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We present UV–optical–near-infrared observations and modeling of supernova (SN) 2024ggi, a type II supernova (SN II) located in NGC 3621 at 7.2 Mpc. Early-time (“flash”) spectroscopy of SN 2024ggi within +0.8 days of discovery shows emission lines of Hi, Hei, Ciii, and Niiiwith a narrow core and broad, symmetric wings (i.e., “IIn-like”) arising from the photoionized, optically thick, unshocked circumstellar material (CSM) that surrounded the progenitor star at shock breakout (SBO). By the next spectral epoch at +1.5 days, SN 2024ggi showed a rise in ionization as emission lines of Heii, Civ, Niv/v, and Ovbecame visible. This phenomenon is temporally consistent with a blueward shift in the UV–optical colors, both likely the result of SBO in an extended, dense CSM. The IIn-like features in SN 2024ggi persist on a timescale oft_IIn= 3.8 ± 1.6 days, at which time a reduction in CSM density allows the detection of Doppler-broadened features from the fastest SN material. SN 2024ggi has peak UV–optical absolute magnitudes ofM_w2= −18.7 mag andM_g= −18.1 mag, respectively, that are consistent with the known population of CSM-interacting SNe II. Comparison of SN 2024ggi with a grid of radiation hydrodynamics and non–local thermodynamic equilibrium radiative-transfer simulations suggests a progenitor mass-loss rate of$\dot{M}={10}^{-2}{M}_{\odot }$yr⁻¹(v_w= 50 km s⁻¹), confined to a distance ofr< 5 × 10¹⁴cm. Assuming a wind velocity ofv_w= 50 km s⁻¹, the progenitor star underwent an enhanced mass-loss episode in the last ∼3 yr before explosion.

 

Fast radio bursts (FRBs) are millisecond-duration pulses of radio emission originating from extragalactic distances. Radio dispersion is imparted on each burst by intervening plasma, mostly located in the intergalactic medium. In this work, we observe the burst FRB 20220610A and localize it to a morphologically complex host galaxy system at redshift 1.016 ± 0.002. The burst redshift and dispersion measure are consistent with passage through a substantial column of plasma in the intergalactic medium and extend the relationship between those quantities measured at lower redshift. The burst shows evidence for passage through additional turbulent magnetized plasma, potentially associated with the host galaxy. We use the burst energy of 2 × 10⁴²erg to revise the empirical maximum energy of an FRB.

 

We present ultraviolet/optical/near-infrared observations and modeling of Type II supernovae (SNe II) whose early time (δt< 2 days) spectra show transient, narrow emission lines from shock ionization of confined (r< 10¹⁵cm) circumstellar material (CSM). The observed electron-scattering broadened line profiles (i.e., IIn-like) of Hi, Hei/ii, Civ, and Niii/iv/vfrom the CSM persist on a characteristic timescale (t_IIn) that marks a transition to a lower-density CSM and the emergence of Doppler-broadened features from the fast-moving SN ejecta. Our sample, the largest to date, consists of 39 SNe with early time IIn-like features in addition to 35 “comparison” SNe with no evidence of early time IIn-like features, all with ultraviolet observations. The total sample includes 50 unpublished objects with a total of 474 previously unpublished spectra and 50 multiband light curves, collected primarily through the Young Supernova Experiment and Global Supernova Project collaborations. For all sample objects, we find a significant correlation between peak ultraviolet brightness and botht_IInand the rise time, as well as evidence for enhanced peak luminosities in SNe II with IIn-like features. We quantify mass-loss rates and CSM density for the sample through the matching of peak multiband absolute magnitudes, rise times,t_IIn, and optical SN spectra with a grid of radiation hydrodynamics and non-local thermodynamic equilibrium radiative-transfer simulations. For our grid of models, all with the same underlying explosion, there is a trend between the duration of the electron-scattering broadened line profiles and inferred mass-loss rate:$t_{\mathrm{IIn}}\approx 3.8[\dot{M}/$(0.01M_⊙yr⁻¹)] days.

