11,480 research outputs found
Study of hot hardness characteristics of tool steels
Hardness measurements of tool steel materials in electric furnace at elevated temperatures and low oxygen environment are discussed. Development of equation to predict short term hardness as function of intial room temperature hardness of steel is reported. Types of steel involved in the process are identified
X-ray Spectroscopy of Candidate Ultracompact X-ray Binaries
We present high-resolution spectroscopy of the neutron star/low-mass X-ray
binaries (LMXBs) 4U 1850-087 and 4U 0513-40 as part of our continuing study of
known and candidate ultracompact binaries. The LMXB 4U 1850-087 is one of four
systems in which we had previously inferred an unusual Ne/O ratio in the
absorption along the line of sight, most likely from material local to the
binaries. However, our recent Chandra X-ray Observatory LETGS spectrum of 4U
1850-087 finds a Ne/O ratio by number of 0.22+/-0.05, smaller than previously
measured and consistent with the expected interstellar value. We propose that
variations in the Ne/O ratio due to source variability, as previously observed
in these sources, can explain the difference between the low- and
high-resolution spectral results for 4U 1850-087. Our XMM-Newton RGS
observation of 4U 0513-40 also shows no unusual abundance ratios in the
absorption along the line of sight. We also present spectral results from a
third candidate ultracompact binary, 4U 1822-000, whose spectrum is well fit by
an absorbed power-law + blackbody model with absorption consistent with the
expected interstellar value. Finally, we present the non-detection of a fourth
candidate ultracompact binary, 4U 1905+000, with an upper limit on the source
luminosity of < 1 x 10^{32} erg s^{-1}. Using archival data, we show that the
source has entered an extended quiescent state.Comment: 8 pages, 3 figures, accepted for publication to the Astrophysical
Journa
Short-term hot hardness characteristics of rolling-element steels
Short-term hot hardness studies were performed with five vacuum-melted steels at temperatures from 294 to 887 K (70 to 1140 F). Based upon a minimum Rockwell C hardness of 58, the temperature limitation on all materials studied was dependent on the initial room temperature hardness and the tempering temperature of each material. For the same room temperature hardness, the short-term hot hardness characteristics were identical and independent of material composition. An equation was developed to predict the short-term hardness at temperature as a function of initial room temperature hardness for AISI 52100, as well as the high-speed tool steels
1.6 GHz VLBI Observations of SN 1979C: almost-free expansion
We report on 1.6 GHz Very-Long-Baseline-Interferometry (VLBI) observations of
supernova SN 1979C made on 18 November 2002. We derive a model-dependent
supernova size. We also present a reanalysis of VLBI observations made by us on
June 1999 and by other authors on February 2005. We conclude that, contrary to
our earlier claim of strong deceleration in the expansion, SN 1979C has been
undergoing almost-free expansion (; ) for over
25 years.Comment: 4 pages, 4 figures; submitted to A&A on 14 May 2009. Accepted on 7
Jul 200
Gamma-Ray Burst Environments and Progenitors
Likely progenitors for the GRBs (gamma-ray bursts) are the mergers of compact
objects or the explosions of massive stars. These two cases have distinctive
environments for the GRB afterglow: the compact object explosions occur in the
ISM (interstellar medium) and those of massive stars occur in the preburst
stellar wind. We calculate the expected afterglow for a burst in a Wolf-Rayet
star wind and compare the results to those for constant, interstellar density.
The optical afterglow for the wind case is generally expected to decline more
steeply than in the constant density case, but this effect may be masked by
variations in electron spectral index, and the two cases have the same
evolution in the cooling regime. Observations of the concurrent radio and
optical/X-ray evolution are especially useful for distinguishing between the
two cases. The different rates of decline of the optical and X-ray afterglows
of GRB 990123 suggest constant density interaction for this case. We have
previously found strong evidence for wind interaction in SN 1998bw/GRB 980425
and here present a wind model for GRB 980519. We thus suggest that there are
both wind type GRB afterglows with massive star progenitors and ISM type
afterglows with compact binary star progenitors. The wind type bursts are
likely to be accompanied by a supernova, but not the ISM type.Comment: 11 pages, 1 figure, revised version, ApJ Letters, in pres
Aql X-1 in Outburst and Quiescence
We present photometry and spectroscopy of the soft x-ray transient Aql X-1.
