X-rays from Eridanus

"What are the sources of X-rays from Eridanus?" The X-ray astronomy of the constellation Eridanus focuses on answering this question. The Earth is irradiated by X-rays from all of the constellations. The Earth's atmosphere is opaque to X-rays so that none reach the surface. X-radiation, in the form of X-rays, span 3 decades in wavelength ~(8 nm - 8 pm), frequency ~(50 PHz - 50 EHz) and energy ~(0.12 - 120 keV). In terms of temperature, 1 eV = 11,604 K. X-rays (0.12 to 120 keV) correspond to 1.39 x 10 (1.39 MK) to 1.39 x 10 K (1.39 GK). X-ray generation occurs by many processes.
Eridanus as a constellation
Eridanus is one of the 88 modern constellations, and it is the sixth largest in terms of area of the sky. Although the center of Eridanus is in equatorial coordinates at right ascension (RA) and declination (Dec) , it actually stretches from close to the galactic plane to its brightest visual star Achernar. The nebula known as the Milky Way does not pass through Eridanus, but the celestial equator does. Like the Sun the visual star Achernar is in the Milky Way.
The astronomy of Eridanus is a branch of science that deals with or focuses on celestial objects that occur within or at the borders of Eridanus, their magnitudes, motions, the materials that compose them, and their general exterior and interior constitution, in relation to space and the physical universe as a whole.
As a source of X-radiation, if these sources are uniformly distributed, Eridanus should contain about 2.76 %. For example, of the 842 astronomical X-ray sources detected by the X-ray observatory satellite HEAO 1 experiment A1, at least 23 should be in Eridanus. The HEAO 1 A1 catalog has 30 X-ray sources within Eridanus.
The first X-ray source discovered in the constellation appears to have been detected very near the end of the observing period for the two early Aerobee-Hi rocket flights on September 20, 1962, and March 15, 1963. The source is apparently a visibly dark X-ray source.
The fourth catalog of sources from X-ray astronomy satellite Uhuru includes four sources that may not have been detected by HEAO 1 A1. Each of these is at least a visibly dark X-ray source.
Of the thirty HEAO 1 A1 X-ray sources, according to SIMBAD, twenty are at least visibly dark X-ray sources, eight are galaxies or galaxy clusters, one is a quasar, and the remaining object is EF Eridani.
Listed in SIMBAD are about 7000 astronomical X-ray sources within Eridanus.
Visibly dark X-ray source
Of the first X-ray sources discovered in each constellation (126 for 89 areas), some 63% are visibly dark. These X-ray sources can be radiative cosmic dust, hydrogen gas such as an H II region (e.g. the Orion Nebula), an H I region of hydrogen, a molecular cloud, or a coronal cloud. Many of the visibly dark X-ray sources are also X-ray transients.
==Eridanus "hot spot"==
Of the 24 visibly dark X-ray sources detected by Uhuru and HEAO 1 A1, ten are located within or on the border of the Eridanus "hot spot".
The southern galactic hemisphere is dominated by the X-ray bright localized region or "hot spot" in Eridanus centered on RA Dec with an angular size of 15°. There is a weak 2-6 keV X-ray source (3U 0431-10) 2° away from the center of the "hot spot".
EF Eridani
EF Eridani is a variable star of the AM Herculis star type (polars) or magnetic cataclysmic variable stars. It is X-ray source 2A 0311-227.
Epsilon Eridani
"Stars nearest the Sun play an especially important role in understanding the physical phenomena in stellar outer atmospheres, since their proximity permits detection of even low levels of activity."
X-ray emission by ε Eridani
"X-ray emission from ε Eri was first reported by Johnson (1981)." ε Eri is a strong X-ray star. Spectral profiles of Zeeman broadening yield a magnetic field of 2390±424 G with a filling factor of 0.49±0.17. The abundance variations between the photosphere, chromosphere and corona, can be interpreted in terms of the evolution of emerging magnetic fields rather than the topology of these magnetic fields: newly emerging features exhibit photospheric compositions (small compact structures with tightly closed field lines) that gradually evolve to become more open structures with a relative enrichment of low first ionization potential (FIP) elements, such as is found in ε Eri.
Magnetic activity of ε Eridani
Epsilon Eridani has a higher level of magnetic activity than the Sun, with a stellar wind 30 times as strong.
Chromosphere of ε Eridani
The chromosphere of Epsilon Eridani is more magnetically active than the Sun's.
Photosphere of ε Eridani
Approximately 9% of the deep photosphere is found to have a magnetic field with a strength about 0.14 teslas.
ε Eridani as a BY Draconis variable
Its rotation period is a relatively rapid 11.1 d, although this varies by latitude. The mean rotation as compared with the Sun is shorter at 11.68 d. Stars that vary in magnitude because of magnetic activity coupled with rotation are classified as BY Draconis variables. Observations have shown this star to vary as much as 0.050 in magnitude due to starspots and other short-term magnetic activity.
Corona of ε Eridani
Relative to the Sun, the outer atmosphere of Epsilon Eridani appears both larger and hotter. As a result of a systematic study of every known dwarf type K or M star within 6 pc of the Sun, it is believed that all late-type K and M dwarf stars are probably surrounded by hot X-ray-emitting coronae. The existence of a stellar corona seems to be essentially independent of the detailed characteristics of the underlying star.
The coronal temperatures of ε Eri fit two-components of log T<sub>1</sub> 5.95 ± 0.4 (891,251 K) and log T<sub>2</sub> 6.95 ± 0.2 (8,912,509 K). A coronal filling factor of less than one is consistent with the additional presence of active regions. The X-ray emissions from this star's corona indicate an age of less than a billion (10 ) years, compared to 4.6 billion for the Sun, so it is still relatively young for a star of its mass. Starspot activity has also been detected, which varies from year to year.
DY Eridani
Alternate names: 40 Eridani C, Bayer designation (ο Eri C), Flamsteed designation (40 Eri C, Variable star designation (DY Eri), Aitken Double Star Catalogue (ADS 3093 C), Durchmusterung (BD-07°781 B), BD-07°781 C, Catalogue of Components of Double and Multiple Stars (CCDM J04153-0739 C), General Catalogue of Trigonometric Parallaxes (GCTP 945), Gliese Catalogue of Nearby Stars (Gliese 166 C), Luyten Half-Second catalogue (LHS 25), Luyten Two-Tenths catalogue (LTT 1909 is at RA Dec .
1ES 0507-040 is located near β Eridani at RA ~ and Dec . There is no star in the list of stars in Eridanus that is at 1ES 0507-040. Although there is a K3 star at J1950 RA 05 02 45.37 Dec −04° 12′ 36.5″. 1ES 0507-040 is a blazar, designated QSO B0506-039. The earliest catalog entry appears to be 4U 0506-03, which puts the discovery of the X-ray source before January 12, 1974. In the 4th Uhuru catalog QSO B0506-039 has no previous designation, although it may not be the first X-ray source in Eridanus.
GRB 080913
GRB 080913 at RA Dec was a gamma-ray burst (GRB) observed on September 13, 2008. At 12.8 Gly and redshift of 6.7, the burst was the most distant GRB observed to date. This stellar explosion occurred around 825 million years after the Big Bang.
Eridanus Supervoid
Eridanus may also be the location of a CMB cold spot. In the first year of data recorded by the Wilkinson Microwave Anisotropy Probe (WMAP) a region of sky in the constellation Eridanus was found to be cooler than the surrounding area. Although more recent work has called into question the statistical significance of this cold spot.

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