A Mildly Relativistic Outflow Launched Two Years after Disruption in the Tidal Disruption Event AT2018hyz

Abstract

We present late-time radio/millimeter (as well as optical/UV and X-ray) detections of the tidal disruption event (TDE) AT2018hyz, spanning $970-1300$ d after optical discovery. In conjunction with earlier deeper limits, including at $\approx 700$ d, our observations reveal rapidly rising emission at $0.8-240$ GHz, steeper than $F_{\nu }\propto t^5$ relative to the time of optical discovery. Such a steep rise cannot be explained in any reasonable scenario of an outflow launched at the time of disruption (e.g., off-axis jet, sudden increase in the ambient density), and instead points to a delayed launch. Our multi-frequency data allow us to directly determine the radius and energy of the radio-emitting outflow, showing that it was launched $\approx 750$ d after optical discovery. The outflow velocity is mildly relativistic, with $\beta \approx 0.25$ and $\approx 0.6$ for a spherical and a $10^{\circ }$ jet geometry, respectively, and the minimum kinetic energy is $E_K\approx 5.8\times 10^{49}$ and $\approx 6.3\times 10^{49}$ erg, respectively. This is the first definitive evidence for the production of a delayed mildly-relativistic outflow in a TDE; a comparison to the recently-published radio light curve of ASASSN-15oi suggests that the final re-brightening observed in that event (at a single frequency and time) may be due to a similar outflow with a comparable velocity and energy. Finally, we note that the energy and velocity of the delayed outflow in AT2018hyz are intermediate between those of past non-relativistic TDEs (e.g., ASASSN-14li, AT2019dsg) and the relativistic TDE Sw\,J1644+57. We suggest that such delayed outflows may be common in TDEs.

arXiv commentSubmitted to ApJ

References in corpus (42)

• emcee: The MCMC Hammer
• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• Spectra and Light Curves of Gamma-Ray Burst Afterglows
• The Swift Ultra-Violet/Optical Telescope
• Chandra X-ray Spectroscopic Imaging of Sgr A* and the Central Parsec of the Galaxy
• The Shape of Spectral Breaks in GRB Afterglows
• Hydrodynamical Simulations to Determine the Feeding Rate of Black Holes by the Tidal Disruption of Stars: The Importance of the Impact Parameter and Stellar Structure
• The Birth of a Relativistic Outflow in the Unusual γ-ray Transient Swift J164449.3+573451
• Radio Remnants of Compact Binary Mergers - the Electromagnetic Signal that will follow the Gravitational Waves
• A tidal disruption event coincident with a high-energy neutrino
• Consequences of Strong Compression in Tidal Disruption Events
• Discovery of an outflow from radio observations of the tidal disruption event ASASSN-14li
• Radio Properties of Tidal Disruption Events
• Swift J1644+57 gone MAD: the case for dynamically-important magnetic flux threading the black hole in a jetted tidal disruption event
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. I. Jet Energetics and the Pristine Parsec-Scale Environment of a Supermassive Black Hole
• Radio transients from stellar tidal disruption by massive black holes
• Large-Scale Poloidal Magnetic Field Dynamo Leads to Powerful Jets in GRMHD Simulations of Black Hole Accretion with Toroidal Field
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. II. The Relativistic Jet Shuts Off and a Transition to Forward Shock X-ray/Radio Emission
• Inside the Bondi radius of M87
• Observing Lense-Thirring Precession in Tidal Disruption Flares
• The dynamics, appearance and demographics of relativistic jets triggered by tidal disruption of stars in quiescent supermassive black holes
• Smooth Light Curves from a Bumpy Ride: Relativistic Blast Wave Encounters a Density Jump
• Radius constraints and minimal equipartition energy of relativistically moving synchrotron sources
• Afterglow Model for the Radio Emission from the Jetted Tidal Disruption Candidate Swift J1644+57
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. III. Late-time Jet Energetics and a Deviation from Equipartition
• Delayed Radio Flares from a Tidal Disruption Event
• Radio Observations of an Ordinary Outflow from the Tidal Disruption Event AT2019dsg
• The Tidal Disruption Event AT 2018hyz I: Double-peaked emission lines and a flat Balmer decrement
• AT2019azh: an unusually long-lived, radio-bright thermal tidal disruption event
• Radio observations of the tidal disruption event XMMSL1 J0740$-$85
• The radio afterglow of Swift J1644+57 reveals a powerful jet with fast core and slow sheath
• Caltech-NRAO Stripe 82 Survey (CNSS). III: The First Radio-discovered Tidal Disruption Event, CNSS J0019+00
• The Tidal Disruption Event AT 2018hyz II: Light Curve Modeling of a Partially Disrupted Star
• The influence of circumnuclear environment on the radio emission from TDE jets
• Tidal Disruption and Magnetic Flux Capture: Powering a Jet from a Quiescent Black Hole
• A Late-Time Radio Flare following a Possible Transition in Accretion State in the Tidal Disruption Event AT 2019azh
• Are Delayed Radio Flares Common in Tidal Disruption Events? The Case of the TDE iPTF16fnl
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. IV. Continued Fading and Non-Relativistic Expansion
• Radio Emission from the unbound Debris of Tidal Disruption Events
• Variable and polarized radio emission from the T6 brown dwarf WISEP J112254.73+255021.5
• Unbound Debris Streams and Remnants Resulting From the Tidal Disruptions of Stars by Supermassive Black Holes
• From Pericenter and Back: Full Debris Stream Evolution in Tidal Disruption Events