arXiv subjects

Jennifer Barnes

Publications and source records attributed to Jennifer Barnes.

At least 19 recordsLinked to original sources

arXiv2026

Las Cumbres Observatory Gravitational-Wave Follow-up in the Third and Fourth Observing Runs: Strengths and Weaknesses of a Rapid Response Galaxy Targeted Strategy

We present a summary of gravitational-wave (GW) follow-up using the Las Cumbres Observatory global network of telescopes during the third (O3) and fourth (O4) observing runs of the GW detectors. As in O2, we implemented the Gehrels et al. 2016 galaxy-targeted strategy. Here we test its efficacy in O3 and O4 and analyze the Las Cumbres Observatory response time and depth for nine GW alerts that showed a possibility of having an electromagnetic counterpart (GW190425, GW190426_152155, S190510g, GW190728_064510, GW190814, S190822c, GW191216_213338, S240422ed and S250206dm). We find that Las Cumbres Observatory is able to begin observations in response to GW alerts within minutes of the alert, with the observations being deep enough to detect possible GW170817-like kilonovae out to a median distance of 250 Mpc. In this sense a global rapid-response network of telescopes like Las Cumbres is an excellent GW follow-up facility. However, the galaxy-targeted follow-up strategy was much less efficient in O3 and O4 than originally predicted, given the larger than assumed GW localizations. We conclude that coordination between various facilities to include both wide-field and rapid-response capabilities is required to achieve efficient and comprehensive follow-up of GW events.

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arXiv2023

JWST Observations of the Extraordinary GRB 221009A Reveal an Ordinary Supernova Without Signs of $r$-Process Enrichment in a Low-Metallicity Galaxy

Identifying the astrophysical sites of the $r$-process, one of the primary mechanisms by which heavy elements are formed, is a key goal of modern astrophysics. The discovery of the brightest gamma-ray burst of all time, GRB 221009A, at a relatively nearby redshift, presented the first opportunity to spectroscopically test the idea that $r$-process elements are produced following the collapse of rapidly rotating massive stars. Here we present spectroscopic and photometric $\textit{James Webb Space Telescope}$ (JWST) observations of GRB 221009A obtained $+168$ and $+170$ rest-frame days after the initial gamma-ray trigger, and demonstrate they are well-described by a supernova (SN) and power-law afterglow, with no evidence for an additional component from $r$-process emission, and that the SN component strongly resembles the near-infrared spectra of previous SNe, including SN 1998bw. We further find that the SN associated with GRB 221009A is slightly fainter than the expected brightness of SN 1998bw at this phase, concluding that the SN is therefore not an unusual GRB-SN. We infer a nickel mass of $\approx0.09$ M$_{\odot}$, consistent with the lack of an obvious SN detection in the early-time data. We find that the host galaxy of GRB 221009A has a very low metallicity of $\approx0.12$ Z$_{\odot}$ and our resolved host spectrum shows that GRB 221009A occurred in a unique environment in its host characterized by strong H$_2$ emission lines consistent with recent star formation, which may hint at environmental factors being responsible for its extreme energetics.

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arXiv2023

Hydrodynamic mixing of accretion disk outflows in collapsars: implications for r-process signatures

The astrophysical environments capable of triggering heavy-element synthesis via rapid neutron capture (the r-process) remain uncertain. While binary neutron star mergers (NSMs) are known to forge r-process elements, certain rare supernovae (SNe) have been theorized to supplement, or even dominate, r-production by NSMs. However, the most direct evidence for such SNe, unusual reddening of the emission caused by the high opacities of r-process elements, has not been observed. Recent work identified the distribution of r-process material within the SN ejecta as a key predictor of the ease with which signals associated with r-process enrichment could be discerned. Though this distribution results from hydrodynamic processes at play during the SN explosion, thus far it has been treated only in a parameterized way. We use hydrodynamic simulations to model how disk winds, the alleged locus of r-production in rare SNe, mix with initially r-process-free ejecta. We study mixing as a function of the wind mass and duration and of the initial SN explosion energy, and find that it increases with the first two of these and decreases with the third. This suggests that SNe accompanying the longest long-duration gamma-ray bursts are promising places to search for signs of r-process enrichment. We use semianalytic radiation transport to connect hydrodynamics to electromagnetic observables, allowing us to assess the mixing level at which the presence of r-process material can be diagnosed from SN light curves. Analytic arguments constructed atop this foundation imply that a wind-driven r-process-enriched SN model is unlikely to explain standard energetic SNe.

