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van Velzen, S., Stein, R., Gilfanov, M., Kowalski, M., Hayasaki, K., Reusch, S., . . . Rusholme, B. (2024). Establishing accretion flares from supermassive black holes as a source of high-energy neutrinos. Monthly notices of the Royal Astronomical Society, 529(3), 2559-2576
Open this publication in new window or tab >>Establishing accretion flares from supermassive black holes as a source of high-energy neutrinos
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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. 2559-2576Article in journal (Refereed) Published
Abstract [en]

The origin of cosmic high-energy neutrinos remains largely unexplained. For high-energy neutrino alerts from IceCube, a coincidence with time-variable emission has been seen for three different types of accreting black holes: (1) a gamma-ray flare from a blazar (TXS 0506+056), (2) an optical transient following a stellar tidal disruption event (TDE; AT2019dsg), and (3) an optical outburst from an active galactic nucleus (AGN; AT2019fdr). For the latter two sources, infrared follow-up observations revealed a powerful reverberation signal due to dust heated by the flare. This discovery motivates a systematic study of neutrino emission from all supermassive black hole with similar dust echoes. Because dust reprocessing is agnostic to the origin of the outburst, our work unifies TDEs and high-amplitude flares from AGN into a population that we dub accretion flares. Besides the two known events, we uncover a third flare that is coincident with a PeV-scale neutrino (AT2019aalc). Based solely on the optical and infrared properties, we estimate a significance of 3.6σ for this association of high-energy neutrinos with three accretion flares. Our results imply that at least ∼10 per cent of the IceCube high-energy neutrino alerts could be due to accretion flares. This is surprising because the sum of the fluence of these flares is at least three orders of magnitude lower compared to the total fluence of normal AGN. It thus appears that the efficiency of high-energy neutrino production in accretion flares is increased compared to non-flaring AGN. We speculate that this can be explained by the high Eddington ratio of the flares.

Keywords
neutrinos, galaxies: active, transients: tidal disruption events
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-228649 (URN)10.1093/mnras/stae610 (DOI)001190047400003 ()
Available from: 2024-05-07 Created: 2024-05-07 Last updated: 2024-05-07Bibliographically approved
Kool, E. C., Pearson Johansson, J., Sollerman, J., Moldón, J., Moriya, T. J., Mattila, S., . . . Stern, D. (2023). A radio-detected type Ia supernova with helium-rich circumstellar material. Nature, 617(7961), 477-482
Open this publication in new window or tab >>A radio-detected type Ia supernova with helium-rich circumstellar material
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2023 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 617, no 7961, p. 477-482Article in journal (Refereed) Published
Abstract [en]

Type Ia supernovae (SNe Ia) are thermonuclear explosions of degenerate white dwarf stars destabilized by mass accretion from a companion star1, but the nature of their progenitors remains poorly understood. A way to discriminate between progenitor systems is through radio observations; a non-degenerate companion star is expected to lose material through winds2 or binary interaction3 before explosion, and the supernova ejecta crashing into this nearby circumstellar material should result in radio synchrotron emission. However, despite extensive efforts, no type Ia supernova (SN Ia) has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate white dwarf star4,5. Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich circumstellar material, as demonstrated by its spectral features, infrared emission and, for the first time in a SN Ia to our knowledge, a radio counterpart. On the basis of our modelling, we conclude that the circumstellar material probably originates from a single-degenerate binary system in which a white dwarf accretes material from a helium donor star, an often proposed formation channel for SNe Ia (refs. 6,7). We describe how comprehensive radio follow-up of SN 2020eyj-like SNe Ia can improve the constraints on their progenitor systems.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-223960 (URN)10.1038/s41586-023-05916-w (DOI)001078324200011 ()37198310 (PubMedID)2-s2.0-85159611552 (Scopus ID)
Available from: 2023-11-24 Created: 2023-11-24 Last updated: 2023-11-24Bibliographically approved
Ho, A. Y. Q., Perley, D. A., Gal-Yam, A., Lunnan, R., Sollerman, J., Schulze, S., . . . Winters, J. M. (2023). A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients. Astrophysical Journal, 949(2), Article ID 120.
Open this publication in new window or tab >>A Search for Extragalactic Fast Blue Optical Transients in ZTF and the Rate of AT2018cow-like Transients
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2023 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 949, no 2, article id 120Article in journal (Refereed) Published
Abstract [en]

