Thomas G. Brink

We present the first X-ray detection of the supernova (SN) impostor AT 2016blu in NGC 4559. AT 2016blu exhibited 27 detected quasiperiodic (∼113 day) outbursts between 2012 and 2026 June, presumably triggered by periastron passages in an eccentric binary system in which the primary is a ≳33 M _⊙ luminous blue variable (LBV). AT 2016blu was serendipitously observed by Chandra in 2001–2002, prior to its first documented outburst in 2012, but the stacked archival data show no X-ray detection. We monitored the source’s visual-wavelength variability around its predicted outburst time and triggered a Chandra Target of Opportunity (ToO) program in 2026 March, obtaining observations with detections over five closely spaced epochs. These data indicate an X-ray luminosity of log L X ≈ 38.64 ± 0.11 erg s ⁻¹ and an accretion rate of M ̇ ≳ 8 × 1 0 − 8 M ⊙ yr − 1 , consistent with the presence of a compact companion. We therefore conclude that AT 2016blu is the first known case of an LBV SN impostor where X-ray observations clearly favor intermittent accretion onto a compact object as the cause of the outbursts. Given that the system consists of a massive star and a compact companion, AT 2016blu is a high-mass X-ray binary (HMXB), similar to SN 2010da, although the donor star in SN 2010da is a red supergiant (RSG).

We present the photometric and spectroscopic analysis of the luminous and long-lasting Type IIn supernova (SN) 2019vxm. The SN reaches a peak V -band absolute magnitude of M _V = −20.01 ± 0.13 mag in 35.0 days and displays slow evolution in both the light curves and spectra, resembling those of long-lived SNe IIn. A mid-infrared excess is detected starting from seven months after maximum brightness, suggesting a few 10 ⁻³ M _⊙ of dust are newly formed at ≳210 days (and up to 0.01 M _⊙ at +4.5 yr). The spectra are dominated by a blue continuum at early stages, with narrow, symmetric Balmer lines and flash-ionisation emission lines of C III , N III , and He II . Comparing our flash-ionised spectrum with early interacting SN spectral models, we estimate a lower limit for the mass-loss rate of the progenitor of Ṁ ≳ 10 ⁻² M _⊙ yr ⁻¹ . A weak P Cygni absorption feature is detected in the H β profile of the high-resolution Echelle spectrum at +19.7 d, suggesting the presence of slow-moving (60 ± 10 km s ⁻¹ ), unshocked circumstellar material (CSM) arising from the pre-SN wind of the progenitor. The H α and H β profiles gradually evolve and become broader and asymmetric, showing a progressively increasing blueshift, with a clear flux deficit in the red wings of the broad velocity component after +102 days. Our observed bolometric light curve before ∼100 days can be well fitted by a power-law function ( L ( t ) = 2 × 10 ⁴⁴ ( t /day) ^−0.49 erg s ⁻¹ ), which is very similar to SN 2010jl. The bolometric luminosity evolution indicates that the progenitor mass-loss rate was ∼ 0.02 − 0.04 M _⊙ yr ⁻¹ if we assume ρ _CSM ∝ r ⁻² and the wind velocity of 60 km s ⁻¹ . These findings are consistent with an asymmetric, dense circumstellar environment, indicative of a massive, compact progenitor such as a luminous blue variable (LBV) embedded in a clumpy, asymmetric medium. However, we cannot entirely rule out an extreme red supergiant (RSG) with superwinds or a transitional post-RSG/LBV star as the potential progenitor.

We present panchromatic observations of the Type Ia supernova (SN Ia) 2023qov, ranging from ∼2 weeks before to ∼1 yr after maximum light. JWST near- and mid-infrared spectra at +276 and +363 days show ∼400 K dust emission that cools by ∼75 K between epochs, the first unambiguous spectroscopic detection of dust emission in a normal SN Ia. We find that the emission is well described by models of carbonaceous dust placed within ∼1 lt-yr of the SN, with a dust mass of ∼10 ⁻⁴ M _⊙ . We do not see evidence of active dust creation, suggesting an infrared light echo by preexisting circumstellar dust as the likely source of the emission. The JWST nebular line profiles suggest asymmetric, stratified ejecta, similar to other normal SNe Ia, though a slight double-horn structure in the argon lines indicates a toroidal enhancement. SN 2023qov exhibits a slightly red, fast-declining early light curve (Δ m ₁₅ ( B ) = 1.47 ± 0.05 mag), from which we determine a ⁵⁶ Ni mass of M ₅₆ = 0.21 ± 0.04 M _⊙ , and a distance of d = 36.0 ± 1.8 Mpc to the SN and its host, NGC 7029. The presence of circumstellar dust around a normal SN Ia has implications both for the progenitor system, suggesting a less than pristine environment, and for cosmology, as a possible source of reddening and extinction that can affect distance inferences.