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arXiv2023

Superheavy Elements in Kilonovae

As LIGO-Virgo-KAGRA enters its fourth observing run, a new opportunity to search for electromagnetic counterparts of compact object mergers will also begin. The light curves and spectra from the first "kilonova" associated with a binary neutron star binary (NSM) suggests that these sites are hosts of the rapid neutron capture ("$r$") process. However, it is unknown just how robust elemental production can be in mergers. Identifying signposts of the production of particular nuclei is critical for fully understanding merger-driven heavy-element synthesis. In this study, we investigate the properties of very neutron rich nuclei for which superheavy elements ($Z\geq 104$) can be produced in NSMs and whether they can similarly imprint a unique signature on kilonova light-curve evolution. A superheavy-element signature in kilonovae represents a route to establishing a lower limit on heavy-element production in NSMs as well as possibly being the first evidence of superheavy element synthesis in nature. Favorable NSMs conditions yield a mass fraction of superheavy elements is $X_{Z\geq 104}\approx 3\times 10^{-2}$ at 7.5 hours post-merger. With this mass fraction of superheavy elements, we find that the component of kilonova light curves possibly containing superheavy elements may appear similar to those arising from lanthanide-poor ejecta. Therefore, photometric characterizations of superheavy-element rich kilonova may possibly misidentify them as lanthanide-poor events.

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arXiv2023

Collapsars as Sites of r-process Nucleosynthesis: Systematic Near-Infrared Follow-up of Type Ic-BL Supernovae

One of the open questions following the discovery of GW170817 is whether neutron star mergers are the only astrophysical sites capable of producing $r$-process elements. Simulations have shown that 0.01-0.1M$_\odot$ of $r$-process material could be generated in the outflows originating from the accretion disk surrounding the rapidly rotating black hole that forms as a remnant to both neutron star mergers and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature of $r$-process nucleosynthesis in the binary neutron star merger GW170817 was its long-lasting near-infrared emission, thus motivating a systematic photometric study of the light curves of broadlined stripped-envelope (Ic-BL) supernovae (SNe) associated with collapsars. We present the first systematic study of 25 SNe Ic-BL -- including 18 observed with the Zwicky Transient Facility and 7 from the literature -- in the optical/near-infrared bands to determine what quantity of $r$-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account for $r$-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on the $r$-process mass for these SNe. We also perform independent light curve fits to models without $r$-process. We find that the $r$-process-free models are a better fit to the light curves of the objects in our sample. Thus we find no compelling evidence of $r$-process enrichment in any of our objects. Further high-cadence infrared photometric studies and nebular spectroscopic analysis would be sensitive to smaller quantities of $r$-process ejecta mass or indicate whether all collapsars are completely devoid of $r$-process nucleosynthesis.

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arXiv2023

Bayesian model selection for GRB 211211A through multi-wavelength analyses

Although GRB 211211A is one of the closest gamma-ray bursts (GRBs), its classification is challenging because of its partially inconclusive electromagnetic signatures. In this paper, we investigate four different astrophysical scenarios as possible progenitors for GRB~211211A: a binary neutron-star merger, a black-hole--neutron-star merger, a core-collapse supernova, and an r-process enriched core collapse of a rapidly rotating massive star (a collapsar). We perform a large set of Bayesian multi-wavelength analyses based on different models describing these scenarios and priors to investigate which astrophysical scenarios and processes might be related to GRB~211211A. Our analysis supports previous studies in which the presence of an additional component, likely related to $r$-process nucleosynthesis, is required to explain the observed light curves of GRB~211211A, as it can not solely be explained as a GRB afterglow. Fixing the distance to about $350~\rm Mpc$, namely the distance of the possible host galaxy SDSS J140910.47+275320.8, we find a statistical preference for a binary neutron-star merger scenario.