We present a search for extragalactic fast blue optical transients (FBOTs) during Phase I of the Zwicky Transient Facility (ZTF). We identify 38 candidates with durations above half-maximum light 1 day < t (1/2) < 12 days, of which 28 have blue (g - r less than or similar to -0.2 mag) colors at peak light. Of the 38 transients (28 FBOTs), 19 (13) can be spectroscopically classified as core-collapse supernovae (SNe): 11 (8) H- or He-rich (Type II/IIb/Ib) SNe, 6 (4) interacting (Type IIn/Ibn) SNe, and 2 (1) H&He-poor (Type Ic/Ic-BL) SNe. Two FBOTs (published previously) had predominantly featureless spectra and luminous radio emission: AT2018lug (The Koala) and AT2020xnd (The Camel). Seven (five) did not have a definitive classification: AT 2020bdh showed tentative broad H alpha in emission, and AT 2020bot showed unidentified broad features and was 10 kpc offset from the center of an early-type galaxy. Ten (eight) have no spectroscopic observations or redshift measurements. We present multiwavelength (radio, millimeter, and/or X-ray) observations for five FBOTs (three Type Ibn, one Type IIn/Ibn, one Type IIb). Additionally, we search radio-survey (VLA and ASKAP) data to set limits on the presence of radio emission for 24 of the transients. All X-ray and radio observations resulted in nondetections; we rule out AT2018cow-like X-ray and radio behavior for five FBOTs and more luminous emission (such as that seen in the Camel) for four additional FBOTs. We conclude that exotic transients similar to AT2018cow, the Koala, and the Camel represent a rare subset of FBOTs and use ZTF's SN classification experiments to measure the rate to be at most 0.1% of the local core-collapse SN rate.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-218369 (URN)10.3847/1538-4357/acc533 (DOI)001001445700001 ()2-s2.0-85161632715 (Scopus ID)
Available from: 2023-06-27 Created: 2023-06-27 Last updated: 2023-06-27Bibliographically approved
Sharma, Y., Sollerman, J., Fremling, C., Kulkarni, S. R., De Kishalay, K., Irani, I., . . . Yao, Y. (2023). A Systematic Study of Ia-CSM Supernovae from the ZTF Bright Transient Survey. Astrophysical Journal, 948(1), Article ID 52.
Open this publication in new window or tab >>A Systematic Study of Ia-CSM Supernovae from the ZTF Bright Transient Survey
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2023 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 948, no 1, article id 52Article in journal (Refereed) Published
Abstract [en]

Among the supernovae (SNe) that show strong interaction with a circumstellar medium (CSM), there is a rare subclass of Type Ia supernovae, SNe Ia-CSM, which show strong narrow hydrogen emission lines much like SNe IIn but on top of a diluted Type Ia spectrum. The only previous systematic study of this class identified 16 SNe Ia-CSM, eight historic and eight from the Palomar Transient Factory (PTF). Now using the successor survey to PTF, the Zwicky Transient Facility (ZTF), we have classified 12 additional SNe Ia-CSM through the systematic Bright Transient Survey (BTS). Consistent with previous studies, we find these SNe to have slowly evolving optical light curves with peak absolute magnitudes between -19.1 and -21, spectra having weak H ss and large Balmer ldecrements of similar to 7. Out of the 10 SNe from our sample observed by NEOWISE, nine have 3 sigma detections, with some SNe showing a reduction in the red wing of Ha, indicative of newly formed dust. We do not find our SN Ia-CSM sample to have a significantly different distribution of equivalent widths of He I.5876 than SNe IIn as observed in Silverman et al. The hosts tend to be late-type galaxies with recent star formation. We derive a rate estimate of 29+(27)(21) Gpc(-3) yr(-1) for SNe Ia-CSM, which is similar to 0.02%-0.2% of the SN Ia rate. We also identify six ambiguous SNe IIn/Ia-CSM in the BTS sample and including them gives an upper limit rate of 0.07%-0.8%. This work nearly doubles the sample of well-studied Ia-CSM objects in Silverman et al., increasing the total number to 28.

