) 1987A taken 35 yr after the explosion. In the NIRCam images, we identify: (1) faint H2 crescents, which are emissions located between the ejecta and the equatorial ring, (2) a bar, which is a substructure of the ejecta, and (3) the bright 3–5  |$\mu$| m continuum emission exterior to the equatorial ring. The emission of the remnant in the NIRCam 1–2.3  |$\mu$| m images is mostly due to line emission, which is mostly emitted in the ejecta and in the hotspots within the equatorial ring. In contrast, the NIRCam 3–5  |$\mu$| m images are dominated by continuum emission. In the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. In contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. Dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. This shows that dust cooling and destruction time-scales are shorter than the synchrotron cooling time-scale, and the time-scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time-scale. With the advent of high sensitivity and high angular resolution images provided by JWST /NIRCam, our observations of SN 1987A demonstrate that NIRCam opens up a window to study particle-acceleration and shock physics in unprecedented details, probed by near-infrared synchrotron emission, building a precise picture of how an SN evolves. [ABSTRACT FROM AUTHOR]

The supernova remnant (SNR) IC 443 is one of the best-studied Galactic SNRs at many wavelengths. It is interacting with a very complex environment, including the SNR G189.6 + 3.3 and H ii regions. In this paper, we report on observations of IC 443 and G189.6 + 3.3 using 1.5- and 1-m telescopes to better understand the nature of these SNRs in the optical band. We obtain H |$\alpha$| images showing both filamentary and diffuse structures, and long-slit spectra from many locations, with Balmer and forbidden lines detected for IC 443 and G189.6 + 3.3. The [S  ii ]/ H |$\alpha$| ratios confirm the SNR nature of G189.6 + 3.3. The ranges of our estimated electron density and pre-shock cloud density clearly indicate the complex structure surrounding IC 443 and G189.6 + 3.3. We also investigate the archival H  i data and newly find some shell-like distributions of H i that are possibly associated with G189.6 |$+$| 3.3. [ABSTRACT FROM AUTHOR]

Heating of charged particles via collisionless shocks, while ubiquitous in the universe, is an intriguing yet puzzling plasma phenomenon. One outstanding question is how electrons and ions approach an equilibrium after they were heated to different immediate-postshock temperatures. In order to fill the significant lack of observational information of the downstream temperature-relaxation process, we observe a thermal-dominant X-ray filament in the northwest of SN 1006 with Chandra. We divide this region into four layers with a thickness of |$15^{\prime \prime }$| or |$0.16\:$| pc each, and fit each spectrum by a non-equilibrium ionization collisional plasma model. The electron temperature was found to increase toward downstream from 0.52–0.62 to 0.82– |$0.95\:$| keV on a length scale of |$60^{\prime \prime }$| (or |$0.64\:$| pc). This electron temperature is lower than thermal relaxation processes via Coulomb scattering, requiring some other effects such as plasma mixture due to turbulence and/or projection effects, etc. which we hope will be resolved with future X-ray calorimeter missions such as XRISM and Athena. [ABSTRACT FROM AUTHOR]

Suzaku X-ray observations of the Type Ia supernova remnant (SNR) 3C 397 discovered exceptionally high mass ratios of Mn/Fe, Ni/Fe, and Cr/Fe, consistent with a near M Ch progenitor white dwarf (WD). The Suzaku observations have established 3C 397 as our best candidate for a near- M Ch SNR Ia, and opened the way to address additional outstanding questions about the origin and explosion mechanism of these transients. In particular, subsequent XMM–Newton observations revealed an unusually clumpy distribution of iron group elemental (IGE) abundances within the ejecta of 3C 397. In this paper, we undertake a suite of two-dimensional hydrodynamical models, varying both the explosion mechanism – either deflagration-to-detonation (DDT), or pure deflagration – WD progenitors, and WD progenitor metallicity, and analyse their detailed nucleosynthetic abundances and associated clumping. We find that pure deflagrations naturally give rise to clumpy distributions of neutronized species concentrated towards the outer limb of the remnant and confirm DDTs have smoothly structured ejecta with a central concentration of neutronization. Our findings indicate that 3C 397 was most likely a pure deflagration of a high central density WD. We discuss a range of implications of these findings for the broader SN Ia progenitor problem. [ABSTRACT FROM AUTHOR]

Context. Supernova remnants (SNRs) are likely to be significant sources of cosmic rays up to the knee of the local cosmic-ray (CR) spectrum. They produce gamma rays in the very-high-energy (VHE) (E > 0.1 TeV) range mainly via two mechanisms: hadronic interactions of accelerated protons with the interstellar medium and leptonic interactions of accelerated electrons with soft photons. Observations with current instruments have lead to the detection of about a dozen SNRs emitting VHE gamma rays and future instruments should significantly increase this number. Yet, the details of particle acceleration at SNRs and of the mechanisms producing VHE gamma-rays at SNRs remain poorly understood. Aims. We aim to study the population of SNRs detected in the TeV range and its properties and confront it to simulated samples in order to address fundamental questions concerning particle acceleration at SNR shocks. Such questions concern the spectrum of accelerated particles, the efficiency of particle acceleration, and the gamma-ray emission being dominated by hadronic or leptonic interactions. Methods. By means of Monte Carlo methods, we simulated the population of SNRs in the gamma-ray domain and confronted our simulations to the catalogue of sources from the High Energy Stereoscopic System (H.E.S.S.) Galactic Plane Survey (HGPS). Results. We systematically explored the parameter space defined in our model, including for example, the slope of accelerated particles α, the electron-to-proton ratio Kep, and the efficiency of particle acceleration ξ. In particular, we found possible sets of parameters for which ≳90% of Monte Carlo realisations are found to be in agreement with the HGPS. These parameters are typically found at 4.2 ≳ α ≳ 4.1, 10−5 ≲ Kep ≲ 10−4.5, and 0.03 ≲ ξ ≲ 0.1. We are able to strongly argue against some regions of the parameter space describing the population of Galactic SNRs in the TeV range, such as α ≲ 4.05, α ≳ 4.35, or Kep ≳ 10−3. Conclusions. Our model is so far able to explain the SNR population of the HGPS. Our approach, when confronted with the results of future systematic surveys, such as the Cherenkov Telescope Array Observatory, will help remove degeneracy from the solutions and to better understand particle acceleration at SNR shocks in the Galaxy. [ABSTRACT FROM AUTHOR]

