13,050 research outputs found
Deep Chandra Observations of the Compact Starburst Galaxy Henize 2-10: X-rays from the Massive Black Hole
We present follow-up X-ray observations of the candidate massive black hole
(BH) in the nucleus of the low-mass, compact starburst galaxy Henize 2-10.
Using new high-resolution observations from the Chandra X-ray Observatory
totaling 200 ks in duration, as well as archival Chandra observations from
2001, we demonstrate the presence of a previously unidentified X-ray point
source that is spatially coincident with the known nuclear radio source in
Henize 2-10 (i.e., the massive BH). We show that the hard X-ray emission
previously identified in the 2001 observation is dominated by a source that is
distinct from the nucleus, with the properties expected for a high-mass X-ray
binary. The X-ray luminosity of the nuclear source suggests the massive BH is
radiating significantly below its Eddington limit (~10^-6 L_Edd), and the soft
spectrum resembles other weakly accreting massive BHs including Sagittarius A*.
Analysis of the X-ray light curve of the nucleus reveals the tentative
detection of a ~9-hour periodicity, although additional observations are
required to confirm this result. Our study highlights the need for sensitive
high-resolution X-ray observations to probe low-level accretion, which is the
dominant mode of BH activity throughout the Universe.Comment: Accepted for publication in ApJ Letters. 7 pages, 4 figure
Construction of 2-factors in the middle layer of the discrete cube
Define the middle layer graph as the graph whose vertex set consists of all
bitstrings of length that have exactly or entries equal to 1,
with an edge between any two vertices for which the corresponding bitstrings
differ in exactly one bit. In this work we present an inductive construction of
a large family of 2-factors in the middle layer graph for all . We
also investigate how the choice of certain parameters used in the construction
affects the number and lengths of the cycles in the resulting 2-factor
D-brane gauge theories from toric singularities of the form and
We discuss examples of D-branes probing toric singularities, and the
computation of their world-volume gauge theories from the geometric data of the
singularities. We consider several such examples of D-branes on partial
resolutions of the orbifolds , and .Comment: 34+1 pages, References added, Version to appear in Nuclear Physics
D-Brane Gauge Theories from Toric Singularities and Toric Duality
Via partial resolution of Abelian orbifolds we present an algorithm for
extracting a consistent set of gauge theory data for an arbitrary toric variety
whose singularity a D-brane probes. As illustrative examples, we tabulate the
matter content and superpotential for a D-brane living on the toric del Pezzo
surfaces as well as the zeroth Hirzebruch surface. Moreover, we discuss the
non-uniqueness of the general problem and present examples of vastly different
theories whose moduli spaces are described by the same toric data. Our methods
provide new tools for calculating gauge theories which flow to the same
universality class in the IR. We shall call it ``Toric Duality.''Comment: 38 pages, 6 figures, 2 references added and 1 equation correcte
D-particles on T^4/Z_n orbifolds and their resolutions
We formulate the effective field theory of a D-particle on orbifolds of
by a cyclic group as a gauge theory in a -bundle over the dual orbifold. We
argue that this theory admits Fayet-Iliopoulos terms analogous to those present
in the case of noncompact orbifolds. In the case, we present some
evidence that turning on such terms resolves the orbifold singularities and may
lead to a surface realized as a blow up of the fixed points of the cyclic
group action.Comment: 34 pages, 3 figures; very minor typos corrected, 2 references adde
Hazard Assessment of Personal Protective Clothing for Hydrogen Peroxide Service
Selection of personal protective equipment (PPE) for hydrogen peroxide service is an important part of the hazard assessment process. But because drip testing of chemical protective clothing for hydrogen peroxide service has not been reported for about 40 years, it is of great interest to test new protective clothing materials with new, high-concentration hydrogen peroxide following similar procedures. The suitability of PPE for hydrogen peroxide service is in part determined by observations made when hydrogen peroxide is dripped onto swatches of protective clothing material. Protective clothing material was tested as received, in soiled condition, and in grossly soiled condition. Materials were soiled by pretreating the material with potassium permanganate (KMnO4) solution then drying to promote a reaction. Materials were grossly soiled with solid KMnO4 to greatly promote reaction. Observations of results including visual changes to the hydrogen peroxide and materials, times to ignition, and self-extinguishing characteristics of the materials are reported
Orbifold Resolution by D-Branes
We study topological properties of the D-brane resolution of
three-dimensional orbifold singularities, C^3/Gamma, for finite abelian groups
Gamma. The D-brane vacuum moduli space is shown to fill out the background
spacetime with Fayet--Iliopoulos parameters controlling the size of the
blow-ups. This D-brane vacuum moduli space can be classically described by a
gauged linear sigma model, which is shown to be non-generic in a manner that
projects out non-geometric regions in its phase diagram, as anticipated from a
number of perspectives.Comment: 26 pages, 2 figures (TeX, harvmac big, epsf
Removal of Perfluorinated Grease Components from NTO Oxidizer
Perfluorinated greases are typically used as a thread lubricant in the assembly of non-welded nitrogen tetroxide (NTO) oxidizer systems. These greases, typically a perfluoroalkylether, with suspended polytetrafluoroethylene (PTFE) micro-powder, have attractive lubricating properties toward threaded components and are relatively chemically inert toward NTO oxidizers. A major drawback, however, is that perfluoroalkylether greases are soluble or dispersible in NTO oxidizers and can contaminate the propellant. The result is propellant that fails the non-volatile residue (NVR) specification analyses and that may have negative effects on test hardware performance and lifetime. Consequently, removal of the grease contaminants from NTO may be highly desirable. Methods for the removal of perfluorinated grease components from NTO oxidizers including distillation, adsorption, filtration, and adjustment of temperature are investigated and reported in this work. Solubility or dispersibility data for the perfluoroalkylether oil (Krytox(tm)143 AC) component of a perfluorinated grease (Krytox 240 AC) and for Krytox 240 AC in NTO were determined and are reported
Variable Hard X-ray Emission from the Candidate Accreting Black Hole in Dwarf Galaxy Henize 2-10
We present an analysis of the X-ray spectrum and long-term variability of the
nearby dwarf starburst galaxy Henize 2-10. Recent observations suggest that
this galaxy hosts an actively accreting black hole with mass ~10^6 M_sun. The
presence of an AGN in a low-mass starburst galaxy marks a new environment for
active galactic nuclei (AGNs), with implications for the processes by which
"seed" black holes may form in the early Universe. In this paper, we analyze
four epochs of X-ray observations of Henize 2-10, to characterize the long-term
behavior of its hard nuclear emission. We analyze observations with Chandra
from 2001 and XMM-Newton from 2004 and 2011, as well as an earlier, less
sensitive observation with ASCA from 1997. Based on detailed analysis of the
source and background, we find that the hard (2-10 keV) flux of the putative
AGN has decreased by approximately an order of magnitude between the 2001
Chandra observation and exposures with XMM-Newton in 2004 and 2011. The
observed variability confirms that the emission is due to a single source. It
is unlikely that the variable flux is due to a supernova or ultraluminous X-ray
source, based on the observed long-term behavior of the X-ray and radio
emission, while the observed X-ray variability is consistent with the behavior
of well-studied AGNs.Comment: 7 pages, 4 figures, 2 tables; accepted for publication in Ap
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