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تسجيل مستخدم جديدRadio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. III. Late-time Jet Energetics and a Deviation from Equipartition
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We present continued radio and X-ray observations of the relativistic tidal disruption event Swift J164449.3+573451 extending to $delta t approx 2000$ d after discovery. The radio data were obtained with the VLA as part of a long-term program to monitor the energy and dynamical evolution of the relativistic jet and to characterize the parsec-scale environment around a previously dormant supermassive black hole. We combine these data with $textit{Chandra}$ X-ray observations and demonstrate that the X-ray emission following the sharp decline at $delta t approx 500$ d is due to the forward shock. Using the X-ray data, in conjunction with optical/NIR data, we constrain the synchrotron cooling frequency and the microphysical properties of the outflow for the first time. We find that the cooling frequency evolves through the optical/NIR band at $delta t approx 10 - 200$ d, corresponding to a magnetic field energy density fraction of $epsilon_B approx 10^{-3}$, well below equipartition; the X-ray data demonstrate that this deviation from equipartition holds to at least $delta t approx 2000$ d. We thus recalculate the physical properties of the jet over the lifetime of the event, no longer assuming equipartition. We find a total kinetic energy of $E_K approx 4 times 10^{51}$ erg and a transition to non-relativistic expansion on the timescale of our latest observations ($delta t approx 700$ d). The density profile is approximately $R^{-3/2}$ at $lesssim 0.3$ pc and $gtrsim 0.7$ pc, with a plateau at intermediate scales, characteristic of Bondi accretion. Based on its evolution thus far, we predict that Sw 1644+57 will be detectable at centimeter wavelengths for decades to centuries with existing and upcoming radio facilities. Similar off-axis events should be detectable to $z sim 2$, but with a slow evolution that may inhibit their recognition as transient events.
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We present continued radio observations of the tidal disruption event SwiftJ164449.3+573451 extending to sim216 days after discovery. The data are part of a long-term program to monitor the expansion and energy scale of the relativistic outflow, and
to trace the parsec-scale environment around a previously-dormant supermassive black hole (SMBH). The new observations reveal a significant change in the radio evolution starting at sim1 month, with a brightening at all frequencies that requires an increase in the energy by about an order of magnitude, and an overall density profile around the SMBH of rho propto r^{-3/2} (0.1-1.2 pc) with a significant flattening at rsim0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an L propto t^{-5/3} tail, which is observed in the X-rays. Instead, we conclude that the relativistic jet was launched with a wide range of Lorentz factors, obeying E(>Gamma) propto Gamma^{-2.5}. The similar ratio of duration to dynamical timescale for Sw1644+57 and GRBs suggests that this result may be applicable to GRBs as well. The radial density profile may be indicative of Bondi accretion, with the inferred flattening at rsim0.5 pc in good agreement with the Bondi radius for a sim10^6 M_sun black hole. The density at sim0.5 pc is about a factor of 30 times lower than inferred for the Milky Way galactic center, potentially due to a smaller number of mass-shedding massive stars. From our latest observations (sim216 d) we find that the jet energy is E_{iso}sim5x10^{53} erg (E_jsim2.4x10^{51} erg for theta_j=0.1), the radius is rsim1.2 pc, the Lorentz factor is Gammasim2.2, the ambient density is nsim0.2 cm^{-3}, and the projected size is r_{proj}sim25 microarcsec. Assuming no future changes in the observed evolution we predict that the radio emission from Sw1644+57 should be detectable with the EVLA for several decades, and will be resolvable with VLBI in a few years.
We present continued radio and X-ray observations of the previously relativistic tidal disruption event (TDE) Swift J164449.3+573451 (sw) extending to about 9.4 years post disruption, as part of ongoing campaigns with the Jansky Very Large Array (VLA
) and the textit{Chandra} X-ray observatory. We find that the X-ray emission has faded below detectable levels, with an upper limit of $lesssim 3.5times 10^{-15}$ erg cm$^{-2}$ s$^{-1}$ in a 100 ks observation, while the radio emission continues to be detected and steadily fade. Both are consistent with forward shock emission from a non-relativistic outflow, although we find that the radio spectral energy distribution is better fit at these late times with an electron power law index of $papprox 3$ (as opposed to $papprox 2.5$ at earlier times). With the revised spectral index we find $epsilon_Bapprox 0.01$ using the radio and X-ray data, and a density of $approx 0.04$ cm$^{3}$ at a radius of $Rapprox 0.65$ pc ($R_{rm sch}approx 2times 10^6$ R$_odot$) from the black hole. The energy scale of the blastwave is $approx 10^{52}$ erg. We also report detections of sw at 3 GHz from the first two epochs of the VLA Sky Survey (VLASS), and find that $sim 10^2$ off-axis sw-like events to $zsim 0.5$ may be present in the VLASS data. Finally, we find that sw itself will remain detectable for decades at radio frequencies, although observations at sub-GHz frequencies will become increasingly important to characterize its dynamical evolution.
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