The Radio Evolution of SN 2001gd Stockdale, Christopher J; Williams, Christopher L; Weiler, Kurt W ...
The Astrophysical journal,
12/2007, Letnik:
671, Številka:
1
Journal Article
Recenzirano
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We present the results of observations of the radio emission from SN 2001gd in NGC5033 from 2002 February 8 through 2006 September 25. The data were obtained using the VLA at wavelengths of 1.3 cm ...(22.4 GHz), 2 cm (14.9 GHz), 3.6 cm (8.4 GHz), 6 cm (4.9 GHz), and 20 cm (1.5 GHz), with one upper limit at 90 cm (0.3 GHz). In addition, one detection has been provided by the GMRT at 21 cm (1.4 GHz). SN 2001gd was discovered in the optical well past maximum light, so that it was not possible to obtain many of the early radio "turn-on" measurements that are important for estimating the local CSM properties. Only at 20 cm were turn-on data available. However, our analysis and fitting of the radio light curves, along with the assumption that the Type IIb SN 2001gd resembles the much better studied Type IIb SN 1993J, enables us to describe the radio evolution as being very regular through day similar to 550 and consistent with a nonthermal-emitting model with a thermal absorbing CSM. The presence of SSA at early times is implied by the data, but determination of the exact relationship between the SSA component from the emitting region and the free-free absorption component from the CSM is not possible, as there are insufficient early measurements to distinguish between models. After day similar to 550, the radio emission exhibits a dramatically steeper decline rate, which, assuming similarity to SN 1993J, can be described as an exponential decrease with an e-folding time of 500 days. We interpret this abrupt change in the radio flux density decline rate as implying a transition of the shock front into a more tenuous region of circumstellar material. A similar change in radio evolution has been seen earlier in other SNe, such as SN 1988Z, SN 1980K, and SN 1993J.
We report the results of 15 years of radio observations of the six historical supernovae (SNe) in M83 using the Very Large Array. We note the near-linear decline in radio emission from SN 1957D, a ...Type II SN, which remains a nonthermal radio emitter. The measured flux densities from SNe 1923A and 1950B have flattened as they begin to fade below detectable limits; they are also Type II SNe. The luminosities for these three SNe are comparable with the radio luminosities of other decades-old SNe at similar epochs. SNe 1945B, 1968L, and 1983N were not detected in the most recent observations, and these nondetections are consistent with previous studies. We report the X-ray nondetections of all six historical SNe using the Chandra X-Ray Observatory, consistent with previous X-ray searches of other decades-old SNe and low inferred mass-loss rates of the progenitors .
While aerial photography and satellite imagery are the usual data sources used in remote sensing, land based oblique photographs can also be used to measure ecological change. By using such ...historical photographs, the time frame for change detection can be extended into the late 1800s and early 1900s, predating the era of aerial imagery by decades. Recent advancements in computing power have enabled the development of techniques for georeferencing oblique angle photographs. The WSL Monoplotting Tool is a new piece of software that opens the door to analyzing such photographs by allowing for extraction of spatially referenced vector data from oblique photographs. A very large repeat photography collection based on the world's largest systematic collection of historical mountain topographic survey images, the Mountain Legacy Project, contains >6000 high resolution oblique image pairs showing landscape changes in the Rocky Mountains of Alberta between ca. 1900 – today. We used a subset of photographs from this collection to assess the accuracy and utility of the WSL Monoplotting Tool for georeferencing oblique photographs and measuring landscape change. We determined that the tool georeferenced objects to within less than 15 m of their real world 3D spatial location, and the displacement of the geographic center of over 121 control points was less than 3 m from the real world spatial location. Most of the error in individual object placement was due to the angle of viewing incidence with the ground (i.e., low angle/highly oblique angles resulted in greater horizontal error). Simple rules of control point selection are proposed to reduce georeferencing errors. We further demonstrate a method by which raster data can be rapidly extracted from an image pair to measure changes in vegetation cover over time. This new process permits the rapid evaluation of a large number of images to facilitate landscape scale analysis of oblique imagery.
