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Summary: Climate change has prompted many communities to set targets for carbon-free power supplies, but they often lack data-driven strategies to achieve them. We present a comprehensive analysis of an entirely renewable electric power system that can maintain operating reliability and resource adequacy using detailed models of the city of Los Angeles power grid. In consultation with the operating utility, the Los Angeles Department of Water and Power (LADWP), and the local community, we develop four supply scenarios across three demand projections to analyze which types of infrastructure and operational changes would achieve reliable electricity at least cost. We find that a reliable, 100%-renewable power system yielding more than $1 billion annually in health and climate co-benefits is achievable. Solar can supply most future energy needs, while combustion turbines that use renewable, storable carbon-neutral fuels are key to maintaining reliability. This study provides a replicable methodology that other jurisdictions globally can follow. Science for society: Communities and businesses nationwide have set ambitious goals to combat climate change by generating 100% of their electricity from carbon-free or renewable energy sources. Until now, there has been no comprehensive analysis of the possible pathways to achieve these goals on the scale needed to power the largest US cities. Here, we present findings from the Los Angeles 100% Renewable Energy Study (LA100), a thorough and wide-reaching assessment of the factors needed to make a fully renewable utility system operate reliably and deliver adequate electricity to more than 4 million residents. Our analysis uses detailed models of the city’s power grid to examine not just renewable resource options and technical solutions related to generation, transmission, and distribution systems but also the balance of supply and demand, variability and reliability, and affordability and viability—all through the lens of changing demographics and climate conditions.

We present SN 2023zaw—a subluminous ( M _r = −16.7 mag) and rapidly evolving supernova ( t _1/2, _r = 4.9 days), with the lowest nickel mass (≈0.002 M _⊙ ) measured among all stripped-envelope supernovae discovered to date. The photospheric spectra are dominated by broad He i and Ca near-infrared emission lines with velocities of ∼10,000−12,000 km s ^−1 . The late-time spectra show prominent narrow He i emission lines at ∼1000 km s ^−1 , indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of ≈0.2 M _☉ and an envelope radius of ≈50 R _⊙ . The extremely low nickel mass and low ejecta mass (≈0.5 M _⊙ ) suggest an ultrastripped SN, which originates from a mass-losing low-mass He-star (zero-age main-sequence mass < 10 M _⊙ ) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass (

We report observations of the optical counterpart of the long gamma-ray burst (GRB) GRB 230812B and its associated supernova (SN) SN 2023pel. The proximity ( z = 0.36) and high energy ( E _γ _,iso ∼ 10 ^53 erg) make it an important event to study as a probe of the connection between massive star core collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak r -band magnitude of M _r = −19.46 ± 0.18 mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of M _Ni = 0.38 ± 0.01 M _⊙ and a peak bolometric luminosity of L _bol ∼ 1.3 × 10 ^43 erg s ^−1 . We confirm SN 2023pel’s classification as a broad-line Type Ic SN with a spectrum taken 15.5 days after its peak in the r band and derive a photospheric expansion velocity of v _ph = 11,300 ± 1600 km s ^−1 at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass M _ej = 1.0 ± 0.6 M _⊙ and kinetic energy ${E}_{\mathrm{KE}}={1.3}_{-1.2}^{+3.3}\times {10}^{51}\,\mathrm{erg}$ . We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and E _γ _,iso for their associated GRBs across a broad range of 7 orders of magnitude provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.

We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby (≈144 Mpc) quiescent galaxy with a low-mass massive black hole (10 ^4 M _⊙ < M _BH < 10 ^6 M _⊙ ). AT2022lri belongs to the TDE-H+He subtype. More than 1 Ms of X-ray data were collected with NICER, Swift, and XMM-Newton from 187 to 672 days after peak. The X-ray luminosity gradually declined from 1.5 × 10 ^44 erg s ^−1 to 1.5 × 10 ^43 erg s ^−1 and remains much above the UV and optical luminosity, consistent with a super-Eddington accretion flow viewed face-on. Sporadic strong X-ray dips atop a long-term decline are observed, with a variability timescale of ≈0.5 hr–1 days and amplitude of ≈2–8. When fitted with simple continuum models, the X-ray spectrum is dominated by a thermal disk component with inner temperature going from ∼146 to ∼86 eV. However, there are residual features that peak around 1 keV, which, in some cases, cannot be reproduced by a single broad emission line. We analyzed a subset of time-resolved spectra with two physically motivated models describing a scenario either where ionized absorbers contribute extra absorption and emission lines or where disk reflection plays an important role. Both models provide good and statistically comparable fits, show that the X-ray dips are correlated with drops in the inner disk temperature, and require the existence of subrelativistic (0.1–0.3 c ) ionized outflows. We propose that the disk temperature fluctuation stems from episodic drops of the mass accretion rate triggered by magnetic instabilities or/and wobbling of the inner accretion disk along the black hole’s spin axis.