Optical photometry during an active state shows a strong (0.6 mag peak-to-peak)
modulation at a period of 19 hours. Infrared (K'-band) photometry during a
quiescent state limits any ellipsoidal variations to <0.07 mag (peak-to-peak),
which implies an inclination i<31 (90% limit). Spectroscopy in a quiescent
state shows at most very small radial velocity variations, which implies a very
low inclination of i<12 (90% limit). The low inclination is rather unexpected
given the large photometric modulation seen in the active state. The upper
limit to the equivalent width of the anomalous Li 6707A line is <0.3A, which is
similar to the measured strength of this line in several other x-ray
transients.Comment: Accepted for publication in ApJ, 12 pages, 5 figure
Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae
We report the X-ray detection of the Type II-plateau supernova SN 2004et in
the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position
of the X-ray source was found to agree with the optical position within ~0.4
arcsec. Chandra also surveyed the region before the 2004 event, finding no
X-ray emission at the location of the progenitor. For the post-explosion
observations, a total of 202, 151, and 158 photons were detected in three
pointings, each ~29 ks in length, on 2004 October 22, November 6, and December
3, respectively. The spectrum of the first observation is best fit by a thermal
model with a temperature of kT=1.3 keV and a line-of-sight absorption of
N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is
~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and
soft counts on the first and third epochs indicates a softening over this time,
although there is an insufficient number of photons to constrain the variation
of temperature and absorption by spectral fitting. We model the emission as
arising from the reverse shock region in the interaction between the supernova
ejecta and the progenitor wind. For a Type IIP supernova with an extended
progenitor, the cool shell formed at the time of shock wave breakout from the
star can affect the initial evolution of the interaction shell and the
absorption of radiation from the reverse shock. The observed spectral softening
might be due to decreasing shell absorption. We find a pre-supernova mass loss
rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is
in line with expectations for a Type IIP supernova.Comment: total 19 pages including 7 figures. ApJ, in press. See
http://spider.ipac.caltech.edu/staff/rho/preprint/SN2004etms.ps for the paper
including full resolution image
BATSE Soft Gamma-Ray Observations of GROJ0422+32
We report results of a comprehensive study of the soft gamma-ray (30 keV to
1.7 MeV) emission of GROJ0422+32 during its first known outburst in 1992. These
results were derived from the BATSE earth-occultation database with the JPL
data analysis package, EBOP (Enhanced BATSE Occultation Package). Results
presented here focus primarily on the long-term temporal and spectral
variability of the source emission associated with the outburst. The light
curves with 1-day resolution in six broad energy-bands show the high-energy
flux (>200 keV) led the low-energy flux (<200 keV) by ~5 days in reaching the
primary peak, but lagged the latter by ~7 days in starting the declining phase.
We confirm the "secondary maximum" of the low-energy (<200 keV) flux at TJD
8970-8981, ~120 days after the first maximum. Our data show that the "secondary
maximum" was also prominent in the 200-300 keV band, but became less pronounced
at higher energies. During this 200-day period, the spectrum evolved from a
power-law with photon index of 1.75 on TJD 8839, to a shape that can be
described by a Comptonized model or an exponential power law below 300 keV,
with a variable power-law tail above 300 keV. The spectrum remained roughly in
this two-component shape until ~9 November (TJD 8935) and then returned to the
initial power-law shape with an index of ~2 until the end of the period. The
correlation of the two spectral shapes with the high and low luminosities of
the soft gamma-ray emission is strongly reminiscent of that seen in Cygnus X-1.
We interpret these results in terms of the Advection Dominated Accretion Flow
(ADAF) model with possibly a "jet-like" region that persistently produced the
non-thermal power-law gamma rays observed throughout the event.Comment: 40 pages total, including 10 figures and 2 table
Radio emission of SN1993J. The complete picture: II. Simultaneous fit of expansion and radio light curves
We report on a simultaneous modelling of the expansion and radio light curves
of SN1993J. We have developed a simulation code capable of generating synthetic
expansion and radio light curves of supernovae by taking into consideration the
evolution of the expanding shock, magnetic fields, and relativistic electrons,
as well as the finite sensitivity of the interferometric arrays used in the
observations. Our software successfully fits all the available radio data of SN
1993J with an standard emission model for supernovae extended with some
physical considerations, as an evolution in the opacity of the ejecta material,
a radial drop of the magnetic fields inside the radiating region, and a
changing radial density profile of the circumstellar medium beyond day 3100
after explosion.Comment: 12 pages, 12 figures, accepted for publication in A&
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