 

We present the first X-ray census of fast radio burst (FRB) host galaxies to conduct the deepest search for active galactic nuclei (AGN) and X-ray counterparts to date. Our sample includes seven well-localized FRBs with unambiguous host associations and existing deep Chandra observations, including two events for which we present new observations. We find evidence for AGN in two FRB host galaxies based on the presence of X-ray emission coincident with their centers, including the detection of a luminous (L_X≈ 5 × 10⁴²erg s⁻¹) X-ray source at the nucleus of FRB 20190608B’s host, for which we infer an SMBH mass ofM_BH∼ 10⁸M_⊙and an Eddington ratioL_bol/L_Edd≈ 0.02, characteristic of geometrically thin disks in Seyfert galaxies. We also report nebular emission-line fluxes for 24 highly secure FRB hosts (including 10 hosts for the first time), and assess their placement on a BPT diagram, finding that FRB hosts trace the underlying galaxy population. We further find that the hosts of repeating FRBs are not confined to the star-forming locus, contrary to previous findings. Finally, we place constraints on associated X-ray counterparts to FRBs in the context of ultraluminous X-ray sources (ULXs), and find that existing X-ray limits for FRBs rule out ULXs brighter thanL_X≳ 10⁴⁰erg s⁻¹. Leveraging the CHIME/FRB catalog and existing ULX catalogs, we search for spatially coincident ULX–FRB pairs. We identify a total of 28 ULXs spatially coincident with the localization regions for 17 FRBs, but find that the DM-inferred redshifts for the FRBs are inconsistent with the ULX redshifts, disfavoring an association between these specific ULX–FRB pairs.

 

The modern study of astrophysical transients has been transformed by an exponentially growing volume of data. Within the last decade, the transient discovery rate has increased by a factor of ∼20, with associated survey data, archival data, and metadata also increasing with the number of discoveries. To manage the data at this increased rate, we require new tools. Here we presentYSE-PZ, a transient survey management platform that ingests multiple live streams of transient discovery alerts, identifies the host galaxies of those transients, downloads coincident archival data, and retrieves photometry and spectra from ongoing surveys.YSE-PZalso presents a user with a range of tools to make and support timely and informed transient follow-up decisions. Those subsequent observations enhance transient science and can reveal physics only accessible with rapid follow-up observations. Rather than automating out human interaction,YSE-PZfocuses on accelerating and enhancing human decision making, a role we describe as empowering the human-in-the-loop. Finally,YSE-PZis built to be flexibly used and deployed;YSE-PZcan support multiple, simultaneous, and independent transient collaborations through group-level data permissions, allowing a user to view the data associated with the union of all groups in which they are a member.YSE-PZcan be used as a local instance installed via Docker or deployed as a service hosted in the cloud. We provideYSE-PZas an open-source tool for the community.

 

We present the discovery of FRB 20210410D with the MeerKAT radio interferometer in South Africa, as part of the MeerTRAP commensal project. FRB 20210410D has a dispersion measure DM = 578.78 ± 2 ${\rm pc \, cm^{-3}}$ and was localized to subarcsec precision in the 2 s images made from the correlation data products. The localization enabled the association of the FRB with an optical galaxy at z = 0.1415, which when combined with the DM places it above the 3σ scatter of the Macquart relation. We attribute the excess DM to the host galaxy after accounting for contributions from the Milky Way’s interstellar medium and halo, and the combined effects of the intergalactic medium and intervening galaxies. This is the first FRB that is not associated with a dwarf galaxy to exhibit a likely large host galaxy DM contribution. We do not detect any continuum radio emission at the FRB position or from the host galaxy down to a 3σ rms of 14.4 $\mu$Jy beam−1. The FRB has a scattering delay of $29.4^{+2.8}_{-2.7}$ ms at 1 GHz, and exhibits candidate subpulses in the spectrum, which hint at the possibility of it being a repeating FRB. Although not constraining, we note that this FRB has not been seen to repeat in 7.28 h at 1.3 GHz with MeerKAT, 3 h at 2.4 GHz with Murriyang, and 5.7 h at simultaneous 2.3 GHz and 8.4 GHz observations with the Deep Space Network. We encourage further follow-up to establish a possible repeating nature.

