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The Einstein Probe (EP) has detected several fast X-ray transients (FXTs) associated with broad-lined Type Ic supernovae (SNe), including EP240414a and EP250108a. The observations reveal common features among these FXTs, but the corresponding physical origin remains debated. By comparing the FXTs with low-luminosity gamma-ray bursts (GRBs; e.g., GRB 171205A), we propose a unified model that explains the common features in these events. In this model, a rapidly spinning magnetar generates a collimated Poynting-flux-dominated jet and an isotropic wind. As the jet propagates through the stellar envelope, it generates a hot cocoon. In addition, a pulsar wind nebula (PWN) is formed during the interaction of the wind and the ejecta. As the surrounding cocoon gradually becomes transparent, the emission from the PWN escapes and is observed. This model provides a unified explanation for the observations: (1) early thermal emission originates from the cocoon, (2) midterm nonthermal emission comes from the PWN, (3) late-term emission originates from SNe driven by <SUP>56</SUP>Ni radioactive decay and magnetar, and (4) the X-ray afterglow originates from the structured jet. Our research thus provides a natural explanation for the observed thermal-to-nonthermal evolution in such FXTs and reveals their shared physical origin with some GRB-SNe.

We present a comprehensive Bayesian spectral analysis of the black hole X-ray binary 4U 1630−47 during its 2022 outburst, using simultaneous NICER and NuSTAR observations. Using the traditional frequentist approach, we build our model combining reflection spectroscopy with continuum-fitting techniques and analyze the data. In the Bayesian framework, we jointly constrain the black hole's spin, mass, and inclination within a unified framework. Employing nested sampling, we capture parameter degeneracies and rigorously propagate both statistical and systematic uncertainties. Our results yield robust evidence for a high spin, with the exact value still subject to model-dependent systematic uncertainties from both approaches. Our Bayesian analysis infers spin <inline-formula> <mml:math><mml:msup><mml:mrow><mml:mi>a</mml:mi></mml:mrow><mml:mrow><mml:mo>*</mml:mo></mml:mrow></mml:msup><mml:mo>=</mml:mo><mml:mn>0.9</mml:mn><mml:msubsup><mml:mrow><mml:mn>6</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>0.03</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.02</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula>, mass <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>BH</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>12.1</mml:mn><mml:msubsup><mml:mrow><mml:mn>9</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>1.46</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>1.22</mml:mn></mml:mrow></mml:msubsup><mml:mspace></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math> </inline-formula>, and inclination angle <inline-formula> <mml:math><mml:mi>i</mml:mi><mml:mo>=</mml:mo><mml:mn>55.7</mml:mn><mml:msubsup><mml:mrow><mml:mn>5</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>1.37</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>1.60</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula> degrees, obtained via the relxillNS version of our model. It also demonstrates the power of Bayesian inference in providing valuable insights into the complex physics of black hole accretion and enabling high-confidence measurements of fundamental parameters.

The optical counterpart of the gravitational wave event GW170817, known as kilonova, has provided strong evidence that binary neutron star mergers are favourable sites to host the r-process nucleosynthesis. Kilonova is a quasi-thermal electromagnetic emission powered by the radioactive decay of heavy neutron-rich nuclei produced by the r-process. Considering the variety of elements contributing to kilonova ejecta, essential information about its composition can be achieved through spectral characterisation, radiative transfer simulations, and opacities. The latter represents one of the most challenging aspects of the modelling, as it relies on accurate atomic structure calculations of energy levels and transitions. Since light r-process elements are major opacity contributors in early (&lt;2 days) scenario, this work focuses on atomic calculations for Zr I--IV. Energy levels and bound-bound transitions are determined using the GRASP2018 code, assuming two different datasets for each ionisation stage: one including, and one excluding core-core and core-valence correlations. Results demonstrate that the inclusion of f shell and core correlations impacts on both energy levels and transitions. A systematic assessment of the accuracy is performed through detailed comparisons with the NIST ASD and literature references. Finally, these Zr data are integrated on the open access MARTINI platform.

