An official website of the United States government
Abstract Despite recent progress, the astrophysical channels responsible for rapid neutron capture (r-process) nucleosynthesis remain an unsettled question. Observations of the kilonova following the gravitational-wave-detected neutron star merger GW170817 established mergers as one site of ther-process, but additional sources may be needed to fully explainr-process enrichment in the universe. One intriguing possibility is that rapidly rotating massive stars undergoing core collapse launchr-process-rich outflows off the accretion disks formed from their infalling matter. In this scenario,r-process winds are one component of the supernova (SN) ejecta produced by “collapsar” explosions. We present the first systematic study of the effects ofr-process enrichment on the emission from collapsar-generated SNe. We semianalytically modelr-process SN emission from explosion out to late times and determine its distinguishing features. The ease with whichr-process SNe can be identified depends on how effectively wind material mixes into the initiallyr-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 ther-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 ofr-process collapsar candidates also lays the foundation for nebular-phase spectroscopic follow-up in the NIR and mid-infrared, for example, with the James Webb Space Telescope.
more »
« less
Collapsars as Sites of r-process Nucleosynthesis: Systematic Photometric Near-infrared Follow-up of Type Ic-BL Supernovae
Abstract One of the open questions following the discovery of GW170817 is whether neutron star (NS) mergers are the only astrophysical sites capable of producingr-process elements. Simulations have shown that 0.01–0.1M⊙ofr-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 NS mergers and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature ofr-process nucleosynthesis in the binary NS merger GW170817 was its long-lasting near-infrared (NIR) emission, thus motivating a systematic photometric study of the light curves of broad-lined 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/NIR bands to determine what quantity ofr-process material, if any, is synthesized in these explosions. Using semi-analytic models designed to account forr-process production in SNe Ic-BL, we perform light curve fitting to derive constraints on ther-process mass for these SNe. We also perform independent light curve fits to models without ther-process. We find that ther-process-free models are a better fit to the light curves of the objects in our sample. Thus, we find no compelling evidence ofr-process enrichment in any of our objects. Further high-cadence infrared photometric studies and nebular spectroscopic analysis would be sensitive to smaller quantities ofr-process ejecta mass or indicate whether all collapsars are completely devoid ofr-process nucleosynthesis.
more »
« less
- Award ID(s):
- 2002577
- PAR ID:
- 10489968
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 962
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 68
- Size(s):
- Article No. 68
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract While the spectroscopic classification scheme for stripped-envelope supernovae (SESNe) is clear, and we know that they originate from massive stars that lost some or all of their envelopes of hydrogen and helium, the photometric evolution of classes within this family is not fully characterized. Photometric surveys, like the Vera C. Rubin Legacy Survey of Space and Time, will discover tens of thousands of transients each night, and spectroscopic follow-up will be limited, prompting the need for photometric classification and inference based solely on photometry. We have generated 54 data-driven photometric templates for SESNe of subtypes IIb, Ib, Ic, Ic-bl, and Ibn inU/u,B,g,V,R/r,I/i,J,H,Ks, and Swiftw2,m2,w1 bands using Gaussian processes and a multisurvey data set composed of all well-sampled open-access light curves (165 SESNe, 29,531 data points) from the Open Supernova Catalog. We use our new templates to assess the photometric diversity of SESNe by comparing final per-band subtype templates with each other and with individual, unusual and prototypical SESNe. We find that SNe Ibn and SNe Ic-bl exhibit a distinctly faster rise and decline compared to other subtypes. We also evaluate the behavior of SESNe in the PLAsTiCC and ELAsTiCC simulations of LSST light curves, highlighting differences that can bias photometric classification models trained on the simulated light curves. Finally, we investigate in detail the behavior of fast-evolving SESNe (including SNe Ibn) and the implications of the frequently observed presence of two peaks in their light curves.more » « less
-
Abstract The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)1, sources of high-frequency gravitational waves (GWs)2and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (ther-process)3. Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers4–6and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs. 7–12). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic massA = 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can creater-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe.more » « less
-
Abstract The heaviest elements in the universe are synthesized through rapid neutron capture (r-process) in extremely neutron-rich outflows. Neutron star mergers were established as an importantr-process source through the multimessenger observation of GW170817. Collapsars were also proposed as a potentially major source of heavy elements; however, this is difficult to probe through optical observations due to contamination by other emission mechanisms. Here we present observational constraints onr-process nucleosynthesis by collapsars based on radio follow-up observations of nearby long gamma-ray bursts (GRBs). We make the hypothesis that late-time radio emission arises from the collapsar wind ejecta responsible for forgingr-process elements, and consider the constraints that can be set on this scenario using radio observations of a sample of Swift/Burst Alert Telescope GRBs located within 2 Gpc. No radio counterpart was identified in excess of the radio afterglow of the GRBs in our sample. This gives the strictest limit to the collapsarr-process contribution of ≲0.2M⊙for GRB 060505 and GRB 05826, under the models we considered. Our results additionally constrain energy injection by a long-lived neutron star remnant in some of the considered GRBs. While our results are in tension with collapsars being the majority ofr-process production sites, the ejecta mass and velocity profile of collapsar winds, and the emission parameters, are not yet well modeled. As such, our results are currently subject to large uncertainties, but further theoretical work could greatly improve them.more » « less
-
Abstract Core-collapse supernovae (SNe) are candidate sites for rapid neutron capture process (r-process) nucleosynthesis. We explore the effects of enrichment fromr-process nuclei on the light curves of hydrogen-rich SNe and assess the detectability of these signatures. We modify the radiation hydrodynamics code, SuperNova Explosion Code, to include the approximate effects of opacity and radioactive heating fromr-process elements in the supernova (SN) ejecta. We present models spanning a range of totalr-process massesMrand their assumed radial distribution within the ejecta, finding thatMr≳ 10−2M⊙is sufficient to induce appreciable differences in their light curves as compared to ordinary hydrogen-rich SNe (without anyr-process elements). The primary photometric signatures ofr-process enrichment include a shortening of the plateau phase, coinciding with the hydrogen-recombination photosphere retreating to ther-process-enriched layers, and a steeper post-plateau decline associated with a reddening of the SN colors. We compare ourr-process-enriched models to ordinary SNe models and observational data, showing that yields ofMr≳ 10−2M⊙are potentially detectable across several of the metrics used by transient observers, provided thatr-process-rich layers are mixed at least halfway to the ejecta surface. This detectability threshold can roughly be reproduced analytically using a two-zone (kilonova-within-an-SN) picture. Assuming that a small fraction of SNe produce a detectabler-process yield ofMr≳ 10−2M⊙, and respecting constraints on the total Galactic production rate, we estimate that ≳103–104SNe need be observed to find oner-enriched event, a feat that may become possible with the Vera Rubin Observatory.more » « less