Core-collapse (CC) supernova remnants (SNRs) are the nebular leftovers of defunct massive stars that died during a supernova explosion, mostly while undergoing the red supergiant phase of their evolution. The morphology and emission properties of those remnants are a function of the distribution of circumstellar material at the moment of the supernova, as well as the intrinsic properties of the explosion and those of the ambient medium. By means of 2.5-dimensional (2.5D) numerical magneto-hydrodynamic (MHD) simulations, we modelled the long-term evolution of SNRs generated by runaway rotating massive stars moving into a magnetised interstellar medium (ISM). Radiative transfer calculations reveal that the projected non-thermal emission of SNRs decreases over time, namely: older remnants are fainter than younger ones. Older (80 kyr) SNRs whose progenitors were moving with a space velocity corresponding to a Mach number of M = 1 (v⋆ = 20 km s−1) in the Galactic plane of the interstellar medium (nISM = 1 cm−3) are brighter in synchrotron than when moving with a Mach number of M = 2 (v⋆ = 40 km s−1). We show that runaway red supergiant progenitors first induce an asymmetric non-thermal 1.4 GHz barrel-like synchrotron SNRs (at the age of about 8 kyr), before further evolving to adopt a Cygnus-loop-like shape (at about 80 kyr). It is conjectured that a significative fraction of SNRs are currently in this bilateral-to-Cygnus loop evolutionary sequence. Therefore, this population should be taken into account with repect to interpreting the data as part of the forthcoming Cherenkov Telescope Array (CTA) observatory. [ABSTRACT FROM AUTHOR]

Aims. Recent simulations have shown that asymmetries in the ejecta distribution of supernova remnants (SNRs) may be a reflection of asymmetries left over from the initial supernova explosion. Thus, SNR studies provide a vital means for testing and constraining model predictions in relation to the distribution of heavy elements, which are key to improving our understanding of the explosion mechanisms in Type Ia supernovae. Methods. The use of a novel blind source separation method applied to the megasecond X-ray observations of the historic Kepler and Tycho supernova remnants has revealed maps of the ejecta distribution. These maps are endowed with an unprecedented level of detail and clear separations from the continuum emission. Our method also provides a three-dimensional (3D) view of the ejecta by individually disentangling red- and blueshifted spectral components associated with images of the Si, S, Ar, Ca, and Fe emission. This approach provides insights into the morphology of the ejecta distribution in those two remnants. Results. Those mappings have allowed us to thoroughly investigate the asymmetries in the intermediate-mass elements and Fe distribution in two Type Ia supernova remnants. We also compared the results with the core-collapse Cassiopeia A remnant, which we had studied previously. The images obtained confirm, as expected for Type Ia SNRs, that the Fe distribution is mostly closer to the core than that of intermediate-mass elements. They also highlight peculiar features in the ejecta distribution, such as the Fe-rich southeastern knot in Tycho. [ABSTRACT FROM AUTHOR]

Mixed-morphology supernova remnants (MMSNRs) are characterized by a shell-like morphology in the radio and centrally peaked thermal emission in the X-ray band. The nature of this peculiar class of supernova remnants (SNRs) remains a controversial issue. In this work, by pairing the predictions of stellar evolution theory with two-dimensional hydrodynamic simulations, we show that the mixed morphology properties of an SNR can arise by the interaction of the SNR with the circumstellar medium shaped by a red supergiant progenitor star, embedded in a dense environment. As a study case, we model the circumstellar medium formation and the subsequent interaction of the SNR with it of a |$15~\rm {\rm M}_{\odot }$| progenitor star. The reflected shock, formed by the collision of the SNR with the density walls of the surrounding circumstellar cavity, accumulates and re-shocks the supernova ejecta at the centre of the remnant, increasing its temperature so that the gas becomes X-ray bright. Such a formation mechanism may naturally explain the nature of MMSNRs resulted from Type II supernovae without the demand of additional physical mechanisms and/or ambient medium inhomogeneities. We discuss alternative evolutionary paths that potentially could be ascribed for the MMSNR formation within the framework of the reflected shock model. [ABSTRACT FROM AUTHOR]

