Hitoshi Negoro

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Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the(More)
The Monitor of All Sky X-ray Image (MAXI) mission is the first astronomical payload to be installed on the Japanese Experiment Module-Exposed Facility (JEM-EF or Kibo-EF) on the International Space Station (ISS). It is scheduled for launch in the middle of 2009 to monitor all-sky X-ray objects on every ISS orbit. It will be more powerful than any previous(More)
We determine the spin of a supermassive black hole in the context of discseismology by comparing newly detected quasi-periodic oscillations (QPOs) of radio emission in the Galactic centre, Sagittarius A* (Sgr A*), as well as infrared and X-ray emissions with those of the Galactic black holes. We find that the spin parameters of black holes in Sgr A* and in(More)
The black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005 October, while it was in a low/hard state with a 0.7–300 keV luminosity of 4.6 × 10 37 erg s −1. The XIS and HXD spectra, spanning 0.7–400 keV, were reproduced successfully incorporating a cool accretion disk and a hot Comptonizing corona. The corona is(More)
An improvement of Fourier synthesis optics for hard x-ray imaging is described, and the basic performance of the new optics is confirmed through numerical simulations. The original concept of the Fourier synthesis imager utilizes nonposition-sensitive hard x-ray detectors coupled to individual bigrid modulation collimators. The improved concept employs a(More)
Prompted by recent discoveries of log-normal distributions in gamma-ray/X-ray temporal variabilities of gamma-ray bursts (GRBs) and blazars, we reexamine the X-ray variability of Cygnus X-1 in the hard/low state using Ginga data in 1990. It was previously reported that the distributions of the time intervals between X-ray shots (flares) deviated from the(More)
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