Chandra view of Kes 79: a nearly isothermal SNR with rich spatial structure

A 30 ks \chandra ACIS-I observation of Kes 79 reveals rich spatial structures, including many filaments, three partial shells, a loop and a ``protrusion''. Most of them have corresponding radio features. Regardless of the different results from two non-equilibrium ionization (NEI) codes, temperatures of different parts of the remnant are all around 0.7 keV, which is surprisingly constant for a remnant with such rich structure. If thermal conduction is responsible for smoothing the temperature gradient, a lower limit on the thermal conductivity of $\sim$ 1/10 of the Spitzer value can be derived. Thus, thermal conduction may play an important role in the evolution of at least some SNRs. No spectral signature of the ejecta is found, which suggests the ejecta material has been well mixed with the ambient medium. From the morphology and the spectral properties, we suggest the bright inner shell is a wind-driven shell (WDS) overtaken by the blast wave (the outer shell) and estimate the age of the remnant to be $\sim$ 6 kyr for the assumed dynamics. Projection is also required to explain the complicated morphology of Kes 79.Comment: 12 pages, 6 figures (3 in color), ApJ, in press, April 20, 200

Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 SNR

The N206 supernova remnant (SNR) in the Large Magellanic Cloud (LMC) has long been considered a prototypical "mixed morphology" SNR. Recent observations, however, have added a new twist to this familiar plot: an elongated, radially-oriented radio feature seen in projection against the SNR face. Utilizing the high resolution and sensitivity available with the Hubble Space Telescope, Chandra, and XMM-Newton, we have obtained optical emission-line images and spatially resolved X-ray spectral maps for this intriguing SNR. Our findings present the SNR itself as a remnant in the mid to late stages of its evolution. X-ray emission associated with the radio "linear feature" strongly suggests it to be a pulsar-wind nebula (PWN). A small X-ray knot is discovered at the outer tip of this feature. The feature's elongated morphology and the surrounding wedge-shaped X-ray enhancement strongly suggest a bow-shock PWN structure.Comment: 41 pages including 7 figures, accepted for publication by the Astrophysical Journa

X-Ray Light Curves of Gamma-ray Bursts Detected with the All-Sky Monitor on RXTE

We present X-ray light curves (1.5-12 keV) for fifteen gamma-ray bursts (GRBs) detected by the All-Sky Monitor on the Rossi X-ray Timing Explorer. We compare these soft X-ray light curves with count rate histories obtained by the high-energy (>12 keV) experiments BATSE, Konus-Wind, the BeppoSAX Gamma-Ray Burst Monitor, and the burst monitor on Ulysses. We discuss these light curves within the context of a simple relativistic fireball and synchrotron shock paradigm, and we address the possibility of having observed the transition between a GRB and its afterglow. The light curves show diverse morphologies, with striking differences between energy bands. In several bursts, intervals of significant emission are evident in the ASM energy range with little or no corresponding emission apparent in the high-energy light curves. For example, the final peak of GRB 970815 as recorded by the ASM is only detected in the softest BATSE energy bands. We also study the duration of bursts as a function of energy. Simple, singly-peaked bursts seem consistent with the E^{-0.5} power law expected from an origin in synchrotron radiation, but durations of bursts that exhibit complex temporal structure are not consistent with this prediction. Bursts such as GRB 970828 that show many short spikes of emission at high energies last significantly longer at low energies than the synchrotron cooling law would predict.Comment: 15 pages with 20 figures and 2 tables. In emulateapj format. Accepted by ApJ

A Comparison of Three Electrophysiological Methods for the Assessment of Disease Status in a Mild Spinal Muscular Atrophy Mouse Model

Objectives: There is a need for better, noninvasive quantitative biomarkers for assessing the rate of progression and possible response to therapy in spinal muscular atrophy (SMA). In this study, we compared three electrophysiological measures: compound muscle action potential (CMAP) amplitude, motor unit number estimate (MUNE), and electrical impedance myography (EIM) 50 kHz phase values in a mild mouse model of spinal muscular atrophy, the Smn1c/c mouse. Methods: Smn1c/c mice (N = 11) and wild type (WT) animals (−/−, N = 13) were measured on average triweekly until approximately 1 year of age. Measurements included CMAP, EIM, and MUNE of the gastrocnemius muscle as well as weight and front paw grip strength. At the time of sacrifice at one year, additional analyses were performed on the animals including serum survival motor neuron (SMN) protein levels and muscle fiber size. Results: Both EIM 50 kHz phase and CMAP showed strong differences between WT and SMA animals (repeated measures 2-way ANOVA, P<0.0001 for both) whereas MUNE did not. Both body weight and EIM showed differences in the trajectory over time (p<0.001 and p = 0.005, respectively). At the time of sacrifice at one year, EIM values correlated to motor neuron counts in the spinal cord and SMN levels across both groups of animals (r = 0.41, p = 0.047 and r = 0.57, p = 0.003, respectively), while CMAP did not. Motor neuron number in Smn1c/c mice was not significantly reduced compared to WT animals. Conclusions: EIM appears sensitive to muscle status in this mild animal model of SMA. The lack of a reduction in MUNE or motor neuron number but reduced EIM and CMAP values support that much of the pathology in these animals is distal to the cell body, likely at the neuromuscular junction or the muscle itself

Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE

We report on the discovery of hard spectral tails for energies above 10 keV in the total and pulsed spectra of anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 using RXTE PCA (2-60 keV) and HEXTE (15-250 keV) data and INTEGRAL IBIS ISGRI (20-300 keV) data. Improved spectral information on 1E 1841-045 is presented. The pulsed and total spectra measured above 10 keV have power-law shapes and there is so far no significant evidence for spectral breaks or bends up to ~150 keV. The pulsed spectra are exceptionally hard with indices measured for 4 AXPs approximately in the range -1.0 -- 1.0. We also reanalyzed archival CGRO COMPTEL (0.75-30 MeV) data to search for signatures from our set of AXPs. No detections can be claimed, but the obtained upper-limits in the MeV band indicate that for 1RXS J1708-4009, 4U 0142+61 and 1E 1841-045 strong breaks must occur somewhere between 150 and 750 keV.Comment: Accepted for publication in ApJ; 19 pages; 4 Tables; 15 Figures (6 color

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

Pliocene-Pleistocene marine cyclothems, Wanganui Basin, New Zealand: a lithostratigraphic framework

The Rangitikei River valley between Mangaweka and Vinegar Hill and the surrounding Ohingaiti region in eastern Wanganui Basin contains a late Pliocene to early Pleistocene (c. 2.6-1.7 Ma), c. 1100 m thick, southward-dipping (4-9deg.), marine cyclothemic succession. Twenty sedimentary cycles occur within the succession, each of which contains coarse-grained (siliciclastic sandstone and coquina) and fine-grained (siliciclastic siltstone) units. Nineteen of the cycles are assigned to the Rangitikei Group (new). Six new formations are defined within the Rangitikei Group, and their distribution in the Ohingaiti region is represented in a new geologic map. The new formations are named: Mangarere, Tikapu, Makohine, Orangipongo, Mangaonoho, and Vinegar Hill. Each formation comprises one or more cyclothems and includes a previously described and named distinctive basal horizon. Discrete sandstones, siltstones, and coquinas within formations are assigned member status and correspond to systems tracts in sequence stratigraphic nomenclature. The members provide the link between the new formational lithostratigraphy and the sequence stratigraphy of the Rangitikei Group. Base of cycle coquina members accumulated during episodes of sediment starvation associated with stratigraphic condensation on an open marine shelf during sea-level transgressions. Siltstone members accumulated in mid-shelf environments (50-100 m water depth) during sea-level highstands, whereas the overlying sandstone members are ascribed to inner shelf and shoreface environments (0-50 m water depth) and accumulated during falling eustatic sea-level conditions. Repetitive changes in water depth of 50-100 m magnitude are consistent with a glacio-eustatic origin for the cyclothems, which correspond to an interval of Earth history when successive glaciations in the Northern Hemisphere are known to have occurred. Moreover, the chronology of the Rangitikei River section indicates that Rangitikei Group cyclothems accumulated during short duration, 41 ka cycles in continental ice volume attributed to the dominance of the Milankovitch obliquity orbital parameter. The Ohingaiti region has simple postdepositional structure. The late Pliocene formations dip generally to the SSW between 4deg. and 9deg.. Discernible discordances of c. 1deg. between successively younger formations are attributed to synsedimentary tilting of the shelf concomitant with migration of the tectonic hingeline southward into the basin. The outcrop distribution of the Rangitikei Group is strongly influenced by this regional tilt and also by three major northeast-southwest oriented, high-angle reverse faults (Rauoterangi, Pakihikura, and Rangitikei Faults)

The first orbital solution for the massive colliding-wind binary HD93162 (=WR25)

Since the discovery, with the EINSTEIN satellite, of strong X-ray emission associated with HD93162 (=WR25), this object has been predicted to be a colliding-wind binary system. However, radial-velocity variations that would prove the suspected binary nature have yet to be found. We spectroscopically monitored this object to investigate its possible variability to address this discordance. We compiled the largest available radial-velocity data set for this star to look for variations that might be due to binary motion. We derived radial velocities from spectroscopic data acquired mainly between 1994 and 2006, and searched these radial velocities for periodicities using different numerical methods. For the first time, periodic radial-velocity variations are detected. Our analysis definitively shows that the Wolf-Rayet star WR25 is an eccentric binary system with a probable period of about 208 days.Comment: 7 pages, 4 figures, accepted by A+

RXTE Observations of an Outburst of Recurrent X-ray Nova GS 1354-644

We present the results of Rossi X-ray Timing Explorer observations of GS 1354-644 during a modest outburst in 1997-1998. The source is one of a handful of black hole X-ray transients that are confirmed to be recurrent in X-rays. A 1987 outburst of the same source observed by Ginga was much brighter, and showed a high/soft spectral state. In contrast the 1997-1998 outburst showed a low/hard spectral state. Both states are typical for black hole binaries. The RXTE All Sky Monitor observed an outburst duration of 150 to 200 days. PCA and HEXTE observations covered ~70 days near the maximum of the light curve and during the flux decline. Throughout the observations, the spectrum can be approximated by Compton upscattering of soft photons by energetic electrons. The hot electron cloud has a temperature kT ~30 keV and optical depth tau~4--5. To fit the data well an additional iron fluorescent line and reflection component are required, which indicates the presence of optically thick cool material, most probably in the outer part of the accretion disk. Dramatic fast variability was observed, and has been analyzed in the context of a shot noise model. The spectrum appeared to be softest at the peaks of the shot-noise variability. The shape of the power spectrum was typical for black hole systems in a low/hard state. We note a qualitative difference in the shape of the dependence of fractional variability on energy, when we compare systems with black holes and with neutron stars. Since it is difficult to discriminate these systems on spectral grounds, at least in their low/hard states, this new difference might be important.Comment: 12 pages, 9 figures, accepted for publication in ApJ (Feb. 2000, v.530), uses emulateapj.st

Practical free-space quantum key distribution over 1 km

A working free-space quantum key distribution (QKD) system has been developed and tested over an outdoor optical path of ~1 km at Los Alamos National Laboratory under nighttime conditions. Results show that QKD can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite QKD.Comment: 5 pages, 2 figures, 2 tables. Submitted to Physics Review Letters, May 199