The question about what causes a supernova remnant (SNR) to be a thermal composite rather than have a typical shell-like morphology remains unsolved, as does what causes the plasma inside it to recombine. With the 13-ks observation of the Following-up X-ray Telescope on board the Einstein Probe, we give an overall X-ray picture of W28, one of the prototypical thermal composite SNRs. The observation revealed a shell-like structure west of W28 in radio, optical, and X-ray images. This may revise the known extent of the SNR to 72′ × 45′. A spectral analysis explicitly maps the special relation in which the plasma experiences recombination in the interior of the remnant, spatially coincident with Hα emissions, while in other regions, the plasma is dominated by ionization. We found that W28 is generally isobaric from its center to the newly discovered shell, and it is even isothermal with a temperature of ∼0.6-0.7 keV in the center before the plasma cools. Saturated thermal conduction and cloud evaporation may cool down the plasma within ∼3 kyr, which is the estimated recombination timescale. We revised the SNR dynamical age to ∼8 kyr, which is much younger than previous estimates. The complex structure and complex ionization state distribution may suggest that centrally filled and shell-like morphologies coexist in W28. This state may depend on the environment in which the SNR evolves.

Supernova remnants (SNRs) strongly influence the physical and chemical properties of the molecular clouds (MCs) with which they interact. We carried out a high-resolution observation toward W28F, a chemically rich MC interacting with SNR W28, with the Atacama Compact Array (ACA) in Band 7. Significant emission (> 10 sigma) of CO, CH3OH, p-H2CO, SiO and SO is detected. We reveal the clumpy structures of the shocked MC, with different spatial distributions between CH3OH and SiO. We select six molecular clumps to conduct spectral decomposition and non-local-thermodynamic-equilibrium analysis with the CH3OH and p-H2CO lines. The best-fit results show a H2 density of nH2 (1-3) * 10^5 cm^-3 and a gas temperature of Tgas 50-170 K in most of the fitted components. The H2 density and gas temperature show a clear anti-correlation across different regions, with the thermal pressure consistent with that of the adjacent X-ray-emitting hot plasma. This is consistent with the picture that the SNR shocks propagate into multi-phase gas, with a pressure balance existing between different phases. We propose that the high abundance ratio between E-CH3OHand A-CH3OH (> 0.9) suggests extra gas-phase processes to enhance this ratio, such as proton exchange with H3+ and HCO+. The chemical segregation between CH3OH and SiO, in both the spatial and spectral regime, can be explained by the fact that CH3OH traces slow shocks while SiO traces fast shocks.

RCW 86 is a supernova remnant whose origin has recently been linked to an off-center explosion within a cavity created by its progenitor star. In the southwestern region, the forward shock is thought to have reached the cavity wall, encountering diverse environmental conditions. We report on the spatially resolved X-ray polarimetric observation of RCW 86 with the Imaging X-ray Polarimetry Explorer (IXPE). In the 2-4.5 keV energy band we find no significant detection of polarization. Employing a dedicated background subtraction procedure and Bayesian spectropolarimetric fitting, we derive 99% upper limits on the polarization degree of the synchrotron component: 15% in higher-statistics regions and 30%-40% in lower-statistics regions. These upper limits on the polarization degree in several regions exclude the possibility of a strongly coherent magnetic field down to the subparsec scale, and that of a moderately coherent one on the scale of the synchrotron features as resolved by IXPE. The results indicate that the shocks in the southwestern rim of RCW 86 propagate more slowly than the unshocked ejecta at their locations, yet exceed the measured proper motion speeds. This behavior is consistent with reflected shocks occurring in tenuous regions of the shocked ejecta, distinct from regions that are radio-bright.