Though the time-domain millimeter sky is yet to be well characterized, the scarcity of millimeter observing resources in the world at present hampers progress toward it. In efforts to bolster the exploration of millimeter transients, we present the Stokes Polarization Radio Interferometer for Time-Domain Experiments (SPRITEly). Located at the Owens Valley Radio Observatory, SPRITEly is currently deployed as a two-element short-baseline 90 GHz interferometer uniquely focused on monitoring bright variable millimeter-continuum sources. We leverage two existing 10.4 m antennas and their existing receiver systems to begin, but we make significant upgrades to the back-end system during the commissioning process. With the ability to achieve rms noise of a few mJy, we plan to monitor known variable sources along with new nearby transients detected from optical surveys at high cadence, with the goal of producing well-sampled light curves. Interpreting these data in conjunction with multiwavelength observations stands to provide insight into the physical properties of the sources that produce transient millimeter emission. We present commissioning and early-science observations that demonstrate the performance of the instrument, including observations of the flaring BL Lac object S2 0109+22 and a periastron passage of the binary T Tauri system DQ Tau.

Recent radio surveys have revealed pulsars with dispersion and scattering delays induced by ionized gas that are larger than the rest of the observed pulsar population, in some cases with electron column densities (or dispersion measures, DMs) larger than the maximum predictions of Galactic electron density models. By cross-matching the observed pulsar population against H ii region catalogs, we show that the majority of pulsars with DM > 600 pc cm ^−3 and scattering delays τ (1 GHz) > 10 ms lie behind H ii regions, and that H ii region intersections may be relevant to as much as a third of the observed pulsar population. The fraction of the full pulsar population with sightlines intersecting H ii regions is likely larger. Accounting for H ii regions resolves apparent discrepancies where Galactic electron density models place high-DM pulsars beyond the Galactic disk. By comparing emission measures inferred from recombination line observations to pulsar DMs, we show that H ii regions can contribute tens to hundreds of parsecs per cubic centimeter in electron column density along a pulsar line of sight. We find that nearly all pulsars with significant excess (and deficit) scattering from the mean τ –DM relation are spatially coincident with known discrete ionized gas structures, including H ii regions. Accounting for H ii regions is critical to the interpretation of radio dispersion and scattering measurements as electron density tracers, both in the Milky Way and in other galaxies.

Fast radio bursts (FRBs) are a powerful and mysterious new class of transients that are luminous enough to be detected at cosmological distances. By associating FRBs to host galaxies, we can measure intrinsic and environmental properties that test FRB origin models, in addition to using them as precise probes of distant cosmic gas. The Deep Synoptic Array (DSA-110) is a radio interferometer built to maximize the rate at which it can simultaneously detect and localize FRBs. Here, we present the first sample of FRBs and host galaxies discovered by the DSA-110. This sample of 11 FRBs is the largest, most uniform sample of localized FRBs to date, as it is selected based on association with host galaxies identified in optical imaging by Pan-STARRS1. These FRBs have not been observed to repeat, and their radio properties (dispersion, temporal scattering, energy) are similar to that of the known nonrepeating FRB population. Most host galaxies have ongoing star formation, as has been identified before for FRB hosts. Two hosts of the new sample are massive, quiescent galaxies. The distribution of star formation history across this host-galaxy sample shows that the delay time distribution is wide, with a power-law model that spans from ∼100 Myr to ≳2 Gyr. This requires the existence of one or more progenitor formation channels associated with old stellar populations, such as the binary evolution of compact objects.

