Purple Mountain Observatory

Since April 2023, solar flares have been simultaneously observed by the Spectrometer/Telescope for Imaging X-ray (STIX) onboard ESA’s Solar Orbiter and by the Hard X-ray Imager (HXI) onboard the Chinese ASO-S mission. The two telescopes independently measure 2D Fourier components (visibilities) of the flaring X-ray radiation from different vantage points. However, by combining their datasets, it is possible to obtain a sampling of the 3D Fourier transform of thermal hard X-ray sources in solar flares. This combined dataset allows reconstructing the 3D morphology of the flaring sources by solving an inverse imaging problem.In this presentation, we describe the methodology we developed for 3D reconstruction of thermal hard X-ray sources in solar flares from combined STIX/HXI data. We present the results obtained in the case of the X9.1 GOES class event which occurred on October 3, 2024. During this event, the two instruments were in an ideal configuration, where the separation angle between them and the flaring site was approximately 90 degrees. We validate the 3D reconstruction by comparing them with the 2D images independently reconstructed from STIX and HXI data. Finally, we determine the altitude of the reconstructed X-ray source above the solar surface as a function of time, and we derive estimates of its radial velocity.

Quasi-periodic pulsations (QPPs) at sub-second periods are frequently detected in the time series of X-rays and radio emissions during stellar flares, and they can be seen in solar radio emissions. However, such short-period QPPs are rarely reported in the hard X-ray (HXR) emission of solar flares. We explored the QPP patterns at short periods in HXRs, γ-ray continuum and radio emissions produced in two solar flare on 2024 October 03 (X9.0) and 2025 January 19 (C8.2). The short period at about 1 s is simultaneously observed in wavebands of HXR and γ-ray continuum during the X9.0 flare, and the restructured images show that the HXR sources move significantly during the short-period QPP, suggesting that the short-period QPP may be caused by the interaction of hot plasma loops that are rooted in double footpoints. The similar short-period QPP is also detected in wavebands of HXR and low-frequency radio emission during the impulsive phase of a C8.2 flare, which could be associated with non-thermal electrons that are periodically accelerated by the intermittent magnetic reconnection.

Abstract Many long gamma-ray bursts (GRBs) exhibit complex prompt emission structures with multiple temporally distinct episodes, such as early-time precursors preceding the main burst. Whether these subcomponents share the same physical origin and classification properties, or represent different emission mechanisms within a single event, remains an open question. Here, we present a systematic pulse-by-pulse analysis of 22 long-duration GRBs observed by Swift, each exhibiting a well-separated precursor before the main burst. We compare duration, spectral hardness ratio, minimum variability timescale (MVT), and spectral lag between these components. Both precursors and main bursts have durations and hardness broadly consistent with Type II (collapsar-origin) GRBs. However, precursors show longer MVTs (by factors of 3–10) and diverse lags with near-zero median values, while main bursts display variable MVTs and positive lags. These differences suggest precursors may originate from distinct dissipation conditions, possibly due to cocoon shock breakout or early magnetically dominated outflows. Despite temporal differences, both episodes are consistent with a single collapsar origin, providing no evidence for dual-progenitor events. Our findings support pulse-resolved classification and show that precursors offer critical insights into jet formation and preburst activity.

Abstract The special conditions of illumination in the outermost portions of the Orion Nebula have allowed the identification in visual light of two spherical clouds that may become local centers of star formation. Multiple emission line and continuum images reveal these objects through scattering by their dust particle components. These objects fall outside the present surveys of the Orion Nebula in [C ii ] and CO and merit dedicated follow-up infrared and radio studies.

Abstract In this Letter, we present the direct observations of a mode conversion from a large-amplitude transverse propagating kink wave to antiphase large-amplitude longitudinal oscillations (LALOs) in a quiescent prominence observed on 2014 February 25. This event was simultaneously recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Behind Solar Terrestrial Relation Observatory/Extreme Ultraviolet Imager. The transverse oscillation was triggered when a global extreme-ultraviolet wave associated with an X4.9 flare swept over the northern end of the prominence. For the first time, a clearly visible, coherent large-amplitude propagating kink wave was observed in the prominence, traveling southward along the prominence spine with a phase speed of ∼380 km s −1 . The propagating wave reached its largest initial amplitude (∼15 Mm) and period (∼24 minutes) near the spine center. After one cycle of the transverse oscillation, antiphase LALOs were detected simultaneously near both ends of the prominence, exhibiting similar physical parameters (period ∼79 minutes, initial displacement amplitude ∼10 Mm, and velocity amplitude ∼12 km s −1 ). Their strict antiphase relation, supported by quantitative order-of-magnitude consistency, demonstrates that the LALOs were directly triggered by a nonlinear magnetic pressure gradient (ponderomotive effect) induced by the large-amplitude propagating kink wave. These results provide the first direct evidence of the large-amplitude transverse-to-longitudinal wave-mode conversion and reveal the nonlinear coupling mechanism in a prominence.

