Jake A. J. Mitchell

The AGN Space Telescope and Optical Reverberation Mapping (STORM) 2 campaign targeted Mrk 817 with intensive multiwavelength monitoring and found its soft X-ray emission to be strongly absorbed. We present results from 157 near-IR spectra with an average cadence of a few days. Whereas the hot dust reverberation signal as tracked by the continuum flux does not have a clear response, we recover a dust reverberation radius of ∼90 lt-days from the blackbody dust temperature light curve. This radius is consistent with previous photometric reverberation mapping results when Mrk 817 was in an unobscured state. The heating/cooling process we observe indicates that the inner limit of the dusty torus is set by a process other than sublimation, rendering it a luminosity-invariant “dusty wall” of a carbonaceous composition. Assuming thermal equilibrium for dust optically thick to the incident radiation, we derive a luminosity of ∼6 × 10 ⁴⁴ erg s ⁻¹ for the source heating it. This luminosity is similar to that of the obscured spectral energy distribution, assuming a disk with an Eddington accretion rate of m ̇ ∼ 0.2 . Alternatively, the dust is illuminated by an unobscured lower luminosity disk with m ̇ ∼ 0.1 , which permits the UV–optical continuum lags in the high-obscuration state to be dominated by diffuse emission from the broad-line region. Finally, we find hot dust extended on scales ≳ 140–350 pc, associated with the rotating disk of ionised gas we observe in spatially resolved [S III ] λ 9531 images. Its likely origin is in the compact bulge of the barred spiral host galaxy, where it is heated by a nuclear starburst.

Aims. In this study, we examine the evolution of the plasma parameters, elemental abundances, and X-ray emission source during a long-duration M1-class solar flare and analyze the results in relation to the accompanying coronal mass ejection (CME). Methods. We used SUNSTORM 1/XFM-CS soft X-ray data to study flare characteristics during an eruption that occurred on the Sun on June 24, 2024, from Active Region 13712. The XFM-CS data were fit with a two-component thermal model using PyXspec. Soft X-ray results were connected with X-ray image reconstructions from SolO/STIX data. The X-ray analysis was complemented with remote-sensing data from STEREO-A/SECCHI and EUVI, SOHO/LASCO, and SDO/AIA to provide a detailed account of the event. Results. The CME onset corresponds to an increase in X-ray flux, plasma temperature, and emission measure. Prominent X-ray loops are observed in extreme ultraviolet (EUV) after the eruption and remain visible throughout the day. STIX imaging results reveal a large, gradually evolving thermal loop-top emission source. The first ionization potential (FIP) bias does not show signs of recovery even hours after the eruption for any of the fitted elements. The results strongly support the claim that the associated CME delays elemental abundance recovery, providing a connection between flares and CMEs that can be observed and studied with X-rays.

Solar jets are collimated plasma ejections driven by magnetic reconnection, which play a critical role in the energy release and mass transport in the solar atmosphere. Using Solar Orbiter’s Extreme Ultraviolet Imager (EUI) with its unprecedented spatiotemporal resolution, we report the discovery of nine transient coronal jets associated with a filament eruption on September 30, 2024. These jets, with a median lifetime of only 22 seconds, have significantly shorter timescales than previously observed coronal jets. They exhibit diverse morphologies and properties, evolving through three distinct phases of the filament eruption: initiation, rise, and peak. The spatial and temporal distribution of the jets suggests they are driven by dynamic magnetic reconnection between the erupting filament and overlying magnetic fields. These jets represent a distinct class of phenomena different from traditional mini-filament-driven jets, being directly associated with large-scale filament eruption processes. This study reveals a previously unrecognised class of highly transient jets, highlighting the complexity of reconnection-driven processes during filament eruptions and underscoring the importance of high-resolution observations in uncovering fundamental plasma dynamics in the solar atmosphere.

Solar jets are collimated plasma ejections driven by magnetic reconnection, which play a critical role in the energy release and mass transport in the solar atmosphere. Using Solar Orbiter's Extreme Ultraviolet Imager (EUI) with its unprecedented spatiotemporal resolution, we report the discovery of nine transient coronal jets associated with a filament eruption on September 30, 2024. These jets, with a median lifetime of only 22 seconds, have significantly shorter timescales than previously observed coronal jets. They exhibit diverse morphologies and properties, evolving through three distinct phases of the filament eruption: initiation, rise, and peak. The spatial and temporal distribution of the jets suggests they are driven by dynamic magnetic reconnection between the erupting filament and overlying magnetic fields. These jets represent a distinct class of phenomena different from traditional mini-filament-driven jets, being directly associated with large-scale filament eruption processes. This study reveals a previously unrecognised class of highly transient jets, highlighting the complexity of reconnection-driven processes during filament eruptions and underscoring the importance of high-resolution observations in uncovering fundamental plasma dynamics in the solar atmosphere.

