scholarly journals Modeling the Local Bubble

1997 ◽  
Vol 166 ◽  
pp. 121-131 ◽  
Author(s):  
Donald P. Cox
Keyword(s):  
Solar System ◽  
Facial Expressions ◽  
Simplified Model ◽  
Observational Constraints ◽  
Local Bubble ◽  
Interstellar Absorption ◽  
Modeling Effort ◽  
X Ray ◽  
Idealized Modeling ◽  
X Ray Background

AbstractModeling the Local Bubble is one of those activities fraught with danger. It is very easy to be too naive, to fail to consider the dependence of the model on assumptions about the nearby ambient state, or the likelihood of such a structure. It is similarly easy to become so caught up in the details of the vicinity that it is unclear where to begin a necessarily idealized modeling effort. And finally, it is important to remember that the data we have may in some cases be lying to us, and that we have not yet learned to read their facial expressions quite carefully enough.That said, I’ve tried in this paper to be helpful to those who may wish to take the risks. I surveyed the very most basic stories that the data seem to tell, and pointed out the standard coincidences that may be telling us a lot about what is happening, but may turn out once again to have been just coincidences. I’ve described 5 distinct conceptions that in one flavor or another pretty well survey the collection of mental images that have so far been carried by those who’ve attempted models. One may be right, or something entirely different may be more appropriate. It’s at least vital to realize that a conception comes first, followed by a simplified model of details. I’ve also included a long list of questions directed at observers. Some have partial answers, some one wouldn’t know today quite how to approach. But it is a list that students of the soft x-ray background, interstellar absorption lines, possible instrumentation, and the heliosphere may wish to review from time to time, just to see whether they can figure out how to be more helpful. There is another list for modelers, things the models must address, however-so-flimsily if necessary, because there are strong observational constraints (and stronger ones coming) on what can and cannot be present in the local ISM. To that I’ve added a few remarks concerning x-ray emission coming from beyond the Local Bubble, and another few on how x-ray emission from within the solar system might be contaminating what we see. That last bit is new, exciting, and possibly wrong, but it is an example of the ongoing wariness I believe one has to take toward the facts in the case. By the way, Dieter, it really was a great meeting.

scholarly journals The Evaporation of Nearby Clouds and the Soft X-ray Background

1997 ◽  
Vol 166 ◽  
pp. 169-172
Author(s):  
Jonathan D. Slavin
Keyword(s):  
Solar System ◽  
Thermal Conduction ◽  
Low Density ◽  
Local Bubble ◽  
X Ray ◽  
Hot Gas ◽  
Single Temperature ◽  
Temperature Equilibrium ◽  
X Ray Background ◽  
The One

AbstractIn recent years the nature of the low density clouds within the Local Bubble has been increasingly well characterized. These clouds, including the one which surrounds the solar system, are embedded in the hot gas and therefore should be evaporating via thermal conduction. If several evaporation fronts exist within the Local Bubble, the emissivity and spectrum of the hot gas is significantly different from a single temperature, equilibrium ionization plasma. We explore models in which the the temperature, density and ionization in the hot gas are influenced by cloud evaporation and compare the results with the observed Soft X-ray Background.

scholarly journals The Soft X-ray Background Spectrum from DXS

1997 ◽  
Vol 166 ◽  
pp. 83-90 ◽  
Author(s):  
W.T. Sanders ◽  
R.J. Edgar ◽  
D.A. Liedahl ◽  
J.P. Morgenthaler
Keyword(s):  
Galactic Plane ◽  
Emission Lines ◽  
Background Spectrum ◽  
Local Bubble ◽  
X Ray ◽  
Hot Plasma ◽  
Solar Abundances ◽  
Ionic Emission ◽  
X Ray Background ◽  
Ionization Balance

AbstractThe Diffuse X-ray Spectrometer (DXS) obtained spectra of the low energy X-ray (44 – 83 Å) diffuse background near the galactic plane from galactic longitudes 150° ≲ l ≲ 300° with ≲ 3 Å spectral resolution and ~ 15° angular resolution. Thus, DXS measured X-ray spectra that arise almost entirely from within the Local Bubble. The DXS spectra show emission lines and emission-line blends, indicating that the source of the X-ray emission is thermal – hot plasma in the Local Bubble. The measured spectra are not consistent with those predicted by standard coronal models, either with solar abundances or depleted abundances, over the temperature range 105 – 107 K. The measured spectra are also inconsistent with the predictions of various non-equilibrium models. A nearly acceptable fit to DXS spectra can be achieved using a hybrid model that combines the Raymond & Smith ionization balance calculation with recently calculated (by DAL) ionic emission lines.

scholarly journals The Influence of the Local Bubble on the Ionization of the Local Interstellar Cloud

