29 research outputs found
The human exosome: an autoantigenic complex of exoribonucleases in myositis and scleroderma
The anti-PM/Scl autoantibodies are known to characterize a subset of autoimmune patients with myositis, scleroderma (Scl), and the PM/Scl overlap syndrome. The major autoantigens that are recognized by anti-PM/Scl autoantibodies are designated PM/Scl-100 and PM/Scl-75. These autoantigens have been reported to associate into a large complex consisting of 11 to 16 proteins and to play a role in ribosome synthesis. Recently, it was discovered that the PM/Scl complex is the human counterpart of the yeast (Saccharomyces cerevisiae) exosome, which is an RNA-processing complex consisting of 11 3' â 5' exoribonucleases. To date, 10 human exosome components have been identified, although only some of these were studied in more detail. In this review, we discuss some recent advances in the characterization of the PM/Scl complex
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Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster
© 2017. The American Astronomical Society. All rights reserved. High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E â 3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S xvi (E â 3.44 keV rest-frame) - a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment
The Chandra deep survey of the Hubble Deep Field North area. IV. Anultradeep image of the DHF-N
We present results from a 479.7 ks Chandra exposure of the Hubble Deep Field
North (HDF-N) and its immediate vicinity. In our X-ray image, the deepest ever
reported with a 0.5-2.0 keV flux limit of about 4.9 x 10^{-17} erg/cm^2/s, we
detect four new HDF-N X-ray sources bringing the total number of such sources
to 12. The new sources include two optically bright (R=18.3-18.8), low-redshift
(z<0.15) galaxies, a Fanaroff-Riley I radio galaxy, and an edge-on spiral
hosting either a powerful starburst or a low-luminosity active galactic nucleus
(AGN). Notably, we have now detected X-ray emission from all luminous galaxies
(M_V<-18) with z<0.15 known in the HDF-N. We have also detected the remarkable
microJy radio source VLA J123642.09+621331.4, which is located just outside the
HDF-N and has a likely redshift of z=4.424. We have detected X-ray variability
from two of the previously known HDF-N X-ray sources, and spectral fitting
shows clear evidence for X-ray absorption in the brightest X-ray source in the
HDF-N, a z=0.960 broad-line AGN with associated Mg II absorption. Stacking
analyses of optically bright HDF-N galaxies not individually detected in X-rays
have provided estimates of their average X-ray fluxes, and we find that the
X-ray luminosities of `normal' spirals at z~0.5 are not more than a factor of
\~2 larger (per unit B-band luminosity) than those of spirals in the local
Universe (z<0.01). This constrains models for the evolution of low-mass X-ray
binary populations in galaxies in response to the declining cosmic
star-formation rate. Monte-Carlo simulations support the validity of the
stacking analyses and show that the Chandra Advanced CCD Imaging Spectrometer
(ACIS) performs source detection well even with effective exposure times of ~8
Ms. (Abridged)Comment: 40 pages, AJ, in press, improved and expanded to address referee
Comments, also available at
http://www.astro.psu.edu/users/niel/hdf/hdf-chandra.htm
The Chandra Deep Field North Survey. XV. Optically bright, X-ray-faintsources
We have analyzed optically bright, X-ray faint [OBXF; i.e., log(fX/fR) < -2]
sources identified in an 178.9 square arcminute area within the Chandra Deep
Field-North (CDF-N) 2 Ms survey. We find 43 OBXF sources in this area,
comprising ~15% of the X-ray sources above a 0.5--2 keV flux of 2.3e-17 erg
cm^-2 s^-1. We present spectroscopic identifications for 42 of the OBXF sources
and optical spectra for 25, including 5 previously unpublished redshifts. Deep
optical imaging data (either HST or ground-based) are presented for all the
OBXF sources. The OBXF population consists mainly of normal and starburst
galaxies detected out to cosmologically significant distances (i.e., to a
median redshift of z=0.297 and a full redshift range z=0.06-0.845). This is
notable since these distances equate to look-back times of up to ~8 Gyr; we are
thus provided with a window on the X-ray emission from galaxies at redshifts
much closer to the cosmic star formation peak than was possible prior to
Chandra.
The X-ray luminosity distribution of OBXF sources extends to higher
luminosity than does that of "normal" galaxies indicating that a significant
fraction are likely dominated by low-luminosity AGN (LLAGN) or vigorous star
formation. By combining the detected X-ray counts, we find the average OBXF
X-ray spectrum to be consistent with a Gamma=2.0 power law. The 0.5--2 keV log
N-log S for the OBXF galaxies is much steeper (alpha=-1.7) than for the general
X-ray source population. Indeed, the number of OBXF sources has doubled between
the 1~Ms and 2~Ms survey, rising sharply in numbers at faint fluxes. The
extragalactic OBXF sources are found to contribute ~1-2% of the soft
extragalactic X-ray background.Comment: Accepted for publication in the Astronomical Journal Paper with
full-resolution figures available at
http://www.astro.psu.edu/users/niel/hdf/hdf-chandra.htm