We present a photometric and spectroscopic study of the superluminous Type Ia supernova SN 2022erq. Its early spectra, dominated by iron-group elements with weak intermediate-mass features, might indicate highly efficient nuclear burning, broadly similar to that inferred for some overluminous Type Ia supernovae. The rapid emergence and persistence of narrow Balmer emission lines superposed on this iron-rich spectrum provide clear evidence of long-lived interaction with a hydrogen-rich circumstellar medium (CSM), establishing SN 2022erq as a member of the rare Ia–CSM class. SN 2022erq reached a peak bolometric luminosity of ∼8 × 10 ⁴³ erg s ⁻¹ and exhibited an exceptionally slow postpeak decline, indicating that its light curve is dominated by long duration ejecta–CSM interaction. By combining H α diagnostics with bolometric light-curve modeling, we reconstruct the preexplosion mass-loss history of the progenitor. The mass-loss rate escalated by 1 order of magnitude over the final decades, rising from ∼0.04 to ∼0.6 M _⊙ yr ⁻¹ . This surge produced a massive, extended CSM shell of ∼3 M _⊙ out to ∼3.5 × 10 ¹⁶ cm. The young stellar environment (∼100 Myr) together with this substantial, extensive CSM points to a progenitor system consisting of a white dwarf and an intermediate-mass companion that underwent increasing mass loss prior to explosion.

We present new transit-timing measurements for the white dwarf-cold Jupiter system WD 1856+534, extending the baseline of observations from 311 epochs to 1498 epochs. The planet is unlikely to have survived the host star’s red-giant phase at its present location and is likely too small for common envelope evolution to take place. As such, a plausible explanation for the short semimajor axis is that the exoplanet started out on a much larger orbit and then spiraled inward through high-eccentricity tidal migration (HETM). A past study found tentative evidence for orbital growth, which could have been interpreted as a residual effect of HETM, but we find the data are consistent with a constant-period model after adding 18 new transit measurements. We use the estimated period derivative P ̇ = 0.04 ± 0.43 ms yr ⁻¹ to place a lower limit on the planetary tidal quality factor of Q p ′ ≳ 3.1 × 1 0 6 , if the planet has not already achieved spin–orbit synchronization. We also test for the presence of companion planets in the system, which could have excited WD 1856 b onto an eccentric orbit via the Kozai–Lidov process, and ultimately rule out the presence of an additional planet with mass greater than 4.0 M _J and period shorter than 1500 days. We find no evidence for nonzero eccentricity, with an upper limit of e ≲ 10 ⁻² . If the planet reached its current orbit through HETM, the low present-day eccentricity indicates that the migration process has now ceased, and any further orbital evolution, if any, will likely be governed by weak planetary tides.

We present early (≲1 yr) multiwavelength observations and analysis of six luminous fast blue optical transients (LFBOTs). We identified these LFBOTs in Zwicky Transient Facility survey data from their fast light-curve evolution ( t _1/2 ≤ 12 days), blue colors at peak brightness ( g − r ≤ −0.2 mag), a visible host galaxy, high optical luminosity ( M _g < −20 mag), and an X-ray and/or radio detection. With the exception of AT2024aehp (ZTF24abygbss), these transients exhibit peaks in their 10 GHz radio light curves at t _rest ≈ 50–100 days, with peak radio luminosities ranging from 10 ³⁸ to 10 ⁴⁰ erg s ⁻¹ . Modeling the radio emission as synchrotron radiation indicates a fast ( v = 0.1–0.3 c ) shock in a dense ( n _e ≈ 10 ³ –10 ⁴ cm ⁻³ ) medium. The X-ray emission varies by ≈2 orders of magnitude in luminosity (10 ⁴² –10 ⁴⁴ erg s ⁻¹ ) at t _rest ∼ 20 days. Analysis of the host-galaxy photometry and spectroscopy for each transient shows that LFBOTs are predominantly nonnuclear (a few kiloparsecs offset) with star-forming host galaxies of stellar masses = 10 ⁹ –10 ¹¹ M _⊙ . Unlike all other LFBOTs to date, AT2024aehp exhibited a luminous ( M < −19 mag) plateau in the optical light curve and its 6–15 GHz radio emission brightened by over an order of magnitude from t _rest ≈ 70 to 130 days. The mostly consistent radio behavior between these LFBOTs implies a similar circumburst medium, leading us to prefer a progenitor scenario in which mass is lost in a consistent way shortly prior to the terminal event.

