Investigating the Circumnuclear Medium of Tidal Disruption Events with Radio Observations

Abstract

Tidal disruption events (TDEs) are unique tools for investigating quiescent supermassive black hole (SMBH), accretion physics, and circumnuclear medium (CNM) environments. The CNM density profile is of great astrophysical significance, since it provides key diagnostics for the accretion history of dormant SMBH. TDEs can launch outflows that produce radio emission when propagating into the CNM. The closure relation (CR), i.e., the relation between the temporal indices and the spectral indices, are therefore monitoring the CNM density profile. In this work, we first collect 53 TDEs with radio observations to date. We then obtain the predicted CR for arbitrary CNM and different dynamical phases of the outflow, and apply to the radio TDE sample. We constrain the CNM density profile for 26 radio TDEs with good data quality. The results are generally consistent with those estimated with equipatition method, suggesting that CR analysis is efficient in the study of CNM profile for a quiescent SMBH.

Figures (4)

• Figure 1: The radio light curves for our collected TDEs. To date, 53 TDEs have published radio detections. Although most of the detected TDEs were observed at multiple frequencies, for simplicity we show only a single frequency for each event. The triangles indicate the observations with published upper limits. The data can be available at https://github.com/leiwh/RadioTDEs.
• Figure 2: The relation between temporal index $\alpha_{CR}$ and the CNM density profile $k$ for $\nu_a<\nu_c<\nu_m$ (top), $\nu_{\rm a}<\nu_{\rm m}<\nu_{\rm c}$ (middle), and $\nu_m<\nu_a<\nu_c$ (bottom). The solid lines and dotted lines represent the coasting phase and the deceleration phase of relativistic outflow. Different colored lines represent different electron spectral index $p$, where red, green, blue, magenta and gray represent $p$ = 2.01, 2.5, 3.0 and 3.5, respectively. When the relativistic outflow is in the deceleration phase, the CNM density profile cannot be derived from the CRs at high frequencies ($\nu_a < \nu_c < \nu < \nu_m$, $\nu_a < \nu_c < \nu_m < \nu$, $\nu_a < \nu_m < \nu_c < \nu$, and $\nu_m < \nu_a < \nu_c < \nu$). When the outflow is in the coasting phase, the CNM density profile cannot be derived from the CRs at low frequencies ($\nu < \nu_a < \nu_m < \nu_c$ and $\nu < \nu_m < \nu_a < \nu_c$).
• Figure 3: Radio SEDs for AT2022cmc, CNSS J0019+00, and ASASSN-14li. These lines represent the best-fit model from the MCMC fitting and some randomly sampled MCMC lines.
• Figure 4: Left panel: The CNM density profile for our TDE sample, as inferred from equipartition and CRs. Right panel: The distributions of the CNM density profile $k_{\rm CR}$ and $k_{\rm eq}$, along with the Gaussian curves fitted to their distributions.