Keywords
Unified Astronomy Thesaurus concepts: Supernovae (1668), Type Ia supernovae (1728)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-218365 (URN)10.3847/1538-4357/acbc16 (DOI)000982386400001 ()2-s2.0-85157998944 (Scopus ID)
Available from: 2023-06-28 Created: 2023-06-28 Last updated: 2023-06-28Bibliographically approved
Agudo, I., Chen, T.-W. -., Kool, E. C., Schulze, S., Sollerman, J., Yang, S. & Young, D. R. (2023). Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations. Astronomy and Astrophysics, 675, Article ID A201.
Open this publication in new window or tab >>Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 675, article id A201Article in journal (Refereed) Published
Abstract [en]

We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (similar to SIM;150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude (M-i similar to -16.7 mag), and the r-band decline rate of similar to 1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only similar to 0.1 M circle dot, with Ni-56 comprising similar to 20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.

Keywords
supernovae, general, supernovae, individual, SN2019wxt, binaries, general, stars, evolution, gravitational waves
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-220837 (URN)10.1051/0004-6361/202244751 (DOI)001033667500004 ()2-s2.0-85166914315 (Scopus ID)
Available from: 2023-09-14 Created: 2023-09-14 Last updated: 2023-09-14Bibliographically approved
Hammerstein, E., van Velzen, S., Gezari, S., Cenko, S. B., Yao, Y., Ward, C., . . . Yan, L. (2023). The Final Season Reimagined: 30 Tidal Disruption Events from the ZTF-I Survey. Astrophysical Journal, 942(1), Article ID 9.
Open this publication in new window or tab >>The Final Season Reimagined: 30 Tidal Disruption Events from the ZTF-I Survey
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2023 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 942, no 1, article id 9Article in journal (Refereed) Published
Abstract [en]

Tidal disruption events (TDEs) offer a unique way to study dormant black holes. While the number of observed TDEs has grown thanks to the emergence of wide-field surveys in the past few decades, questions regarding the nature of the observed optical, UV, and X-ray emission remain. We present a uniformly selected sample of 30 spectroscopically classified TDEs from the Zwicky Transient Facility Phase I survey operations with follow-up Swift UV and X-ray observations. Through our investigation into correlations between light-curve properties, we recover a shallow positive correlation between the peak bolometric luminosity and decay timescales. We introduce a new spectroscopic class of TDE, TDE-featureless, which are characterized by featureless optical spectra. The new TDE-featureless class shows larger peak bolometric luminosities, peak blackbody temperatures, and peak blackbody radii. We examine the differences between the X-ray bright and X-ray faint populations of TDEs in this sample, finding that X-ray bright TDEs show higher peak blackbody luminosities than the X-ray faint subsample. This sample of optically selected TDEs is the largest sample of TDEs from a single survey yet, and the systematic discovery, classification, and follow-up of this sample allows for robust characterization of TDE properties, an important stepping stone looking forward toward the Rubin era.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-213890 (URN)10.3847/1538-4357/aca283 (DOI)000905301300001 ()
Available from: 2023-02-06 Created: 2023-02-06 Last updated: 2023-02-06Bibliographically approved
Burdge, K. B., Marsh, T. R., Fuller, J., Bellm, E. C., Caiazzo, I., Chakrabarty, D., . . . Prince, T. A. (2022). A 62-minute orbital period black widow binary in a wide hierarchical triple. Nature, 605(7908), 41-45
Open this publication in new window or tab >>A 62-minute orbital period black widow binary in a wide hierarchical triple
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2022 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 605, no 7908, p. 41-45Article in journal (Refereed) Published
Abstract [en]

Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original 'black widow', the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20)(1), high-energy emission originating from the pulsar2 is irradiating and may eventually destroy(3) a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars(4), allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models(5), falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics(6) and binary evolution.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-205199 (URN)10.1038/s41586-022-04551-1 (DOI)000790960500011 ()35508781 (PubMedID)2-s2.0-85129391395 (Scopus ID)
Available from: 2022-06-09 Created: 2022-06-09 Last updated: 2022-06-09Bibliographically approved
Sagués Carracedo, A., Schulze, S., Sollerman, J., Bulla, M. & Kool, E. C. (2022). A very luminous jet from the disruption of a star by a massive black hole. Nature, 612(7940), 430-434
Open this publication in new window or tab >>A very luminous jet from the disruption of a star by a massive black hole
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2022 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 612, no 7940, p. 430-434Article in journal (Refereed) Published
Abstract [en]

Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close1. TDEs provide a window through which to study accretion onto supermassive black holes; in some rare cases, this accretion leads to launching of a relativistic jet2,3,4,5,6,7,8,9, but the necessary conditions are not fully understood. The best-studied jetted TDE so far is Swift J1644+57, which was discovered in γ-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical detection of AT2022cmc, a rapidly fading source at cosmological distance (redshift z = 1.19325) the unique light curve of which transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-ray, submillimetre and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ‘afterglow’, probably launched by a supermassive black hole with spin greater than approximately 0.3. Using four years of Zwicky Transient Facility10 survey data, we calculate a rate of 0.02+0.04−0.01 Gpc−3 yr−1 for on-axis jetted TDEs on the basis of the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations11. Correcting for the beaming angle effects, this rate confirms that approximately 1 per cent of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-215888 (URN)10.1038/s41586-022-05465-8 (DOI)000936400900029 ()36450988 (PubMedID)2-s2.0-85143175488 (Scopus ID)
Available from: 2023-03-30 Created: 2023-03-30 Last updated: 2023-03-30Bibliographically approved
Gal-Yam, A., Bruch, R., Schulze, S., Yang, Y., Perley, D. A., Irani, I., . . . Knezevic, N. (2022). A WC/WO star exploding within an expanding carbon-oxygen-neon nebula. Nature, 601(7892), 201-204
Open this publication in new window or tab >>A WC/WO star exploding within an expanding carbon-oxygen-neon nebula
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2022 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 601, no 7892, p. 201-204Article in journal (Refereed) Published
Abstract [en]

The final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf-Rayet stars(1) emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. A fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types WC/WO). Evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types Ib/Ic) cannot result from massive WC/WO stars(2,3), leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion(4). Here we report observations of SN 2019hgp, beginning about a day after the explosion. Its short rise time and rapid decline place it among an emerging population of rapidly evolving transients(5-8). Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. Narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive Wolf-Rayet stars may be the progenitors of some rapidly evolving transients.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-201938 (URN)10.1038/s41586-021-04155-1 (DOI)000742123100009 ()35022591 (PubMedID)2-s2.0-85122889405 (Scopus ID)
Available from: 2022-02-10 Created: 2022-02-10 Last updated: 2022-11-14Bibliographically approved
Reusch, S., Stein, R., Kowalski, M., van Velzen, S., Franckowiak, A., Lunardini, C., . . . Zimmerman, E. (2022). Candidate Tidal Disruption Event AT2019fdr Coincident with a High-Energy Neutrino. Physical Review Letters, 128(22), Article ID 221101.
Open this publication in new window or tab >>Candidate Tidal Disruption Event AT2019fdr Coincident with a High-Energy Neutrino
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2022 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 128, no 22, article id 221101Article in journal (Refereed) Published
Abstract [en]

The origins of the high-energy cosmic neutrino flux remain largely unknown. Recently, one high-energy neutrino was associated with a tidal disruption event (TDE). Here we present AT2019fdr, an exceptionally luminous TDE candidate, coincident with another high-energy neutrino. Our observations, including a bright dust echo and soft late-time x-ray emission, further support a TDE origin of this flare. The probability of finding two such bright events by chance is just 0.034%. We evaluate several models for neutrino production and show that AT2019fdr is capable of producing the observed high-energy neutrino, reinforcing the case for TDEs as neutrino sources.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-207841 (URN)10.1103/PhysRevLett.128.221101 (DOI)000811308400010 ()35714251 (PubMedID)2-s2.0-85131869176 (Scopus ID)
Available from: 2022-08-18 Created: 2022-08-18 Last updated: 2022-11-14Bibliographically approved
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