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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]

We present new radio continuum images and a source catalogue from the MeerKAT survey in the direction of the Small Magellanic Cloud. The observations, at a central frequency of 1.3 GHz across a bandwidth of 0.8 GHz, encompass a field of view ∼7° × 7° and result in images with resolution of 8 arcsec. The median broad-band Stokes I image Root Mean Squared noise value is ∼11  μ Jy beam−1. The catalogue produced from these images contains 108 330 point sources and 517 compact extended sources. We also describe a UHF (544–1088 MHz) single pointing observation. We report the detection of a new confirmed Supernova Remnant (SNR; MCSNR J0100–7211) with an X-ray magnetar at its centre and 10 new SNR candidates. This is in addition to the detection of 21 previously confirmed SNRs and two previously noted SNR candidates. Our new SNR candidates have typical surface brightness an order of magnitude below those previously known, and on the whole they are larger. The high sensitivity of the MeerKAT survey also enabled us to detect the bright end of the SMC Planetary Nebulae (PNe) sample – point-like radio emission is associated with 38 of 102 optically known PNe, of which 19 are new detections. Lastly, we present the detection of three foreground radio stars amidst 11 circularly polarized sources, and a few examples of morphologically interesting background radio galaxies from which the radio ring galaxy ESO 029–G034 may represent a new type of radio object. [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]

We investigated the ionized and atomic gas kinematics and excitation state in the central region of ongoing star formation of the nearby low-metallicity dwarf galaxy Sextans B. The analysis is based on the new observations performed in the H α emission line with high resolution (R ∼ 16 000) scanning Fabry–Perot interferometer at the 6-m BTA Special Astrophysical Observatory of the Russian Academy of Sciences telescope, and on the long-slit spectral observations at the 9.2-m SALT and 2.5-m Caucasian Mountain Observatory of Sternberg Astronomical Institute of Moscow State University telescopes. Strong non-circular gas motions detected in the studied regions probably resulted from the off-plane gas motions and impact of stellar feedback. We identified six regions of elevated H α velocity dispersion, five of which exhibit asymmetric or two-component H α line profiles. Three of these regions are young (<1.1 Myr) expanding (⁠|$V_\mathrm{exp} \sim 25-50 \, \mbox{km}\, \mbox{s}^{-1}$|⁠) superbubbles. We argue that at least three regions in the galaxy could be supernova remnants. We conclude that supernovae feedback is the dominant source of energy for superbubbles in Sextans B, which is expected for such a low metallicity, although we cannot rule out a strong impact of pre-supernova feedback for one superbubble. [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]

We perform a set of two-dimensional, non-relativistic, hydrodynamics simulations for supernova-like explosions associated with stellar core collapse of rotating massive stars into a system of a black hole and a disc connected by the transfer of matter and angular momentum. Our model of the central engine also includes the contribution of the disc wind. This study is carried out using the open-source hydrodynamic code athena ++ , for which we implement a method to calculate self-gravity for axially symmetric density distributions. We investigate the explosion properties and the 56Ni production of a star with the zero-age main-sequence mass of |$M_\mathrm{ZAMS}=20\, M_\odot$| varying some features of the wind injection. We find a large variety of explosion energy with E expl ranging from ∼0.049 × 1051 to ∼34 × 1051 erg and ejecta mass M ej from 0.58 to 6 M ⊙, which shows a bimodal distribution in high- and low-energy branches. We demonstrate that the resulting outcome of a highly or sub-energetic explosion for a certain stellar structure is mainly determined by the competition between the ram pressure of the injected matter and that of the infalling envelope. In the nucleosynthesis analysis the 56Ni mass produced in our models goes from <0.2  M ⊙ in the sub-energetic explosions to 2.1  M ⊙ in the highly energetic ones. These results are consistent with the observational data of stripped-envelope and high-energy SNe such as broad-lined Type Ic SNe. [ABSTRACT FROM AUTHOR]

