3,706 research outputs found

    Magnetic Coupling of a Rotating Black Hole with Advection-Dominated Accretion Flows

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    A model of magnetic coupling (MC) of a rotating black hole (BH) with advection- dominated accretion flow (MCADAF) is proposed. It turns out that MCADAF providers a natural explanation for the transition radius between ADAF and SSD, and could be used to interpret the highest luminosity of GX 339-4 in hard-state. A very steep emissivity index can be produced in the innermost part of the MCADAF,which is consistent with the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and with two X-ray binaries (XRBs): XTE J1655-500 and GX 339-4. In addition, we estimate the BH spins in Seyfert 1 galaxy MCG-6-30-15 and in the two XRBs based on this model.Comment: 18 pages, 9 figures,acceptted by New Astronom

    Detectable MeV neutrinos from black hole neutrino-dominated accretion flows

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    Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) have been theorized as the central engine of relativistic jets launched in massive star core collapse events or compact star mergers. In this work, we calculate the electron neutrino/anti-neutrino spectra of NDAFs by fully taking into account the general relativistic effects, and investigate the effects of viewing angle, BH spin, and mass accretion rate on the results. We show that even though a typical NDAF has a neutrino luminosity lower than that of a typical supernova (SN), it can reach 10501051 erg s110^{50}-10^{51}~{\rm erg~s^{-1}} peaking at 10\sim 10 MeV, making them potentially detectable with the upcoming sensitive MeV neutrino detectors if they are close enough to Earth. Based on the observed GRB event rate in the local universe and requiring that at least 3 neutrinos are detected to claim a detection, we estimate a detection rate up to \sim (0.10-0.25) per century for GRB-related NDAFs by the Hyper-Kamiokande (Hyper-K) detector if one neglects neutrino oscillation. If one assumes that all Type Ib/c SNe have an engine-driven NDAF, the Hyper-K detection rate would be \sim (1-3) per century. By considering neutrino oscillations, the detection rate may decrease by a factor of 2-3. Detecting one such event would establish the observational evidence of NDAFs in the universe.Comment: 7 pages, 2 figures, 2 tables, accepted for publication in PR

    The effects of large extra dimensions on associated ttˉh0t\bar{t} h^0 production at linear colliders

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    In the framework of the large extra dimensions (LED) model, the effects of LED on the processes \rrtth and \eetth at future linear colliders are investigated in both polarized and unpolarized collision modes. The results show that the virtual Kaluza-Klein (KK) graviton exchange can significantly modify the standard model expectations for these processes with certain polarizations of initial states. The process \rrtth with s=3.5TeV\sqrt{s}=3.5 TeV allows the effective scale ΛT\Lambda_T to be probed up to 7.8 and 8.6 TeV in the unpolarized and Pγ=0.9P_{\gamma} = 0.9, J=2 polarized γγ\gamma \gamma collision modes, respectively. For the \eetth process with s=3.5TeV\sqrt{s}=3.5 TeV, the upper limits of ΛT\Lambda_T to be observed can be 6.7 and 7.0 TeV in the unpolarized and Pe+=0.6P_{e^+} = 0.6, Pe=0.8P_{e^-} = 0.8, +-+ polarized e+ee^+e^- collision modes, respectively. We find the \rrtth channel in J=2 polarized photon collision mode provides a possibility to improve the sensitivity to the graviton tower exchange.Comment: To be appeard in Physical Review