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Schulze, S., Fransson, C., Jerkstrand, A., Sollerman, J., Omand, C. M. B., Sarin, N., . . . Pessi, P. J. (2024). 1100 days in the life of the supernova 2018ibb The best pair-instability supernova candidate, to date. Astronomy and Astrophysics, 683, Article ID A223.
Open this publication in new window or tab >>1100 days in the life of the supernova 2018ibb The best pair-instability supernova candidate, to date
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 683, article id A223Article in journal (Refereed) Published
Abstract [en]

Stars with zero-age main sequence masses between 140 and 260 M are thought to explode as pair-instability supernovae (PISNe). During their thermonuclear runaway, PISNe can produce up to several tens of solar masses of radioactive nickel, resulting in luminous transients similar to some superluminous supernovae (SLSNe). Yet, no unambiguous PISN has been discovered so far. SN 2018ibb is a hydrogen-poor SLSN at z = 0.166 that evolves extremely slowly compared to the hundreds of known SLSNe. Between mid 2018 and early 2022, we monitored its photometric and spectroscopic evolution from the UV to the near-infrared (NIR) with 2–10 m class telescopes. SN 2018ibb radiated > 3 × 1051 erg during its evolution, and its bolometric light curve reached > 2 × 1044 erg s−1 at its peak. The long-lasting rise of > 93 rest-frame days implies a long diffusion time, which requires a very high total ejected mass. The PISN mechanism naturally provides both the energy source (56Ni) and the long diffusion time. Theoretical models of PISNe make clear predictions as to their photometric and spectroscopic properties. SN 2018ibb complies with most tests on the light curves, nebular spectra and host galaxy, and potentially all tests with the interpretation we propose. Both the light curve and the spectra require 25–44 M of freshly nucleosynthesised 56Ni, pointing to the explosion of a metal-poor star with a helium core mass of 120–130 M at the time of death. This interpretation is also supported by the tentative detection of [Co II] λ 1.025 μm, which has never been observed in any other PISN candidate or SLSN before. We observe a significant excess in the blue part of the optical spectrum during the nebular phase, which is in tension with predictions of existing PISN models. However, we have compelling observational evidence for an eruptive mass-loss episode of the progenitor of SN 2018ibb shortly before the explosion, and our dataset reveals that the interaction of the SN ejecta with this oxygen-rich circumstellar material contributed to the observed emission. That may explain this specific discrepancy with PISN models. Powering by a central engine, such as a magnetar or a black hole, can be excluded with high confidence. This makes SN 2018ibb by far the best candidate for being a PISN, to date.

Keywords
supernovae: individual: SN 2018ibb, supernovae: individual: ATLAS18unu, supernovae: individual: Gaia19cvo supernovae, individual: PS19crg, supernovae: individual: ZTF18acenqto
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-229343 (URN)10.1051/0004-6361/202346855 (DOI)001190051800002 ()
Available from: 2024-05-24 Created: 2024-05-24 Last updated: 2024-05-24Bibliographically approved
Chen, P., Gal-Yam, A., Sollerman, J., Schulze, S., Post, R. S., Liu, C., . . . Yan, L. (2024). A 12.4-day periodicity in a close binary system after a supernova. Nature, 625(7994), 253-258
Open this publication in new window or tab >>A 12.4-day periodicity in a close binary system after a supernova
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2024 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 625, no 7994, p. 253-258Article in journal (Refereed) Published
Abstract [en]

