Radio constraint on outflows from tidal disruption events

Abstract

Radio flares from tidal disruption events (TDEs) are generally interpreted as synchrotron emission arising from the interaction of an outflow with the surrounding circumnuclear medium (CNM). We generalize the common equipartition analysis to be applicable in cases lacking a clear spectral peak or even with just an upper limit. We show that, for detected events, there is a lower limit on the combination of the outflow's velocity $v$ and solid angle $\Omega$, $\simeq v{\Omega }^a$ (with $a\simeq 0.5$) that constrains the outflow's properties. Considering several possible outflow components accompanying TDEs, we find that: Isotropic outflows such as disk winds with $v\sim 10^4\mathrm{km}{\mathrm{s}}^{-1}$ and $\Omega =4\pi$ can easily produces the observed flares; The bow shock of the unbound debris has a wedge-like geometry and it must be geometrically thick with $\Omega \gtrsim 1$ and a fraction of its mass ($\gtrsim 0.01M_{\odot }$), has to move at $v\gtrsim 2\times 10^4\mathrm{km}{\mathrm{s}}^{-1}$; Conical Newtonian outflows such as jets can also be a radio source but both their velocity and the CNM density should be larger than those of isotropic winds by a factor of $\sim (\Omega /4\pi {)}^{-0.5}$. Our limits on the CNM densities are typically 30-100 times larger than those found by previous analysis that ignored non-relativistic electrons that do not emit synchrotron radiation. We show that unless $v$ and $\Omega$ are known radio observation alone cannot determine the CNM density. We also find that late (a few years after the TDE) radio upper-limits rule out energetic, $\sim 10^{51-52}\mathrm{erg}$, relativistic jets like the one observed in TDE Sw J1644+57, implying that such jets are rare.

16 pages, 10 figures, 2 tables, accepted for publication in MNRAS

References in corpus (9)

• PLUTO: a Numerical Code for Computational Astrophysics
• A Continuum of H- to He-Rich Tidal Disruption Candidates With a Preference for E+A Galaxies
• Radio Properties of Tidal Disruption Events
• Delayed Radio Flares from a 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
• Constraints on off-axis jets from stellar tidal disruption flares
• 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

Cited by in corpus (4)

• The radio detection and accretion properties of the peculiar nuclear transient AT 2019avd
• Radio emission of tidal disruption events from wind-cloud interaction
• Radiative hydrodynamical simulations of super-Eddington accretion flow in tidal disruption event: the accretion flow and wind
• Quasi-perpendicular shock acceleration and TDE radio flares