Interpreting the diversity of afterglow emission from radio-detected tidal disruption events with instantaneous and delayed outflows

TL;DR

The paper tackles the diversity of radio afterglows in radio-detected tidal disruption events by comparing three outflow scenarios—instantaneous wind, delayed wind, and delayed jet—using AMES-based modeling of synchrotron emission in a power-law circumnuclear medium. It shows that instantaneous winds cannot account for late-time radio flares, whereas delayed winds or jets can, with some events requiring two outflows to reproduce the light curves; iPTF16fnl illustrates degeneracy where a delayed component is not strictly necessary. Multiwavelength predictions reveal that delayed jets can produce detectable x-ray and optical counterparts (Chandra and Rubin), offering a practical route to break model degeneracies in nearby TDEs, while TeV gamma rays are unlikely to be detectable in these scenarios. Overall, the findings imply that delayed accretion processes or magnetic flux evolution can power late-time, energetic outflows in TDEs, and emphasize the value of coordinated radio, optical, and x-ray monitoring to uncover and characterize this hidden population of delayed TDE components.

Abstract

Tidal disruption events (TDEs) occur when a star is gravitationally disrupted by the tidal field of a supermassive black hole during a close encounter. Radio emission has recently been detected in TDEs and is commonly attributed to synchrotron radiation from both wind and jetted outflows. However, several TDEs exhibit bright radio flares at late times, which cannot be easily explained if the wind is launched promptly after the stellar disruption. In this study, we model the radio light curves of TDEs with delayed radio flares using three scenarios: an instantaneous wind, a delayed wind, and a delayed relativistic jet. We show that the instantaneous wind model struggles to reproduce delayed radio flare events, indicating the necessity of an additional delayed outflow component. In contrast, the delayed wind model provides a consistent explanation for the observed radio phenomenology, successfully reproducing events both with and without delayed radio flares. For some delayed radio flare events (e.g., ASASSN-15oi and AT 2019dsg), both the delayed wind and delayed jet models can reproduce the observed radio light curves. The delayed jet model produces x-ray and optical emission that is detectable at typical TDE distances, in contrast to wind-driven scenarios. This highlights how multiwavelength observations offer an effective means of distinguishing among possible outflow mechanisms.

Figures (8)

• Figure 1: Schematic illustration of the instantaneous wind model. A nonrelativistic wind is launched from the accretion disk after the stellar disruption. The wind drives a forward shock into the CNM with a power-law density profile, $n(R)$, producing synchrotron emission from shock-accelerated electrons.
• Figure 2: Schematic illustration of the delayed wind model. At $T = 0$, the initial nonrelativistic wind is launched from the accretion disk. Subsequently, a second wind component is launched at a time delay $T = T_{\rm del}$, following the initial wind. Similar to the initial nonrelativistic wind, the delayed wind also interacts with the CNM, driving a shock that produces renewed synchrotron emission.
• Figure 3: Schematic illustration of the delayed jet model. At $T = 0$, the initial nonrelativistic wind is launched from the accretion disk. Subsequently, at $T = T_{\rm del}$, a relativistic jet is launched. The jet propagates into the CNM, driving a forward shock that forms a thin shell. Synchrotron radiation is emitted from this shocked region as the jet decelerates and evolves.
• Figure 4: Observed radio data for ASASSN-14ae in panel (a), ASASSN-15oi in panel (b), PS16dtm in panel (c), and AT 2019dsg in panel (d) are shown (see plot legends for frequencies corresponding to radio observations considered). These are compared with the radio light curves calculated from our theoretical models. In each panel, the dotted, solid, and dashed lines represent the emission from the instantaneous wind, delayed wind and delayed jet, respectively. The upper limits in radio flux are shown with downward triangles. For these four events, the observed radio data suggests the presence of delayed outflows, either in the form of a jet or a wind.
• Figure 5: Observed radio data for iPTF16fnl in panel (a), ASASSN-19bt in panel (b), and AT 2020vwl in panel (c) are shown (see plot legends for frequencies corresponding to radio observations considered). The radio observations are compared with the predictions of our theoretical models. The line types and downward triangles shown here have the same meaning as in Figure \ref{['fig:result1']}. For these three events, the radio emission from a delayed jet is inconsistent with the observed radio flux.