Evidence for a compact object in the aftermath of the extragalactic transient AT2018cow

Pasham, Dheeraj; Ho, Wynn C. G.; Alston, W. N.; Remillard, Ron; Ng, Mason; Gendreau, Keith C.; Metzger, Brian D.; Altamirano, D.; Chakrabarty, Deepto; Fabian, A. C.; Miller, J. M.; Bult, Peter; Arzoumanian, Zaven; Steiner, James F.; Strohmayer, Tod E.; Tombesi, Francesco; Homan, J.; Cackett, Edward M.; Harding, A. K.

doi:10.1038/s41550-021-01524-8

Cited by 40 publications

(43 citation statements)

References 62 publications

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“…The X-ray emission observed in all FBOTs does not align with the electron population inferred from the SSA radio spectrum. The spectral and temporal evolution, as well as the variability of the X-ray emission in AT2018cow, suggest that the X-ray signal is powered by a rapidly evolving central engine, a magnetar or an accretion disk around a black hole (Ho et al 2019;Margutti et al 2019;Quataert et al 2019;Pasham et al 2021).…”

Section: Introductionmentioning

confidence: 99%

“…However, the photospheric evolution, peak optical luminosity, fast decay and fast velocities indicate that these are not typical SNe powered by the radioactive decay of expanding photospheric shells. The fast rise and fall times, as well as the interaction of the ejecta with the CSM imply that numerous FBOTs could be related to the special stripped envelope SNe (see e.g., Ho et al 2021;Pellegrino et al 2021), possibly of type Ib/c, for which asphericity as it is for FBOTs can also be common (Maeda et al 2008). The progenitors of some of these SNe are considered to be massive Wolf-Rayet (WR) stars that shed their outer H and helium (He) layers through strong winds (Crowther 2007), which may constitute the necessitated dense CSM.…”

Section: Introductionmentioning

confidence: 99%

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Shocked jets in CCSNe can power the zoo of fast blue optical transients

Gottlieb,

Tchekhovskoy,

Margutti

2022

Preprint

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Evidence is mounting that recent multi-wavelength detections of fast blue optical transients (FBOTs) in star-forming galaxies comprise a new class of transients, whose origin is yet to be understood. We show that hydrogen-rich collapsing stars that launch relativistic jets near the central engine can naturally explain the entire set of FBOT observables. The jet-star interaction forms a mildly-relativistic shocked jet (inner cocoon) component, which powers cooling emission that dominates the high velocity optical signal during the first few weeks, with a typical energy of ∼ 10 50 − 10 51 erg. During this time, the cocoon radial energy distribution implies that the optical lightcurve exhibits a fast decay of L ∝ ∼ t −2.4 . After a few weeks, when the velocity of the emitting shell is ∼ 0.01 c, the cocoon becomes transparent, and the cooling stellar envelope governs the emission. During this transition, discontinuities may emerge in the lightcurve and spectra, as have been observed in a few FBOTs, such as AT2018cow. The interaction between the cocoon forward shock and the dense circumstellar winds generates synchrotron selfabsorbed emission in the radio bands, featuring a steady rise on a month timescale. After a few months, if the jet successfully pierces the stellar envelope, it decelerates, enters the observer's line of sight, and powers the peak of the radio lightcurve, which rapidly decays thereafter. The jet (and the inner cocoon) become optically thin to X-rays ∼ day after the collapse, allowing X-ray photons to diffuse from the central engine that launched the jet to the observer. Cocoon cooling emission is expected at higher volumetric rates than gamma-ray bursts (GRBs) by a factor of a few, similar to FBOTs. We rule out uncollimated outflows, however both GRB jets and failed collimated jets are compatible with all observables.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Shocked jets in CCSNe can power the zoo of fast blue optical transients

Gottlieb,

Tchekhovskoy,

Margutti

2022

Preprint

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“…Hard 10 keV X-ray emission was also detected (Margutti et al 2019) with a distinct spectrum characterized by broadened Fe emission lines and a spectral peak around 30 keV (similar to the "Compton hump" feature observed in AGN accretion disk reflection spectra; e.g., Reynolds 1999) and that faded over the first weeks. A quasiperiodic feature in the X-ray timing properties was recently reported at 225 Hz (Pasham et al 2022).…”

Section: Lessons From At2018cow and Its Analogsmentioning

confidence: 67%

“…Such a large energy in ejecta expanding at trans-relativistic speeds (up to ∼0.5c; Coppejans et al 2020) also points to a BH or NS central engine. As does the quasiperiodic X-ray feature, which, if interpreted as an orbital frequency in an accretion disk, constrains the central object mass 850M e (Pasham et al 2022).…”