Line-intensity mapping is a promising probe of the Universe’s large-scale structure. We explore the sensitivity of the DSA-2000, a forthcoming array consisting of over 2000 dishes, to the statistical power spectrum of neutral hydrogen’s 21 cm emission line. These measurements would reveal the distribution of neutral hydrogen throughout the near-redshift Universe without necessitating resolving individual sources. The success of these measurements relies on the instrument’s sensitivity and resilience to systematics. We show that the DSA-2000 will have the sensitivity needed to detect the 21 cm power spectrum at z ≈ 0.5 and across power spectrum modes of 0.03–35.12 h Mpc ^−1 with 0.1 h Mpc ^−1 resolution. We find that supplementing the nominal array design with a dense core of 200 antennas will expand its sensitivity at low power spectrum modes and enable measurement of Baryon Acoustic Oscillations. Finally, we present a qualitative discussion of the DSA-2000's unique resilience to sources of systematic error that can preclude 21 cm intensity mapping.

We report on a full-polarization analysis of the first 25 as yet nonrepeating fast radio bursts (FRBs) detected at 1.4 GHz by the 110-antenna Deep Synoptic Array (DSA-110) during commissioning observations. We present details of the data-reduction, calibration, and analysis procedures developed for this novel instrument. Faraday rotation measures (RMs) are searched between ±10 ^6 rad m ^−2 and detected for 20 FRBs, with magnitudes ranging from 4 to 4670 rad m ^−2 . Fifteen out of 25 FRBs are consistent with 100% polarization, 10 of which have high (≥70%) linear-polarization fractions and two of which have high (≥30%) circular-polarization fractions. Our results disfavor multipath RM scattering as a dominant depolarization mechanism. Polarization-state and possible RM variations are observed in the four FRBs with multiple subcomponents. We combine the DSA-110 sample with polarimetry of previously published FRBs, and compare the polarization properties of FRB subpopulations and FRBs with Galactic pulsars. Although FRB polarization fractions are typically higher than those of Galactic pulsars, and cover a wider range than those of pulsar single pulses, they resemble those of the youngest (characteristic ages

To demonstrate how a mega city can lead in decarbonizing beyond legal mandates, the city of Los Angeles (LA) developed science-based, feasible pathways towards utilizing 100% renewable energy for its municipally-owned electric utility. Aside from decarbonization, renewable energy adoption can lead to co-benefits such as improving urban air quality from reductions in combustion-related emissions of oxides of nitrogen (NO _x ), primary fine particulate matter (PM _2.5 ) and others. Herein, we quantify changes to air pollutant concentrations and public health from scenarios of 100% renewable electricity adoption in LA in 2045, alongside aggressive electrification of end-use sectors. Our analysis suggests that while ensuring reliable electricity supply, reductions in emissions of air pollutants associated with the 100% renewable electricity scenarios can lead to 8% citywide reductions of PM _2.5 concentration while increasing ozone concentration by 5% relative to a 2012 baseline year, given identical meteorology conditions. The combination of these concentration changes could result in net monetized public health benefits (driven by avoided deaths) of up to $1.4 billion in year 2045 in LA, results potentially replicable for other city-scale decarbonization scenarios.

Faraday rotation measures (RMs) of fast radio bursts (FRBs) offer the prospect of directly measuring extragalactic magnetic fields. We present an analysis of the RMs of 10 as yet nonrepeating FRBs detected and localized to host galaxies with robust redshift measurements by the 63-antenna prototype of the Deep Synoptic Array (DSA-110). We combine this sample with published RMs of 15 localized FRBs, nine of which are repeating sources. For each FRB in the combined sample, we estimate the host-galaxy dispersion measure (DM) contributions and extragalactic RM. We find compelling evidence that the extragalactic components of FRB RMs are often dominated by contributions from the host-galaxy interstellar medium (ISM). Specifically, we find that both repeating and as yet nonrepeating FRBs show a correlation between the host DM and host RM in the rest frame, and we find an anticorrelation between extragalactic RM (in the observer frame) and redshift for nonrepeaters, as expected if the magnetized plasma is in the host galaxy. Important exceptions to the ISM origin include a dense, magnetized circumburst medium in some repeating FRBs, and the intracluster medium of host or intervening galaxy clusters. We find that the estimated ISM magnetic-field strengths, ${\bar{B}}_{| | }$ , are characteristically ∼1–2 μ G larger than those inferred from Galactic radio pulsars. This suggests either increased ISM magnetization in FRB hosts in comparison with the Milky Way, or that FRBs preferentially reside in regions of increased magnetic-field strength within their hosts.