 

We present the Keck Infrared Transient Survey, a NASA Key Strategic Mission Support program to obtain near-infrared (NIR) spectra of astrophysical transients of all types, and its first data release, consisting of 105 NIR spectra of 50 transients. Such a data set is essential as we enter a new era of IR astronomy with the James Webb Space Telescope (JWST) and the upcoming Nancy Grace Roman Space Telescope (Roman). NIR spectral templates will be essential to search JWST images for stellar explosions of the first stars and to plan an effective Roman SN Ia cosmology survey, both key science objectives for mission success. Between 2022 February and 2023 July, we systematically obtained 274 NIR spectra of 146 astronomical transients, representing a significant increase in the number of available NIR spectra in the literature. Here, we describe the first release of data from the 2022A semester. We systematically observed three samples: a flux-limited sample that includes all transients <17 mag in a red optical band (usually ZTFror ATLASobands); a volume-limited sample including all transients within redshiftz< 0.01 (D≈ 50 Mpc); and an SN Ia sample targeting objects at phases and light-curve parameters that had scant existing NIR data in the literature. The flux-limited sample is 39% complete (60% excluding SNe Ia), while the volume-limited sample is 54% complete and is 79% complete toz= 0.005. Transient classes observed include common Type Ia and core-collapse supernovae, tidal disruption events, luminous red novae, and the newly categorized hydrogen-free/helium-poor interacting Type Icn supernovae. We describe our observing procedures and data reduction usingPypeIt, which requires minimal human interaction to ensure reproducibility.

 

We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span ∼40–2793 days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the explosion’s forward shock as it expands in the circumstellar medium (CSM) previously sculpted by the mass-loss history of the stellar progenitor. VLBA observations and modeling of the VLA data point to a blastwave with average velocity ∼0.06cthat carries an energy of ≈10⁴⁹erg. Our modeling further reveals a flat CSM density profileρ_CSM∝R^{−0.03±0.22}up to a break radiusR_br≈ (1.96 ± 0.10) × 10¹⁶cm, with a steep density gradient followingρ_CSM∝R^−2.3±0.5at larger radii. We infer that the flat part of the density profile corresponds to a CSM shell with mass ∼0.021M_☉, and that the progenitor’s effective mass-loss rate varied with time over the range (50–500) × 10⁻⁵M_☉yr⁻¹for an adopted wind velocityv_w= 1000 km s⁻¹and shock microphysical parametersϵ_e= 0.1,ϵ_B= 0.01. These results add to the mounting observational evidence for departures from the traditional single-wind mass-loss scenarios in evolved, massive stars in the centuries leading up to core collapse. Potentially viable scenarios include mass loss powered by gravity waves and/or interaction with a binary companion.

 

Context. Fast radio bursts (FRBs) are extremely energetic pulses of millisecond duration and unknown origin. To understand the phenomenon that emits these pulses, targeted and un-targeted searches have been performed for multiwavelength counterparts, including the optical. Aims. The objective of this work is to search for optical transients at the positions of eight well-localized (< 1″) FRBs after the arrival of the burst on different timescales (typically at one day, several months, and one year after FRB detection). We then compare this with known optical light curves to constrain progenitor models. Methods. We used the Las Cumbres Observatory Global Telescope (LCOGT) network to promptly take images with its network of 23 telescopes working around the world. We used a template subtraction technique to analyze all the images collected at differing epochs. We have divided the difference images into two groups: In one group we use the image of the last epoch as a template, and in the other group we use the image of the first epoch as a template. We then searched for optical transients at the localizations of the FRBs in the template subtracted images. Results. We have found no optical transients and have therefore set limiting magnitudes to the optical counterparts. Typical limits in apparent and absolute magnitudes for our LCOGT data are ∼22 and −19 mag in the r band, respectively. We have compared our limiting magnitudes with light curves of super-luminous supernovae (SLSNe), Type Ia supernovae (SNe Ia), supernovae associated with gamma-ray bursts (GRB-SNe), a kilonova, and tidal disruption events (TDEs). Conclusions. Assuming that the FRB emission coincides with the time of explosion of these transients, we rule out associations with SLSNe (at the ∼99.9% confidence level) and the brightest subtypes of SNe Ia, GRB-SNe, and TDEs (at a similar confidence level). However, we cannot exclude scenarios where FRBs are directly associated with the faintest of these subtypes or with kilonovae.