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arXiv2023

A collapsar origin for GRB 211211A is (just barely) possible

Gamma-ray bursts (GRBs) have historically been divided into two classes. Short-duration GRBs are associated with binary neutron-star mergers (NSMs), while long-duration bursts are connected to a subset of core-collapse supernovae (SNe). GRB 211211A recently made headlines as the first long-duration burst purportedly generated by an NSM. The evidence for an NSM origin was excess optical and near-infrared emission consistent with the kilonova observed after the gravitational wave-detected NSM GW170817. Kilonovae derive their unique electromagnetic signatures from the properties of the heavy elements synthesized by rapid neutron capture (the r-process) following the merger. Recent simulations suggest that the "collapsar" SNe that trigger long GRBs may also produce r-process elements. While observations of GRB 211211A and its afterglow ruled out an SN typical of those that follow long GRBs, an unusual collapsar could explain both the duration of GRB 211211A and the r-process-powered excess in its afterglow. We use semianalytic radiation transport modeling to evaluate low-mass collapsars as the progenitors of GRB 211211A-like events. We compare a suite of collapsar models to the afterglow-subtracted emission that followed GRB 211211A, and find the best agreement for models with high kinetic energies and an unexpected pattern of Ni-56 enrichment. We discuss how core-collapse explosions could produce such ejecta, and how distinct our predictions are from those generated by more straightforward kilonova models. We also show that radio observations can distinguish between kilonovae and the more massive collapsar ejecta we consider here.

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arXiv2022

Signatures of R-process Enrichment in Supernovae from Collapsars

Despite recent progress, the astrophysical channels responsible for rapid neutron capture (r-process) nucleosynthesis remain an unsettled question. Observations of kilonovae following gravitational wave-detected neutron star mergers established mergers as one site of the r-process, but additional sources may be needed to fully explain r-process enrichment in the Universe. One intriguing possibility is that rapidly rotating massive stars undergoing core collapse launch r-process-rich outflows off the accretion disks formed from their infalling matter. In this scenario, r-process winds comprise one component of the supernova (SN) ejecta produced by "collapsar" explosions. We present the first systematic study of the effects of r-process enrichment on the emission from collapsar-generated SNe. We semi-analytically model r-process SN emission from explosion out to late times, and determine its distinguishing features. The ease with which r-process SNe can be identified depends on how effectively wind material mixes into the initially r-process-free outer layers of the ejecta. In many cases, enrichment produces a near infrared (NIR) excess that can be detected within ~75 days of explosion. We also discuss optimal targets and observing strategies for testing the r-process collapsar theory, and find that frequent monitoring of optical and NIR emission from high-velocity SNe in the first few months after explosion offers a reasonable chance of success while respecting finite observing resources. Such early identification of r-process collapsar candidates also lays the foundation for nebular-phase spectroscopic follow-up in the near- and mid-infrared, for example with the James Webb Space Telescope.

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arXiv2021

"Super-Kilonovae" from Massive Collapsars as Signatures of Black-Hole Birth in the Pair-instability Mass Gap

The core collapse of rapidly rotating massive ~10 Msun stars ("collapsars"), and resulting formation of hyper-accreting black holes, are a leading model for the central engines of long-duration gamma-ray bursts (GRB) and promising sources of r-process nucleosynthesis. Here, we explore the signatures of collapsars from progenitors with extremely massive helium cores >130 Msun above the pair-instability mass gap. While rapid collapse to a black hole likely precludes a prompt explosion in these systems, we demonstrate that disk outflows can generate a large quantity (up to >50 Msun) of ejecta, comprised of >5-10 Msun in r-process elements and ~0.1-1 Msun of $^{56}$Ni, expanding at velocities ~0.1c. Radioactive heating of the disk-wind ejecta powers an optical/infrared transient, with a characteristic luminosity $\sim 10^{42}$ erg s$^{-1}$ and spectral peak in the near-infrared (due to the high optical/UV opacities of lanthanide elements) similar to kilonovae from neutron star mergers, but with longer durations $\gtrsim$ 1 month. These "super-kilonovae" (superKNe) herald the birth of massive black holes >60 Msun, which, as a result of disk wind mass-loss, can populate the pair-instability mass gap 'from above' and could potentially create the binary components of GW190521. SuperKNe could be discovered via wide-field surveys such as those planned with the Roman Space Telescope or via late-time infrared follow-up observations of extremely energetic GRBs. Gravitational waves of frequency ~0.1-50 Hz from non-axisymmetric instabilities in self-gravitating massive collapsar disks are potentially detectable by proposed third-generation intermediate and high-frequency observatories at distances up to hundreds of Mpc; in contrast to the "chirp" from binary mergers, the collapsar gravitational-wave signal decreases in frequency as the disk radius grows ("sad trombone").