Power color─color diagrams provide a useful diagnostic tool for studying the evolution of outbursts in black hole X-ray binaries. In this paper, we present power color─color diagrams of three sources (MAXI J1348─630, MAXI J1820+070, and Swift J1727.8─1613) observed with Insight-HXMT in a wide energy range of 2─80 keV. We compared the hue regions defined by RXTE, which are associated with different spectral states, with the Insight-HXMT results. We find that, for hard and hard-intermediate states (IMSs), the trajectories of Insight-HXMT in the power color─color diagrams are generally consistent with those of RXTE. In the soft and soft-IMSs, weak variability generally prevents robust hue constraints. Nevertheless, a few points in MAXI J1348─630 deviate from the RXTE-defined regions, possibly because of averaged variable power spectra and the presence of a type-A quasi-periodic oscillation. The trajectories of MAXI J1348─630 and MAXI J1820+070 exhibited roughly consistent patterns over different energy bands, whereas Swift J1727.8─1613 was an exception during its very high state, caused by an additional low-frequency component in the low-energy band. We found that the very high state can be identified through the power color─color diagram, exhibiting a hue similar to that of the hard-IMS but not forming a loop pattern. We also investigated the relationship between hue and hardness, and find that although they are generally anticorrelated, they provide consistent timing for the spectral state transitions.

The origins of fast radio bursts (FRBs) remain uncertain, although magnetars are a leading progenitor candidate. Because magnetars are thought to form primarily through core-collapse supernovae in young stellar populations, the discovery of FRB 20200120E in a globular cluster (GC) in the nearby galaxy M81 was unexpected given the ancient stellar populations of GCs. Expanding the sample of FRBs localized to nearby galaxies is therefore essential for testing FRB formation channels in old stellar environments. M49 (NGC 4472) is a nearby (<inline-formula><tex-math>$\approx 17$</tex-math></inline-formula> Mpc), radio-quiet giant elliptical galaxy in the Virgo cluster hosting an extensive GC system (<inline-formula><tex-math>$\approx 7000$</tex-math></inline-formula> GCs), making it an ideal target for GC FRB searches. We conducted a 9-h SnapShotCal observation of M49 using the Five-hundred-meter Aperture Spherical Telescope (FAST) 19-beam receiver, covering approximately 4230 GCs (<inline-formula><tex-math>$T_{\rm eff}={2.1}$</tex-math></inline-formula> h per GC), and performed a comprehensive single-pulse search with TRANSIENTX over a dispersion-measure range of 0─<inline-formula><tex-math>$5000\, \mathrm{pc\, cm^{-3}}$</tex-math></inline-formula>. No unambiguous astrophysical FRBs were detected. The most significant trigger reached a post-processed signal-to-noise ratio of <inline-formula><tex-math>$8.6\, \sigma$</tex-math></inline-formula> at a dispersion measure of <inline-formula><tex-math>$412.2\, \mathrm{pc\, cm^{-3}}$</tex-math></inline-formula>, but is statistically consistent with thermal noise after accounting for the false-alarm rate. Using the radiometer equation, we derive a beam-averaged peak flux-density sensitivity of <inline-formula><tex-math>$\approx 16.5$</tex-math></inline-formula> mJy (corresponding to a fluence limit of <inline-formula><tex-math>$\approx 16.5\, \mathrm{mJy\, ms}$</tex-math></inline-formula> for a 1 ms burst) and place an upper limit on the FRB occurrence rate of <inline-formula><tex-math>${4.7}\times 10^{-4}\, \mathrm{FRB\, GC^{-1}\, h^{-1}}$</tex-math></inline-formula>. Our non-detection implies that no bright bursts were observed above this fluence threshold during the observing window. The derived rate limit is therefore sensitivity-limited and applies only to bursts above <inline-formula><tex-math>$\approx 16.5\, \mathrm{mJy\, ms}$</tex-math></inline-formula> (for a 1 ms burst), constraining only the detectable (high-fluence) portion of the GC FRB population.