We report on our discovery of the radio pulsar, PSR J2016+3711, in supernova remnant (SNR) CTB 87, with a ∼10.8σ significance of pulses, which confirms the compact nature of the X-ray point source in CTB 87. It is the first pulsar discovered in SNRs using Five-hundred-meter Aperture Spherical radio Telescope (FAST). Its integrated radio pulse profile can be well described by a single component, with a width at 50 per cent of the peak flux density of about 28.1○ and an effective width of about 32.2○. The mean flux density at 1.25 GHz is estimated to be about 15.5  |$\mu$| Jy. Combined with the non-detection of the radio pulse at lower frequencies, the radio spectral index of the pulsar is constrained to be ≲2.3. We also present the timing solution based on 28 follow-up FAST observations. Our results reveal a period of 50.81 ms, period derivative of 7.2 × 10−14 s s−1, and dispersion measure of 428 pc cm−3. The strength of the equatorial surface magnetic dipole magnetic field is inferred to be about 1.9 × 1012 G. Using the ephemeris obtained from the radio observations, we searched Fermi -LAT data for gamma-ray pulsations but detected no pulsed signal. We also searched for radio pulses with FAST towards the X-ray counterpart of the gamma-ray binary HESS J1832−093 proximate to SNR G22.7−00.2 but found no signal. [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 activity of at least one repeating fast radio burst (FRB) source is periodically modulated. If this modulation is the result of precession of the rotation axis and throat of an accretion disc around a black hole, driven by a companion that is also the source of accreted mass, then it may be possible to constrain the mass of the black hole. The dynamics is analogous to that of superorbital periods in ordinary mass-transfer binaries in which the accreting object may be a stellar-mass black hole, a neutron star or a white dwarf, but in the FRB source it may be an intermediate-mass black hole. In a semidetached (mass-transferring) binary, the orbital period is nearly proportional to the −1/2 power of the mean density of the mass-losing star and nearly independent of the mass of the primary, but the ratio of precessional to orbital periods scales approximately as the −2/3 power of the mass ratio for small mass ratios (massive accretors). Assuming a value for the secondary's density and identifying the observed modulation period as a disc precession period would determine the mass ratio and the mass of the black hole. This model and magnetar-SNR (supernova remnant) models make distinguishable predictions of the evolution of the rotation measure that may soon be tested in FRB 121102. [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 explore systematically the shocked gas in the first Galactic quadrant of the Milky Way using the United Kingdom Infrared Telescope (UKIRT) Wide-field Infrared Survey for Fe+ (UWIFE). The UWIFE survey is the first imaging survey of the Milky Way in the [Fe  ii ] 1.644 μm emission line and covers the Galactic plane in the first Galactic quadrant (7° < |$\mathit {l}$| < 62°; |$|b| $| ≲ 1 |$_{.}^{\circ }$| 5). We identify 204 extended ionized Fe objects (IFOs) using a combination of a manual and automatic search. Most of the IFOs are detected for the first time in the [Fe  ii ] 1.644 μm line. We present a catalogue of the measured sizes and fluxes of the IFOs and searched for their counterparts by performing positional cross-matching with known sources. We found that IFOs are associated with supernova remnants (25), young stellar objects (100), H  ii regions (33), planetary nebulae (17), and luminous blue variables (4). The statistical and morphological properties are discussed for each of these. [ABSTRACT FROM AUTHOR]

A massive molecular cloud complex represents local gravitational potential that can constrain the vertical distribution of surrounding stars and gas. This pinching effect results in the local corrugation of the scale height of stars and gas which is in addition to the global corrugation of the mid-plane of the disc. For the first time, we report observational evidence for this pinching on the H  i vertical structures in the Galactic region (20° < l < 40°), also called W41–W44 region. The H  i vertical distribution is modelled by a double Gaussian profile that physically represents a narrow dense gas distribution confined to the mid-plane embedded in a wider diffuse H  i. We find that the estimate of the H  i scale height distribution of wider components shows corrugated structures at the locations of molecular complexes, as theoretically predicted in literature. While the narrow component is less affected by the pinching, we found a hint of the disc being disrupted by the active dynamics in the local environment of the complex, for example, supernova explosions. Molecular complexes of mass of several |$10^6 \rm M_{\odot } $|⁠ , associated with the mini-starburst region W43 and the supernova remnant W41 show the strongest evidence for the pinching; here a broad trough, with an average width of ∼400 pc and height ∼300 pc, in the disc thickness of the wider component is prominently visible. Searching for similar effect on the stars as well as in the location of other complexes in the Milky Way and other galaxies will be useful to establish this phenomenon more firmly. [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]

The origin of the diffuse gamma-ray background in the range from hundreds keV to several MeV is not known conclusively. From current models and observations it is believed that, at least partially, this background is formed by blazars and remnants of supernovae (SN) of type Ia in distant galaxies. However, these contributions are not sufficient to reproduce the observed level of the signal. In this work we propose another source which could contribute to this background, namely the jets of active galactic nuclei (AGN). The composition of jets is not known, but there are observational hints that the fraction of positrons there is substantial. Positrons are partially evacuated to the intergalactic medium and partially mix with the circumgalactic medium and annihilate there comparatively quickly. Using the AGN luminosity function, we estimated the positron production rate and the contribution of the positron annihilation to the cosmic background below 511 keV. We also estimated the analogous contribution from positron annihilation within SN Ia remnants in distant galaxies. The contribution of AGNs is estimated to be a factor of 5–10 smaller than the observed background intensity, and the contribution from SNe is yet smaller by one order of magnitude. Nevertheless, the contribution of AGNs appeared to be larger than the contribution of blazars estimated from Swift-BAT and Fermi-LAT observations. The main uncertainty in our model is the fraction of positrons remaining in the circumgalactic medium which makes our estimation an upper limit. [ABSTRACT FROM AUTHOR]

To understand the nature of gas flows in star-forming regions of nearby galaxies, the relationship between the surface brightness values in the H line and the velocity dispersion of ionized gas, known as the "surface brightness–velocity dispersion" diagram, is often used. Based on three-dimensional gas-dynamic calculations, we examined the evolution of synthetic diagrams for supershells formed as a result of multiple supernova explosions in a star cluster located in the galactic disk. Based on the results of a study of changes in the shape and structure of the diagram depending on the gas density, its metallicity, and the disk scale height, it is possible to identify ranges of values in the diagram that are characteristic of young bubbles developing in dense or rarefied gas at large heights above the plane of the disk. We found that the structure of the diagram depends on the age of the supershells and the physical properties of the gas in the disk. For nearby dwarf galaxies, the structure of the observed "surface brightness–velocity dispersion" diagrams can only be explained by describing the dynamics of bubbles formed by multiple SN explosions in small star clusters of different ages. [ABSTRACT FROM AUTHOR]

Synchrotron emission from the shocked regions in supernova remnants provides, through its polarization, crucial details about the magnetic field strength and orientation in these regions. This, in turn, provides information on particle acceleration in these shocks. Due to the rapid losses of the highest-energy relativistic electrons, X-ray polarization measurements allow for investigations of the magnetic field to be carried outvery close to the sites of particle acceleration. Measurements of both the geometry of the field and the levels of turbulence implied by the observed polarization degree thus provide unique insights into the conditions leading to efficient particle acceleration in fast shocks. The Imaging X-ray Polarimetry Explorer (IXPE) has carried out observations of multiple young SNRs, including Cas A, Tycho, SN 1006, and RX J1713.7−3946. In each, significant X-ray polarization detections provide measurements of magnetic field properties that show some common behavior but also considerable differences between these SNRs. Here, we provide a summary of results from IXPE studies of young SNRs, providing comparisons between the observed polarization and the physical properties of the remnants and their environments.

