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 ($m = 0.91\pm0.09$; $R \propto t^m$) 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&