1997 ◽  
Vol 166 ◽  
pp. 305-308
Author(s):  
Jonathan D. Slavin ◽  
Priscilla C. Frisch
Keyword(s):  
Interstellar Cloud ◽  
Diffuse Emission ◽  
Ionization State ◽  
Interstellar Gas ◽  
Local Bubble ◽  
X Ray ◽  
Hot Gas ◽  
Local Interstellar Cloud ◽  
Ionization Sources ◽  
X Ray Background

AbstractThe ionization of the the Local Interstellar Cloud (LIC) is quite unusual compared with most warm (T ~ 104 K) interstellar gas. Hydrogen and helium are both partially ionized with helium surprisingly more ionized than hydrogen. Directly observed ionization sources including nearby stellar EUV sources and the diffuse emission of the Soft X-ray Background (SXRB), do not provide enough ionization and heating to account for both the ionization state and temperature of the LIC. We propose that an evaporative boundary between the LIC and the hot gas of the Local Bubble can provide the necessary ionizing radiation. Results of detailed models of the emission from the interface are presented and shown to be adequate to explain the observations.

scholarly journals The Soft X-Ray Background

1973 ◽  
Vol 55 ◽  
pp. 215-234
Author(s):  
H. Friedman ◽  
G. Fritz ◽  
S. D. Shulman ◽  
R. C. Henry
Keyword(s):  
Background Radiation ◽  
Substantial Evidence ◽  
Interstellar Absorption ◽  
X Ray ◽  
Diffuse Background ◽  
X Ray Background

A survey of soft X-ray background observations in the 0.1–10 keV range is presented. In the region above 1 keV, recent results on point X-ray sources are discussed and their integrated contribution to the diffuse background is estimated. However, the average luminosity of various classes of extragalactic X-ray sources is still not sufficiently well known to permit this estimate to be made with any certainty. A discussion is given of recent observations at energies below 1 keV where the effects of interstellar absorption are important. It is argued that although some fraction of the background radiation in the 0.1–1 keV range must be galactic in origin, there is still substantial evidence for an extragalactic component. Proposed theories for generating both the galactic and extragalactic X-ray background are briefly reviewed.

scholarly journals Fluctuations in the Diffuse Soft X-ray Background; Probably of Galactic Halo Origin

1997 ◽  
Vol 166 ◽  
pp. 333-336
Author(s):  
T.J. Sumner ◽  
S.D. Sidher ◽  
J.J. Quenby ◽  
M. Hernandez ◽  
A. Mian ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Emission Measure ◽  
Local Bubble ◽  
Spherical Distribution ◽  
X Ray ◽  
Hot Gas ◽  
Galactic Emission ◽  
Global Trend ◽  
Background Data ◽  
X Ray Background

AbstractSoft X-ray background data from the ROSATPSPC have been fitted by a model including emission from the local bubble, embedded hot gas within the disk, hot gas in the Galactic halo and extra-galactic emission, together with local and disk absorption. In all directions a halo component at 106.2 K (0.2 keV) is required for an acceptable fit. The halo emission measure shows spatial variability and the global trend suggests a disk-like planar rather than more extended spherical distribution. New values for the emission measure within the local bubble are derived.

Crystal Forms of Semisynthetic Ergot Alkaloid Terguride

2002 ◽  
Vol 67 (4) ◽  
pp. 479-489 ◽  
Author(s):  
Michal Hušák ◽  
Bohumil Kratochvíl ◽  
Ivana Císařová ◽  
Ladislav Cvak ◽  
Alexandr Jegorov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Ergot Alkaloid ◽  
Simplified Model ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
X Ray Diffraction ◽  
Torsion Angles ◽  
Crystal Forms ◽  
X Ray ◽  
Independent Molecules

Two new structures of semisynthetic ergot alkaloid terguride created by unusual number of symmetry-independent molecules were determined by X-ray diffraction methods at 150 K. Form A (monoclinic, P212121, Z = 12) contains three symmetry-independent terguride molecules and two molecules of water in the asymmetric part of the unit cell. The form CA (monoclinic, P21, Z = 8) is an anhydrate remarkable by the presence of four symmetry-independent molecules in the crystal structure. Conformations of twelve symmetry-independent molecules that were found in four already described terguride structures are compared with torsion angles obtained by ab initio quantum-mechanical calculations for the simplified model of N-cyclohexyl-N'-diethylurea.

scholarly journals Can the Local Bubble explain the radio background?

2021 ◽  
Vol 502 (2) ◽  
pp. 2807-2814
Author(s):  
Martin G H Krause ◽  
Martin J Hardcastle
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Radio Emission ◽  
Magnetic Energy ◽  
Cosmic Ray ◽  
Observational Constraints ◽  
Local Bubble ◽  
Magnetic Energy Density ◽  
Magnetic Field Model ◽  
Radio Background

ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

scholarly journals The unified Seyfert scheme and the origin of the cosmic X-ray background

1994 ◽  
Vol 270 (1) ◽  
pp. L17-L21 ◽  
Author(s):  
P. Madau ◽  
G. Ghisellini ◽  
A. C. Fabian
Keyword(s):  
X Ray ◽  
X Ray Background
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