The nearby supernova 1987A was accompanied by a burst of neutrino emission, which indicates that a compact object (a neutron star or black hole) was formed in the explosion. There has been no direct observation of this compact object. In this work, we observe the supernova remnant with JWST spectroscopy, finding narrow infrared emission lines of argon and sulfur. The line emission is spatially unresolved and blueshifted in velocity relative to the supernova rest frame. We interpret the lines as gas illuminated by a source of ionizing photons located close to the center of the expanding ejecta. Photoionization models show that the line ratios are consistent with ionization by a cooling neutron star or a pulsar wind nebula. The velocity shift could be evidence for a neutron star natal kick. [ABSTRACT FROM AUTHOR]

As the reconstruction of the star formation histories (SFHs) of galaxies from spectroscopic data becomes increasingly popular, we explore the best age resolution achievable with stellar population synthesis (SPS) models, relying on different constraints: broad-band colours, absorption indices, a combination of the two, and the full spectrum. We perform idealized experiments on SPS models and show that the minimum resolvable relative duration of a star formation episode (time difference between 10 per cent and 90 per cent of the stellar mass formed divided by the median age) is never better than 0.4, even when using spectra with signal-to-noise ratio (SNR) larger than 100 per Å. Typically, the best relative age resolution ranges between 0.4 and 0.7 over most of the age–metallicity plane, corresponding to minimum bin sizes for SFH sampling between 0.15 and 0.25 dex. This resolution makes the spectroscopic exploration of distant galaxies mandatory in order to reconstruct the early phases of galaxies' SFHs. We show that spectroscopy with |${\rm SNR} \gtrsim 20\,$|  Å−1 is essential for good age resolution. Remarkably, using the full spectrum does not prove significantly more effective than relying on absorption indices, especially at SNR ≲ 20 Å−1. We discuss the physical origins of the age resolution trends as a function of age and metallicity, and identify the presence of maxima in age resolution (i.e. minima in measurable relative time duration) at the characteristic ages that correspond to quick time variations in spectral absorption features. We connect these maxima to bumps commonly observed in reconstructed SFHs. [ABSTRACT FROM AUTHOR]

We present an analysis of the XMM–Newton observation of luminous infrared merging galaxies Arp 302 and a joint re-analysis of its Chandra observation. In particular, we focus on the more significant X-ray emitter of the pair, Arp 302N. Chandra detects significant soft X-ray emission from the hot gas in the star-forming region of Arp 302N spreading up to 12 kpc. We estimate the star formation rate of Arp 302N to be around 1–2 M⊙ yr−1 based on the X-ray luminosity of the star-forming region, similar to previous measurements at longer wavelengths. Chandra and XMM – Newton observations show evidence of a Si  xiii emission line with 86 per cent confidence. Our best-fitting model infers a super-solar silicon abundance in the star-forming region, likely related to the past core-collapse supernovae in this galaxy. Similar silicon overabundance was reported in the circumstellar medium of core-collapse supernova remnants in our Galaxy. We also detect narrow Fe Kα and Fe Kβ (98.6 per cent confidence) emission lines as part of the active galactic nucleus (AGN) emission. Our best-fitting spectral model using mytorus indicates the evidence of a heavily obscured power-law emission with N H > 3 × 1024 cm−2 in addition to a weak, unobscured power-law emission. The scattering fraction of the unobscured power-law emission from Compton-thin materials is 0.7 per cent. All these spectral features suggest evidence of a Seyfert 2-like AGN in Arp 302N. The X-ray measurement of its AGN activity is consistent with the previous Spitzer measurement of the same object. [ABSTRACT FROM AUTHOR]

We report a detailed multi-wavelength study of the supernova remnant G296.5+10.0 using archival data from XMM–Newton and Fermi -LAT complemented with ATCA observations. In the X-ray band, we performed an adaptive smoothing on the double background subtracted images to construct an X-ray mosaic map with six individual observations. Below 2.0 keV, G296.5+10.0 is asymmetrical, with the south-east side of the radio shell brighter than the south-west one. The spatially resolved X-ray spectral study confirms the thermal origin of the plasma, with enhanced metal abundances, probably arising from ejecta material according to the H  i and infrared (⁠|$140~{\mu \rm m}$|⁠) distributions. In the γ-ray band, we analysed 14 years of accumulated Fermi observations below 500 GeV via different fitting processes. To discuss the origin of the γ-ray emission, we compare the GeV results with H  i structures probably associated with the SNR and with the radio spectral indices found at various positions towards the radio shell. Moreover, we identified diverse sources candidates to contribute γ-ray emissions observed. Also, we calculated the lepto-hadronic spectral energy distribution of the remnant for synchrotron, inverse Compton, Bremsstrahlung, and proton–proton processes. The emission at low energies can be explained by electron-synchrotron radiation, with a weak magnetic field of |$B=25\, {\rm \mu G}$|⁠ , while the γ-ray data can be explained by hadronic interactions. Employing the reddening-distance method, we computed a distance of 1.4 kpc for the SNR, implying an age of 14 000 yr. [ABSTRACT FROM AUTHOR]