We searched for OB-runaway stars inside supernova remnants (SNRs) as a pre-supernova binary companion. As the majority of massive stars are found in close binary systems, a runaway star ejected by the orbital energy after the supernova (SN) is expected to be found. Considering a binary mass fraction, q = 0.25−1.0, the runaway star is likely to have an OB spectral type. We selected 12 SNRs at Galactic longitudes 109°−189°. Using Gaia astrometry, we selected stars having consistent distances with those of the SNRs and showing a peculiar proper motion directed away from the central region of the SNRs. We also determined the radial distribution of the extinction towards the SNRs and estimated the spectral types of the OB-runaway candidates through Gaia and Two Micron All Sky Survey photometry. We found two candidates among 12 SNRs. By spectroscopic observations, Gaia DR3 195632152560621440 inside SNR G166.0 + 4.3 was found to be an evolved A3 type star that cannot be the pre-SN binary companion to the progenitor. Gaia DR3 513927750767375872 inside SNR HB 3 is the only OB-runaway candidate (2D space velocity of 33.3 ± 3.3 km s−1). Based on photometric study, the star can be an early B-type main-sequence star with a slightly higher extinction relative to the SNR; however, it might instead be an evolved A-type star at the same distance. The other 11 SNRs do not host an OB-runaway star within their central regions. Although the runaway search was performed in a large interval of distance and extinction, we also estimated distances to the SNRs. [ABSTRACT FROM AUTHOR]

We present the description and initial results of the TRAPUM (TRAnsients And PUlsars with MeerKAT) search for pulsars associated with supernova remnants (SNRs), pulsar wind nebulae, and unidentified TeV emission. The list of sources to be targeted includes a large number of well-known candidate pulsar locations but also new candidate SNRs identified using a range of criteria. Using the 64-dish MeerKAT radio telescope, we use an interferometric beamforming technique to tile the potential pulsar locations with coherent beams which we search for radio pulsations, above a signal-to-noise of 9, down to an average flux density upper limit of 30  μ Jy. This limit is target-dependent due to the contribution of the sky and nebula to the system temperature. Coherent beams are arranged to overlap at their 50 per cent power radius, so the sensitivity to pulsars is not degraded by more than this amount, though realistically averages around 65 per cent if every location in the beam is considered. We report the discovery of two new pulsars; PSR J1831−0941 is an adolescent pulsar likely to be the plerionic engine of the candidate PWN G20.0+0.0, and PSR J1818−1502 appears to be an old and faint pulsar that we serendipitously discovered near the centre of a SNR already hosting a compact central object. The survey holds importance for better understanding of neutron star birth rates and the energetics of young pulsars. [ABSTRACT FROM AUTHOR]

The sensitivity of the MeerKAT radio interferometer is an opportunity to probe deeper into the population of rare and faint extragalactic pulsars. The TRAPUM (TRAnsients and PUlsars with MeerKAT) collaboration has conducted a radio-domain search for accelerated pulsars and transients in the Small Magellanic Cloud (SMC). This partially targeted survey, performed at L band (856–1712 MHz) with the core array of the MeerKAT telescope in 2-h integrations, is twice as sensitive as the latest SMC radio pulsar survey. We report the discovery of seven new SMC pulsars, doubling this galaxy's radio pulsar population and increasing the total extragalactic population by nearly a quarter. We also carried out a search for accelerated millisecond pulsars in the SMC globular cluster NGC 121 using the full array of MeerKAT. This improved the previous upper limit on pulsed radio emission from this cluster by a factor of 6. Our discoveries reveal the first radio pulsar-PWN systems in the SMC, with only one such system previously known outside our Galaxy (the 'Crab pulsar twin' in the Large Magellanic Cloud, PSR J0540−6919). We associate the 59 ms pulsar discovery PSR J0040−7337, now the fastest spinning radio pulsar in the SMC, with the bow-shock Pulsar Wind Nebula (PWN) of supernova remnant DEM S5. We also present a new young pulsar with a 79 ms period, PSR J0048−7317, in a PWN recently discovered in a MeerKAT radio continuum image. Using the multibeam capability of MeerKAT, we localized our pulsar discoveries, and two previous Murriyang discoveries, to a positional uncertainty of a few arcseconds. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae (CCSNe) are considered the primary magnetar formation channel, with 15 magnetars associated with supernova remnants (SNRs). A large fraction of these should occur in massive stellar binaries that are disrupted by the explosion, meaning that |$\sim 45~{{\ \rm per\ cent}}$| of magnetars should be nearby high-velocity stars. Here, we conduct a multiwavelength search for unbound stars, magnetar binaries, and SNR shells using public optical (uvgrizy bands), infrared (J, H, K , and Ks bands), and radio (888 MHz, 1.4 GHz, and 3 GHz) catalogues. We use Monte Carlo analyses of candidates to estimate the probability of association with a given magnetar based on their proximity, distance, proper motion, and magnitude. In addition to recovering a proposed magnetar binary, a proposed unbound binary, and 13 of 15 magnetar SNRs, we identify two new candidate unbound systems: an OB star from the Gaia catalogue we associate with SGR J1822.3−1606, and an X-ray pulsar we associate with 3XMM J185246.6 + 003317. Using a Markov Chain Monte Carlo simulation that assumes all magnetars descend from CCSNe, we constrain the fraction of magnetars with unbound companions to |$5\lesssim f_u \lesssim 24~{{\ \rm per\ cent}}$|⁠ , which disagrees with neutron star population synthesis results. Alternate formation channels are unlikely to wholly account for the lack of unbound binaries as this would require |$31\lesssim f_{nc} \lesssim 66~{{\ \rm per\ cent}}$| of magnetars to descend from such channels. Our results support a high fraction (⁠|$48\lesssim f_m \lesssim 86~{{\ \rm per\ cent}}$|⁠) of pre-CCSN mergers, which can amplify fossil magnetic fields to preferentially form magnetars. [ABSTRACT FROM AUTHOR]