Neutron stars and stellar-mass black holes are the remnants of massive star explosions1. Most massive stars reside in close binary systems2, and the interplay between the companion star and the newly formed compact object has been theoretically explored3, but signatures for binarity or evidence for the formation of a compact object during a supernova explosion are still lacking. Here we report a stripped-envelope supernova, SN 2022jli, which shows 12.4-day periodic undulations during the declining light curve. Narrow Hα emission is detected in late-time spectra with concordant periodic velocity shifts, probably arising from hydrogen gas stripped from a companion and accreted onto the compact remnant. A new Fermi-LAT γ-ray source is temporally and positionally consistent with SN 2022jli. The observed properties of SN 2022jli, including periodic undulations in the optical light curve, coherent Hα emission shifting and evidence for association with a γ-ray source, point to the explosion of a massive star in a binary system leaving behind a bound compact remnant. Mass accretion from the companion star onto the compact object powers the light curve of the supernova and generates the γ-ray emission.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-226987 (URN)10.1038/s41586-023-06787-x (DOI)001143579000018 ()38200292 (PubMedID)2-s2.0-85181900770 (Scopus ID)
Available from: 2024-03-04 Created: 2024-03-04 Last updated: 2024-03-04Bibliographically approved
Schady, P., Yates, R. M., Christensen, L., De Cia, A., Rossi, A., D'Elia, V., . . . Wiseman, P. (2024). Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z =2-4 using JWST. Monthly notices of the Royal Astronomical Society, 529(3), 2807-2831
Open this publication in new window or tab >>Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z =2-4 using JWST
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2024 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 529, no 3, p. 2807-2831Article in journal (Refereed) Published
Abstract [en]

Much of what is known of the chemical composition of the universe is based on emission line spectra from star-forming galaxies. Emission-based inferences are, nevertheless, model-dependent and they are dominated by light from luminous star-forming regions. An alternative and sensitive probe of the metallicity of galaxies is through absorption lines imprinted on the luminous afterglow spectra of long gamma ray bursts (GRBs) from neutral material within their host galaxy. We present results from a JWST/NIRSpec programme to investigate for the first time the relation between the metallicity of neutral gas probed in absorption by GRB afterglows and the metallicity of the star-forming regions for the same host galaxy sample. Using an initial sample of eight GRB host galaxies at z = 2.1–4.7, we find a tight relation between absorption and emission line metallicities when using the recently proposed 𝑅^ metallicity diagnostic (±0.2 dex). This agreement implies a relatively chemically homogeneous multiphase interstellar medium and indicates that absorption and emission line probes can be directly compared. However, the relation is less clear when using other diagnostics, such as R23 and R3. We also find possible evidence of an elevated N/O ratio in the host galaxy of GRB 090323 at z = 4.7, consistent with what has been seen in other z > 4 galaxies. Ultimate confirmation of an enhanced N/O ratio and of the relation between absorption and emission line metallicities will require a more direct determination of the emission line metallicity via the detection of temperature-sensitive auroral lines in our GRB host galaxy sample.

Keywords
gamma-ray burst: general, ISM: abundances, galaxies: abundances, galaxies: high-redshift, galaxies: ISM, quasars: absorption lines
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-228652 (URN)10.1093/mnras/stae677 (DOI)001188770300012 ()2-s2.0-85188705507 (Scopus ID)
Available from: 2024-04-26 Created: 2024-04-26 Last updated: 2024-04-26Bibliographically approved
Sarin, N. & Schulze, S. (2024). Heavy-element production in a compact object merger observed by JWST. Nature, 626, 737-741
Open this publication in new window or tab >>Heavy-element production in a compact object merger observed by JWST
2024 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 626, p. 737-741Article in journal (Refereed) Published
Abstract [en]

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)2 and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the r-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 mergers4,5,6 and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs. 7,8,9,10,11,12). 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 mass A = 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 create r-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe.

National Category
Atom and Molecular Physics and Optics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-227416 (URN)10.1038/s41586-023-06759-1 (DOI)001169196100001 ()37879361 (PubMedID)2-s2.0-85182219102 (Scopus ID)
Available from: 2024-03-14 Created: 2024-03-14 Last updated: 2024-04-29Bibliographically approved
Irani, I., Chen, P., Morag, J., Schulze, S., Gal-Yam, A., Strotjohann, N. L., . . . Medford, M. S. (2024). SN 2022oqm-A Ca-rich Explosion of a Compact Progenitor Embedded in C/O Circumstellar Material. Astrophysical Journal, 962(2), Article ID 109.
Open this publication in new window or tab >>SN 2022oqm-A Ca-rich Explosion of a Compact Progenitor Embedded in C/O Circumstellar Material
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2024 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 962, no 2, article id 109Article in journal (Refereed) Published
Abstract [en]

