Joint Space Science Institute

Magnetic reconnection at the near-Sun heliospheric current sheet (HCS) dissipates the Parker spiral and converts magnetic energy into kinetic energy of the plasma constituents. Observations at a radial distance of ~16.25 Rs by Parker Solar Probe associated with the encounter 14 (E14) HCS crossing have shown that reconnection-driven particle acceleration mechanisms, likely facilitated by the merging of large-scale flux tubes, are able to accelerate protons up to ~400 keV, which is ≈1000 times greater than the available magnetic energy per particle during this crossing (Desai et al. 2025; Phan et al. 2024). In this paper, we present a detailed analysis of the pitch-angle distributions, differential energy spectra, and maximum energies and spectra of protons and heavy ions (He, O, and Fe) in conjunction with observations of local wave activity during the E14 HCS crossing. Our results show the following: 1) First direct observations of the energization of protons and heavy ions during reconnection. 2) First direct observations that the power-law spectral slopes of heavy ions differ from that of protons, which contradicts previous simulation results where the spectral indices of all ion species are essentially identical. 3) First demonstration that the anisotropies and beams of ions produced during reconnection drive waves in the ion cyclotron range of frequencies. 4) First evidence that the pitch angle scattering of protons is stronger than that of the other ion species and that this might be responsible for the harder spectral slopes of the heavy ions compared with protons. In summary, PSP observations during the E14 HCS crossing provide strong evidence for in-situ reconnection-driven acceleration of protons and heavy ions at the near-Sun HCS that will need to be fully accounted for by contemporary reconnection-driven energization models.

Abstract The General Coordinates Network (GCN) is NASA’s time-domain and multimessenger alert system. GCN distributes two data products: automated “Notices” and human-generated “Circulars” that report the observations of high-energy and multimessenger astronomical transients. The flexible and nonstructured format of GCN Circulars, comprising more than 40,500 Circulars accumulated over three decades, makes it challenging to manually extract observational information, such as redshift or observed wave bands. In this work, we employ large language models (LLMs) to facilitate the automated parsing of transient reports. We develop a neural topic modeling pipeline with open-source tools for the automatic clustering and summarization of astrophysical topics in the Circulars archive. Using neural topic modeling and contrastive fine-tuning, we classify Circulars based on their observation wave bands and messengers. Additionally, we separate gravitational-wave event clusters and their electromagnetic counterparts from the Circulars archive. Finally, using the open-source Mistral model, we implement a system to automatically extract gamma-ray burst (GRB) redshift information from the Circulars archive, without the need for any training. Evaluation against the manually curated Neil Gehrels Swift Observatory GRB table shows that our simple system, with the help of prompt-tuning, output parsing, and retrieval augmented generation (RAG), can achieve an accuracy of 97.2% for redshift-containing Circulars. Our neural search-enhanced RAG pipeline accurately retrieved 96.8% of redshift Circulars from the manually curated archive. Our study demonstrates the potential of LLMs to automate and enhance astronomical text mining and provides a foundational work for future advances in transient alert analysis.

Abstract Stellar feedback drives multiphase gas outflows from starburst galaxies, but the interpretation of dust emission in these winds remains uncertain. To investigate this, we analyze new JWST mid-infrared images tracing polycyclic aromatic hydrocarbon (PAH) emission at 7.7 and 11.3 μ m from the outflow of the prototypical starburst M82 out to 3.2 kpc. We find that PAH emission shows significant correlations with CO, H α , and X-ray emission within the outflow, though the strengths and behaviors of these correlations vary with gas phase and distance from the starburst. PAH emission correlates strongly with cold molecular gas, with PAH–CO scaling relations in the wind nearly identical to those in galaxy disks despite the very different conditions. The H α –PAH correlation indicates that H α traces the surfaces of PAH-bearing clouds, consistent with arising from ionized layers produced by shocks. Meanwhile, the PAH–X-ray correlation disappears once distance effects are controlled for past 2 kpc, suggesting that PAHs are decoupled from the hot gas and the global correlation merely reflects the large-scale structure of the outflow. The PAH-to-neutral gas ratio remains nearly flat to 2 kpc, with variations following changes in the radiation field. This implies that the product of PAH abundance and dust-to-gas ratio does not change significantly over the inner portion of the outflow. Together, these results demonstrate that PAHs robustly trace the cold phase of M82’s wind, surviving well beyond the starburst and providing a powerful, high-resolution proxy for mapping the life cycle of entrained cold material in galactic outflows.