Abstract Primordial gravitational waves (PGWs) can only be detected by measuring the B-mode polarization of the cosmic microwave background (CMB) and large-scale arrays based on superconducting transition-edge sensors (TES) are the detectors of the choice thanks to the background-limited sensitivity. Different multiplexing readout techniques have been developed to combine the signals from multiple detectors into a reduced number of readout channels. Microwave SQUID multiplexing (μMUX) has the highest multiplexing factor, suitable for large-scale TES array readout. We are developing μMUX chips to read out TES array for the detection of PGWs. We have designed and fabricated a prototype of a 5-channel μMUX chip consisting of distributed quarter-wavelength coplanar waveguide (CPW) resonators and radio-frequency superconducting quantum interference devices (RF SQUIDs). The measured quality factor of the CPW resonators working at 4.7-4.9 GHz is higher than 104. The maximum frequency shift is about 290 kHz on average, compatible with the resonator bandwidth (~380 kHz). The mean value of magnetic flux noise is 1.1 μ$\Phi_0 / \sqrt{\mathrm{Hz}} @ 5$ kHz, corresponding to a current noise of 40 $\mathrm{pA} / \sqrt{\mathrm{Hz}}$.

Abstract Solar white-light flares (WLFs) are solar flares exhibiting enhanced emission in the optical continuum. They are critical for understanding energy release and transport mechanisms in solar flares and for conducting comparative studies with stellar WLFs. However, the scarcity of accurately and reliably measured optical continuum light curves for solar WLFs significantly hampers related studies. Based on the optimized solar WLF identification method, we construct a dataset of optical continuum light curves for 70 solar WLFs using 6173 {\AA} continuum intensity images from the Solar Dynamics Observatory. Moreover, for each solar WLF event, we also provide the location of the white-light emission enhancement signals and key parameters including bolometric energies and durations derived from both the traditional fixed-temperature blackbody model and the refined variable-temperature blackbody model. This dataset will serve as a valuable resource for future statistical investigations of solar WLFs and for comparative studies between solar and stellar flares.

Abstract We present a time-resolved joint Swift–Fermi spectral study of GRB 241030A ( z = 1.411) that cleanly isolates the synchrotron origin of its prompt emission and favors a matter-dominated internal-shock scenario. The light curve shows two episodes separated by a quiescent gap. Episode 1 (0–45 s) is well described by a single power law with photon index ≃ –3/2, consistent with the fast-cooling synchrotron slope below the peak. Episode 2 (100–200 s) exhibits two robust spectral breaks: a low-energy break at E b ∼ 2–3 keV that remains nearly constant in time, and a spectral peak E p that tracks the flux within pulses but steps down between them. The photon indices below and above E b cluster around −2/3 and −3/2, respectively, as expected for fast-cooling synchrotron emission. The burst displays an unusually small (consistent with zero) spectral lag across Fermi Gamma-ray Burst Monitor bands. At later times (≳230 s), the spectrum softens toward ∼–2.7, as expected when the observing band lies above both ν m and ν c . These behaviors are difficult to reconcile with a globally magnetized outflow with a decaying field, which naturally produces hard-to-soft E p evolution, growing ν c , and appreciable lags. By contrast, internal shocks with a roughly steady effective magnetic field and a time-variable minimum electron Lorentz factor (equivalently, for example, a varying fraction of accelerated electrons) simultaneously account for: (1) the stable E b ; (2) the intensity-tracking yet stepped-down E p ; (3) the canonical −2/3 and −3/2 slopes; and (4) the near-zero lag.

Abstract Superconducting low-loss transmission line resonators are crucial for various applications, including quantum computation and photon detection in submillimeter and far-infrared astronomy. Their performance is sensitive to both their geometry and material, with energy dissipation mainly due to two-level systems (TLS) located in amorphous dielectrics. This paper presents a lab-on-chip experiment to measure the TLS losses of sputtered SiO x and AlO x films in superconducting Nb coplanar waveguide (CPW) resonators at sub-Kelvin temperatures. Different CPW geometries are adopted for these experiments. The measurement results provide quantitative insights into TLS contributions in superconducting resonators, providing empirical evidence for material screening and circuit design.

Recent observations with SRG/eROSITA reveal the average X-ray surface brightness profile of the X-ray-emitting circumgalactic medium (CGM) around Milky Way (MW)-mass galaxies, offering valuable insights into the baryon budget in these systems. However, the estimation of the baryon mass depends critically on several assumptions regarding the gas density profile, temperature, metallicity, and the underlying halo mass distribution. Here, we assess how these assumptions affect the inferred baryon mass of the X-ray-emitting CGM in MW-mass galaxies, based on the stacked eROSITA signal. We find that variations in temperature profiles and uncertainties in the halo mass introduce the dominant sources of uncertainty, resulting in X-ray-emitting baryon mass estimates that vary by nearly a factor of four (0.8–3.5 × 10 11 M ⊙ ). Assumptions about metallicity contribute an additional uncertainty of approximately 50%. We emphasize that accurate X-ray spectral constraints on gas temperature and metallicity, along with careful modeling of halo mass uncertainty, are essential for accurately estimating the baryon mass for MW-mass galaxies. Future X-ray microcalorimeter missions will be crucial for determining the hot CGM properties and closing the baryon census at the MW-mass scale.