We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete sample of 33 TDEs is constructed using the Zwicky Transient Facility over 3 yr (from 2018 October to 2021 September). We infer the black hole (BH) mass ( M _BH ) with host galaxy scaling relations, showing that the sample M _BH ranges from 10 ^5.1 M _⊙ to 10 ^8.2 M _⊙ . We developed a survey efficiency corrected maximum volume method to infer the rates. The rest-frame g -band luminosity function can be well described by a broken power law of $\phi ({L}_{g})\propto {\left[{\left({L}_{g}/{L}_{\mathrm{bk}}\right)}^{0.3}+{\left({L}_{g}/{L}_{\mathrm{bk}}\right)}^{2.6}\right]}^{-1}$ , with L _bk = 10 ^43.1 erg s ^−1 . In the BH mass regime of 10 ^5.3 ≲ ( M _BH / M _⊙ ) ≲ 10 ^7.3 , the TDE mass function follows $\phi ({M}_{\mathrm{BH}})\propto {M}_{\mathrm{BH}}^{-0.25}$ , which favors a flat local BH mass function ( ${{dn}}_{\mathrm{BH}}/d\mathrm{log}{M}_{\mathrm{BH}}\approx \mathrm{constant}$ ). We confirm the significant rate suppression at the high-mass end ( M _BH ≳ 10 ^7.5 M _⊙ ), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of M _gal ∼ 10 ^10 M _⊙ , the average optical TDE rate is ≈3.2 × 10 ^−5 galaxy ^−1 yr ^−1 . We constrain the optical TDE rate to be [3.7, 7.4, and 1.6] × 10 ^−5 galaxy ^−1 yr ^−1 in galaxies with red, green, and blue colors.

The hot gas that constitutes the intracluster medium (ICM) has been studied at X-ray and millimeter/submillimeter wavelengths (Sunyaev–Zel’dovich effect) for decades. Fast radio bursts (FRBs) offer an additional method of directly measuring the ICM and gas surrounding clusters via observables such as dispersion measure (DM) and Faraday rotation measure. We report the discovery of two FRB sources detected with the Deep Synoptic Array whose host galaxies belong to massive galaxy clusters. In both cases, the FRBs exhibit excess extragalactic DM, some of which likely originate in the ICM of their respective clusters. FRB 20220914A resides in the galaxy cluster A2310 at z = 0.1125 with a projected offset from the cluster center of 520 ± 50 kpc. The host of a second source, FRB 20220509G, is an elliptical galaxy at z = 0.0894 that belongs to the galaxy cluster A2311 at the projected offset of 870 ± 50 kpc. These sources represent the first time an FRB has been localized to a galaxy cluster. We combine our FRB data with archival X-ray, Sunyaev–Zel'dovich (SZ), and optical observations of these clusters in order to infer properties of the ICM, including a measurement of gas temperature from DM and y _SZ of 0.8–3.9 keV. We then compare our results to massive cluster halos from the IllustrisTNG simulation. Finally, we describe how large samples of localized FRBs from future surveys will constrain the ICM, particularly beyond the virial radius of clusters.

We report the detection and interferometric localization of the repeating fast radio burst (FRB) source FRB 20220912A during commissioning observations with the Deep Synoptic Array (DSA-110). Two bursts were detected from FRB 20220912A, one each on 2022 October 18 and 2022 October 25. The best-fit position is (R.A. J2000, decl. J2000) = (23:09:04.9, +48:42:25.4), with a 90% confidence error ellipse with radii ±2″ and ±1″ in R.A. and decl., respectively. The two bursts are polarized, and we find a Faraday rotation measure that is consistent with the low value of +0.6 rad m ^−2 reported by CHIME/FRB. The DSA-110 localization overlaps with the galaxy PSO J347.2702+48.7066 at a redshift z = 0.0771, which we identify as the likely host. PSO J347.2702+48.7066 has a stellar mass of approximately 10 ^10 M _⊙ , modest internal dust extinction, and a star formation rate likely in excess of 0.1 M _⊙ yr ^−1 . The host-galaxy contribution to the dispersion measure is likely ≲50 pc cm ^−3 . The FRB 20220912A source is therefore likely viewed along a tenuous plasma column through the host galaxy.

