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1. Longtime Monitoring of TeV Radio Galaxies with HAWC

   https://doi.org/10.3847/1538-4357/ae1009  

   Alfaro, R; Alvarez, C; Anita-Rangel, E; Arteaga-Velázquez, J C; Avila_Rojas, D; Ayala_Solares, H A; Babu, R; Bangale, P; Belmont-Moreno, E; Bernal, A; et al (November 2025, The Astrophysical Journal)

   Abstract We present the monitoring of the TeV-emitting radio galaxies M87, NGC 1275, 3C 264, and IC 310 with the High-Altitude Water Cherenkov Observatory (HAWC) over a period of approximately 7.5 yr. The analysis includes light curves at daily, weekly, and monthly timescales for the four sources. We report the detection of gamma-ray emission from M87 with a significance exceeding 5σ, providing the integrated TeV spectrum from the longest temporal coverage to date. The source is well described as a point-like source modeled by a power-law spectrum with spectral index Γ = 2.53 ± 0.29 and a flux of (7.09 ± 1.24) × 10⁻¹³cm⁻²s⁻¹TeV⁻¹at 1 TeV. The maximum energy of the detected emission in M87, at 1σconfidence level, reaches 26.5 TeV. HAWC’s observation of M87 reveals a low flux spectrum for the longest observation to date of this radio galaxy. 3C 264 is marginally detected with a significance slightly below 4σ, while NGC 1275 and IC 310 are not detected. The weekly light curves show an increased number of fluxes above 2σfor M87 starting in 2019 and for 3C 264 starting in 2018, which can be interpreted as the moments at which these sources start to exhibit an enhanced steady TeV emission. Cumulative significance analysis reveals quantitative evidence for long-term variability. M87 shows enhanced emission from 2019, while 3C 264 exhibits increased activity from 2018, resembling variable sources like Markarian 421 rather than steady sources like the Crab. This supports the importance of monitoring radio galaxies to identify periods of higher activity and flares, enabling further multimessenger studies. 

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2. Gone with the Wind: JWST-MIRI Unveils a Strong Outflow from the Quiescent Stellar-mass Black Hole A0620-00

   https://doi.org/10.3847/1538-4357/adf6b9  

   Zuo, Zihao; Cugno, Gabriele; Michail, Joseph; Gallo, Elena; Russell, David M; Plotkin, Richard M; Zou, Fan; Baglio, M Cristina; Casella, Piergiorgio; Cowie, Fraser J; et al (September 2025, The Astrophysical Journal)

   Abstract We present new observations of the black hole X-ray binary A0620-00 using the Mid-Infrared (MIR) Instrument on the James Webb Space Telescope, during a state where the X-ray luminosity is 9 orders of magnitude below Eddington, and coordinated with radio, near-infrared, and optical observations. The goal is to understand the nature of the excess MIR emission originally detected by Spitzer redward of 8μm. The stellar-subtracted MIR spectrum is well modeled by a power law with a spectral index ofα = 0.72 ± 0.01, where the flux density scales with frequency asF_ν ∝ ν^α. The spectral characteristics, along with rapid variability—a 40% flux flare at 15μm and 25% achromatic variability in the 5–12μm range—rule out a circumbinary disk as the source of the MIR excess. The Low Resolution Spectrometer reveals a prominent emission feature at 7.5μm, resulting from the blend of three hydrogen recombination lines. While the contribution from partially self-absorbed synchrotron radiation cannot be ruled out, we argue that thermal bremsstrahlung from a warm (a few tens of thousands of Kelvin) wind accounts for the MIR excess; the same outflow is responsible for the emission lines. The inferred mass outflow rate indicates that the system’s low luminosity is due to a substantial fraction of the mass supplied by the donor star being expelled through a wind rather than accreted onto the black hole. 

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3. X-Ray Polarization of the High-synchrotron-peak BL Lacertae Object 1ES 1959+650 during Intermediate and High X-Ray Flux States

   https://doi.org/10.3847/1538-4357/adbbe2  

   Pacciani, Luigi; Kim, Dawoon E; Middei, Riccardo; Marshall, Herman L; Marscher, Alan P; Liodakis, Ioannis; Agudo, Iván; Jorstad, Svetlana G; Poutanen, Juri; Errando, Manel; et al (April 2025, The Astrophysical Journal)