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arXiv2021

Proto-magnetar jets as central engines for broad-lined type Ic supernovae

A subset of type Ic supernovae (SNe Ic), broad-lined SNe Ic (SNe Ic-bl), show unusually high kinetic energies ($\sim 10^{52}$ erg) which cannot be explained by the energy supplied by neutrinos alone. Many SNe Ic-bl have been observed in coincidence with long gamma-ray bursts (GRBs) which suggests a connection between SNe and GRBs. A small fraction of core-collapse supernovae (CCSNe) form a rapidly-rotating and strongly-magnetized protoneutron star (PNS), a proto-magnetar. Jets from such magnetars can provide the high kinetic energies observed in SNe Ic-bl and also provide the connection to GRBs. In this work we use the jetted outflow produced in a 3D CCSN simulation from a consistently formed proto-magnetar as the central engine for full-star explosion simulations. We extract a range of central engine parameters and find that the extracted engine energy is in the range of $6.231 \times 10^{51}-1.725 \times 10^{52}$ erg, the engine time-scale in the range of $0.479-1.159$ s and the engine half-opening angle in the range of $\sim 9-19^{\circ}$. Using these as central engines, we perform 2D special-relativistic (SR) hydrodynamic (HD) and radiation transfer simulations to calculate the corresponding light curves and spectra. We find that these central engine parameters successfully produce SNe Ic-bl which demonstrates that jets from proto-magnetars can be viable engines for SNe Ic-bl. We also find that only the central engines with smaller opening angles ($\sim 10^{\circ}$) form a GRB implying that GRB formation is likely associated with narrower jet outflows and Ic-bl's without GRBs may be associated with wider outflows.

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arXiv2020

Kilonovae across the nuclear physics landscape: The impact of nuclear physics uncertainties on r-process-powered emission

Merging neutron stars produce "kilonovae"---electromagnetic transients powered by the decay of unstable nuclei synthesized via rapid neutron capture (the r-process) in material that is gravitationally unbound during inspiral and coalescence. Kilonova emission, if accurately interpreted, can be used to characterize the masses and compositions of merger-driven outflows, helping to resolve a long-standing debate about the origins of r-process material in the Universe. We explore how the uncertain properties of nuclei involved in the r-process complicate the inference of outflow properties from kilonova observations. Using r-process simulations, we show how nuclear physics uncertainties impact predictions of radioactive heating and element synthesis. For a set of models that span a large range in both predicted heating and final abundances, we carry out detailed numerical calculations of decay product thermalization and radiation transport in a kilonova ejecta with a fixed mass and density profile. The light curves associated with our models exhibit great diversity in their luminosities, with peak brightness varying by more than an order of magnitude. We also find variability in the shape of the kilonova light curves and their color, which in some cases runs counter to the expectation that increasing levels of lanthanide and/or actinide enrichment will be correlated with longer, dimmer, redder emission.

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arXiv2020

Variability in Short Gamma-ray Bursts: Gravitationally Unstable Tidal Tails

Short gamma-ray bursts are thought to result from the mergers of two neutron stars or a neutron star and stellar mass black hole. The final stages of the merger are generally accompanied by the production of one or more tidal "tails" of ejecta, which fall back onto the remnant-disc system at late times. Using the results of a linear stability analysis, we show that if the material comprising these tails is modeled as adiabatic and the effective adiabatic index satisfies $\gamma \ge 5/3$, then the tails are gravitationally unstable and collapse to form small-scale knots. We analytically estimate the properties of these knots, including their spacing along the tidal tail and the total number produced, and their effect on the mass return rate to the merger remnant. We perform hydrodynamical simulations of the disruption of a polytropic (with the polytropic and adiabatic indices $\gamma$ equal), $\gamma =2$ neutron star by a black hole, and find agreement between the predictions of the linear stability analysis and the distribution of knots that collapse out of the instability. The return of these knots to the black hole induces variability in the fallback rate, which can manifest as variability in the lightcurve of the GRB and -- depending on how rapidly the instability operates -- the prompt emission. The late-time variability induced by the return of these knots is also consistent with the extended emission observed in some GRBs.