Estimating precise metallicity of M dwarfs is a well-known difficult problem due to their complex spectra. In this work, we empirically calibrate the metallicity using wide binaries with a F, G, or K dwarf and a M dwarf companion. With 1308 FGK+M wide binaries well observed by LAMOST, we calibrated M dwarf's [Fe/H] by using the Stellar LAbel Machine (SLAM) model, a data-driven method based on support vector regression. The [Fe/H] labels of the training data are from FGK companions in range of [−1,0.5] dex. The T effs are based on APOGEE, spanning [3100, 4400] K. The uncertainties in SLAM estimates of [Fe/H] and T eff are ∼0.15 dex and ∼40 K, respectively, at snri >100, where snri is the signal-to-noise ratio (SNR) at i band of M dwarf spectra. We applied the trained SLAM model to determine the [Fe/H] and T eff for ∼630 000 M dwarfs with low-resolution spectra in LAMOST DR9. Compared to other literature also using FGK+M wide binaries for calibration, our [Fe/H] estimates show no bias but a scatter of ∼0.14–0.18 dex. However, the [Fe/H] compared to APOGEE shows a systematic difference of ∼0.10–0.15 dex with a scatter of ∼0.15–0.20 dex. While the T eff compared to APOGEE has a bias of 3 K with a scatter of 62 K, it is systematically higher by 180 K compared to other calibrations based on the bolometric temperature. Finally, we calculated the ζ index for 1308 M dwarf secondaries and presents a moderate correlation between ζ and [Fe/H]. [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]

We present extensive photometric and spectroscopic observations of the peculiar Type Ia supernova (SN Ia) 2022vqz. It shares many similarities with the SN 2002es-like SNe Ia, such as low luminosity (⁠|$M_{B,\rm max}=-18.11\pm 0.16$| mag) and moderate post-peak decline rate (Δ m 15, B  = 1.33 ± 0.11 mag). The nickel mass synthesized in the explosion is estimated as 0.20 ± 0.04 M⊙ from the bolometric light curve, which is obviously lower than that of normal SNe Ia. SN 2022vqz is also characterized by slowly expanding ejecta, with Si  ii velocities persisting around 7000 km s−1 since 16 d before peak brightness, unique among all known SNe Ia. While all of these properties imply a lower energy thermonuclear explosion that should leave a considerable amount of unburnt materials, the absent signature of unburnt carbon in spectra of SN 2022vqz is puzzling. A prominent early peak is clearly detected in the Asteroid Terrestrial-impact Last Alert System c - and o -band light curves and in the Zwicky Transient Facility gr -band data within days after the explosion. Possible mechanisms for the early peak are discussed, including the sub-Chandrasekhar-mass double-detonation model and interaction of SN ejecta with circumstellar material. We find that both models face some difficulties in replicating all aspects of the observed data. As an alternative, we propose a hybrid C–O–Ne white dwarf as the progenitor of SN 2022vqz; it can simultaneously reconcile the tension between low ejecta velocity and the absence of carbon. We further discuss the diversity of SN 2002es-like objects and their origin in the context of different scenarios. [ABSTRACT FROM AUTHOR]

The investigation of very high energy gamma‐ray sources touches on the problem of the cosmic ray origin and the role of the Galaxy in their generation. The SHALON observations have yielded the results on γ$$ \gamma $$Cygni SNR Galactic supernova remnant. The observation results are presented with spectral energy distribution and emission map by SHALON in comparison with other experiment data obtained by ROSAT in x‐ray energy range, radio‐data by CGPS, and also observations of GeV–TeV gamma‐rays by Fermi LAT. The overall γ$$ \gamma $$Cygni SNR characteristics detected in radio, x‐rays, and GeV–TeV gamma‐rays can be a result of the shocks at the interaction of the supernova ejecta and the surrounding medium. The collected experimental data help to make clear the origin of TeV γ$$ \gamma $$‐ray emission in the γ$$ \gamma $$Cygni SNR. The density of target material in the SNR surroundings is enough to produce the observable TeV gamma‐ray flux via the shock acceleration of hadrons in the detected regions. The detection of gamma‐ray emission at 0.8–60 TeV from the North‐West and South‐East shells of γ$$ \gamma $$Cygni SNR by SHALON would favor the hadronic origin of the gamma‐rays in this supernova remnant. [ABSTRACT FROM AUTHOR]

The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma‐rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma‐ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non‐thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of 1014−1015$$ {10}^{14}-{10}^{15} $$ eV. Whereas, the forward shock model predicts the spectral characteristics of the TeV‐gamma‐emission corresponding to ones detected at 800 GeV–40 TeV that are the evidence of acceleration of the hadronic cosmic rays in shells of SNRs up to 1017$$ {10}^{17} $$ eV [ABSTRACT FROM AUTHOR]