Ion Weibel instability is considered to be the dominant physics for the dissipation in high-Mach number astrophysical shocks such as supernova remnant shocks and gamma-ray burst shocks. We study the instability dependence on various parameters using theory and particle-in-cell simulations. We demonstrate that electron physics determines the saturation level of the Weibel-generated magnetic field, even though the instability is driven by the ions. We discuss the application to astrophysical and laboratory laser experiment environments to clarify the roles of the ion Weibel instability. We develop a model for the isotropization length-scale in Weibel-mediated shocks and compare its value to other characteristic length-scales of each system. We find that electron heating to near equipartition is crucial for the formation of ultrarelativistic Weibel-mediated shocks. On the other hand, our results imply that non-relativistic shocks in the typical interstellar medium are not purely mediated by the Weibel instability. [ABSTRACT FROM AUTHOR]

While 30 Dor C is a unique superbubble in the Large Magellanic Cloud for its luminous non-thermal X-ray emission, the thermal X-ray emission it emanates has not yet been thoroughly investigated and well constrained. Based on the separate ∼1 Ms deep XMM–Newton and Chandra observations, we report the discovery of the thermally emitting plasma in some portions of the western half of 30 Dor C. The thermal emission can be reproduced by a collisional-ionization-equilibrium plasma model with an average electron temperature of ∼0.4 keV. We find a significant overabundance of the intermediate-mass elements such as O, Ne, Mg, and Si, which may be indicative of a recent supernova explosion in 30 Dor C. Dynamical properties in combination with the information of the OB association LH 90 suggest that the internal post-main-sequence stars dominate the power of the superbubble and blow it out in the past ∼1 Myr. [ABSTRACT FROM AUTHOR]

Based on the 13.7 yr Fermi-LAT data, Yeung, Bamba, and Sano (2023 , PASJ, 75, 384) claimed detection of two γ-ray sources (namely Src-NE and Src-NW) associated with the supernova remnant (SNR) G298.6−0.0, and interpreted it as an old GeV SNR interacting with molecular clouds (MCs). In this follow-up study, we refine the flux measurements below 2 GeV with Fermi-LAT event types of better angular reconstruction. Then, we report our γ-ray spectral fittings and cosmic-ray phenomenology in a hadronic scenario, considering both the shell and MC regions of SNR G298.6−0.0. We confirm that the γ-ray spectra of both Src-NE and Src-NW exhibit spectral breaks, at |$1.50_{-0.50}^{+0.60}$| and |$0.68_{-0.11}^{+0.32}\:$| GeV, respectively. Src-NW has a harder broad-band photon index than Src-NE, suggesting an appreciable difference between the physical separations of their respective emission sites from SNR G298.6−0.0. The cosmic-ray spectrum responsible for Src-NE starts with a minimum energy |$E_\mathrm{CR,min}=1.38_{-0.16}^{+0.47}\:$| GeV, and has a proton index |$\Gamma _\mathrm{CR}=2.57_{-0.21}^{+0.18}$| below the exponential cutoff energy |$E_\mathrm{CR,max}=240_{-150}^{+240}\:$| GeV. Accordingly, we argue that Src-NE is dominated by the SNR shell, while only a minor portion of lower-energy emission is contributed by the MCs interacting with the SNR. The cosmic-ray population for Src-NW starts at a higher energy such that the E CR, min ratio of Src-NW to Src-NE is ≳2. The high E CR, min, as well as the high cosmic-ray energy density required (∼26 eV cm−3), supports the interpretation that Src-NW is predominantly the γ-ray emission from the farther MCs being bombarded by protons that had earlier escaped from SNR G298.6−0.0. By comparing the high-energy features of G298.6−0.0 with those of analogical SNRs, especially SNR W 28 and SNR W 44, we further constrain the age of SNR G298.6−0.0 to be 10–30 kyr, under the assumption of a purely hadronic scenario. [ABSTRACT FROM AUTHOR]

The remnant of the historical supernova 1181 is claimed to be associated with a white dwarf merger remnant J005311. The supernova remnant (SNR) shock, and a termination shock expected to be formed by the intense wind of J005311, are potential sites for radio emission via synchrotron emission from shock-accelerated electrons. In this paper, we estimate the radio emission from these two shocks, and find the peak radio flux to be 0.1–10 mJy (at 0.01–1 GHz) in the outer SNR shock and 0.01–0.1 mJy (at 1–10 GHz) in the inner termination shock. We also search for radio emission from this source in the archival data of the Karl G. Jansky Very Large Array (VLA) Sky Survey at 3 GHz, the NRAO VLA Sky Survey at 1.4 GHz and the Canadian Galactic Plane Survey at 408 MHz, finding no significant detection. While targeted observations with higher sensitivity are desired, we particularly encourage those at higher frequency and angular resolution to probe the inner termination shock and its evolution. [ABSTRACT FROM AUTHOR]