   Abstract We report the Imaging X-ray Polarimetry Explorer (IXPE) polarimetric and simultaneous multiwavelength observations of the high-energy-peaked BL Lacertae object (HBL) 1ES 1959+650, performed in 2022 October and 2023 August. In 2022 October, IXPE measured an average polarization degree Π_X= 9.4% ± 1.6% and an electric-vector position angleψ_X= 53° ± 5°. The polarized X-ray emission can be decomposed into a constant component, plus a rotating component, with the rotation velocityω_EVPA= (−117 ± 12) deg day⁻¹. In 2023 August, during a period of pronounced activity of the source, IXPE measured an average Π_X= 12.4% ± 0.7% andψ_X= 20° ± 2°, with evidence (∼0.4% chance probability) for a rapidly rotating component withω_EVPA= 1864 ± 34 deg day⁻¹. These findings suggest the presence of a helical magnetic field in the jet of 1ES 1959+650 or stochastic processes governing the field in turbulent plasma. Our multiwavelength campaigns from radio to X-ray reveal variability in both polarization and flux from optical to X-rays. We interpret the results in terms of a relatively slowly varying component dominating the radio and optical emission, while rapidly variable polarized components dominate the X-ray and provide minor contribution at optical wavelengths. The radio and optical data indicate that on parsec scales the magnetic field is primarily orthogonal to the jet direction. On the contrary, X-ray measurements show a magnetic field almost aligned with the parsec jet direction. Confronting with other IXPE observations, we guess that the magnetic field of HBLs on subparsec scale should be rather unstable, often changing its direction with respect to the Very Long Baseline Array jet. 

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4. Nonstop Variability of Sgr A* Using JWST at 2.1 and 4.8 μ m Wavelengths: Evidence for Distinct Populations of Faint and Bright Variable Emission

   https://doi.org/10.3847/2041-8213/ada88b  

   Yusef-Zadeh, F; Bushouse, H; Arendt, R G; Wardle, M; Michail, J M; Chandler, C J (February 2025, The Astrophysical Journal Letters)

   Abstract We present the first results of JWST Cycle 1 and 2 observations of Sgr A* using NIRCam taken simultaneously at 2.1 and 4.8μm for a total of ∼48 hr over seven different epochs in 2023 and 2024. We find correlated variability at 2.1 and 4.8μm in all epochs, continual short-timescale (a few seconds) variability, and epoch-to-epoch variable emission implying long-term (∼days to months) variability of Sgr A*. A highlight of this analysis is the evidence for subminute, horizon-scale time variability of Sgr A*, probing inner accretion disk size scales. The power spectra of the light curves in each observing epoch also indicate long-term variable emission. With continuous observations, JWST data suggest that the flux of Sgr A* is fluctuating constantly. The flux density correlation exhibits a distinct break in the slope at ∼3 mJy at 2.1μm. The analysis indicates two different processes contributing to the variability of Sgr A*. Brighter emission trends toward shallower spectral indices than the fainter emission. Cross-correlation of the light curves indicates for the first time a time delay of 3–40 s in the 4.8μm variability with respect to 2.1μm. This phase shift leads to loops in plots of flux density versus spectral index as the emission rises and falls. Modeling suggests that the synchrotron emission from the evolving, age-stratified electron population reproduces the shape of the observed light curves with a direct estimate of the magnetic field strengths in the range between 40 and 90 G and an upper cutoff energy,E_c, between 420 and 720 MeV. 

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5. SN2019wxt: An Ultrastripped Supernova Candidate Discovered in the Electromagnetic Follow-up of a Gravitational Wave Trigger

   https://doi.org/10.3847/1538-4357/acd5d5  

   Shivkumar, Hinna; Jaodand, Amruta D.; Balasubramanian, Arvind; Fremling, Christoffer; Corsi, Alessandra; Tzanidakis, Anastasios; Nissanke, Samaya; Kasliwal, Mansi; Brightman, Murray; Raaijmakers, Geert; et al (July 2023, The Astrophysical Journal)

   Abstract We present optical, radio, and X-ray observations of a rapidly evolving transient SN2019wxt (PS19hgw), discovered during the search for an electromagnetic counterpart to the gravitational-wave (GW) trigger S191213g. Although S191213g was not confirmed as a significant GW event in the off-line analysis of LIGO-Virgo data, SN2019wxt remained an interesting transient due to its peculiar nature. The optical/near-infrared (NIR) light curve of SN2019wxt displayed a double-peaked structure evolving rapidly in a manner analogous to currently known ultrastripped supernovae (USSNe) candidates. This double-peaked structure suggests the presence of an extended envelope around the progenitor, best modeled with two components: (i) early-time shock-cooling emission and (ii) late-time radioactive⁵⁶Ni decay. We constrain the ejecta mass of SN2019wxt atM_ej≈ 0.20M_⊙, which indicates a significantly stripped progenitor that was possibly in a binary system. We also followed up SN2019wxt with long-term Chandra and Jansky Very Large Array observations spanning ∼260 days. We detected no definitive counterparts at the location of SN2019wxt in these long-term X-ray and radio observational campaigns. We establish the X-ray upper limit at 9.93 × 10⁻¹⁷erg cm⁻²s⁻¹and detect an excess radio emission from the region of SN2019wxt. However, there is little evidence for SN1993J- or GW170817-like variability of the radio flux over the course of our observations. A substantial host-galaxy contribution to the measured radio flux is likely. The discovery and early-time peak capture of SN2019wxt in optical/NIR observations during EMGW follow-up observations highlight the need for dedicated early, multiband photometric observations to identify USSNe. 

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