A concordance scenario for the observed neutrino from a tidal disruption event

Abstract

During a tidal disruption event, a star is torn apart by the tidal forces of a supermassive black hole, with about 50% of the star's mass eventually accreted by the black hole. The resulting flare can, in extreme cases of super-Eddington mass accretion, result in a relativistic jet [1][2][3][4] . While tidal disruption events have been theoretically proposed as sources of high-energy cosmic rays 5,6 and neutrinos 7-14 , stacking searches indicate that their contribution to the diffuse extragalactic neutrino flux is very low 15 . However, a recent association of a track-like astrophysical neutrino (IceCube-191001A 16 ) with a tidal disruption event (AT2019dsg 17 ) indicates that some tidal disruption events can accelerate cosmic rays to petaelectronvolt energies. Here we introduce a phenomenological concordance scenario with a relativistic jet to explain this association: an expanding cocoon progressively obscures the X-rays emitted by the accretion disk, while at the same time providing a sufficiently intense external target of backscattered X-rays for the production of neutrinos via proton-photon interactions. We also reproduce the delay (relative to the peak) of the neutrino emission by scaling the production radius with the black-body radius. Our energetics and assumptions for the jet and the cocoon are compatible with expectations from numerical simulations of tidal disruption events.On 1 October 2019, a track-like astrophysical neutrino (named IceCube-191001A) was detected 16 ; a dedicated multimessenger follow-up programme revealed the tidal disruption event (TDE) AT2019dsg as a candidate source, with a P value of 0.2% to 0.5% of random association 17 , corresponding to ~3σ significance. The neutrino followed the peak of the AT2019dsg light curve by t − t peak = 154 d and had a most likely energy E ≈ 0.2 PeV (ref. 16 and links therein). Its observation reveals a new class of cosmic ray sources, as it indicates that some TDEs can accelerate cosmic rays to petaelectronvolt energies.The TDE AT2019dsg is located at redshift z ≈ 0.05, or luminosity distance d L ≈ 230 Mpc. It was discovered in the optical-ultraviolet (UV) bands by the Zwicky Transient Facility (ZTF) on 9 April 2019 18 , and it reached its luminosity peak in this band on 30 April 2019 (t peak = 58603 modified Julian date). Several follow-up observations were conducted in the optical-UV 18 , radio 17,19,20 and X-ray 17,21,22 bands, the latter starting at t − t peak = 17 d. The picture that emerged from the observations shows a several-months-long flare, with black body (BB) spectra observed in both the optical-UV (temperature T BB = 38,900 K, photospheric radius R BB ≈ 5 × 10 14 cm) and X-ray (T X ≈ 0.06 keV, R X ≈ 3 × 10 11 -7 × 10 11 cm) bands, and luminosities L exponentially decaying over an (initial) timescale of 57.5 d and 10.3 d starting at L BB = 2.88 × 10 44 erg s −1 and L X ≈ 2.5 × 10 43 erg s −1 , respectively (Fig. 1, thick black and blue curves). The quoted X-ray luminosity is for an energy window [0.3-8.0] keV, whereas an X-ray

Tidal Disruption Events and High-energy Neutrinos

“…These are checked to see whether they belong to populations that have been proposed as possible cosmic-ray and neutrino sources. Such populations include Gamma-Ray Bursts (GRBs) [32], supernovae with evidence of circumstellar medium interaction [33] or choked jets [34], Active Galactic Nuclei (AGN) [35] and in particular blazars [36], and TDEs [37][38][39][40][41][42][43][44][45][46][47]. Right: Properties of the neutrinos observed in that period, from [28].…”

Theoretical interpretation of the observed neutrino emission from Tidal Disruption Events

“…See Ref. [1] for details of the model. This contains actually two factors: the fraction converted into non-thermal protons, and a spectral index-dependent bolometric correction because only a small fraction of particles will reach the highest energies.…”

“…Our recent work, Ref. [1], gives an interpretation in terms of a relativistic jet, which could be be off-axis (see [5]); we refer to [6] for an overview of all models.…”

“…In this proceeding we present our jetted model, Following Ref. [1]. To lay the context, let us overview the basic ingredients of the neutrino production which that can be inferred from data.…”

Astro-COLIBRI—The COincidence LIBrary for Real-time Inquiry for Multimessenger Astrophysics

“…A TDE typically results from an orbiting star approaching its hosting supermassive black hole (SMBH) closely enough to be disrupted by the gravitational forces. Recently published studies (Stein et al 2021;Winter & Lunardini 2021) highlight the importance of these events for transient astronomy, through the very bright, long-lasting flares that extend over a broad wavelength spectrum. The possible association of neutrinos with TDEs (Stein et al 2021) triggered renewed interest in this research direction, to be confirmed by future observations.…”