A thorough inspection of known Galactic supernova remnants (SNRs) along the Galactic plane with SRG/eROSITA yielded the detection of the X-ray counterpart of the SNR G279.0+01.1. The SNR is located just 1.5° above the Galactic plane. Its X-ray emission emerges as an incomplete, partial shell of ~3° angular extension. It is strongly correlated to the fragmented shell-type morphology of its radio continuum emission. The X-ray spatial morphology of the SNR seems to be linked to the presence of dust clouds in the surroundings. The majority of its X-ray emission is soft (exhibiting strong O, Ne, and Mg lines), and it occurs in a narrow range of energies between 0.3 and 1.5 keV. Above 2.0 keV the remnant remains undetected. The remnant's X-ray spectrum is purely of a thermal nature. Constraining the X-ray absorption column to values which are consistent with optical extinction data from the remnant's location favors nonequilibrium over equilibrium models. A nonequilibrium two-temperature plasma model of kT ~ 0.3 keV and kT ~ 0.6 keV, as well as an absorption column density of NH ~ 0.3 cm−2 describe the spectrum of the entire remnant well. Significant temperature variations across the remnant have been detected. Employing 14.5 yr of Fermi-LAT data, we carried out a comprehensive study of the extended giga-electronvolt source 4FGL J1000.0-5312e. By refining and properly modeling the giga-electronvolt excess originating from the location of the remnant, we conclude that the emission is likely related to the remnant itself rather than being colocated by chance. The remnant's properties as determined by the X-ray spectra are consistent with the ~2.5 kpc distance estimates from the literature, which implies a source diameter of ~140 pc and an old age of >7 × 105 yr. However, if the source is associated with any of the pulsars previously considered to be associated with the SNR, then the updated nearby pulsar distance estimates from the YMW16 electron density model rather place the SNR at a distance of ~0.4 kpc. This would correspond to a ~20 pc linear size and a younger age of 104− < 7 × 105 yr, which would be more in line with the nonequilibrium state of the plasma. [ABSTRACT FROM AUTHOR]

Context. Supernovae remnants (SNRs) represent a major source of feedback from stars on the interstellar medium of galaxies. During the latest stage of supernova explosions (which lasts 10–100 kyr), shock waves produced by the initial blast modify the chemistry of gas and dust, inject kinetic energy in the surroundings, and may alter star formation characteristics. Simultaneously, γ-ray emission is generated by the interaction between the ambient medium and cosmic rays, in particular those locally accelerated in the early stages of the explosion. Aims. We aim to estimate the total molecular mass, local density, and total column density of H2 and the temperature structure in a shocked clump interacting with the supernova remnant IC443 located in a region where cosmic rays interact with the interstellar medium. Measuring the mass of the dense and neutral component of the medium is a prerequisite to understanding the chemistry, energetics, and GeV to TeV γ-ray emission. Methods. Assuming that the emission of H2 pure rotational lines is produced by a collection of gas layers with variable temperature, we compared Spitzer/IRS emission maps for the ν = 0–0 S(0) to S(7) lines with a thermal admixture model. Our description is based on a power-law distribution of thermalized components with temperatures varying between Tmin = 25 K and Tmax = 1500 K. Results. Our thermal admixture model allows the level populations of H2 to be described by a power-law distribution dN = ΛT−ΓdT, with Γ ~ 2.2−4.7. We measured a total mass MH2 = 220−80+110M⊙ across the Spitzer/IRS field of observations. Conclusions. Our analysis shows that an estimate of the cold molecular gas temperature is paramount to accurately constraining the H2 mass, although the mass remains affected by significant uncertainties due to the assumptions on the gas temperature distribution. [ABSTRACT FROM AUTHOR]

In this study, we use MUSE Integral Field Spectroscopy (IFS), along with multiline diagnostics, for the optical identification of supernova remnants (SNRs) in the galaxy NGC 7793. We find in total 238 SNR candidates, 225 of them new identifications, increasing significantly the number of known SNRs in this galaxy. The velocity dispersion of the candidate SNRs was calculated, giving a mean value of |$\rm 27\, km\, s^{-1}$|⁠. We construct the H  |$\rm {\alpha }$|⁠ , [S  ii ], [O  iii ], and [S  ii ]–H  |$\rm {\alpha }$| luminosity functions, and for the first time, the [N  ii ], [N  iI ]–H  |$\rm {\alpha }$|⁠ , [N  ii ]–[S  ii ], [O  iii ]–[S  ii ], and [O  iii ]–[N  ii ] luminosity functions of the candidate SNRs. Shock models, along with the observed multiline information were used, in order to estimate shock velocities. The |$\rm \sim 65{{\ \rm per\ cent}}$| of the SNRs present velocities < 300  |$\rm km\, s^{-1}$|⁠. There is a clear correlation between shock velocity and [O  iii ]/H  |$\rm {\beta }$| ratio, and a less clear but still evident correlation in the relation between shock velocity and the [S  ii ]/H  |$\rm {\alpha }$|⁠ , [N  ii ]/H  |$\rm {\alpha }$| ratios. We also use the [S  ii ]6716/31 ratio of the SNR candidates to calculate their post-shock density, assuming different temperatures. The median value of the density of our sample is |$\rm \sim 80\, cm^{-3}$|⁠ , for a temperature of |$\rm T = 10^4\, K$|⁠. No correlation between shock velocity and density, or density and SNRs with [S  ii ]/H  |$\rm {\alpha }$| > 0.4 and [S  ii ]/H  |$\rm {\alpha }$| < 0.4 is observed. [ABSTRACT FROM AUTHOR]

