1,046 research outputs found
Multitarget Sputtering Using Decoupled Plasma
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryJoint Services Electronics Program / DAAB-07-72-C-025
Impulse Stimulated Crystallization in Amorphous Semiconducting Films
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryJoint Services Electronics Program / DAAB-07-72-C-025
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 (BH) with mass ~106 . The presence of an active galactic nucleus (AGN) in a low-mass starburst galaxy marks a new environment for AGNs, with implications for the processes by which "seed" BHs 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 a 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
Low-Energy Electron Microscopy Studies of Interlayer Mass Transport Kinetics on TiN(111)
In situ low-energy electron microscopy was used to study interlayer mass
transport kinetics during annealing of three-dimensional (3D) TiN(111) mounds,
consisting of stacked 2D islands, at temperatures T between 1550 and 1700 K. At
each T, the islands decay at a constant rate, irrespective of their initial
position in the mounds, indicating that mass is not conserved locally. From
temperature-dependent island decay rates, we obtain an activation energy of
2.8+/-0.3 eV. This is consistent with the detachment-limited decay of 2D TiN
islands on atomically-flat TiN(111) terraces [Phys. Rev. Lett. 89 (2002)
176102], but significantly smaller than the value, 4.5+/-0.2 eV, obtained for
bulk-diffusion-limited spiral step growth [Nature 429, 49 (2004)]. We model the
process based upon step flow, while accounting for step-step interactions, step
permeability, and bulk mass transport. The results show that TiN(111) steps are
highly permeable and exhibit strong repulsive temperature-dependent step-step
interactions that vary between 0.003 and 0.076 eV-nm. The rate-limiting process
controlling TiN(111) mound decay is surface, rather than bulk, diffusion in the
detachment-limited regime.Comment: 26 pages, 5 figure
Galaxy-scale Bars in Late-type Sloan Digital Sky Survey Galaxies Do Not Influence the Average Accretion Rates of Supermassive Black Holes
Galaxy-scale bars are expected to provide an effective means for driving material toward the central region in spiral galaxies, and possibly feeding supermassive black holes (BHs). Here we present a statistically complete study of the effect of bars on average BH accretion. From a well-selected sample of 50,794 spiral galaxies (with {M}_{* }\sim 0.2\mbox{--}30\times {10}^{10}\,{M}_{\odot }) extracted from the Sloan Digital Sky Survey Galaxy Zoo 2 project, we separate those sources considered to contain galaxy-scale bars from those that do not. Using archival data taken by the Chandra X-ray Observatory, we identify X-ray luminous () active galactic nuclei and perform an X-ray stacking analysis on the remaining X-ray undetected sources. Through X-ray stacking, we derive a time-averaged look at accretion for galaxies at fixed stellar mass and star-formation rate, finding that the average nuclear accretion rates of galaxies with bar structures are fully consistent with those lacking bars ( yr−1). Hence, we robustly conclude that large-scale bars have little or no effect on the average growth of BHs in nearby () galaxies over gigayear timescales
Finding Faint Intermediate-mass Black Holes in the Radio Band
We discuss the prospects for detecting faint intermediate-mass black holes,
such as those predicted to exist in the cores of globular clusters and dwarf
spheroidal galaxies. We briefly summarize the difficulties of stellar dynamical
searches, then show that recently discovered relations between black hole mass,
X-ray luminosity and radio luminosity imply that in most cases, these black
holes should be more easily detected in the radio than in the X-rays. Finally,
we show upper limits from some radio observations of globular clusters, and
discuss the possibility that the radio source in the core of the Ursa Minor
dwarf spheroidal galaxy might be a black hole.Comment: 10 pages, no figures, to appear in From X-ray Binaries to Quasars:
Black Hole Accretion on All Mass Scales, ed. T. J. Maccarone, R. P. Fender,
and L. C. Ho (Dordrecht: Kluwer
Extrapolating SMBH correlations down the mass scale: the case for IMBHs in globular clusters
Empirical evidence for both stellar mass black holes M_bh<10^2 M_sun) and
supermassive black holes (SMBHs, M_bh>10^5 M_sun) is well established.
Moreover, every galaxy with a bulge appears to host a SMBH, whose mass is
correlated with the bulge mass, and even more strongly with the central stellar
velocity dispersion sigma_c, the `M-sigma' relation. On the other hand,
evidence for "intermediate-mass" black holes (IMBHs, with masses in the range
1^2 - 10^5 M_sun) is relatively sparse, with only a few mass measurements
reported in globular clusters (GCs), dwarf galaxies and low-mass AGNs. We
explore the question of whether globular clusters extend the M-sigma
relationship for galaxies to lower black hole masses and find that available
data for globular clusters are consistent with the extrapolation of this
relationship. We use this extrapolated M-sigma relationship to predict the
putative black hole masses of those globular clusters where existence of
central IMBH was proposed. We discuss how globular clusters can be used as a
constraint on theories making specific predictions for the low-mass end of the
M-sigma relation.Comment: 14 pages, 3 figures, accepted for publication in Astrophysics and
Space Science; fixed typos and a quote in Sec.
Constraints on the Local Sources of Ultra High-Energy Cosmic Rays
Ultra high-energy cosmic rays (UHECRs) are believed to be protons accelerated
in magnetized plasma outflows of extra-Galactic sources. The acceleration of
protons to ~10^{20} eV requires a source power L>10^{47} erg/s. The absence of
steady sources of sufficient power within the GZK horizon of 100 Mpc, implies
that UHECR sources are transient. We show that UHECR "flares" should be
accompanied by strong X-ray and gamma-ray emission, and that X-ray and
gamma-ray surveys constrain flares which last less than a decade to satisfy at
least one of the following conditions: (i) L>10^{50} erg/s; (ii) the power
carried by accelerated electrons is lower by a factor >10^2 than the power
carried by magnetic fields or by >10^3 than the power in accelerated protons;
or (iii) the sources exist only at low redshifts, z<<1. The implausibility of
requirements (ii) and (iii) argue in favor of transient sources with L>10^{50}
erg/s.Comment: 7 pages, 1 figure, submitted to JCA
The Centurion 18 telescope of the Wise Observatory
We describe the second telescope of the Wise Observatory, a 0.46-m Centurion
18 (C18) installed in 2005, which enhances significantly the observing
possibilities. The telescope operates from a small dome and is equipped with a
large-format CCD camera. In the last two years this telescope was intensively
used in a variety of monitoring projects.
The operation of the C18 is now automatic, requiring only start-up at the
beginning of a night and close-down at dawn. The observations are mostly
performed remotely from the Tel Aviv campus or even from the observer's home.
The entire facility was erected for a component cost of about 70k$ and a labor
investment of a total of one man-year.
We describe three types of projects undertaken with this new facility: the
measurement of asteroid light variability with the purpose of determining
physical parameters and binarity, the following-up of transiting extrasolar
planets, and the study of AGN variability. The successful implementation of the
C18 demonstrates the viability of small telescopes in an age of huge
light-collectors, provided the operation of such facilities is very efficient.Comment: 16 pages, 13 figures, some figures quality was degraded, accepted for
publication in Astrophysics and Space Scienc
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