Section: Progenitor Modelsmentioning

confidence: 95%

Luminous Fast Blue Optical Transients and Type Ibn/Icn SNe from Wolf-Rayet/Black Hole Mergers

Metzger

2022

ApJ

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Progenitor models for the “luminous” subclass of Fast Blue Optical Transients (LFBOTs; prototype: AT2018cow) are challenged to simultaneously explain all of their observed properties: fast optical rise times of days or less; peak luminosities ≳1044 erg s−1; low yields ≲0.1M ⊙ of 56Ni; aspherical ejecta with a wide velocity range (≲3000 km s−1 to ≳0.1–0.5c with increasing polar latitude); presence of hydrogen-depleted-but-not-free dense circumstellar material (CSM) on radial scales from ∼1014 cm to ∼3 × 1016 cm; embedded variable source of non-thermal X-ray/γ-rays, suggestive of a compact object. We show that all of these properties are consistent with the tidal disruption and hyper-accretion of a Wolf-Rayet (WR) star by a black hole or neutron star binary companion. In contrast with related previous models, the merger occurs with a long delay (≳100 yr) following the common envelope (CE) event responsible for birthing the binary, as a result of gradual angular momentum loss to a relic circumbinary disk. Disk-wind outflows from the merger-generated accretion flow generate the 56Ni-poor aspherical ejecta with the requisite velocity range. The optical light curve is powered primarily by reprocessing X-rays from the inner accretion flow/jet, though CSM shock interaction also contributes. Primary CSM sources include WR mass loss from the earliest stages of the merger (≲1014 cm) and the relic CE disk and its photoevaporation-driven wind (≳1016 cm). Longer delayed mergers may instead give rise to supernovae Type Ibn/Icn (depending on the WR evolutionary state), connecting these transient classes with LFBOTs.

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“…An additional piece of evidence of the presence of a CO might be the persistent ultraviolet source observed at the location of AT2018cow (Sun et al 2022). The presence of a CO may also be supported by the observation in AT2018cow of high-amplitude quasi periodic oscillations in soft X-rays (Pasham et al 2022).…”

Section: Introductionmentioning

confidence: 85%

Looking at Luminous Fast Blue Optical Transients through Neutrino Glasses

Guarini,

Tamborra,

Margutti

2022

Preprint

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Mounting evidence suggests that Luminous Fast Blue Optical Transients (LFBOTs) are powered by a compact object, launching an asymmetric and fast outflow responsible for the radiation observed in the ultraviolet, optical, infrared, radio, and X-ray bands. Proposed scenarios aiming to explain the electromagnetic emission include an inflated cocoon, surrounding a jet choked in the extended stellar envelope. In alternative, the observed radiation may arise from the disk formed by the delayed merger of a black hole with a Wolf-Rayet star. We explore the neutrino production in these scenarios, i.e. internal shocks in a choked jet and interaction between the outflow and the circumstellar medium (CSM). The choked jet provides the dominant contribution to the neutrino fluence. Intriguingly, the IceCube upper limit on the neutrino emission inferred from the closest LF-BOT, AT2018cow, excludes a region of the parameter space otherwise allowed by electromagnetic observations. After correcting for the Eddington bias on the observation of cosmic neutrinos, we conclude that the emission from a choked jet and CSM interaction is compatible with the detection of two track-like neutrino events observed by the IceCube Neutrino Observatory in coincidence with AT2018cow, and otherwise considered to be of atmospheric origin. While the neutrino emission from LFBOTs does not constitute the bulk of the diffuse background of neutrinos observed by IceCube, detection prospects of nearby LFBOTs with IceCube and the upcoming IceCube-Gen2 are encouraging; neutrinos could be observed up to 300 Mpc and 10 4 Mpc from the CSM interaction and choked jet, respectively. Follow-up neutrino searches will be crucial for unravelling the mechanism powering this emergent transient class.

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Evidence for a compact object in the aftermath of the extragalactic transient AT2018cow

Abstract: The brightest Fast Blue Optical Transients (FBOTs) are mysterious extragalactic explosions that may represent a new class of astrophysical phenom-

Cited by 40 publications

References 62 publications

Shocked jets in CCSNe can power the zoo of fast blue optical transients

Shocked jets in CCSNe can power the zoo of fast blue optical transients

Luminous Fast Blue Optical Transients and Type Ibn/Icn SNe from Wolf-Rayet/Black Hole Mergers

Looking at Luminous Fast Blue Optical Transients through Neutrino Glasses

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