We present a study of the nearby low-metallicity dwarf galaxy IC 1613, focusing on the search for massive stars and related feedback processes, as well as for faint supernova remnants (SNR) in late stages of evolution. We obtained the deepest images of IC 1613 in the narrow-band H α, He  ii and [S  ii ] emission lines and new long-slit spectroscopy observations using several facilities (6-m BTA, 2.5m SAI MSU, and 150RTT telescopes), in combination with the multiwavelength archival data from MUSE/VLT, VLA, XMM–Newton , and Swift /XRT. Our deep narrow-band photometry identifies several faint shells in the galaxy, and we further investigate their physical characteristics with the new long-slit spectroscopy observations and the archival multiwavelength data. Based on energy balance calculations and assumptions about their possible nature, we propose that one of the shells is a possible remnant of a supernova explosion. We study five out of eight Wolf–Rayet (WR) star candidates previously published for this galaxy using the He  ii emission line mapping, MUSE/VLT archival spectra, and new long-slit spectra. Our analysis discards the considered WR candidates and finds no new ones. We found P Cyg profiles in H α line in two stars, which we classify as Luminous Blue Variable (LBV) star candidates. Overall, the galaxy IC 1613 may have a lower rate of WR star formation than previously suggested. [ABSTRACT FROM AUTHOR]

G352.7−0.1 is a mixed-morphology (MM) supernova remnant (SNR) with multiple radio arcs and has a disputed supernova origin. We conducted a spatially resolved spectroscopic study of the remnant with XMM–Newton X-ray data to investigate its explosion mechanism and explain its morphology. The global X-ray spectra of the SNR can be adequately reproduced using a metal-rich thermal plasma model with a temperature of ∼2 keV and ionization time-scale of ∼3 × 1010 cm−3 s. Through a comparison with various supernova nucleosynthesis models, we found that observed metal properties from Mg to Fe can be better described using core-collapse supernova models, while thermonuclear models fail to explain the observed high Mg/Si ratio. The best-fit supernova model suggests a ∼13 M⊙ progenitor star, consistent with previous estimates using the wind bubble size. We also discussed the possible mechanisms that may lead to SNR G352.7−0.1 being an MMSNR. By dividing the SNR into several regions, we found that the temperature and abundance do not significantly vary with regions, except for a decreased temperature and abundance in a region interacting with molecular clouds. The brightest X-ray emission of the SNR spatially matches with the inner radio structure, suggesting that the centrally filled X-ray morphology results from a projection effect. [ABSTRACT FROM AUTHOR]

We report a detection of GeV γ-ray emission potentially originating from the pulsar wind nebula in CTA 1 by analysing about 15 yr of Fermi Large Area Telescope data. By selecting an energy range from 50 GeV to 1 TeV to remove contamination from the γ-ray pulsar PSR J0007+7303, we have discovered an extended γ-ray source with a test statistic value of ∼44.94 in the region of CTA 1. The obtained flux is measured to be 6.71 ± 2.60 × 10−12 erg cm−2 s−1 with a spectral index of 1.61 ± 0.36, which allows for a smooth connection with the flux in the TeV band. CTA 1 is also considered to be associated with 1LHAASO J0007+7303u, which is an ultra-high-energy source listed in the recently published catalogue of the Large High Altitude Air Shower Observatory. We assume that the radiation originates from the pulsar wind nebula and that its multiwavelength spectral energy distribution can be explained well with a time-dependent one-zone model. [ABSTRACT FROM AUTHOR]

Context. The supernova remnant (SNR) G288.8–6.3 was recently discovered as a faint radio shell at high Galactic latitude using observations with the Australian Square Kilometre Array Pathfinder (ASKAP) in the Evolutionary Map of the Universe (EMU) survey. Aims. We performed the first detailed investigation of the γ-ray emission from the G288.8–6.3 region, aiming to characterise the high-energy emission in the GeV regime from the newly discovered SNR, dubbed Ancora. Methods. Fifteen years of Fermi-Large Area Telescope (LAT) data were analysed at energies between 400 MeV and 1 TeV, and the excess seen in the region was modelled using different spatial and spectral models. Results. We detect spatially extended γ-ray emission coinciding with the radio SNR, with detection significance up to 8.8 σ. A radial disk spatial model in combination with a power-law spectral model with an energy flux of (4.80 ± 0.91) × 10−6 MeV cm−2 s−1, with the spectrum extending up to around 5 GeV was found to be the preferred model. Morphologically, hotspots seen above 1 GeV are well correlated with the bright western part of the radio shell. The emission is more likely to be of leptonic origin, given the estimated gas density in the region and the estimated distance and age of the SNR, but a hadronic scenario cannot be ruled out. Conclusions. Ancora is the seventh confirmed SNR detected at high Galactic latitude with Fermi-LAT. The study of this new population of remnants can provide insights into the evolutionary aspects of SNRs and their properties, and further advance efforts of constraining the physics of particle diffusion and escape from SNRs into the Galaxy. [ABSTRACT FROM AUTHOR]

To identify progenitors and investigate evidence of He burning, we searched for decay radiation of freshly synthesized 44Ti in four young nearby thermonuclear supernova remnants: Kepler, SN 1885, G1.9+0.3, and SN 1006, by analysing the up-to-date NuSTAR archival data. No apparent flux excess from the 68 and 78 keV line emissions accompanying decay was detected above the power-law continuum applied for the remnants and the absorbed stray light. By comparing the inferred upper limits of the line flux and the initial 44Ti masses with a wide variety of supernova nucleosynthesis models, we placed constraints on the supernova progenitors. We derived the first NuSTAR line flux upper limit for Kepler and ruled out most of the double-detonation scenarios with a thick He layer under low density. We estimated, for the first time, the upper limit for SN 1885, which is high because of the large distance, yet still remains consistent with the He shell detonation. The new flux and mass limit of G1.9+0.3 derived from a longer total exposure is lower than the results from previous studies and evidently excludes explosive burning of He-rich matter. The relatively advanced age and the large spatial extent of SN 1006 have prevented meaningful constraints. [ABSTRACT FROM AUTHOR]

