H-Alpha and Hard X-Ray Observations of a Two-Ribbon Flare Associated with a Filament Eruption

We perform a multi-wavelength study of a two-ribbon flare on 2002 September 29 and its associated filament eruption, observed simultaneously in the H-alpha line by a ground-based imaging spectrograph and in hard X-rays by RHESSI. The flare ribbons contain several H-alpha bright kernels that show different evolutional behaviors. In particular, we find two kernels that may be the footpoints of a loop. A single hard X-ray source appears to cover these two kernels and to move across the magnetic neutral line. We explain this as a result of the merging of two footpoint sources that show gradually asymmetric emission owing to an asymmetric magnetic topology of the newly reconnected loops. In one of the H-alpha kernels, we detect a continuum enhancement at the visible wavelength. By checking its spatial and temporal relationship with the hard X-ray emission, we ascribe it as being caused by electron beam precipitation. In addition, we derive the line-of-sight velocity of the filament plasma based on the Doppler shift of the filament-caused absorption in the H-alpha blue wing. The filament shows rapid acceleration during the impulsive phase. These observational features are in principal consistent with the general scenario of the canonical two-ribbon flare model.Comment: 15 pages, 5 figures, accepted for publication in Ap

Magnetic coupling of a rotating black hole with its surrounding accretion disk

Effects of magnetic coupling (MC) of a rotating black hole (BH) with its surrounding accretion disk are discussed in detail in the following aspects: (i) The mapping relation between the angular coordinate on the BH horizon and the radial coordinate on the disk is modified based on a more reasonable configuration of magnetic field, and a condition for coexistence of the Blandford-Znajek (BZ) and the MC process is derived. (ii) The transfer direction of energy and angular momentum in MC process is described equivalently by the co-rotation radius and by the flow of electromagnetic angular momentum and redshifted energy, where the latter is based on an assumption that the theory of BH magnetosphere is applicable to both the BZ and MC processes. (iii) The profile of the current on the BH horizon and that of the current density flowing from the magnetosphere onto the horizon are given in terms of the angular coordinate of the horizon. It is shown that the current on the BH horizon varies with the latitude of the horizon and is not continuous at the angular boundary between the open and closed magnetic field lines. (iv) The MC effects on disk radiation are discussed, and a very steep emissivity is produced by MC process, which is consistent with the recent XMM-Newton observation of the nearby bright Seyfert 1 galaxy MCG-6-30-15 by a variety of parameters of the BH-disk system.Comment: 24 pages, 19 figures. Accepted by Ap

Evolution of the Fermi surface with carrier concentration in Bi_2Sr_2CaCu_2O_{8+\delta}

We show, by use of angle-resolved photoemission spectroscopy, that underdoped Bi_2Sr_2CaCu_2O_{8+\delta} appears to have a large Fermi surface centered at (\pi,\pi), even for samples with a T_c as low as 15 K. No clear evidence of a Fermi surface pocket around (\pi/2,\pi/2) has been found. These conclusions are based on a determination of the minimum gap locus in the pseudogap regime T_c < T < T^*, which is found to coincide with the locus of gapless excitations in momentum space (Fermi surface) determined above T^*. These results suggest that the pseudogap is more likely of precursor pairing rather than magnetic origin.Comment: 4 pages, revtex, 4 postscript color figure

Screw instability of the magnetic field connecting a rotating black hole with its surrounding disk

Screw instability of the magnetic field connecting a rotating black hole (BH) with its surrounding disk is discussed based on the model of the coexistence of the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process (CEBZMC). A criterion for the screw instability with the state of CEBZMC is derived based on the calculations of the poloidal and toroidal components of the magnetic field on the disk. It is shown by the criterion that the screw instability will occur, if the BH spin and the power-law index for the variation of the magnetic field on the disk are greater than some critical values. It turns out that the instability occurs outside some critical radii on the disk. It is argued that the state of CEBZMC always accompanies the screw instability. In addtition, we show that the screw instability contributes only a small fraction of magnetic extraction of energy from a rotating BH.Comment: 18 pages, 13 figures; Accepted by Ap

Signal-Jamming in a Sequential Auction

In a recurring auction early bids may reveal bidders’ types, which in turn affects bidding in later auctions. Bidders take this into account and may bid in a way that conceals their private information until the last auction is played. The present paper analyzes the equilibrium of a sequence of ?rst-price auctions assuming bidders have stable private values. We show that signal-jamming occurs and explore the dynamics of equilibrium prices

BZ-MC-BP Model for Jet Production from Black Hole Accretion Disc

Three energy mechanisms invoking large-scale magnetic fields are incorporated in a model to interpret jet production in black hole (BH) systems, i.e., the Blandford-Znajek (BZ), the magnetic coupling (MC) and Blandford-Payne (BP) processes. These energy mechanisms can coexist in BH accretion disc based on the magnetic field configurations constrained by the screw instability, provided that the BH spin and the power-law index indicating the variation of the magnetic field at an accretion disc are greater than some critical values. In this model the jets are driven by the BZ process in the Poynting flux regime and by the BP process in the hydromagnetic regime, being consistent with the spine/sheath jet structure observed in BH sources of stellar and supermassive size.Comment: 9 pages, 6 figures, accepted by MNRA

Extraction of the Electron Self-Energy from Angle Resolved Photoemission Data: Application to Bi2212

The self-energy $\Sigma({\bf k},\omega)$, the fundamental function which describes the effects of many-body interactions on an electron in a solid, is usually difficult to obtain directly from experimental data. In this paper, we show that by making certain reasonable assumptions, the self-energy can be directly determined from angle resolved photoemission data. We demonstrate this method on data for the high temperature superconductor $Bi_2Sr_2CaCu_2O_{8+x}$ (Bi2212) in the normal, superconducting, and pseudogap phases.Comment: expanded version (6 pages), to be published, Phys Rev B (1 Sept 99