Context. The spatial distribution of metals in the intracluster medium (ICM) is a sensitive tracer of the chemical and dynamical history of galaxy clusters. While most cool-core (CC) clusters exhibit a centrally peaked Fe abundance profile, several outliers show an anomalous central Fe drop, potentially associated with the active galactic nucleus (AGN) activities. Aims. We revisit the reported large-scale (∼100 kpc) central Fe drop in the massive CC cluster MACS J1931.8-2634 using new XMM-Newton observations. We aim to verify this feature and search for imprints of AGN feedback on the ICM metallicity distribution. Methods. We analyzed ∼ 170 ks of new XMM-Newton observations and reanalyzed ∼100 ks of archived Chandra observations. We derived radial and two-dimensional (2D) Fe abundance maps from CCD spectra. High-resolution RGS spectra were used to constrain the Ne/Fe abundance ratio to test the dust-depletion scenario. Spectral fitting was performed in SPEX using an updated atomic database and both single- and multi-temperature collisional ionization equilibrium models. Results. The previously reported central Fe drop is not confirmed in the radial profile from XMM-Newton. However, the 2D Fe distribution is clearly asymmetric: Fe-rich regions are elongated along the axis of the AGN cavities, extending beyond their immediate scale. The Ne/Fe ratio in the core is consistent with solar (Ne/Fe = 1.03+0.25−0.23 1 . 03 − 0.23 + 0.25 $ 1.03^{+0.25}_{-0.23} $ ), arguing against the dust-depletion scenario.

The spatial distribution of metals in the intracluster medium (ICM) is a sensitive tracer of the chemical and dynamical history of galaxy clusters. While most cool-core (CC) clusters exhibit a centrally peaked Fe abundance profile, several outliers show an anomalous central Fe drop, potentially associated with the AGN activities. We revisit the reported large-scale (sim 100 kpc) central Fe drop in the massive CC cluster MACS J1931.8-2634 using new XMM-Newton observations. We aim to verify this feature and search for imprints of AGN feedback on the ICM metallicity distribution. We analyzed sim 170 ks of new XMM-Newton observations and re-analyzed sim 100 ks archived Chandra observations. We derived radial and two-dimensional (2D) Fe abundance maps from CCD spectra. High-resolution RGS spectra were used to constrain the Ne/Fe abundance ratio to test the dust depletion scenario. Spectral fitting was performed in SPEX using an updated atomic database and both single- and multi-temperature collisional ionization equilibrium models. The previously reported central Fe drop is not confirmed in the radial profile from XMM-Newton. However, the 2D Fe distribution is clearly asymmetric: Fe-rich regions are elongated along the axis of the AGN cavities, extending beyond their immediate scale. The Ne/Fe ratio in the core is consistent with solar (Ne/Fe = 1.03^+0.25_-0.23), arguing against the dust depletion scenario.

It has been an unsolved question what leads a supernova remnant (SNR) to a thermal composite rather than a typical shell-like morphology, and what causes recombining plasma inside it. With the 13-ks observation of the Following-up X-ray Telescope onboard the Einstein Probe, we give an overall X-ray picture of W28, one of the prototypical thermal composite SNRs. The observation revealed a shell-like structure west of W28 in radio, optical, and X-ray images, which may revise the known extent of the SNR to 72'×45'. Spectral analysis explicitly maps that the special relationship where the plasma experiences recombination in the interior of the remnant, spatially coincident with Hα emissions, while in the other regions, the plasma is ionization-dominated. We found that W28 is generally isobaric from its center to the newly discovered shell, and it is even isothermal with a temperature of ∼0.6-0.7 keV in the center before the cooling of the plasma. Saturated thermal conduction and cloud evaporation may cool down the plasma within ∼3 kyr, the estimated recombination timescale. We revised the SNR dynamical age to ∼8 kyr, much younger than previous estimates. The complex structure and complex ionization state distribution may suggest that centrally filled and shell-like morphologies coexist in W28. This state may depend on the environment in which the SNR evolves.

We regret that this statement “This work was supported by China’s Space Origins Exploration Program.” was omitted in the beginning of the Acknowledgements.

Located at the centres of supernova remnants, central compact objects (CCOs) are among the most puzzling neutron stars. CCOs are bright in thermal X-rays, yet have evaded detection by major radio telescopes for decades, giving rise to the view that they are intrinsically radio-quiet and possess exceptionally weak magnetic fields. Here we show that the prototypical young CCO 1E 1207.4-5209 is in fact a faint radio pulsar rotating at the 0.4-s X-ray period. Analysis of its polarization indicates that the radio beam intersects our line of sight near the magnetic pole, affirming that its radio faintness is intrinsic. Once its supernova remnant dissipates, this source would be misidentified as an apparently gigayear-old pulsar. The CCO's low radio flux density may explain why many supernova remnants lack detectable radio pulsars and suggests a hidden population of young, slowly rotating neutron stars.