Recent studies of supernova remnants (SNRs) have revealed that some SNRs exhibit a neutral iron line emission at 6.4 keV. This line has been proposed to originate from the interaction of high-energy particles formed in the SNR shell with the surrounding cold matter. We searched for the neutral iron line emission in the SNR W 49 B. Significant detection of the 6.4 keV line is found in the north-west region, close to the molecular cloud interacting with the SNR shell. In addition, an excess emission at 8–9 keV, in which Kγ, Kδ, and Kϵ lines of He-like iron exist, is also significantly found in the region where the radio shell is not bright. We discuss the origin of the 6.4 keV line and the excess emission at 8–9 keV. [ABSTRACT FROM AUTHOR]

In this paper, we constrain the density of the interstellar medium (ISM) around the hadronic PeVatron candidate, supernova remnant (SNR) G106.3+2.7, based on X-ray and γ-ray observations. The purpose of this investigation is to understand the influence of the gaseous environment on this SNR as a proton PeVatron candidate. By modelling the self-regulated propagation of the cosmic rays (CRs) injected from the SNR, we calculate the γ-ray emission of CRs via the hadronuclear interactions with the molecular cloud and the ISM, and use the measured γ-ray flux to constrain the ISM density around the SNR. Our results support the picture that the SNR is expanding into a low-density (⁠|$\lt 0.05\, {\rm cm}^{-3}$|⁠) cavity, enabling the SNR to be a potential proton PeVatron despite that it is presently not in the very early phase. [ABSTRACT FROM AUTHOR]

The expanding ejecta of supernova remnants (SNRs) are believed to form dust in dense clumps of gas. Before the dust can be expelled into the interstellar medium and contribute to the interstellar dust budget, it has to survive the reverse shock that is generated through the interaction of the preceding supernova blast wave with the surrounding medium. The conditions under which the reverse shock hits the clumps change with remnant age and define the dust survival rate. To study the dust destruction in the SNR Cassiopeia A, we conduct magnetohydrodynamical simulations of the evolution of a supernova blast wave and of the reverse shock. In a second step, we use these evolving conditions to model clumps that are disrupted by the reverse shock at different remnant ages. Finally, we compute the amount of dust that is destroyed by the impact of the reverse shock. We find that most of the dust in the SNR is hit by the reverse shock within the first  350 yr after the SN explosion. While the dust destruction in the first  200 yr is almost complete, we expect greater dust survival rates at later times and almost total survival for clumps that are first impacted at ages beyond 1000 yr. Integrated over the entire evolution of the SNR, the dust mass shows the lowest survival fraction (17 per cent) for the smallest grains (1 nm) and the highest survival fraction (28 per cent) for the largest grains (1000 nm). [ABSTRACT FROM AUTHOR]

We present the results of a sensitive search for high-velocity gas in interstellar absorption lines associated with the Cygnus Loop supernova remnant (SNR). We examine high-resolution high signal-to-noise ratio optical spectra of six stars in the Cygnus Loop region with distances greater than ∼700 pc. All stars show low-velocity Na  i and Ca  ii absorption. However, only one star, HD 198301, exhibits high-velocity Ca  ii absorption components, at velocities of +62, +82, and  +96 km s−1. The distance to this star of ∼870 pc helps to constrain the distance to the receding edge of the Cygnus Loop's expanding shock front. One of our targets, HD 335334, was previously thought to exhibit high positive and high negative velocity interstellar Na  i and Ca  ii absorption. This was one factor leading Fesen et al. to derive a distance to the Cygnus Loop of 725 ± 15 pc. However, we find that HD 335334 is in fact a double-line spectroscopic binary and shows no evidence of high-velocity interstellar absorption. As such, the distance to HD 335334 cannot be used to constrain the distance to the Cygnus Loop. Our detection of Ca  ii absorption approaching 100 km s−1 toward HD 198301 is the first conclusive detection of high-velocity absorption from a low-ionization species associated with the Cygnus Loop SNR. A large jump in the Na  i column density toward BD+31 4218, a star located beyond the northwestern boundary of the Cygnus Loop, helps to constrain the distance to a large molecular cloud complex with which the Cygnus Loop is evidently interacting. [ABSTRACT FROM AUTHOR]

We report on the first detection of optical emission from the shell-type Galactic supernova remnant (SNR) G108.2−0.6. We obtained Hα images and long-slit spectra using the 1.5-m RTT150 telescope to examine the morphological and spectral characteristics of the SNR. We detected several filaments along its north and south regions, which is consistent with its SNR nature. The spectra exhibit [S  ii ]/Hα ratios in the range of 0.4–1.1, indicating emission from shock-heated gas. The oxygen doublet emission lines [O  i ] λλ6300, 6363 detected in the south region also support the indicator of the presence of shocks. We estimate the electron density using the [S  ii ] 6716/6731 ratio ranging from 15 to 1800 cm−3. The spectra show a relatively low shock velocity of V s ∼ 80 km s−1 with the pre-shock cloud density of n c ∼18–57 cm−3. The Hα/Hβ ratios show significant variation across the observed regions with extinction E (B − V) ranging from 0.22 to 1.65. We also analysed the archival H  i data and estimated the kinematic distance to G108.2−0.6 of ∼0.8 kpc and its dynamical age as ∼70 ± 10 kyr. [ABSTRACT FROM AUTHOR]

