Soft diffuse X-rays in the southern galactic hemisphere

Sanders, W. T.; Kraushaar, W. L.; Nousek, J. A.; Fried, P. M.

doi:10.1086/182545

Cited by 107 publications

(59 citation statements)

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“…The LHB surrounds the Sun with an extent of ∼ 100 pc (Tanaka & Bleeker 1977;Sanders et al 1977;Snowden et al 1990) and a spatially constant temperature of kT = 0.10±0.01 keV (Liu et al , 2016, in prep. ).…”

Section: Local Hot Bubblementioning

confidence: 99%

Discovery of Galactic O iv and O v X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum

Nevalainen

Wakker

Kaastra

et al. 2017

A&A

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FUV observations have revealed the transition temperature gas (TTG; log T (K) ∼5), located in the lower Galactic halo and in the High Velocity Clouds. However, the corresponding X-ray absorption has so far remained mostly undetected. In order to make an improvement in this respect in Galactic X-ray absorption studies, we accumulated very deep (∼ 3 Ms) spectra of the blazar PKS 2155-304 obtained with the spectrometers RGS1, RGS2, LETG/HRC and LETG/ACIS-S and studied the absorption lines due to the intervening Galactic components. The very high quality of the data and the coverage of important wavelengths with at least two independent instruments allowed us to reliably detect ten Galactic lines with better than 99.95% confidence. We discovered significant absorption from blended O iv transitions 1s-2p 2 S (22.571 Å), 1s-2p 2 P (22.741 Å) and 1s-2p 2 D (22.777 Å), and from the O v transition 1s-2p (22.370 Å) from TTG at log T (K) = 5.2 ± 0.1. A joint X-ray and FUV analysis indicated that photoionisation is negligible for this component and that the gas is in a cooling transition phase. However, the temperature is high enough that the column density ratio N(O iv)/N(O v) is not significantly different from that in collisional ionisation equilibrium (CIE). Under CIE we obtained N OIV = 3.6±2.0 × 10 15 cm −2 , corresponding to N H = 1.0±0.5 × 10 19 Z Z TTG cm −2 .

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Section: Local Hot Bubblementioning

confidence: 99%

Discovery of Galactic O iv and O v X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum

Nevalainen

Wakker

Kaastra

et al. 2017

A&A

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“…In the absorption model the ubiquitous soft X-ray background emission was thought to originate outside the Galaxy and to be partially absorbed by Galactic material, although the absorption cross sections could not produce the observed dynamic ranges (McCammon et al 1976) or band ratios (Bloch et al 1986;Juda and Bloch 1991). In the widely accepted displacement model of the Local Hot Bubble (Sanders et al 1977;Cox and Reynolds 1987), the observed soft X-ray background brightness was thought to be proportional to the path length through the hot Local Bubble gas, which is roughly anticorrelated with the total hydrogen gas column density. Although neither model could fully explain all of the observations of the soft X-ray background, the displacement model was stronger.…”

Section: Introductionmentioning

confidence: 99%

The trouble with the Local Bubble

Welsh

Shelton

2009

Astrophys Space Sci

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The model of a Local Hot Bubble has been widely accepted as providing a framework that can explain the ubiquitous presence of the soft X-ray background diffuse emission. We summarize the current knowledge on this local interstellar region, paying particular reference to observations that sample emission from the presumed local million degree K hot plasma. However, we have listed numerous observations that are seemingly in conflict with the concept of a hot Local Bubble. In particular, the discovery of solar wind charge exchange that can generate an appreciable soft X-ray background signal within the heliosphere, has led to a reassessment of the generally accepted model that requires a hot local plasma.In order to explain the majority of observations of the local plasma, we forward two new speculative models that describe the physical state of the local interstellar gas. One possible scenario is similar to the present widely accepted model of the Local Hot Bubble, except that it accounts for only 50% of the soft X-ray emission currently detected in the galactic plane, has a lower thermal pressure than previously thought, and its hot plasma is not as hot as previously believed. Although such a model can solve several difficulties with the traditional hot Local Bubble model, a heating mechanism for the dimmer and cooler gas remains to be found. The second possible explanation is that of the 'Hot Top' model, in which the Local Cavity is an old su-B.Y. Welsh ( ) Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720, USA e-mail: bwelsh@ssl.berkeley.edu R.L. Shelton Department of Physics and Astronomy, University of Georgia, Athens, GA 30602, USA pernova remnant in which no (or very little) million degree local plasma is presently required. Instead, the cavity is now thought to be filled with partially ionized cloudlets of temperature ∼ 7000 K that are surrounded by lower density envelopes of photo-ionized gas of temperature ∼ 20,000 K. Although this new scenario provides a natural explanation for many of the observations that were in conflict with the Local Hot Bubble model, we cannot (as yet) provide a satisfactory explanation or the emission levels observed in the B and Be ultra-soft X-ray bands.

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“…The intensity of the LHB emission can be used to estimate its radial extent from the Sun, which varies between 40 pc and 130 pc. Since the intensities are generally greater at higher Galactic latitudes, they are strongly anticorrelated with total HI column density, presumably due to displacement effects as discussed in Sanders et al (1977), McCammon k Sanders (1990), and SCMS. The LHB extends further toward the Galactic poles than in the plane, although the regions of greatest extent are not at the poles themselves.…”

Section: Resultsmentioning

confidence: 89%

“…By the end of the 1980s, the displacement model (e.g., Sanders et al 1977;Snowden et al 1990, hereafter SCMS) proved to be the most consistent with the available data. The displacement model suggests t h a t the irregularly shaped cavity which surrounds the Sun (known independently from interstellar absorption line studies: e.g., Frisch & York 1983, and NH studies: e.g., Knapp 1975) contains an X-ray-emitting plasma, and t h a t the cavity is extended more toward the Galactic poles than within the Galactic plane.…”

Section: Introductionmentioning

confidence: 73%

A New View of the LHB and ¼ keV X-ray Halo

Snowden

1997

International Astronomical Union Colloquium

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A b s t r a c t . The X-ray sky at \ keV is completely dominated by diffuse emission. It has become clear that it originates as at least three separate components: local emission within the nearest ~ 100 pc from the Sun, halo emission from beyond most of the neutral material of the Galactic disk, and the superposition of unresolved extragalactic sources. The only way to determine the temperatures and relative emission measures of the hot plasma responsible for the Galactic components is to use the X-ray intensity variations due to column density variations in the intervening Hi to separate the components. "Shadowing" studies have been pursued for individual objects using ROSAT data, from both pointed observations and the all-sky survey with considerable success.This paper presents the results of an all-sky analysis of the | keV background from the ROSAT survey. A Local Hot Bubble is found consistent with, although somewhat smaller than, previous models. It has a temperature of 10 6 ' 1 K and an emission measure which varies by a factor of ~ 3.3 over large angles. The halo emission has a temperature near 10 6 0 K with an emission measure which varies from near zero to more than five times that of the local emission.

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Soft diffuse X-rays in the southern galactic hemisphere

Cited by 107 publications

References 0 publications

Discovery of Galactic O iv and O v X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum

Discovery of Galactic O iv and O v X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum

The trouble with the Local Bubble

A New View of the LHB and ¼ keV X-ray Halo

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