We present spectroscopic and photometric observations of SN 2021ukt, a peculiar short-plateau object that was originally identified as a Type IIn supernovae (SN) and later underwent an unprecedented transition to a Type Ib (possibly Type IIb) SN. The early time light curves of SN 2021ukt exhibit an ∼25 day plateau. Such a short phase of hydrogen recombination suggests a rather thin H-rich outer envelope of the progenitor star. The narrow Balmer emission lines in the spectra of SN 2021ukt during the first week indicate the interaction between the expanding ejecta and the immediate circumstellar material (CSM). This H α line is observed throughout its helium-rich ejecta-dominated phase and nebular phase, suggesting persistent interaction with a radially extended CSM profile. We explore synthetic light curves among grids of parameters generated by MESA + STELLA . We also compare the spectrophotometric evolution of SN 2021ukt with several SNe that exhibit a short plateau and persistent ejecta–CSM interaction. An estimate of the progenitor mass of SN 2021ukt is made based on the flux ratio between [Ca ii ] λλ 7291, 7324 and [O i ] λλ 6300, 6364 during its nebular phase. Our analysis suggests that the progenitor star of SN 2021ukt has a zero-age main-sequence mass of M _ZAMS ≈ 12 M _⊙ , a mass of radioactive ⁵⁶ Ni synthesized in the SN ejecta of M _Ni ≈ 0.05 M _⊙ , and a mass of the H-rich envelope of M _H,env ≲ 0.5 M _⊙ . This study adds to the growing sample of transitional SNe, reinforcing evidence for a continuum of underrepresented progenitors whose evolutionary pathways lie between those of standard SN models.

We present new James Webb Space Telescope (JWST) mid-infrared (MIR) spectra and ground-based optical spectra of the lingering source at the position of supernova (SN) 2010jl, which was a relatively nearby superluminous Type IIn supernova (SLSN IIn) having strong interaction with circumstellar material (CSM). Early-time data showed evidence of dust, interpreted as either preexisting CSM dust, or as newly formed dust in the SN ejecta and postshock region. At 13 yr post explosion, JWST reveals a strong MIR excess from warm dust, with broad features at 10–15 μ m. Our analysis reveals a minimum dust mass of >0.11 M _⊙ , and a more likely value of 0.2 M _⊙ or more because the dust is optically thick. This is among the largest masses of SN-produced dust yet measured without far-IR/submillimeter data, and greatly exceeds SN 2010jl’s dust mass inferred around 2–3 yr postexplosion. Ground-based optical spectra confirm the presence of a young massive cluster at the SN position and confirm that blueshifted line profiles persisting until the latest epochs arise from dust formed in the postshock region. The warmest dust emitting in the MIR is likely to be the same post-shock dust causing the blueshift. The JWST spectrum also reveals silicate absorption, which may arise from cool SN ejecta dust along the line of sight to the receding shock. The large mass of postshock dust in SN 2010jl suggests that strong CSM interaction promotes efficient dust production, where the new postshock dust will survive. If strongly interacting SNe are common in the early Universe, this may contribute significantly to dust seen in infant galaxies.

In addition to the traditional hydrogen Balmer emission lines, here, we extend the optical changing-look (CL) phenomenon occurring in some active galactic nuclei (AGNs) to the optical Fe ii complex. Multiepoch spectroscopy allows us to identify OQ 208, a local flat-spectrum radio source, as a new Fe ii CL-AGN owing to the disappearance of both its strong Fe ii complex (RFe ≡ Fe II /H β = 0.64) and its Balmer broad-line emission on a timescale of ∼14 yr. The simultaneous disappearance implies that in this object, both the Fe ii and Balmer emissions come from the same region exposed to the ionizing continuum. We further identify an anticorrelation between the Fe ii strength and the continuum (and also Eddington ratio) during the CL events in dozens of CL-AGNs recently studied by S. Panda & M. Śniegowska, suggesting a negative response of RFe to both L ₅₁₀₀ and L _bol / L _Edd ; this can be understood by the Comptonization process in a hot, optically thin accretion flow.

We report the discovery and multiwavelength follow-up observations of a giant (factor >100) X-ray outburst of the exceptional changing-look active galactic nucleus (AGN) IC 3599. This is the third such outburst after two previous ones serendipitously discovered in 1990 and 2010. Based on our dedicated long-term monitoring of IC 3599 with Swift, the third outburst was detected while it was happening, and we triggered multiple follow-up observations within days to weeks for the first time. The Swift outburst spectra are supersoft and almost no photons are detected beyond 2.5 keV. The XMM-Newton short-term light curve shows a remarkable apparent oscillatory pattern that is reminiscent of quasiperiodic oscillations. The optical high-state spectra reveal a multitude of bright coronal emission lines that have dramatically brightened and were absent or much fainter in low-state spectra. The new results eliminate outburst scenarios that require a constant time interval of repetitions (like certain variants of repeat tidal stripping, or of an orbiting supermassive black hole impacting the inner accretion disk), but remain in excellent agreement with an accretion disk radiation-pressure instability when assuming that local conditions in the disk of this long-lived AGN affect the onset time of each new instability. The combination of recurrent, giant, supersoft outbursts on decadal timescales, the exceptional emission-line response, and the rapid, candidate quasiperiodic, short-term variability on an hours timescale makes IC 3599 unique among AGN, and establishes it as a key system for studying accretion physics under extreme conditions and at the Eddington limit.