The Sagittarius C (Sgr C) complex, located on the western edge of the central molecular zone (CMZ), hosts a mixture of star-forming and nonthermal activity whose X-ray properties remain poorly understood. Using deep archival Chandra and XMM-Newton observations, we resolve the diffuse X-ray emission in Sgr C into two components: an H ii region coincident with the radio peak and a brighter diffuse feature located to its southwest. Spatially resolved spectroscopy reveals the presence of a soft (kT <= 1 keV) plasma with metal abundances consistent with the elevated metallicity expected in the CMZ in both regions, along with a harder (similar to 8 keV) thermal component within the H ii region. The observed diffuse X-ray emission and its association with an expanding [C ii] shell suggest that the hot gas may originate from a young supernova remnant (SNR) embedded in the H ii region. Under this interpretation, the inferred shock velocity (similar to 800 km s-1) and SNR age (>= 1.7 kyr) are consistent with a core-collapse SNR in the Galactic center. These results reveal Sgr C as a potential host of an SNR and highlight the complex interplay between massive-star feedback, magnetic fields, and molecular gas in the CMZ.

Recent optical astrometric and spectroscopic surveys have identified numerous neutron star (NS) candidates in nonaccreting detached binary systems, but their compact-object nature remains unconfirmed. In this work, we present targeted radio observations of 31 such candidates using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the Robert C. Byrd Green Bank Telescope, and the Shanghai TianMa Radio Telescope. Over a total of 46.65 hr of observing time, we detected neither periodic nor single-pulse radio emissions. These nondetections place stringent upper limits on the flux densities of any potential radio signals, reaching ∼4 μ Jy for periodic emission and ∼10 mJy for single pulses with FAST. Since our observations are highly sensitive and the flux density upper limits are well below the median fluxes of known Galactic pulsars, this suggests that geometric beaming is the most likely explanation for the nondetections if these objects are indeed pulsars. Alternatively, the NSs may be sufficiently old (≳10 Gyr) and have become intrinsically radio-quiet. In this case, our findings highlight the inherent difficulty of confirming NSs in such old detached binary systems through radio pulsation searches.

G7.7-3.7 is a possible historical supernova remnant (SNR), with the origin of its cocoon-like morphology and its supernova type remaining unclear. We performed L-band radio polarization observations of G7.7-3.7 using the Very Large Array in C and B configurations. The high-resolution 1.4 GHz continuum image reveals a cocoon-like morphology with multiple shells and faint blowout structures. The total flux density is 9.6 +/- 0.5 Jy and the spectral index map shows predominantly nonthermal emission, with an integrated spectral index of -0.38 +/- 0.04. Polarization images of G7.7-3.7 show high linear polarization fraction (30%-40%) in the northwestern filaments and moderate polarization (10%-20%) in the northeast and south. The magnetic fields aligned with the filamentary structures, consistent with shock compression. Large rotation measure variations across the SNR likely originate from magnetized massive progenitor winds. We suggest that the cocoon-like morphology results from the interaction between the SNR and preexisting circumstellar shells, demonstrating that the radio polarization provides useful constraints on the environments and even the progenitor mass-loss.

Magnetars are highly magnetized neutron stars whose evolution and radiation are governed by the decay and/or reconfiguration of their magnetic fields. The origin of magnetars remains an open question, with proposed progenitor scenarios including core collapse (CC) of very massive stars (>= 25 M-circle dot) or not very massive stars (8 M-circle dot < M-* < 25 M-circle dot), mergers of stellar systems, and accretion-induced collapse of white dwarfs. Investigating the environments of magnetars can offer valuable clues to this issue. In this work, we study the local (radius of 0 degrees.87, similar to 100 pc at 6.6 kpc) stellar environment of SGR 1935+2154, which is spatially associated with the supernova remnant (SNR) G57.2+0.8, based on astrometry from Gaia DR3 and multiband photometry from optical to infrared. We discover that the upper limit of the surface density of massive stars around SGR 1935+2154 is only a quarter of that of the solar neighborhood, where the star formation rate is modest in the Galaxy. This quiet environment implies that the magnetar was likely formed by the CC of either a not very massive star or a binary merger product rather than the CC of a very massive star. Although alternative channels cannot be excluded, their probabilities may be substantially lower. The studies of magnetars associated with SNRs consistently favor not very massive progenitors, implying that such progenitors may produce a considerable fraction of magnetars. We also backtrack the trajectories of SGR 1935+2154 and its surrounding stars to search for its potential massive companions, yet no such companions are found.

