Engineering topics

Reynolds, S. P.

Publications and source records attributed to Reynolds, S. P..

5 records

NASA NTRS2015

Ti-44 Gamma-Ray Emission Lines from SN1987A Reveal an Asymmetric Explosion

In core-collapse supernovae, titanium-44 (Ti-44) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of Ti-44 produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

44Ti gamma-ray emission lines↗

NASA NTRS2014

Asymmetries in Core-Collapse Supernovae from Maps of Radioactiver 44Ti in Cassiopeia A

Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive 44Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surroundingmedium1, directly probes the explosion asymmetries. Cassiopeia A is a young2, nearby3, core-collapse4 remnant from which 44Ti emission has previously been detected5-8 but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed 44Ti emission to estimated 56Ni emission9, from optical light echoes10, and from jet-like features seen in the X-ray11 and optical12 ejecta. Here we report spatial maps and spectral properties of the 44Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the 44Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.

stellarcore-collapse explosions↗

NASA NTRS2003

Chandra Detection of a Pulsar Wind Nebula Associated With Supernova Remnant 3C 396

We present a 100 ks observation of the Galactic supernova remnant 3C396 (G39.2-0.3) with the Chandra X-Ray Observatory that we compare to a 20cm map of the remnant from the Very Large Array. In the Chandra images, a nonthermal nebula containing an embedded pointlike source is apparent near the center of the remnant which we interpret as a synchrotron pulsar wind nebula surrounding a yet undetected pulsar. From the 2-10 keV spectrum for the nebula (N(sub H) = 5.3 plus or minus 0.9 x 10(exp 22) per square centimeter, GAMMA =1.5 plus or minus 0.3) we derive an unabsorbed x-ray flux of S(sub z)=1.62 x 10(exp -12) erg per square centimeter per second, and from this we estimate the spin-down power of the neutron star to be E(sup dot) = 7.2 x 10(exp 36) ergs per second. The central nebula is morphologically complex, showing bent, extended structure. The radio and X-ray shells of the remnant correlate poorly on large scales, particularly on the eastern half of the remnant, which appears very faint in X-ray images. At both radio and X-ray wavelengths the western half of the remnant is substantially brighter than the east.

Olbert, C. M.↗

NASA NTRS2002

X-ray synchronization emitting Fe-rich ejecta in SNR RCW 86

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. In a previous study with ASCA data, we found that the middle-aged supernova remnant RCW 86 showed evidence for both processes, and predicted that observations with much higher spatial resolution would distinguish harder X-rays, which we proposed were primarily synchrotron emission, from softer, thermal X-rays. Here we describe Chandra observations which amply confirm our predictions.

ISM individual (RCW86) supernova remnants↗

NASA NTRS1984

On the X-ray emission from Crab-like supernova remnants

Crab-like supernova remnants are modeled as expanding, homogeneous, pulsar-fed bubbles of magnetic field and relativistic particles. Power-law behavior is assumed, with time of bubble radius and magnetic field, and the evolution of the particle spectrum is calculated. It is shown that, if a single power-law distribution of particles is injected into the bubble, this simple model is substantially too bright in X-rays, compared with several observed remnants; a more complex model is evidently required. It is argued that the most likely possibility is that X-ray and radio-producing particles in fact have different origins altogether, and some of the constraints on processes producing X-ray-emitting particles are discussed.

Reynolds, S. P.↗