32 research outputs found
The Quiescent Intracluster Medium in the Core of the Perseus Cluster
Clusters of galaxies are the most massive gravitationally-bound objects in
the Universe and are still forming. They are thus important probes of
cosmological parameters and a host of astrophysical processes. Knowledge of the
dynamics of the pervasive hot gas, which dominates in mass over stars in a
cluster, is a crucial missing ingredient. It can enable new insights into
mechanical energy injection by the central supermassive black hole and the use
of hydrostatic equilibrium for the determination of cluster masses. X-rays from
the core of the Perseus cluster are emitted by the 50 million K diffuse hot
plasma filling its gravitational potential well. The Active Galactic Nucleus of
the central galaxy NGC1275 is pumping jetted energy into the surrounding
intracluster medium, creating buoyant bubbles filled with relativistic plasma.
These likely induce motions in the intracluster medium and heat the inner gas
preventing runaway radiative cooling; a process known as Active Galactic
Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus
cluster core, which reveal a remarkably quiescent atmosphere where the gas has
a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from
the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s
is found across the 60 kpc image of the cluster core. Turbulent pressure
support in the gas is 4% or less of the thermodynamic pressure, with large
scale shear at most doubling that estimate. We infer that total cluster masses
determined from hydrostatic equilibrium in the central regions need little
correction for turbulent pressure.Comment: 31 pages, 11 Figs, published in Nature July
Hitomi (ASTRO-H) X-ray Astronomy Satellite
The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month
Hitomi X-Ray Studies of Giant Radio Pulses from the Crab Pulsar
To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2300 keV band and the Kashima NICT radio telescope in the 1.41.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 fluctuations of the X-ray fluxes at the pulse peaks, and the 3 upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.510 keV and 70300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) 10(exp 11) erg cm(exp 2), respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a >0.02% brightening of the pulse-peak flux under such conditions
Synchronized Collapse and Formation of Long-Period Stacking and Chemical Orders in
Long period stacking ordered (LPSO) structures that are synchronized with the chemical order in Mg–TM (transition metal)–RE (rare earth) systems have received special attention as a new type of strengthening phase for Mg alloys. For example, the rapidly solidified powder metallurgy alloy with an LPSO phase has a yield strength exceeding 600 MPa [1], while the cast alloy with an LPSO phase produced using a hot extrusion process has a yield strength exceeding 350 MPa, which is sufficient for use in many components for airplanes and automobiles [2].The crystalline structures of the LPSO phases in Mg–TM–RE systems have been reported by many researchers [3], [4], [5] and [6], and four types of LPSO phases (10H, 14H, 18R, and 24R) have been reported. The hexagonal ABAB… stacking sequence is changed due to the incorporation of TM and RE concentrate layers. As a result, long period stacking orders are formed along the c axis. Accordingly, rhombohedral (R) and hexagonal (H) Bravais lattices occur, depending on the stacking period of the hcp stacking layer [6].Furthermore, based on scanning transmission and transmission electron microscopy (STEM and TEM, respectively) observations for Mg-Al-Gd alloy, the existence of in-plane ordering has been proposed by Yokobayashi et al. [7]. They found that ordered clusters were regularly aligned in the segregated layer. Recently, Egusa et al. revised the crystalline structure models for the 18R- and 14H-type LPSOs of Mg–Zn–Y taking into consideration the in-plane order resulting from the alignment of the cluster in the Zn–Y segregated layers [8]. Yamasaki et al. also proposed a 10H-type LPSO crystalline structure in a Mg–Zn–Y alloy [9]. Schematic diagrams of the stacking and in-plane ordering of the 18R-type LPSOs are shown in Fig. 1