•We assess the WSL Monoplotting Tool to georeference oblique angle terrestrial photographs.•Spatially accurate vector data can be extracted from oblique photographs.•We develop a new method to extract raster data from oblique images.•Vegetation change over 94 years is shown using historical paired photos.
A DEEP CHANDRA ACIS SURVEY OF M83 Long, Knox S; Kuntz, Kip D; Blair, William P ...
The Astrophysical journal. Supplement series,
06/2014, Letnik:
212, Številka:
2
Journal Article
Recenzirano
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We have obtained a series of deep X-ray images of the nearby galaxy M83 using Chandra, with a total exposure of 729 ks. Combining the new data with earlier archival observations totaling 61 ks, we ...find 378 point sources within the D sub(25) contour of the galaxy. We find 80 more sources, mostly background active galactic nuclei (AGNs), outside of the D sub(25) contour. Of the X-ray sources, 47 have been detected in a new radio survey of M83 obtained using the Australia Telescope Compact Array. Of the X-ray sources, at least 87 seem likely to be supernova remnants (SNRs), based on a combination of their properties in X-rays and at other wavelengths. We attempt to classify the point source population of M83 through a combination of spectral and temporal analysis. As part of this effort, we carry out an initial spectral analysis of the 29 brightest X-ray sources. The soft X-ray sources in the disk, many of which are SNRs, are associated with the spiral arms, while the harder X-ray sources, mostly X-ray binaries (XRBs), do not appear to be. After eliminating AGNs, foreground stars, and identified SNRs from the sample, we construct the cumulative luminosity function (CLF) of XRBs brighter than 8 x 10 super(35) erg s super(-1). Despite M83's relatively high star formation rate, the CLF indicates that most of the XRBs in the disk are low mass XRBs.
The Nature of SN 1961V Chu, You-Hua; Gruendl, Robert A; Stockdale, Christopher J ...
The Astronomical journal,
05/2004, Letnik:
127, Številka:
5
Journal Article
Summary
Homologous recombination in Trypanosoma brucei is used for moving variant surface glycoprotein (VSG) genes into expression sites during immune evasion by antigenic variation. A major route ...for such VSG switching is gene conversion reactions in which RAD51, a universally conserved recombinase, catalyses homology‐directed strand exchange. In any eukaryote, RAD51‐directed strand exchange in vivo is mediated by further factors, including RAD51‐related proteins termed Rad51 paralogues. These appear to be ubiquitously conserved, although their detailed roles in recombination remain unclear. In T. brucei, four putative RAD51 paralogue genes have been identified by sequence homology. Here we show that all four RAD51 paralogues act in DNA repair, recombination and RAD51 subnuclear dynamics, though not equivalently, while mutation of only one RAD51 paralogue gene significantly impedes VSG switching. We also show that the T. brucei RAD51 paralogues interact, and that the complexes they form may explain the distinct phenotypes of the mutants as well as observed expression interdependency. Finally, we document the Rad51 paralogues that are encoded by a wide range of protists, demonstrating that the Rad51 paralogue repertoire in T. brucei is unusually large among microbial eukaryotes and that one member of the protein family corresponds with a key, conserved eukaryotic Rad51 paralogue.
We report the discovery of a transiting exoplanet, KELT-11b, orbiting the bright (V = 8.0) subgiant HD 93396. A global analysis of the system shows that the host star is an evolved subgiant star with ...K, , , , and . The planet is a low-mass gas giant in a P = 4.736529 0.00006 day orbit, with MP = 0.195 0.018 , , g cm−3, surface gravity , and equilibrium temperature K. KELT-11 is the brightest known transiting exoplanet host in the southern hemisphere by more than a magnitude and is the sixth brightest transit host to date. The planet is one of the most inflated planets known, with an exceptionally large atmospheric scale height (2763 km), and an associated size of the expected atmospheric transmission signal of 5.6%. These attributes make the KELT-11 system a valuable target for follow-up and atmospheric characterization, and it promises to become one of the benchmark systems for the study of inflated exoplanets.
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