Context. The acceleration of particles at the Sun and their propagation through interplanetary space are key topics in heliophysics. Specifically, solar energetic electrons (SEEs) measured in situ can be linked to solar events such as flares and coronal mass ejections (CMEs) since they are also observed remotely in a broad range of electromagnetic emissions such as in radio and X-rays. Solar Orbiter, equipped with a wide range of remote-sensing and in situ detectors, provides an excellent opportunity to investigate SEEs and their solar origin from the inner heliosphere. Aims. We aim to record all SEE events measured in situ by Solar Orbiter, and to identify and characterise their potential solar counterparts. The results have been compiled in the Comprehensive Solar Energetic Electron event Catalogue (CoSEE-Cat), which will be updated regularly as the mission progresses. The catalogue contains key parameters of the SEEs, as well as the associated flares, CMEs, and radio bursts. In this paper, we describe the catalogue and provide a first statistical analysis. Methods. The Energetic Particle Detector (EPD) was used to identify and characterise SEE events, infer the electron release time at the Sun, and determine the composition of related energetic ions. Basic parameters of associated X-ray flares (timing, intensity, source location) were provided by the Spectrometer/Telescope for Imaging X-rays (STIX). This was complemented by the Extreme Ultraviolet Imager (EUI), which added information on eruptive phenomena. CME observations were contributed by the coronagraph Metis and the Solar Orbiter Heliospheric Imager (SoloHI). Type III radio bursts observed by the Radio and Plasma Waves (RPW) instrument provided a link between the SEEs detected at Solar Orbiter and their potential solar sources. The conditions in interplanetary space were characterised using Solar Wind Analyzer (SWA) and Solar Orbiter Magnetometer (MAG) measurements. Finally, data-driven modelling with the Magnetic Connectivity Tool provided an independent estimate of the solar source position of the SEEs. Results. The first data release of the catalogue contains 303 SEE events observed in the period from November 2020 until the end of December 2022. Based on the timing and magnetic connectivity of their solar counterparts, we find a very clear distinction between events with an impulsive ion composition and ones with a gradual one. These results support the flare-related origin of impulsive events and the association of gradual events with extended structures such as CME-driven shocks or erupting flux ropes. We also show that the commonly observed delays of the solar release times of the SEEs relative to the associated X-ray flares and type III radio burst are at least partially due to propagation effects and not exclusively due to an actual delayed injection. This effect is cumulative with heliocentric distance and is probably related to turbulence and cross-field transport.

The looptop region in solar flares is a crucial site to understand the physical processes of magnetic reconnection and particle acceleration. Here, we report novel details of a flare looptop X-ray source that is associated with electron acceleration. The looptop source exhibits an oscillation in height that is statistically anticorrelated with the X-ray intensity, in which the variation in intensity slightly precedes the height. Two oscillation periods are found, i.e., a period of ∼2 minutes with a large amplitude and a relatively weak period of ∼1 minute. The nonthermal electron spectral index and flux deduced from X-ray spectra, and the intensity of flare ribbons/footpoints seen in EUV/UV images all show similar oscillations. In addition, the repeated downward contracting loops/plasmoids from the reconnection current sheet are observed. These observations strongly support a physical scenario where repeated reconnection outflows impinge on the flare looptop, while concurrently accelerated electrons are also quasiperiodically injected into it. These energy inputs (bulk flow and electron beams) subsequently produce oscillations in the looptop X-ray source, and cause brightness fluctuations in the flare ribbons/footpoints in the lower atmosphere.

Near IR spectroscopic reverberation of Active Galactic Nuclei (AGN) potentially allows the IR broad line region (BLR) to be reverberated alongside the disc and dust continua, while the spectra can also reveal details of dust astro-chemistry. Here we describe results of a short pilot study (17 near-IR spectra over a 183 day period) for Mrk 509. The spectra give a luminosity-weighted dust radius of 〈R_{d, lum}〉 = 186 ± 4 light-days for blackbody (large grain dust), consistent with previous (photometric) reverberation campaigns, whereas carbon and silicate dust give much larger radii. We develop a method of calibrating spectral data in objects where the narrow lines are extended beyond the slit width. We demonstrate this by showing our resultant photometric band lightcurves are consistent with previous results, with a hot dust lag at >40 days in the K-band, clearly different from the accretion disc response at z-band. We place this limit of 40 days by demonstrating clearly that the modest variability that we do detect in the H and K-band does not reverberate on timescales of less than 40 days. We also extract the Paβ line lightcurve, and find a lag which is consistent with the optical BLR Hβ line of ∼70 − 90 days. This is important as direct imaging of the near-IR BLR is now possible in a few objects, so we need to understand its relation to the better studied optical BLR.

An intensive reverberation mapping campaign of the Seyfert 1 galaxy Mrk 817 using the Cosmic Origins Spectrograph on the Hubble Space Telescope revealed significant variations in the response of broad UV emission lines to fluctuations in the continuum emission. The response of the prominent UV emission lines changes over an ∼60 day duration, resulting in distinctly different time lags in the various segments of the light curve over the 14 month observing campaign. One-dimensional echo-mapping models fit these variations if a slowly varying background is included for each emission line. These variations are more evident in the C iv light curve, which is the line least affected by intrinsic absorption in Mrk 817 and least blended with neighboring emission lines. We identify five temporal windows with a distinct emission-line response, and measure their corresponding time delays, which range from 2 to 13 days. These temporal windows are plausibly linked to changes in the UV and X-ray obscuration occurring during these same intervals. The shortest time lags occur during periods with diminishing obscuration, whereas the longest lags occur during periods with rising obscuration. We propose that the obscuring outflow shields the broad UV lines from the ionizing continuum. The resulting change in the spectral energy distribution of the ionizing continuum, as seen by clouds at a range of distances from the nucleus, is responsible for the changes in the line response.