We report the results of a search for radio pulsars in five supernova remnants (SNRs) with the FAST telescope. The observations were made using the 19-beam receiver in "snapshot" mode. The integration time for each pointing was 10 min. We discovered a new pulsar, PSR J1845–0306, which has a spin period of 983.6 ms and a dispersion measure of 444.6 ± 2.0 cm−3⋅pc, in observations of SNR G29.6+0.1. To judge the association between the pulsar and the SNR, further verification is needed. We also re-detected some known pulsars in the data from SNRs G29.6+0.1 and G29.7–0.3. No pulsars were detected in the observations of the other three SNRs. [ABSTRACT FROM AUTHOR]

Fukui et al. quantified the hadronic and leptonic gamma-rays in the young TeV gamma-ray shell-type supernova remnant (SNR) RX J1713.7-3946 (RX J1713), and demonstrated that gamma rays are a combination of hadronic and leptonic gamma-ray components with a ratio of ∼6: 4 in gamma-ray counts N g. This discovery, which adopted a new methodology of multi-linear gamma-ray decomposition, was the first quantification of the two gamma-ray components. In the present work, we applied the same methodology to another TeV gamma-ray shell-type SNR RX J0852.0-4622 (RXJ0852) in 3D space characterized by (the interstellar proton column density N p)-(the nonthermal X-ray count N x)-[ N g], and quantified the hadronic and leptonic gamma-ray components as having a ratio of ∼5:5 in N g. The present work adopted the fitting of two/three flat planes in 3D space instead of a single flat plane, which allowed suppression of the fitting errors. This quantification indicates that hadronic and leptonic gamma-rays are of the same order of magnitude in these two core-collapse SNRs, verifying the significant hadronic gamma-ray components. We argue that the target interstellar protons, in particular their spatial distribution, are essential in any attempts to identify the type of particles responsible for gamma-ray emission. The present results confirm that cosmic-ray (CR) energy ≲100 TeV is compatible with a scheme in which SNRs are the dominant source of these Galactic CRs. [ABSTRACT FROM AUTHOR]

We examine the evolution of ion-beam Weibel instability at strong collisionless shocks in weakly magnetized media. We find that a finite background magnetic field substantially affects both the linear and nonlinear phases of the instability, depending on whether the background electrons behave magnetized or not. Particle-in-cell simulations for magnetized electrons identify a dynamo-like mechanism of magnetic field amplification, which eventually leads to spontaneous magnetic reconnection. We conclude that this scenario is applicable to typical young supernova remnant shocks. [ABSTRACT FROM AUTHOR]

Observations and theory suggest that core-collapse supernovae can span a range of explosion energies, and when sub-energetic the shockwave initiating the explosion can decelerate to speeds comparable to the escape speed of the progenitor. In these cases, gravity will complicate the explosion hydrodynamics and conceivably cause the shock to stall at large radii within the progenitor star. To understand these unique properties of weak explosions, we develop a perturbative approach for modeling the propagation of an initially strong shock into a time-steady, infalling medium in the gravitational field of a compact object. This method writes the shock position and the post-shock velocity, density, and pressure as series solutions in the (time-dependent) ratio of the freefall speed to the shock speed, and predicts that the shock stalls within the progenitor if the explosion energy is below a critical value. We show that our model agrees very well with hydrodynamic simulations, and accurately predicts (for example) the time-dependent shock position and velocity and the radius at which the shock stalls. Our results have implications for black hole formation and the newly detected class of fast X-ray transients (FXTs). In particular, we propose that a "phantom shock breakout"—where the outer edge of the star falls through a stalled shock—can yield a burst of X-rays without a subsequent optical/UV signature, similar to FXTs. This model predicts the rise time of the X-ray burst, t d, and the mean photon energy, kT, are anticorrelated, approximately as T ∝ t d − 5 / 8 . [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]

Central compact objects (CCOs), neutron stars found near the centre of some supernova remnants (SNRs), have been almost exclusively studied in X-rays and are thought to lack the wind nebulae typically seen around young, rotation-powered pulsars. We present the first, spatially resolved, morphological and spectroscopic study of the optical nebula observed at the location of CXOU J085201.4−461753, the CCO in the heart of the Vela Junior SNR. It is currently the only Galactic CCO with a spatially coincident nebula detected at optical wavelengths, whose exact nature remains uncertain. New Multi Unit Spectroscopic Explorer integral field spectroscopy data confirm that the nebula, shaped like a smooth blob extending 8 arcsec in diameter, is dominated by [N  ii ] |${\lambda } {\lambda }$| 6548, 6583 emission. The data reveal a distinct and previously unobserved morphology of the H  |${\alpha }$| emission, exhibiting an arc-like shape reminiscent of a bow shock nebula. We observe a significantly strong [N  ii ] emission relative to H  |${\alpha }$|⁠ , with the [N  ii ] |${\lambda } {\lambda }$| 6548, 6583 up to 34 times the intensity of the H  |${\alpha }$| emission within the optical nebula environment. Notably, the [N  ii ] and H  |${\alpha }$| structures are not spatially coincident, with the [N  ii ] nebula concentrated to the south of the CCO and delimited by the H  |${\alpha }$| arc-like structure. We detect additional emission in [N  i ], He  i , [S  ii ], [Ar  iii ], [Fe  ii ], and [S  iii ]. We discuss our findings in the light of a photoionization or Wolf–Rayet nebula, pointing to a very massive progenitor and further suggesting that very massive stars do not necessarily make black holes. [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]