Recent observations suggest that Tycho's supernova remnant (SNR; SN 1572) is expanding into a cavity wall of molecular clouds (MCs), which decelerate the SNR and influence its multiwavelength morphology. To constrain the physical properties of environmental MCs and search for heated gas, we perform a James Clerk Maxwell Telescope 12CO J = 3-2 observation and compare with previous 12CO J = 2-1, 12CO J = 1-0 and 13CO J = 1-0 data. We present the 12CO J = 3-2 map toward Tycho and show that the 12CO J = 3-2 spatial distribution and line profiles are similar to those of the lower-J CO lines. By comparing the multiple transitions of CO and the RADEX models, we constrain the physical properties of molecular gas surrounding Tycho: the northern cloud has a molecular column density of N(H2) = 0.5-4.5 x 1022 cm-2, while other regions have N(H2) = 0.2-3.9 x 1021 cm-2; the kinetic temperatures Tk of these clouds are in the range of 9-22 K, and the volume densities n(H2) are 20-700 cm-3. We also discuss the difficulty in finding hot molecular gas shocked by such a young SNR. We estimate that the shocked molecular layer can be as thin as 0.003 pc, corresponding to 0 .'' 2 at the distance of 2.5 kpc, which is 2 orders of magnitude smaller than the angular resolution of current CO observations. Therefore, our molecular observations are largely insensitive to the thin shocked gas layer; instead, they detect the environmental gas.

The high magnetic fields and rapid spins of young pulsars associated with supernova remnants, such as the Crab and the Vela, established the standard pulsar model in which massive stellar explosions produce rapidly rotating, radio-luminous neutron stars. Central Compact Objects (CCOs), identified in X-rays at the centers of other remnants, challenged this view, as decades of searches yielded no radio detections. Here we show that the prototypical young CCO 1E 1207.4–5209 is in fact a faint radio pulsar rotating at the 0.4s X-ray period. Analysis of its polarization indicates that the radio beam intersects our line of sight near the magnetic pole, affirming its radio faintness’ being intrinsic. Once its supernova remnant dissipates, this source would be misidentified as an apparently gigayear-old pulsar. The CCO's low radio flux density may explain why many supernova remnants lack detectable radio pulsars and suggests a hidden population of young, slowly rotating neutron stars.

Long-period radio transients (LPTs) are a newly discovered class of radio emitters with periods ranging from minutes to hours. The astrophysical nature remains undetermined, particularly of LPTs with no detectable companions. We report the first evidence for a plausible supernova remnant (SNR) association with an LPT (DART J1832-0911, 2656.23 ± 0.15 s period), which supports a neutron star origin of such objects. The dispersion measure of this LPT, SNR's CO emission and neutral hydrogen (HI) absorption, and low probability of chance of alignment with field pulsars are all consistent with such an association. The source displays either phase-locked circular or nearly 100% linear polarization, indicating its strong and geometrically stable magnetic field. No detectable optical counterpart was found, even with a 10 m-class telescope. The SNR association and the stable polarization suggest that DART J1832-0911 most likely originates from a young neutron star, whose spin could have been braked by supernova's fallback materials. This discovery provides critical insights into the nature of ultra-long period transients and their link to stellar remnants.

Magnetars are highly magnetized neutron stars (NSs) whose evolution and radiation are governed by the decay and/or reconfiguration of their magnetic fields. The origin of magnetars remains an open question, with proposed progenitor scenarios including core-collapse (CC) of very massive stars (≥ 25 M_⊙) or non-very massive stars (8<M_*<25 M_⊙), mergers of stellar systems, and accretion-induced collapse (AIC) of white dwarfs (WDs). Investigating the environments of magnetars can offer valuable clues to this issue. In this work, we study the local (a radius of 0.87^∘, ∼ 100 pc at 6.6 kpc) stellar environment of SGR 1935+2154, which is spatially associated with the supernova remnant (SNR) G57.2+0.8, based on astrometry from Gaia DR3 and multi-band photometry from optical to infrared (IR). We discover that the upper limit of the surface density of massive stars around SGR 1935+2154 is only a quarter of that of the solar neighborhood, where the star formation rate is modest in the Galaxy. This quiet environment implies that the magnetar was likely formed by the CC of either a non-very massive star or a binary merger product rather than the CC of a very massive star. Although alternative channels cannot be excluded, their probabilities may be substantially lower. The studies of magnetars associated with SNRs consistently favor non-very massive progenitors, implying that such progenitors may produce a considerable fraction of magnetars. We also backtrack the trajectories of SGR 1935+2154 and its surrounding stars to search for its potential massive companions, yet no such companions are found.