Supernovae (SNe) explosions are thought to be an important source of dust in galaxies. At the same time strong shocks from SNe are known as an efficient mechanism of dust destruction via thermal and kinetic sputtering. A critically important question of how these two hypotheses of SNe activity control the dust budget in galaxies is still not quite clearly understood. In this paper, we address this question within 3D multifluid hydrodynamical simulations, treating separately the SNe injected dust and the dust pre-existed in ambient interstellar gas. We focus primarily on how the injected and the pre-existing dust is destroyed by shock waves and hot gas in the SN bubble depending on the density of ambient gas. Within our model, we estimate an upper limit of the SN-produced dust mass which can be supplied into interstellar medium. For an SN progenitor mass of 30 M⊙ and the ejected dust mass M d = 1 M⊙, we constrain the dust mass that can be delivered into the ISM as ≥0.13 M⊙, provided that the SN has injected large dust particles with a ≥ 0.1 µm. [ABSTRACT FROM AUTHOR]

With almost 15 yr of data taken by the Large Area Telescope (LAT) onboard the Fermi satellite we discovered an extended source of GeV emission in the region of the very high energy (TeV) source 1LHAASO J1945+2424. This TeV source is more extended than the LAT source. The spectrum of the GeV emission is hard (with a photon spectral index ∼1.5) and connects smoothly with that of the TeV source, indicating a likely common origin. In order to explain the origin of the γ-rays we explore scenarios that are typically used for supernova remnants (SNRs) and pulsar wind nebulae (PWNe). For an SNR with a single particle population, a leptonic particle distribution in the form of a broken power law with a break energy of ∼3.7 TeV explains the spectra well, while in the hadronic scenario a simple power law with a hard spectral index of ∼1.64 is necessary. In the PWN scenario, reasonable parameters are obtained for a source age of 10 kyr and current pulsar spin-down luminosity of ∼1034 erg s−1. [ABSTRACT FROM AUTHOR]

G213.0−0.6 is a faint extended source situated in the anticentre region of the Galactic plane. It has been classified as a shell-type supernova remnant (SNR) based on its shell-like morphology, steep radio continuum spectrum, and high ratio of [S  ii ]/Hα. With new optical emission line data of Hα, [S  ii ], and [N  ii ] recently observed by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, the ratios of [S  ii ]/Hα and [N  ii ]/Hα are re-assessed. The lower values than those previously reported put G213.0−0.6 around the borderline of SNR-H  ii region classification. We decompose the steep-spectrum synchrotron and the flat-spectrum thermal free-free emission in the area of G213.0−0.6 with multi-frequency radio continuum data. G213.0−0.6 is found to show a flat spectrum, in conflict with the properties of a shell-type SNR. Such a result is further confirmed by TT-plots made between the 863-MHz, 1.4-GHz, and 4.8-GHz data. Combining the evidence extracted in both optical and radio continuum, we argue that G213.0−0.6 is possibly not an SNR, but an H  ii region instead. The V LSR pertaining to the Hα filaments places G213.0−0.6 approximately 1.9 kpc away in the Perseus Arm. [ABSTRACT FROM AUTHOR]

Pulsar wind nebulae are a possible final stage of the circumstellar evolution of massive stars, where a fast-rotating, magnetized neutron star produces a powerful wind that interacts with the supernova ejecta. The shape of these so-called plerionic supernova remnants is influenced by the distribution of circumstellar matter at the time of the explosion, itself impacted by the magnetic field of the ambient medium, responsible for the expansion of the circumstellar bubble of the progenitor star. To understand the effects of magnetization on the circumstellar medium and resulting pulsar nebulae, we conduct 2D magnetohydrodynamic simulations. Our models explore the impact of the interstellar medium's (ISM) magnetic field on the morphology of a supernova remnant and pulsar wind nebula that develop in the circumstellar medium of massive star progenitor in the warm phase of the Milky Way's ISM. Our simulations reveal that the jet-like structures formed on both sides perpendicularly to the equatorial plane of the pulsar, creating complex radio synthetic synchrotron emissions. This morphology is characterized by a rectangular-like remnant, which is typical of the circumstellar medium of massive stars in a magnetized medium, along with the appearance of a spinning top structure within the projected rectangle. We suggest that this mechanism may be partially responsible for the complex morphologies observed in pulsar wind nebulae that do not conform to the typical torus/jet or bow shock/tail shapes observed in most cases. [ABSTRACT FROM AUTHOR]

We report the discovery of a faint radio filament near PSR J0538+2817 in the NVSS, CGPS, and the Rapid ASKAP Continuum Survey data. This pulsar is plausibly associated with the supernova that gave rise to the Spaghetti nebula (Simeis 147). The structure is one-sided and appears to be almost aligned (within 17 degrees) with the direction of the pulsar's proper motion, but in contrast to the known cases of pulsar radio tails, it is located ahead of the pulsar. At the same time, this direction is also approximately (within 5 degrees) perpendicular to the axis of the extended non-thermal X-ray emission around the pulsar. No X-ray or optical emission is detected from the filament region, although the end point of the radio filament appears to be adjacent to a filament of Hα emission. We speculate that this structure might represent a filament connecting pulsar wind nebula (PWN) with the ambient interstellar medium filled with relativistic electrons escaping the pulsar nebula, i.e. a radio analogue of X-ray filaments of Guitar and Lighthouse PWNs and filaments of non-thermal radio emission in the Galactic Centre. [ABSTRACT FROM AUTHOR]