Observations of pulsar scintillation are among the few astrophysical probes of very small-scale (≲ au) phenomena in the interstellar medium (ISM). In particular, characterization of scintillation arcs, including their curvature and intensity distributions, can be related to interstellar turbulence and potentially overpressurized plasma in local ISM inhomogeneities, such as supernova remnants, H  ii regions, and bow shocks. Here we present a survey of eight pulsars conducted at the Five-hundred-metre Aperture Spherical Telescope (FAST), revealing a diverse range of scintillation arc characteristics at high sensitivity. These observations reveal more arcs than measured previously for our sample. At least nine arcs are observed toward B1929+10 at screen distances spanning |$\sim 90~{{\ \rm per\ cent}}$| of the pulsar's 361 pc path length to the observer. Four arcs are observed toward B0355+54, with one arc yielding a screen distance as close as ∼105 au (<1 pc) from either the pulsar or the observer. Several pulsars show highly truncated, low-curvature arcs that may be attributable to scattering near the pulsar. The scattering screen constraints are synthesized with continuum maps of the local ISM and other well-characterized pulsar scintillation arcs, yielding a three-dimensional view of the scattering media in context. [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]

Supernova remnants are the nebular leftover of defunct stellar environments, resulting from the interaction between a supernova blastwave and the circumstellar medium shaped by the progenitor throughout its life. They display a large variety of non-spherical morphologies such as ears that shine non-thermally. We have modelled the structure and the non-thermal emission of the supernova remnant G1.9 + 0.3 through 3D magnetohydrodynamic numerical simulations. We propose that the peculiar ear-shaped morphology of this supernova remnant results from the interaction of its blast wave with a magnetized circumstellar medium, which was previously asymmetrically shaped by the past stellar wind emanating from the progenitor star or its stellar companion. We created synthetic non-thermal radio and X-ray maps from our simulated remnant structure, which are in qualitative agreement with observations, forming ears on the polar directions. Our synthetic map study explains the discrepancies between the measured non-thermal radio and X-ray surface brightness distributions assuming that the inverse Compton process produces the observed X-ray emission. [ABSTRACT FROM AUTHOR]

The X-ray source CXOU J163802.6−471358 is thought to be a pulsar wind nebula (PWN), as it shows an extended, ≈40 arcsec trail from a compact source. Here, we present Giant Metrewave Radio Telescope observations of this source at 330 and 1390 MHz, which reveal a remarkable linear radio trail ≈90 arcsec in extent. Although the radio trail points back to the supernova remnant (SNR) G338.1+0.4, ≈50 arcmin from CXOU J163802.6−471358, associating it with this remnant would require a very large velocity for the pulsar. There are no known Galactic SNRs close to the PWN and radio trail. No pulsar has yet been identified in CXOU J163802.6−471358, but if one could be found, this would allow more quantitative studies of the PWN and radio trail to be made. [ABSTRACT FROM AUTHOR]

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<'0" full width at half maximum) and broad spectral coverage (0.2-80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. HEX-P is ideally suited to address important problems in the physics and astrophysics of supernova remnants (SNRs) and pulsar wind nebulae (PWNe). For shell SNRs, HEX-P can greatly improve our understanding via more accurate spectral characterization and localization of non-thermal X-ray emission from both non-thermal-dominated SNRs and those containing both thermal and nonthermal components, and can discover previously unknown non-thermal components in SNRs. Multi-epoch HEX-P observations of several young SNRs (e.g., Cas A and Tycho) are expected to detect year-scale variabilities of X-ray filaments and knots, thus enabling us to determine fundamental parameters related to diffusive shock acceleration, such as local magnetic field strengths and maximum electron energies. For PWNe, HEX-P will provide spatially-resolved, broadband X-ray spectral data separately from their pulsar emission, allowing us to study how particle acceleration, cooling, and propagation operate in different evolution stages of PWNe. HEX-P is also poised to make unique and significant contributions to nuclear astrophysics of Galactic radioactive sources by improving detections of, or limits on, 44Ti in the youngest SNRs and by potentially discovering rare nuclear lines as evidence of double neutron star mergers. Throughout the paper, we present simulations of each class of objects, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of SNRs, PWNe, and nuclear astrophysics. [ABSTRACT FROM AUTHOR]

We present new and archival Australia Telescope Compact Array and Atacama Large Millimeter/submillimeter Array data of the Small Magellanic Cloud supernova remnant 1E 0102.2–7219 at 2100, 5500, 9000, and 108 000 MHz; as well as H  i data provided by the Australian Square Kilometre Array Pathfinder. The remnant shows a ring-like morphology with a mean radius of 6.2 pc. The 5500 MHz image reveals a bridge-like structure, seen for the first time in a radio image. This structure is also visible in both optical and X-ray images. In the 9000 MHz image, we detect a central feature that has a flux density of 4.3 mJy but rule out a pulsar wind nebula origin, due to the lack of significant polarization towards the central feature with an upper limit of 4  per cent. The mean fractional polarization for 1E 0102.2–7219 is 7 ± 1 and 12 ± 2  per cent for 5500 and 9000 MHz, respectively. The spectral index for the entire remnant is −0.61 ± 0.01. We estimate the line-of-sight magnetic field strength in the direction of 1E 0102.2–7219 of ∼44 µG with an equipartition field of |$65\pm 5\, \mu$| G. This latter model uses the minimum energy of the sum of the magnetic field and cosmic ray electrons only. We detect an H  i cloud towards this remnant at the velocity range of ∼160–180 km s−1 and a cavity-like structure at the velocity of 163.7–167.6 km s−1. We do not detect CO emission towards 1E 0102.2–7219. [ABSTRACT FROM AUTHOR]