Abstract We present WNTR23bzdiq/WTP19aalzlk, a slow eruption of an early-asymptotic giant branch (AGB) star in M31 identified by the Wide-field Infrared Transient Explorer near-infrared (NIR) and the NEOWISE mid-infrared (MIR) surveyors. This source brightened gradually over 7 yr: a 0.5 mag optical rise (2018–2021), a 1 mag optical outburst lasting ∼1000 days (2021–2023), and another 1 mag optical rebrightening in 2024. This was accompanied by a steady MIR brightening of 1 mag over 10 yr in NEOWISE data. Archival optical data show only erratic, small-amplitude (<0.3 mag) brightness variations from 2003 to 2015, revealing a progenitor star with T eff ≈ 3500 K and L ≈ 1.6 × 10 4 L ⊙ —consistent with a 7 ± 2 M ⊙ star in its early-AGB phase. During the eruption, the luminosity rose to ≈5 × 10 4 L ⊙ with slow photospheric expansion (≈5 km s −1 ) and constant temperatures (≈3600 K) inferred from the spectral energy distribution. Optical and NIR spectra of the eruption resemble late M-type stars, with a mixed-temperature behavior—transitioning from M1 in the optical to M7/M8 in the NIR. These properties of WNTR23bzdiq resemble those of stellar merger transients, particularly the giant star merger OGLE-2002-BLG-360, but on longer timescales. As such, WNTR23bzdiq potentially marks the onset of common envelope evolution (CEE) in a binary with an AGB primary, and is possibly a member of the emerging population of infrared transients from CEE in giant stars. Continued multiwavelength monitoring, particularly MIR observations with JWST to quantify dust production, will shed further light on WNTR23bzdiq.

Abstract The Neil Gehrels Swift Observatory (Swift) Burst Alert Telescope (BAT) is a coded aperture gamma-ray instrument with a large field of view that was designed to detect and localize transient events. When a transient is detected, either on board or externally, the BAT saves time-tagged event (TTE) data, which provide the highest-quality information of the locations of the photons on the detector plane and their energies. These data can be used to produce spectra, lightcurves, and sky images of a transient event. While these data products are produced by the Swift Data Center and can be produced by current software, they are often preset to certain time and energy intervals, which have limited their use in the current time domain and multimessenger environment. Here, we introduce a new capability for the BatAnalysis Python package to download and process TTE data under an open-source Python framework that allows for easy interfacing with other Python packages. The new capabilities of the BatAnalysis software allow for TTE data to be used by the community in a variety of advanced customized analyses of astrophysical sources which BAT may have TTE data for, such as fast radio bursts (FRBs), gamma-ray bursts (GRBs), low-mass X-ray binaries (LMXB), soft gamma repeaters, magnetars, and many other sources. We highlight the usefulness of the BatAnalysis package in analyzing TTE data produced by an onboard GRB trigger, an FRB external trigger, a subthreshold detection of the LMXB EXO 0748–676, and an external trigger of a GRB that BAT detected during a slew.

Abstract We present an analysis of the Hα-emitting ionized gas in the warm phase of the NGC 253 outflow using integral field spectroscopy from the Multi Unit Spectroscopic Explorer. In each spaxel, we decompose Hα, [N ii], and [S ii] emission lines into a system of up to three Gaussian components, accounting for the velocity contributions due to the disk and both intercepted walls of an outflow cone. In the approaching southern lobe of the outflow, we find maximum deprojected outflow velocities down to ∼−500 km s−1. Velocity gradients of this outflowing gas range from ∼−350 to −550 km s−1 kpc−1 with increasing distance from the nucleus. Additionally, [N ii]/Hα and [S ii]/Hα integrated line ratios are suggestive of shocks as the dominant ionization source throughout the wind. Electron densities, inferred from the [S ii] doublet, peak at 2100 cm−3 near the nucleus and reach ≲50 cm−3 in the wind. Finally, at an uncertainty of 0.3 dex on the inferred mass of 4 × 105 M ⊙, the mass-outflow rate of the Hα-emitting gas in the southern outflow lobe is ∼0.4 M ⊙ yr−1. This yields a mass-loading factor of η ∼ 0.1 and a ∼2% starburst energy efficiency.