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arXiv2020

DECam-GROWTH Search for the Faint and Distant Binary Neutron Star and Neutron Star-Black Hole Mergers in O3a

Synoptic searches for the optical counterpart to a binary neutron star (BNS) or neutron star-black hole (NSBH) merger can pose significant challenges towards the discovery of kilonovae and performing multi-messenger science. In this work, we describe the advantage of a global multi-telescope network towards this end, with a particular focus on the key and complementary role the Dark Energy Camera (DECam) plays in multi-facility follow-up. We describe the Global Relay of Observatories Watching Transients Happen (GROWTH) Target-of-Opportunity (ToO) Marshal, a common web application we built to ingest events, plan observations, search for transient candidates, and retrieve performance summary statistics for all of the telescopes in our network. Our infrastructure enabled us to conduct observations of two events during O3a, S190426c and S190510g. Furthermore, our analysis of deep DECam observations of S190814bv conducted by the DESGW team, and access to a variety of global follow-up facilities allowed us to place meaningful constraints on the parameters of the kilonova and the merging binary. We emphasize the importance of a global telescope network in conjunction with a power telescope like DECam in performing searches for the counterparts to gravitational-wave sources.

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arXiv2019

GROWTH on S190510g: DECam Observation Planning and Follow-Up of a Distant Binary Neutron Star Merger Candidate

The first two months of the third Advanced LIGO and Virgo observing run (2019 April-May) showed that distant gravitational wave (GW) events can now be readily detected. Three candidate mergers containing neutron stars (NS) were reported in a span of 15 days, all likely located more than 100 Mpc away. However, distant events such as the three new NS mergers are likely to be coarsely localized, which highlights the importance of facilities and scheduling systems that enable deep observations over hundreds to thousands of square degrees to detect the electromagnetic counterparts. On 2019-05-10 02:59:39.292 UT the GW candidate S190510g was discovered and initially classified as a BNS merger with 98% probability. The GW event was localized within an area of 3462 deg2, later refined to 1166 deg2 (90%) at a distance of 227 +- 92 Mpc. We triggered Target of Opportunity observations with the Dark Energy Camera (DECam), a wide-field optical imager mounted at the prime focus of the 4m Blanco Telescope at CTIO in Chile. This Letter describes our DECam observations and our real-time analysis results, focusing in particular on the design and implementation of the observing strategy. Within 24 hours of the merger time, we observed 65% of the total enclosed probability of the final skymap with an observing efficiency of 94%. We identified and publicly announced 13 candidate counterparts. S190510g was re-classified 1.7 days after the merger, after our observations were completed, with a "binary neutron star merger" probability reduced from 98% to 42% in favor of a "terrestrial" classification.

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arXiv2019

Finding the remnants of the Milky Way's last neutron star mergers

The discovery of a binary neutron star merger (NSM) through both its gravitational wave and electromagnetic emission has revealed these events to be key sites of r-process nucleosynthesis. Here, we evaluate the prospects of finding the remnants of Galactic NSMs by detecting the gamma-ray decay lines from their radioactive r-process ejecta. We find that $^{126}$Sn, which has several lines in the energy range 415-695 keV and resides close to the second r-process peak, is the most promising isotope, because of its half-life $t_{1/2}=2.30(14)\times 10^{5}$ yr being comparable to the ages of recent NSMs. Using a Monte Carlo procedure, we predict that multiple remnants are detectable as individual sources by next-generation gamma-ray telescopes which achieve sub-MeV line sensitivities of $\sim 10^{-8}$-$10^{-6}$ $\gamma$ cm$^{-2}$ s$^{-1}$. However, given the unknown locations of the remnants, the most promising search strategy is a systematic survey of the Galactic plane and bulge extending to high Galactic latitudes. Individual known supernova remnants which may be mis-classified NSM remnants could also be targeted, especially those located outside the Galactic plane. Detection of a moderate sample of Galactic NSM remnants would provide important clues to unresolved issues such as the production of actinides in NSMs, properties of merging NS binaries, and even help distinguish them from rare supernovae as current Galactic r-process sources. We also investigate the diffuse flux from longer-lived nuclei (e.g. $^{182}$Hf) that could in principle trace the Galactic spatial distribution of NSMs over longer timescales, but find that the detection of the diffuse flux appears challenging even with next-generation telescopes.