We present the discovery and analysis of SN 2022oqm, a Type Ic supernova (SN) detected <1 day after the explosion. The SN rises to a blue and short-lived (2 days) initial peak. Early-time spectral observations of SN 2022oqm show a hot (40,000 K) continuum with high ionization C and O absorption features at velocities of 4000 km s−1, while its photospheric radius expands at 20,000 km s−1, indicating a pre-existing distribution of expanding C/O material. After ∼2.5 days, both the spectrum and light curves evolve into those of a typical SN Ic, with line velocities of ∼10,000 km s−1, in agreement with the evolution of the photospheric radius. The optical light curves reach a second peak at t ≈ 15 days. By t = 60 days, the spectrum of SN 2022oqm becomes nearly nebular, displaying strong Ca ii and [Ca ii] emission with no detectable [O i], marking this event as Ca-rich. The early behavior can be explained by 10−3M of optically thin circumstellar material (CSM) surrounding either (1) a massive compact progenitor such as a Wolf–Rayet star, (2) a massive stripped progenitor with an extended envelope, or (3) a binary system with a white dwarf. We propose that the early-time light curve is powered by both the interaction of the ejecta with the optically thin CSM and shock cooling (in the massive star scenario). The observations can be explained by CSM that is optically thick to X-ray photons, is optically thick in the lines as seen in the spectra, and is optically thin to visible-light continuum photons that come either from downscattered X-rays or from the shock-heated ejecta. Calculations show that this scenario is self-consistent.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-226985 (URN)10.3847/1538-4357/ad04d7 (DOI)001159919400001 ()2-s2.0-85184936369 (Scopus ID)
Available from: 2024-03-05 Created: 2024-03-05 Last updated: 2024-03-05Bibliographically approved
Brennan, S. J., Sollerman, J., Irani, I., Schulze, S., Chen, P., Das, K. K., . . . Wold, A. (2024). Spectroscopic observations of progenitor activity 100 days before a Type Ibn supernova. Astronomy and Astrophysics, 684, Article ID L18.
Open this publication in new window or tab >>Spectroscopic observations of progenitor activity 100 days before a Type Ibn supernova
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 684, article id L18Article in journal (Refereed) Published
Abstract [en]

Obtaining spectroscopic observations of the progenitors of core-collapse supernovae is often unfeasible, due to an inherent lack of knowledge as to what stars experience supernovae and when they will explode. In this Letter we present photometric and spectroscopic observations of the progenitor activity of SN 2023fyq before the He-rich progenitor explodes as a Type Ibn supernova. The progenitor of SN 2023fyq shows an exponential rise in flux prior to core collapse. Complex He I emission line features are observed in the progenitor spectra, with a P Cygni-like profile, as well as an evolving broad base with velocities of the order of 10 000 km s−1. The luminosity and evolution of SN 2023fyq is consistent with a Type Ibn, reaching a peak r-band magnitude of −18.8 mag, although there is some uncertainty regarding the distance to the host, NGC 4388, which is located in the Virgo cluster. We present additional evidence of asymmetric He-rich material being present both prior to and after the explosion of SN 2023fyq, which suggests that this material survived the ejecta interaction. Broad [O I], C I, and the Ca II triplet lines are observed at late phases, confirming that SN 2023fyq was a genuine supernova, rather than a non-terminal interacting transient. SN 2023fyq provides insight into the final moments of a massive star’s life, demonstrating that the progenitor is likely highly unstable before core collapse.