We present the kinematic results for the supernova remnant (SNR) CTB 1, obtained with the PUMA equipment of the 2.1-m telescope at San Pedro Mártir National Astronomical Observatory, Baja California, Mexico. The observations were made on the H α line using a Fabry–Perot interferometer. The kinematics derived from the Fabry–Perot velocity cubes allowed us to estimate a kinematic distance for this SNR. We estimate that CTB1 is about 3.8 kpc from the sun, corresponding to a linear diameter of 19 pc, with an expansion velocity of |$286 \rm ~ km ~s^{-1}$|⁠. Additionally, we analyse the diffuse X-ray emission from CTB 1 using data from the XMM–Newton observatory. From the best fits to the spectrum of southwest and northeast regions, we obtained a hot plasma temperature |$\sim 0.1-0.3 ~\rm keV$| with an overabundance in O and Ne and a lower abundance in Fe, which could be caused by a SNR with a stellar progenitor between 10 to |$70 \, \rm {\rm M}_{\odot }$|⁠. The initial energy of the supernova explosion is estimated between (0.6–1.0) × 1050 erg for soft X-ray emission. The X-ray emission also presents a non-thermal component of low surface brightness in the hard X-ray band. Images in radio and X-ray emission allow us to classify CTB 1 as mixed-morphology supernova type. The evolution models show that the cloudy ISM model is the only one that reproduces the mixed morphology type observed in the SNR CTB 1. [ABSTRACT FROM AUTHOR]

We use the new QUIJOTE-MFI wide survey (11, 13, 17, and 19 GHz) to produce spectral energy distributions (SEDs), on an angular scale of 1°, of the supernova remnants (SNRs) CTB 80, Cygnus Loop, HB 21, CTA 1, Tycho, and HB 9. We provide new measurements of the polarized synchrotron radiation in the microwave range. The intensity and polarization SEDs are obtained and modelled by combining QUIJOTE-MFI maps with ancillary data. In intensity, we confirm the curved spectra of CTB 80 and HB 21 with a break frequency νb at 2.0 |$^{+1.2}_{-0.5}$| and 5.0 |$^{+1.2}_{-1.0}$|  GHz, respectively; and spectral indices above the break of |$-0.6^{+0.04}_{-0.05}$| and |$-0.86^{+0.04}_{-0.05}$|⁠. We provide constraints on the Anomalous Microwave Emission, suggesting that it is negligible towards these SNRs. From a simultaneous intensity and polarization fit, we recover synchrotron spectral indices as flat as −0.24, and the whole sample has a mean and scatter of −0.44 ± 0.12. The polarization fractions have a mean and scatter of 6.1 ± 1.9 per cent. When combining our results with the measurements from other QUIJOTE (Q-U-I JOint TEnerife CMB experiment) studies of SNRs, we find that radio spectral indices are flatter for mature SNRs, and particularly flatter for CTB 80 (⁠|$-0.24^{+0.07}_{-0.06}$|⁠) and HB 21 (⁠|$-0.34^{+0.04}_{-0.03}$|⁠). In addition, the evolution of the spectral indices against the SNRs age is modelled with a power-law function, providing an exponent −0.07 ± 0.03 and amplitude −0.49 ± 0.02 (at 10 kyr), which are conservative with respect to previous studies of our Galaxy and the Large Magellanic Cloud. [ABSTRACT FROM AUTHOR]

Fast Radio Bursts (FRBs) are extra-galactic origin milli-second duration bright radio bursts. Theoretically, FRBs may produce optical counterparts with durations from milliseconds to hours. The FRB optical counterparts may be detectable in future large field telescopes, including the China Space Station Telescope (CSST), the 2.5-meter Wide Field Survey Telescope (WFST) lead by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO), and the Earth 2.0 (ET). The fast radio burst optical counterparts are grouped into millisecond time-scale optical counterparts, hourly time-scale optical counterparts, and optical afterglow for our study. The first two can be generated by the high-energy extension of the radio radiation of fast radio bursts and the inverse Compton scattering of high-energy electrons. The event rates highly depend on the optical-to-radio flux ratio η ν. For millisecond duration optical counterparts, the detection rate of WFST, CSST, and ET can reach hundreds per year in an ideal case. If η ν ∼ 10 − 3 , the corresponding annual detection rates of WFST and CSST are in the order of 1, and the annual detection rate of ET is 19.5. For the hourly timescale optical counterparts, ideally, the age of the supernova remnant is 5 years, η ν is about 10 − 6 , and the annual detection rates are above 100. The X-ray counterpart of FRB 200428 indicates that FRBs may produce relativistic outflow, which will interact with the interstellar medium to produce optical afterglows. Combined with the standard afterglow model, the detectability of optical afterglow is explored with a simulation of fast radio bursts following the redshift and energy distribution from the literature. With a total energy-radio energy ratio similar to FRB 200428, (ζ = 10 5), the estimated annual detection rates of CSST, WFST, and ET are 1.3, 1.0, and 67, respectively. [ABSTRACT FROM AUTHOR]