In this paper, we report the detection of the very-high-energy (VHE, 100 GeV < E < 100 TeV) and ultra-high-energy (UHE, E > 100 TeV) γ-ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended γ-ray source was detected with a significance of ∼16 σ by KM2A and ∼17 σ by WCDA, respectively. The angular extension of this γ-ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the γ-ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV.

We present the first deep radio continuum observations of Pa 30, a nebula hosting a unique optical source driven by an ultrafast outflow with a velocity of 16,000 km s-1. The nebula was proposed to be the remnant of a white dwarf merger that occurred in 1181CE. We report no detection of the radio diffuse emission from Pa 30 or radio emission from the central source, setting 3 sigma upper limit flux densities of 0.84 and 0.29 mJy at 1.5 and 6 GHz, respectively, for Pa 30. The radio surface brightness of Pa 30 is similar to 3 orders of magnitude smaller than that of typical supernova remnants (SNRs) with comparable angular size. If Pa 30 is an SNR, our observations show it to be the faintest known in the radio band. Considering that 10% of the supernova (SN) kinetic energy is transferred to cosmic rays (CRs), the absence of radio synchrotron emission suggests that the SN kinetic energy less than or similar to 3 x 1047(B/10 mu G)-1.65 erg, which is 3-4 orders of magnitude lower than that of typical SNRs and the lowest measured among Galactic SNRs. There is also an indication of inefficient CR acceleration for this source. The low SN kinetic energy either implies the potential existence of many more radio-faint, subenergetic SNRs in our Galaxy or challenges the SNR interpretation of Pa 30.

The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5–4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard. In this paper, the science objectives of the EP mission are presented. EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales. Among them, fast extragalactic transients will be surveyed systematically in soft X-rays, which include γ-ray bursts and their variants, supernova shock breakouts, and the predicted X-ray transients associated with binary neutron star mergers. EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei, possibly at an early phase of the flares for some. EP will monitor the variability and outbursts of X-rays from white dwarfs, neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments, and is expected to discover new objects. A large sample of stellar X-ray flares will also be detected and characterised. In the era of multi-messenger astronomy, EP has the potential of detecting the possible X-ray counterparts of gravitational wave events, neutrino sources, and ultra-high energy γ-ray and cosmic ray sources. EP is expected to help advance the studies of extreme objects and phenomena revealed in the dynamic X-ray universe, and their underlying physical processes. Besides EP’s strength in time-domain science, its follow-up telescope, with excellent performance, will also enable advances in many areas of X-ray astronomy.

We present 1.25 GHz observations of the rotating radio transient (RRAT) J2325–0530, conducted with the Five-hundred-meter Aperture Spherical radio Telescope. Approximately 60% of detected single pulses occur in clusters of two to five consecutive bursts. Consequently, the waiting-time distribution between successive single pulses exhibits a pronounced excess at one rotation period, deviating from the exponential distribution expected for a Poisson process. After grouping consecutive bursts into single emission events, the recalculated waiting-time distribution is well described by a Weibull distribution with a shape parameter k ≳ 1. Monte Carlo simulations incorporating both intrinsic burst on-windows and rotational modulation successfully reproduce the observed one-rotation excess. These results suggest that RRAT J2325–0530 emits through a quasi-random process with on-windows slightly longer than its spin period, modulated by the rotation of the emission beam. Additionally, the polarization position angle shows complex behavior that cannot be fully described by the standard rotating vector model, and several pulses exhibit quasiperiodic microstructures. Taken together, these features indicate complex magnetospheric dynamics underlying the sporadic emission behavior of RRAT J2325–0530.