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arXiv2019

Multi-Messenger Astronomy with Extremely Large Telescopes

The field of time-domain astrophysics has entered the era of Multi-messenger Astronomy (MMA). One key science goal for the next decade (and beyond) will be to characterize gravitational wave (GW) and neutrino sources using the next generation of Extremely Large Telescopes (ELTs). These studies will have a broad impact across astrophysics, informing our knowledge of the production and enrichment history of the heaviest chemical elements, constrain the dense matter equation of state, provide independent constraints on cosmology, increase our understanding of particle acceleration in shocks and jets, and study the lives of black holes in the universe. Future GW detectors will greatly improve their sensitivity during the coming decade, as will near-infrared telescopes capable of independently finding kilonovae from neutron star mergers. However, the electromagnetic counterparts to high-frequency (LIGO/Virgo band) GW sources will be distant and faint and thus demand ELT capabilities for characterization. ELTs will be important and necessary contributors to an advanced and complete multi-messenger network.

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arXiv2018

Collapsars as a major source of r-process elements

The production of elements by rapid neutron capture (r-process) in neutron-star mergers is expected theoretically and is supported by multimessenger observations of gravitational-wave event GW170817: this production route is in principle sufficient to account for most of the r-process elements in the Universe. Analysis of the kilonova that accompanied GW170817 identified delayed outflows from a remnant accretion disk formed around the newly born black hole as the dominant source of heavy r-process material from that event. Similar accretion disks are expected to form in collapsars (the supernova-triggering collapse of rapidly rotating massive stars), which have previously been speculated to produce r-process elements. Recent observations of stars rich in such elements in the dwarf galaxy Reticulum II, as well as the Galactic chemical enrichment of europium relative to iron over longer timescales, are more consistent with rare supernovae acting at low stellar metallicities than with neutron-star mergers. Here we report simulations that show that collapsar accretion disks yield sufficient r-process elements to explain observed abundances in the Universe. Although these supernovae are rarer than neutron-star mergers, the larger amount of material ejected per event compensates for the lower rate of occurrence. We calculate that collapsars may supply more than 80 per cent of the r-process content of the Universe.

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arXiv2018

Fingerprints of heavy element nucleosynthesis in the late-time lightcurves of kilonovae

The kilonova emission observed following the binary neutron star merger event GW170817 provided the first direct evidence for the synthesis of heavy nuclei through the r-process. The late-time transition in the spectral energy distribution to near-infrared wavelengths was interpreted as indicating the production of lanthanide nuclei, with atomic mass number A>140. However, compelling evidence for the presence of heavier third-peak r-process elements (e.g., gold, platinum) or translead nuclei remains elusive. At early times (~days) most of the r-process heating arises from a large statistical ensemble of beta-decays, which thermalize efficiently while the ejecta is still dense, generating a heating rate that is reasonably approximated by a single power-law. However, at later times (weeks to months), the decay energy input can possibly be dominated by a discrete number of alpha-decays, 223Ra (half-life t_{1/2}=11.43d), 225Ac (t_{1/2}=10.0d, following the beta-decay of 225Ra with t_{1/2}=14.9d), and the fissioning isotope 254Cf (t_{1/2}=60.5d), which liberate more energy per decay and thermalize with greater efficiency than beta-decay products. Late-time nebular observations of kilonovae which constrain the radioactive power provide the potential to identify signatures of these individual isotopes, thus confirming the production of heavy nuclei. In order to constrain the bolometric light to the required accuracy, multi-epoch & wide-band observations are required with sensitive instruments like the James Webb Space Telescope. In addition, by comparing the nuclear heating rate obtained with an abundance distribution following the Solar r abundance pattern, to the bolometric lightcurve of AT2017gfo, we find that the yet-uncertain r abundance of 72Ge plays a decisive role in powering the lightcurve, if one assumes that GW170817 has produced a full range of the Solar r abundances down to A~70.

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