Near the center of the Puppis A supernova remnant a series of nested, optically emitting rings of high-velocity ejecta (known as "the Swirl") were identified several decades ago by Winkler et al. To date, no follow-up observations of these rings have been published, and their physical origin has remained a mystery. We present results of integral field spectroscopy of the Swirl using the Wide Field Integral Spectrograph on the 2.3 m telescope at Siding Spring Observatory in Australia. The outermost ring exhibits a nitrogen-rich spectrum blueshifted to 1350 km s−1, with smaller blueshifted rings within the first exhibiting mostly oxygen-rich spectra moving at 1000 and 750 km s−1. The structures are connected by material of intermediate velocity and variable composition, including sulfur-rich material. The Swirl is turbulent and shock-excited, and contains as much as 0.5 M ⊙ of metal-rich material. The chemical composition and exclusively blueshifted radial velocities of the Swirl are consistent with progressively deeper nucleosynthetic layers in a massive progenitor star. We suggest the possibility that the Swirl marks a "funnel" carved into the supernova ejecta by a close, massive binary companion at the moment of explosion. [ABSTRACT FROM AUTHOR]

The origin of arcmin-sized odd radio circles (ORCs) found in modern all-sky radio surveys remains uncertain, with explanations ranging from starburst/active galactic nucleus-driven shocks to supernova remnants (SNRs) in the low-density ambient medium. Using well-calibrated radio light-curve models, we assess the possibility that ORCs are radio SNRs in low ambient densities. Our models imply that if ORCs 1–5 are SNRs, they must be within 200–350 kpc from the Sun, given their observed flux densities and sizes. To be evolving in the circumgalactic medium of the Milky Way, our models imply ORCs 1–5 to be ejecta-dominated SNRs within 50 kpc, evolving in ambient densities of (0.2–1.2) × 10−3 cm−3. However, this is statistically unlikely because ORCs 1–5 would have ages <640 yr, much smaller than their expected lifetimes of ≳105 yr at these densities. Additionally, the low SN rate implies only a few SNRs within 50 kpc. On the other hand, the circumgalactic medium SNR scenario for J0624−6948 is more likely (although still low probability) compared to ORCs 1–5, as our models allow J0624−6948 to be ≲3000 yr. The interpretation of J0624−6948 as a Sedov–Taylor SNR in the Large Magellanic Cloud is also possible for a wide range of ambient densities (6 × 10−4 to 0.5 cm−3), consistent with the local H  i environment, and ages ∼(0.2–2.6) × 104 yr. Our work implies that while some ORCs may be SNRs, others are more likely large-scale shocks in distant galaxies. [ABSTRACT FROM AUTHOR]

Cosmic rays generated by supernovae carry away a significant portion of the lifetime energy emission of their parent star, making them a plausible mechanism for heating the early universe intergalactic medium (IGM). Following a review of the existing literature on cosmic ray heating, we develop a flexible model of this heating mechanism for use in 3D seminumerical 21-cm signal simulations and conduct the first investigations of the signatures it imprints on the 21-cm power spectrum and tomographic maps. We find that cosmic ray heating of the IGM is short-ranged, leading to heating clustered around star-forming sites, and a sharp contrast between heated regions of 21-cm emission and unheated regions of absorption. This contrast results in greater small-scale power for cosmic ray heated scenarios compared to what is found for X-ray heating, thus suggesting a way to test the nature of IGM heating with future 21-cm observations. Finally, we find an unexpectedly rich thermal history in models where cosmic rays can only escape efficiently from low-mass haloes, such as in scenarios where these energetic particles originate from population III star supernovae remnants. The interplay of heating and the Lyman–Werner feedback in these models can produce a local peak in the IGM kinetic temperature and, for a limited parameter range, a flattened absorption trough in the global 21-cm signal. [ABSTRACT FROM AUTHOR]

We present an analysis of high-resolution far-UV archival spectra obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the star HD 75309, which probes high-velocity shocked gas in the Vela supernova remnant (SNR). We examine high-velocity features from intrinsically strong absorption lines of O i, Si ii, Si ii *, C ii, C ii *, and Si iii. We also detect high-velocity components in the N v doublet and compare these features to observations of high-velocity O vi absorption, available from archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are derived from the observed fractional abundances of the various ions, while gas densities and thermal pressures are obtained from the relative populations in excited fine-structure levels of C ii and Si ii. Our results indicate that the highly ionized species at high velocity probe gas in a region immediately behind a shock driven into an interstellar cloud, while the lower-ionization species trace material further downstream in the cooling region of the postshock flow. Low-velocity N v and O vi absorption may trace gas in a conductive boundary layer between the unshocked portion of the cloud and the hot X-ray-emitting intercloud medium. Temporal variations in high-velocity Ca ii absorption features observed toward HD 75309 further confirm the highly inhomogeneous nature of the interstellar medium interacting with the Vela SNR. [ABSTRACT FROM AUTHOR]

Transonic (with Mach number ) motion of a pulsar relative to the external medium can help its compact pulsar wind nebula develop a double-torus X-ray morphology. The double-torus structure can reverberate as a whole under the dynamic pressure of the external flow. For a flow aligned with the symmetry axis of the nebula, the response of the double-torus is uniform in azimuth. For a misaligned flow, the leeward sides of the tori respond with some delay relative to their windward sides. The delay can cause a curious swaying in the short midsection of the leeward jet of the compact X-ray nebula. Within the framework of the relativistic magnetohydrodynamical model of a pulsar wind nebula we study the dynamics of the nebular outflows contributing to the swaying of the jet. When applied to the Vela X-ray nebula, the model allows us to naturally relate two distinct phenomena, the swaying of the bright midsection of the Vela lee jet and the reverberation of its double-torus. [ABSTRACT FROM AUTHOR]