FRB 121102 is the first fast radio burst to be spatially associated with a persistent radio source (QRS 121102), the nature of which remains unknown. We constrain the physical size of QRS 121102 by measuring its flux-density variability with the VLA from 12 to 26 GHz. Any such variability would likely be due to Galactic refractive scintillation and would require the source radius to be ≲10 ^17 cm at the host-galaxy redshift. We found the radio variability to be lower than the scintillation theory predictions for such a small source, leaving open the possibility for non-AGN models for QRS 121102. In addition, we roughly estimated the mass of any potential supermassive black hole (BH) associated with QRS 121102 from the line width of the host-galaxy H α emission using a new optical spectrum from the Keck Observatory. The line width indicates a supermassive BH mass of ≲10 ^4∼5 M _⊙ , too low for the observed radio luminosity and X-ray luminosity constraints, if QRS 121102 were an AGN. Finally, some dwarf galaxies that host supermassive BHs may be the stripped cores of massive galaxies during tidal interactions with companion systems. We find no nearby galaxy at the same redshift as the QRS 121102 host from low-resolution Keck spectra or the PanSTARRS catalog. In conclusion, we find no evidence supporting the hypothesis that QRS 121102 is an AGN. We instead argue that the inferred size and flat radio spectrum favor a plerion interpretation. We urge continued broadband radio monitoring of QRS 121102 to search for long-term evolution.

The stellar population environments that are associated with fast radio burst (FRB) sources provide important insights for developing their progenitor theories. We expand the diversity of known FRB host environments by reporting two FRBs in massive galaxy clusters that were discovered by the Deep Synoptic Array (DSA-110) during its commissioning observations. FRB 20220914A has been localized to a star-forming, late-type galaxy at a redshift of 0.1139 with multiple starbursts at lookback times less than ∼3.5 Gyr in the A2310 galaxy cluster. Although the host galaxy of FRB 20220914A is similar to typical FRB hosts, the FRB 20220509G host stands out as a quiescent, early-type galaxy at a redshift of 0.0894 in the A2311 galaxy cluster. The discovery of FRBs in both late- and early-type galaxies adds to the body of evidence that the FRB sources have multiple formation channels. Therefore, even though FRB hosts are typically star-forming, there must exist formation channels that are consistent with old stellar population in galaxies. The varied star formation histories of the two FRB hosts that we report here indicate a wide delay-time distribution of FRB progenitors. Future work in constraining the FRB delay-time distribution, using the methods that we develop herein, will prove crucial in determining the evolutionary histories of FRB sources.

We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag ( L _bol, peak = (6.8 ± 0.3) × 10 ^43 erg s ^−1 ) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting

We present observations of an extreme radio flare, VT J024345.70-284040.08, hereafter VT J0243, from the nucleus of a galaxy with evidence for historic Seyfert activity at redshift z = 0.074. Between NRAO Very Large Array (VLA) Sky Survey observations in 1993 to VLA Sky Survey observations in 2018, VT J0243 rose from a ∼ GHz radio luminosity of ν L _ν ≲ 10 ^38 erg s ^−1 to ν L _ν ∼ 10 ^40 erg s ^−1 , and still continues to brighten. The radio spectral energy distribution evolution is consistent with a nascent jet that has slowed over ∼3000 days with an average 0.1

This work utilizes established models of synchrotron-powered light curves for core-collapse supernovae in dense circumstellar environments, namely, type IIn and Ibn, to demonstrate the potential for detecting millimeter emission from these events. The progenitor types of these supernovae are still an open question, but using the synchrotron light curves as probes for the circumstellar environments could shed light on the mass-loss histories of the progenitors and discern between different theories. Observations in millimeter bands are particularly fruitful, as they probe regions at smaller radii and higher ambient densities, where centimeter emission tends to be self-absorbed. In our application of these light curves, we explore a diversity of progenitor types and mass-loss profiles to understand their effects on the light-curve shapes. Additionally, we fit model parameters to the 8 GHz light curve of type IIn supernova 2006jd and then create millimeter light curves using these parameters to show the possibility of detecting an early millimeter peak from such an event. We predict that next generation millimeter surveys will possess the capability to detect nearby and extreme events. However, there is a pressing need for millimeter follow-up of optically discovered interacting supernovae to more completely sample the true population.

Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index n_{t} and the tensor-to-scalar ratio r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Ω_{GW}(f)