Ubiquitous Late Radio Emission from Tidal Disruption Events

Abstract: We present radio observations of 23 optically discovered tidal disruption events (TDEs) on timescales of 500-3200 days post discovery. We detect nine new TDEs that did not have detectable radio emission at earlier times, indicating a late-time brightening after several hundred (and up to 2300) days; an additional seven TDEs exhibit radio emission whose origin is ambiguous or may be attributed to the host galaxy or an active galactic nucleus. We also report a new rising component in one TDE previously detected in the radio at 10^3 days. While the radio emission in some of the detected TDEs peaked on a timescale 2-4 yr, over half of the sample still show rising emission. The range of luminosities for the sample is 10^37-10^39 erg/s, about 2 orders of magnitude below the radio luminosity of the relativistic TDE Sw J1644+57. Our data set indicates 40% of all optical TDEs are detected in radio hundreds to thousands of days after discovery, and that this is probably more common than early radio emission peaking at 10^2 days. Using an equipartition analysis, we find evidence for a delayed launch of the radio-emitting outflows, with delay timescales of 500-2000 days, inferred velocities of 0.02-0.15c, and kinetic energies of 10^47-10^49 erg. We rule out off axis relativistic jets as a viable explanation for this population, and conclude delayed outflows are a more likely explanation, possibly from delayed disk formation. We conclude late radio emission marks a fairly ubiquitous but heretofore overlooked phase of TDE evolution.

• The paper reveals that approximately 40% of optical TDEs show late-time radio emissions, with 9 events detected for the first time and one exhibiting a new rising component.
• The paper employs equipartition analysis to determine that delayed outflows, rather than off-axis jets, with velocities of 0.02–0.15c and energies of 10^47–10^49 erg drive the observed emissions.
• The paper emphasizes extended radio monitoring as essential for understanding TDE evolution, suggesting longer-term strategies to capture comprehensive emission profiles and disk formation dynamics.

Ubiquitous Late Radio Emission from Tidal Disruption Events: A Comprehensive Analysis

The study conducted by Cendes et al. presents a detailed exploration of radio emissions from tidal disruption events (TDEs) detected via optical methods, focusing on emissions identified well after the initial discoveries. The research encompasses observations of 23 TDEs over variability periods ranging from approximately 500 to 3200 days after optical detection. The comprehensive nature of this dataset facilitates a deeper understanding of the temporal and physical characteristics of late-time radio emissions associated with TDEs.

Key Findings

1. Detection of Late-Time Emissions: Out of the 23 TDEs observed, late-time radio emissions were identified in 9 TDEs for the first time. These emissions became detectable several hundred days post-discovery. Additionally, 7 other TDEs showed radio signals potentially linked to their host galaxies or active galactic nuclei (AGN), while one previously detected TDE exhibited a new rising component in its radio emission after approximately 1,000 days.
2. Prevalence and Temporal Dynamics: The analysis reveals that around 40% of optical TDEs are detected in radio hundreds to thousands of days following discovery, suggesting this late-time radio activity may be more prevalent than earlier radio emissions peaking around 100 days. Furthermore, more than half of the observed sample still exhibited increasing radio emissions beyond the initial detection period.
3. Physical Parameters and Interpretation: The study employs equipartition analysis to infer the physical characteristics of the radio-emitting outflows. The outflows are found to exhibit delay timescales between 500-2000 days after the TDE, with inferred velocities ranging between 0.02 to 0.15c and kinetic energies of approximately 10<sup\>47</sup> to 10<sup\>49</sup> erg. Notably, the study rules out off-axis relativistic jets as a plausible explanation, proposing instead that delayed outflows—potentially resulting from delayed disk formation—are a more reasonable explanation.

Practical and Theoretical Implications

The implications of this study are multifaceted. Practically, the detection of radio emissions at such late stages emphasizes the importance of continued radio monitoring in understanding the lifecycle of TDEs. These observations may influence observational strategies, suggesting that longer-term monitoring is crucial to capturing the full emission profile of TDEs.

Theoretically, the findings challenge preconceived notions about the nature and timing of TDE-related emissions. The ubiquity of late-time radio emissions necessitates a reconsideration of the models describing TDE evolution, particularly concerning the structure and interaction of stellar debris with the central black hole environment. The suggested connection to delayed disk formation highlights the intricate dynamics of accretion processes and their impact on observational signatures.

Future Prospects

The research by Cendes et al. lays the groundwork for further investigation into late-time emissions from TDEs. Future work can leverage forthcoming observations from advanced radio telescopes, such as the next-generation Very Large Array (ngVLA) or the Square Kilometer Array (SKA), to examine larger samples with greater sensitivity and precision. Additionally, multi-wavelength campaigns that integrate radio, optical, and X-ray data will be indispensable in constructing a cohesive model of TDE behavior across different observational spectra.

Overall, the paper elucidates a significant aspect of TDE phenomenology, presenting implications that extend across observational, theoretical, and modeling frameworks, marking an essential contribution to the field of high-energy astrophysics.