Radiative Emission Mechanisms
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Radiative Emission Mechanisms Nathaniel Roth1 · Elena Maria Rossi2 · Julian Krolik3 · Tsvi Piran4 · Brenna Mockler5 · Daniel Kasen6
Received: 16 December 2019 / Accepted: 9 September 2020 © Springer Nature B.V. 2020
Abstract We describe how the various outcomes of stellar tidal disruption give rise to observable radiation. We separately consider the cases where gas circularizes rapidly into an accretion disc, as well as the case when shocked debris streams provide the observable emission without having fully circularized. For the rapid circularization case, we describe how outflows, absorption by reprocessing layers, and Comptonization can cause the observed radiation to depart from that of a bare disc, possibly giving rise to the observed optical/UV emission along with soft X-rays from the disc. If, instead, most of the debris follows highly eccentric orbits for a significant time, many properties of the observed optical/UV emission can be explained by the scale of those eccentric orbits and the shocks embedded in the debris flow near orbital apocenter. In this picture, soft X-ray emission at early times results from the smaller amount of debris mass deflected into a compact accretion disc by weak shocks near the stellar pericenter. A general proposal for the near-constancy of the ultraviolet/optical color temperatures is provided, by linking it to incomplete thermalization of radiation in the atmosphere of the emitting region. We also briefly discuss the radio signals from the interaction of unbound debris and jets with the black hole environment. Keywords Black holes · Thermal radiation · Non-thermal radiation · Accretion The Tidal Disruption of Stars by Massive Black Holes Edited by Peter G. Jonker, Sterl Phinney, Elena Maria Rossi, Sjoert van Velzen, Iair Arcavi and Maurizio Falanga
B N. Roth
[email protected]
1
Joint Space Science Institute, University of Maryland, College Park, MD 20742, USA
2
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, the Netherlands
3
Dept. of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
4
Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel
5
Dept. of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
6
Depts. of Physics and Astronomy, University of California, Berkeley, Berkeley, CA 94720 USA
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1 Introduction In this chapter we describe how the various components of the disrupted star emit the radiation we observe. We immediately face the difficulty that, despite much progress, the underlying hydrodynamics are not fully understood and remain the subject of active research (see for example the Formation of the Accretion Flow Chapter and Accretion Disc Chapter). We also expect the disruption outcome to vary substantially among separate events. We therefore describe the emission that might result from a variety of post-disruption scenarios, with the understanding that no single picture is capable of explaining every feature of the ever-gr
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