Keywords
circumstellar matter, supernovae: general, supernovae: individual: ZTF22abzzvln
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-229038 (URN)10.1051/0004-6361/202449350 (DOI)001203444100006 ()2-s2.0-85190886373 (Scopus ID)
Available from: 2024-05-22 Created: 2024-05-22 Last updated: 2024-05-22Bibliographically approved
Schulze, S., Sollerman, J., Fransson, C. & Pearson Johansson, J. (2024). The complex circumstellar environment of supernova 2023ixf. Nature, 627(8005)
Open this publication in new window or tab >>The complex circumstellar environment of supernova 2023ixf
2024 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 627, no 8005Article in journal (Refereed) Published
Abstract [en]

The early evolution of a supernova (SN) can reveal information about the environment and the progenitor star. When a star explodes in vacuum, the first photons to escape from its surface appear as a brief, hours-long shock-breakout flare1,2, followed by a cooling phase of emission. However, for stars exploding within a distribution of dense, optically thick circumstellar material (CSM), the first photons escape from the material beyond the stellar edge and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating3. Early serendipitous observations2,4 that lacked ultraviolet (UV) data were unable to determine whether the early emission is heating or cooling and hence the nature of the early explosion event. Here we report UV spectra of the nearby SN 2023ixf in the galaxy Messier 101 (M101). Using the UV data as well as a comprehensive set of further multiwavelength observations, we temporally resolve the emergence of the explosion shock from a thick medium heated by the SN emission. We derive a reliable bolometric light curve that indicates that the shock breaks out from a dense layer with a radius substantially larger than typical supergiants.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-229341 (URN)10.1038/s41586-024-07116-6 (DOI)001195792000001 ()38538936 (PubMedID)2-s2.0-85188894094 (Scopus ID)
Available from: 2024-05-27 Created: 2024-05-27 Last updated: 2024-05-27Bibliographically approved
Pessi, T., Prieto, J. L., Anderson, J. P., Galbany, L., Lyman, J. D., Kochanek, C., . . . Shappee, B. (2023). A characterization of ASAS-SN core-collapse supernova environments with VLT+MUSE I. Sample selection, analysis of local environments, and correlations with light curve properties. Astronomy and Astrophysics, 677, Article ID A28.
Open this publication in new window or tab >>A characterization of ASAS-SN core-collapse supernova environments with VLT+MUSE I. Sample selection, analysis of local environments, and correlations with light curve properties
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 677, article id A28Article in journal (Refereed) Published
Abstract [en]

Context. The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the Very Large Telescope (VLT) enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, an untargeted and spectroscopically complete transient survey, has enabled us to perform a minimally biased statistical analysis of CCSN environments.

Aims. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe – 78 II, nine IIn, seven IIb, four Ic, seven Ib, three Ibn, two Ic-BL, one ambiguous Ibc, and one superluminous SN – detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves.

Methods. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all H II regions detected within each galaxy, including the star formation rate (SFR), Hα equivalent width (EW), oxygen abundance, and extinction.

Results. We found that stripped-envelope supernovae (SESNe) occur in environments with a higher median SFR, Hα EW, and oxygen abundances than SNe II and SNe IIn/Ibn. Most of the distributions have no statistically significant differences, except between oxygen abundance distributions of SESNe and SNe II, and between Hα EW distributions of SESNe and SNe II. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, Hα EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and Hα EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, s, of SNe II correlates with the Hα EW, and that the luminosity and the Δm15 parameter of SESNe correlate with the oxygen abundance, Hα EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.

Keywords
supernovae: general, galaxies: abundances
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-223857 (URN)10.1051/0004-6361/202346512 (DOI)001073813400002 ()2-s2.0-85169929131 (Scopus ID)
Available from: 2023-11-22 Created: 2023-11-22 Last updated: 2023-11-22Bibliographically approved
Levan, A. J., Malesani, D. B., Gompertz, B. P., Nugent, A. E., Nicholl, M., Oates, S. R., . . . Tanvir, N. R. (2023). A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy. Nature Astronomy, 7(8), 976-985
Open this publication in new window or tab >>A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy
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2023 (English)In: Nature Astronomy, E-ISSN 2397-3366, Vol. 7, no 8, p. 976-985Article in journal (Refereed) Published
Abstract [en]