Abstract We present Cryoscope, a new 50 deg2 field-of-view, 1.2 m aperture, K dark survey telescope to be located at Dome C, Antarctica. Cryoscope has an innovative optical–thermal design wherein the entire telescope is cryogenically cooled. Cryoscope also explores new detector technology to cost-effectively tile the full focal plane. Leveraging the dark Antarctic sky and minimizing telescope thermal emission, Cryoscope achieves unprecedented deep, wide, fast, and red observations, matching and exceeding volumetric survey speeds from the Ultraviolet Explorer, Vera Rubin Observatory, Nancy Grace Roman Space Telescope, SPHEREx, and NEO Surveyor. By providing coverage beyond wavelengths of 2 μm, we aim to create the most comprehensive dynamic movie of the most obscured reaches of the Universe. Cryoscope will be a dedicated discovery engine for electromagnetic emission from coalescing compact binaries, Earth-like exoplanets orbiting cold stars, and multiple facets of time-domain, stellar, and solar system science. In this paper, we describe the scientific drivers and technical innovations for this new discovery engine operating in the K dark passband, why we choose to deploy it in Antarctica, and the status of a fifth-scale prototype designed as a Pathfinder to retire technological risks prior to full-scale implementation. We plan to deploy the Cryoscope Pathfinder to Dome C in 2026 December and the full-scale telescope by 2030.

Abstract Tidal disruption events (TDEs) that are spatially offset from the nuclei of their host galaxies offer a new probe of massive black hole (MBH) wanderers, binaries, triples, and recoiling MBHs. Here we present AT2024tvd, the first off-nuclear TDE identified through optical sky surveys. High-resolution imaging with the Hubble Space Telescope shows that AT2024tvd is 0 . ″ 914 ± 0 . ″ 010 offset from the apparent center of its host galaxy, corresponding to a projected distance of 0.808 ± 0.009 kpc at z = 0.045. Chandra and Very Large Array observations support the same conclusion for the TDE’s X-ray and radio emission. AT2024tvd exhibits typical properties of nuclear TDEs, including a persistent hot UV/optical component that peaks at L bb ∼ 6 × 1043 erg s−1, broad hydrogen lines in its optical spectra, and delayed brightening of luminous (L X,peak ∼ 3 × 1043 erg s−1), highly variable soft X-ray emission. The MBH mass of AT2024tvd is 106±1 M ⊙, at least 10 times lower than its host galaxy’s central black hole mass (≳108 M ⊙). The MBH in AT2024tvd has two possible origins: a wandering MBH from the lower-mass galaxy in a minor merger during the dynamical friction phase or a recoiling MBH ejected by triple interactions. Combining AT2024tvd with two previously known off-nuclear TDEs discovered in X-rays (3XMM J2150 and EP240222a), which likely involve intermediate-mass black holes in satellite galaxies, we find that the parent galaxies of all three events are very massive (∼1010.9 M ⊙). This result aligns with expectations from cosmological simulations that the number of offset MBHs scales linearly with the host halo mass.

Abstract We present the third phase of the largest high-frequency, high-resolution imaging survey of 231 nearby, hard X-ray selected active galactic nuclei (AGNs), with a very high 98% ± 1% detection fraction. This survey presents VLA 22 GHz radio observations with 1″ spatial resolution covering over 6 orders of magnitude in radio luminosity in nearby AGNs that span ∼4 orders of magnitude in black hole mass and X-ray luminosity. We identify three different radio morphologies: 44% ± 3% (102/231) are compact or unresolved, 46% ± 3% (106/231) show an extended structure (star formation, possible one-sided jets, etc.), and 8% ± 2% (19/231) have a biconical or two-sided jet-like morphology. The remaining 2% ± 1% (4/231) sources are nondetections. The radio-to-X-ray luminosity ratios of the Swift-BAT AGNs in our sample (L R /L 14−195keV ∼ 10−5.5 and L R /L 2−10keV ∼ 10−5 with a scatter of ∼0.5 dex) are similar to that of coronally active stars (L R /L X ∼ 10−5). For most targets, extended emission in radio-quiet objects is broadly consistent with the expectation for star formation from previous far-infrared observations once the contribution from the radio core has been subtracted. Our sample represents nearby analogs of distant AGNs at the peak of black hole growth, and thus the high detection fraction in our work has important implications for future high frequency AGN radio surveys with the next generation Very Large Array or Square Kilometre Array, both of which should detect large fractions of more distant AGNs.