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تسجيل مستخدم جديدSearch for neutrinos from the tidal disruption events AT2019dsg and AT2019fdr with the ANTARES telescope
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On October 1, 2019, the IceCube Collaboration detected a muon track neutrino with high probability of being of astrophysical origin, IC191001A. After a few hours, the tidal disruption event (TDE) AT2019dsg, observed by the Zwicky Transient Facility (ZTF), was indicated as the most likely counterpart of the IceCube track. More recently, the follow-up campaign of the IceCube alerts by ZTF suggested a second TDE, AT2019fdr, as a promising counterpart of another IceCube muon track candidate, IC200530A, detected on May 30, 2020. These are the second and third associations between astrophysical sources and high-energy neutrinos after the compelling identification of the blazar TXS 0506+056. Here, the search for ANTARES neutrinos from the directions of AT2019dsg and AT2019fdr using a time-integrated approach is presented. As no significant evidence for space clustering is found in the ANTARES data, upper limits on the one-flavour neutrino flux and fluence are set.
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Tidal disruption events are an excellent probe for supermassive black holes in distant inactive galaxies because they show bright multi-wavelength flares lasting several months to years. AT2019dsg presents the first potential association with neutrino emission from such an explosive event.
The results of three different searches for neutrino candidates, associated with the IceCube-170922A event or from the direction of TXS 0506+056, by the ANTARES neutrino telescope are presented. The first search refers to the online follow-up of the
IceCube alert; the second is based on the standard time-integrated method employed by the Collaboration to search for point-like neutrino sources; the third uses the information from the IceCube time-dependent analysis reporting a bursting activity centered on December 13, 2014, as input for an ANTARES time-dependent analysis. The online follow-up and the time-dependent analysis yield no events related to the source. The time-integrated study performed over a period from 2007 to 2017 fits 1.03 signal events, which corresponds to a p-value of 3.4% (not considering trial factors). Only for two other astrophysical objects in our candidate list, a smaller p-value had been found. When considering that 107 sources have been investigated, the post-trial p-value for TXS 0506+056 corresponds to 87%.
We present detailed radio observations of the tidal disruption event (TDE) AT2019dsg, obtained with the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and spanning $55-560$ days post-disruption. We find that the p
eak brightness of the radio emission increases until ~200 days and subsequently begins to decrease steadily. Using the standard equipartition analysis, including the effects of synchrotron cooling as determined by the joint VLA-ALMA spectral energy distributions, we find that the outflow powering the radio emission is in roughly free expansion with a velocity of $approx 0.07c$, while its kinetic energy increases by a factor of about 5 from 55 to 200 days and plateaus at $approx 5times 10^{48}$ erg thereafter. The ambient density traced by the outflow declines as $approx R^{-1.6}$ on a scale of $approx (1-4)times 10^{16}$ cm ($approx 6300-25000$ $R_s$), followed by a steeper decline to $approx 6times 10^{16}$ cm ($approx 37500$ $R_s$). Allowing for a collimated geometry, we find that to reach even mildly relativistic velocities ($Gamma=2$) the outflow requires an opening angle of $theta_japprox 2^circ$, which is narrow even by the standards of GRB jets; a truly relativistic outflow requires an unphysically narrow jet. The outflow velocity and kinetic energy in AT2019dsg are typical of previous non-relativistic TDEs, and comparable to those from Type Ib/c supernovae, raising doubts about the claimed association with a high-energy neutrino event.
The discovery of jets from tidal disruption events (TDEs) rejuvenated the old field of relativistic jets powered by accretion onto supermassive black holes. In this Chapter, we first review the extensive multi-wavelength observations of jetted TDEs.
Then, we show that these events provide valuable information on many aspects of jet physics from a new prospective, including the on-and-off switch of jet launching, jet propagation through the ambient medium, $gamma/$X-ray radiation mechanism, jet composition, and the multi-messenger picture. Finally, open questions and future prospects in this field are summarized.
The concept of stars being tidally ripped apart and consumed by a massive black hole (MBH) lurking in the center of a galaxy first captivated theorists in the late 1970s. The observational evidence for these rare but illuminating phenomena for probin
g otherwise dormant MBHs, first emerged in archival searches of the soft X-ray ROSAT All-Sky Survey in the 1990s; but has recently accelerated with the increasing survey power in the optical time domain, with tidal disruption events (TDEs) now regarded as a class of optical nuclear transients with distinct spectroscopic features. Multiwavelength observations of TDEs have revealed panchromatic emission, probing a wide range of scales, from the innermost regions of the accretion flow, to the surrounding circumnuclear medium. I review the current census of 56 TDEs reported in the literature, and their observed properties can be summarized as follows: $bullet$ The optical light curves follow a power-law decline from peak that scales with the inferred central black hole mass as expected for the fallback rate of the stellar debris, but the rise time does not. $bullet$ The UV/optical and soft X-ray thermal emission come from different spatial scales, and their intensity ratio has a large dynamic range, and is highly variable, providing important clues as to what is powering the two components. $bullet$ They can be grouped into three spectral classes, and those with Bowen fluorescence line emission show a preference for a hotter and more compact line-emitting region, while those with only He II emission lines are the rarest class.
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