The majority of long-duration (>2 s) gamma-ray bursts (GRBs) arise from the collapse of massive stars, with a small proportion created from the merger of compact objects. Most of these systems form via standard stellar evolution pathways. However, a fraction of GRBs may result from dynamical interactions in dense environments. These channels could also contribute substantially to the samples of compact object mergers detected as gravitational wave sources. Here we report the case of GRB 191019A, a long GRB (a duration of T90 = 64.4 ± 4.5 s), which we pinpoint close (⪅100 pc projected) to the nucleus of an ancient (>1 Gyr old) host galaxy at z = 0.248. The lack of evidence for star formation and deep limits on any supernova emission disfavour a massive star origin. The most likely route for progenitor formation is via dynamical interactions in the dense nucleus of the host. The progenitor, in this case, could be a compact object merger. These may form in dense nuclear clusters or originate in a gaseous disc around the supermassive black hole. Identifying, to the best of our knowledge, a first example of a dynamically produced GRB demonstrates the role that such bursts may have in probing dense environments and constraining dynamical fractions in gravitational wave populations.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-221078 (URN)10.1038/s41550-023-01998-8 (DOI)001019740000004 ()2-s2.0-85162673864 (Scopus ID)
Available from: 2023-09-25 Created: 2023-09-25 Last updated: 2023-09-25Bibliographically approved
Karamehmetoglu, E., Sollerman, J., Taddia, F., Barbarino, C., Feindt, U., Fremling, C., . . . Zapartas, E. (2023). A population of Type Ibc supernovae with massive progenitors Broad lightcurves not uncommon in (i)PTF. Astronomy and Astrophysics, 678, Article ID A87.
Open this publication in new window or tab >>A population of Type Ibc supernovae with massive progenitors Broad lightcurves not uncommon in (i)PTF
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 678, article id A87Article in journal (Refereed) Published
Abstract [en]

If high-mass stars (≳20 − 25 M) are the progenitors of stripped-envelope (SE) supernovae (SNe), their massive ejecta should lead to broad, long-duration lightcurves. Instead, literature samples of SE SNe have reported relatively narrow lightcurves corresponding to ejecta masses between 1 − 4 M that favor intermediate-mass progenitors (≲20 − 25 M). Working with an untargeted sample from a single telescope to better constrain their rates, we searched the Palomar Transient Factory (PTF) and intermediate-PTF (iPTF) sample of SNe for SE SNe with broad lightcurves. Using a simple observational marker of g- or r-band lightcurve stretch compared to a template to measure broadness, we identified eight significantly broader Type Ibc SNe after applying quantitative sample selection criteria. The lightcurves, broad-band colors, and spectra of these SNe are found to evolve more slowly relative to typical Type Ibc SNe, proportional with the stretch parameter. Bolometric lightcurve modeling and their nebular spectra indicate high ejecta masses and nickel masses, assuming radioactive decay powering. Additionally, these objects are preferentially located in low-metallicity host galaxies with high star formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. Our study thus supports the link between broad lightcurves (as measured by stretch) and high-mass progenitor stars in SE SNe with independent evidence from bolometric lightcurve modeling, nebular spectra, host environment properties, and photometric evolution. In the first systematic search of its kind using an untargeted sample, we used the stretch distribution to identify a higher than previously appreciated fraction of SE SNe with broad lightcurves (∼13%). Correcting for Malmquist and lightcurve duration observational biases, we conservatively estimate that a minimum of ∼6% of SE SNe are consistent with high-mass progenitors. This result has implications for the progenitor channels of SE SNe, including late stages of massive stellar evolution, the origin of the observed oxygen fraction in the universe, and formation channels for stellar-mass black holes.

Keywords
supernovae: general, methods: statistical, surveys, methods: data analysis, techniques: photometric
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-223850 (URN)10.1051/0004-6361/202245231 (DOI)001084587200004 ()2-s2.0-85175010454 (Scopus ID)
Available from: 2023-11-20 Created: 2023-11-20 Last updated: 2023-11-20Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6797-1889

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