21 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 Eââ>ââ2ââkeV, 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
Using qualitative comparative analysis to understand the conditions that produce successful PrEP implementation in family planning clinics
Abstract Background Title X-funded family planning clinics have been identified as optimal sites for delivery of pre-exposure prophylaxis (PrEP) for HIV prevention to U.S. women. However, PrEP has not been widely integrated into family planning services, especially in the Southern U.S., and data suggest there may be significant implementation challenges in this setting. Methods To understand contextual factors that are key to successful PrEP implementation in family planning clinics, we conducted in-depth qualitative interviews with key informants from 38 family planning clinics (11 clinics prescribed PrEP and 27 did not). Interviews were guided by constructs from the Consolidated Framework for Implementation Research (CFIR), and qualitative comparative analysis (QCA) was used to uncover the configurations of CFIR factors that led to PrEP implementation. Results We identified 3 distinct construct configurations, or pathways, that led to successful PrEP implementation: (1) high âLeadership Engagementâ AND high âAvailable Resourcesâ; OR (2) high âLeadership Engagementâ AND NOT located in the Southeast region; OR (3) high âAccess to Knowledge and Informationâ AND NOT located in the Southeast region. Additionally, there were 2 solution paths that led to absence of PrEP implementation: (1) low âAccess to Knowledge and Informationâ AND low âLeadership Engagementâ; OR (2) low âAvailable Resourcesâ AND high âExternal Partnershipsâ. Discussion We identified the most salient combinations of co-occurring organizational barriers or facilitators associated with PrEP implementation across Title X clinics in the Southern U.S. We discuss implementation strategies to promote pathways that led to implementation success, as well as strategies to overcome pathways to implementation failure. Notably, we identified regional differences in the pathways that led to PrEP implementation, with Southeastern clinics facing the most obstacles to implementation, specifically substantial resource constraints. Identifying implementation pathways is an important first step for packaging multiple implementation strategies that could be employed by state-level Title X grantees to help scale up PrEP
Detection of polarized gamma-ray emission from the Crab nebula with the Hitomi Soft Gamma-ray Detector
International audienceWe present the results from the Hitomi Soft Gamma-ray Detector (SGD) observation of the Crab nebula. The main part of SGD is a Compton camera, which in addition to being a spectrometer, is capable of measuring polarization of gamma-ray photons. The Crab nebula is one of the brightest X-ray/gamma-ray sources on the sky, and the only source from which polarized X-ray photons have been detected. SGD observed the Crab nebula during the initial test observation phase of Hitomi. We performed data analysis of the SGD observation, SGD background estimation, and SGD Monte Carlo simulations, and successfully detected polarized gamma-ray emission from the Crab nebula with only about 5âks exposure time. The obtained polarization fraction of the phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1%â±â10.6%), and the polarization angle is || +||/â|| in the energy range of 60â160âkeV (the errors correspond to the 1âÏ deviation). The confidence level of the polarization detection was 99.3%. The polarization angle measured by SGD is about one sigma deviation with the projected spin axis of the pulsar, ||â±â||â
Measurements of resonant scattering in the Perseus Cluster core with Hitomi SXS
International audienceThanks to its high spectral resolution (âŒ5âeV at 6âkeV), the Soft X-ray Spectrometer (SXS) on board Hitomi enables us to measure the detailed structure of spatially resolved emission lines from highly ionized ions in galaxy clusters for the first time. In this series of papers, using the SXS we have measured the velocities of gas motions, metallicities and the multi-temperature structure of the gas in the core of the Perseus Cluster. Here, we show that when inferring physical properties from line emissivities in systems like Perseus, the resonant scattering effect should be taken into account. In the Hitomi waveband, resonant scattering mostly affects the Feâxxv Heα line (w)âthe strongest line in the spectrum. The flux measured by Hitomi in this line is suppressed by a factor of âŒ1.3 in the inner âŒ30âkpc, compared to predictions for an optically thin plasma; the suppression decreases with the distance from the center. The w line also appears slightly broader than other lines from the same ion. The observed distortions of the w line flux, shape, and distance dependence are all consistent with the expected effect of the resonant scattering in the Perseus core. By measuring the ratio of fluxes in optically thick (w) and thin (Feâxxv forbidden, HeÎČ, Lyα) lines, and comparing these ratios with predictions from Monte Carlo radiative transfer simulations, the velocities of gas motions have been obtained. The results are consistent with the direct measurements of gas velocities from line broadening described elsewhere in this series, although the systematic and statistical uncertainties remain significant. Further improvements in the predictions of line emissivities in plasma models, and deeper observations with future X-ray missions offering similar or better capabilities to the Hitomi SXS, will enable resonant scattering measurements to provide powerful constraints on the amplitude and anisotropy of cluster gas motions
Search for thermal X-ray features from the Crab nebula with the Hitomi soft X-ray spectrometer
The Crab nebula originated from a core-collapse supernova (SN) explosion
observed in 1054 A.D. When viewed as a supernova remnant (SNR), it has an
anomalously low observed ejecta mass and kinetic energy for an Fe-core collapse
SN. Intensive searches were made for a massive shell that solves this
discrepancy, but none has been detected. An alternative idea is that the SN1054
is an electron-capture (EC) explosion with a lower explosion energy by an order
of magnitude than Fe-core collapse SNe. In the X-rays, imaging searches were
performed for the plasma emission from the shell in the Crab outskirts to set a
stringent upper limit to the X-ray emitting mass. However, the extreme
brightness of the source hampers access to its vicinity. We thus employed
spectroscopic technique using the X-ray micro-calorimeter onboard the Hitomi
satellite. By exploiting its superb energy resolution, we set an upper limit
for emission or absorption features from yet undetected thermal plasma in the
2-12 keV range. We also re-evaluated the existing Chandra and XMM-Newton data.
By assembling these results, a new upper limit was obtained for the X-ray
plasma mass of <~ 1Mo for a wide range of assumed shell radius, size, and
plasma temperature both in and out of the collisional equilibrium. To compare
with the observation, we further performed hydrodynamic simulations of the Crab
SNR for two SN models (Fe-core versus EC) under two SN environments (uniform
ISM versus progenitor wind). We found that the observed mass limit can be
compatible with both SN models if the SN environment has a low density of <~
0.03 cm-3 (Fe core) or <~ 0.1 cm-3 (EC) for the uniform density, or a
progenitor wind density somewhat less than that provided by a mass loss rate of
10-5 Mo yr-1 at 20 km s-1 for the wind environment.Comment: PASJ in press. Figures are now properly include
Search for thermal X-ray features from the Crab nebula with the Hitomi soft X-ray spectrometer
Temperature structure in the Perseus cluster core observed with Hitomi
International audienceThe present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8â20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338 ks that covered a central region of âŒ7Î in diameter. SXS was operated with an energy resolution of âŒ5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures could be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single-temperature approximation are due to the effects of projecting the known radial temperature gradient in the cluster core along the line of sight. A comparison with the Chandra/ACIS and the XMM-Newton/RGS results, on the other hand, suggests that additional lower-temperature components are present in the intracluster medium (ICM), but not detectable with Hitomi/SXS giving its 1.8â20 keV energy band