First X-ray source in Cancer

The first X-ray source in Cancer may have been any of the early detections of X-rays emanating from the constellation Cancer. Each of the International Astronomical Union (IAU) modern constellations of the celestial sphere has at least one extrasolar astronomical X-ray source detected between June 12, 1962, Scorpius X-1, and April 6, 1980, Corona Australis X-1 (CrA X-1).
Cancer as a celestial X-ray source
Cancer is a relatively large constellation in area (number 31 of 88) of the celestial sphere, which suggests it may have upwards of ten early astronomical X-ray sources among the first 840 or so such sources.
From an average of many sounding rocket passes across Cancer, a figure for the diffuse X-ray background is given by,
: Diffuse X-ray intensity (2-5 keV) = 2.1 x 10 erg cm sec sterad .
Early catalogs
"A Catalogue of Discrete Celestial X-ray Sources" does not contain any X-ray source in Cancer discovered by sounding rocket or balloon.
No X-ray source within Cancer is cataloged as detected by the X-ray astronomy satellite Uhuru.
OSO 7 detected no X-ray source in Cancer.
No X-ray source in Cancer is cataloged as detected by Ariel 5.
None are listed in the HEAO 1 A-2 catalogs. And, no X-ray source in Cancer is listed in the HEAO 1 A-4 catalog.
Extrasolar X-ray source astrometry
A list of all astronomical X-ray sources within the constellation Cancer from the SIMBAD database includes 1H 0801+213, 1H 0823+301, 1H 0827+089, 1H 0833+153, 1H 0856+108, and 1H 0908+289. These are observed before January 10, 1979.
The SIMBAD list also contains H 0815+13 and H 0852+20, which are observed between October 1, 1977, and February 27, 1978, and are within Cancer. Its J2000 position is RA Dec . According to SIMBAD, this X-ray source has not been detected in any other portion of the electromagnetic spectrum. ROSAT detected at least eight X-ray sources within 1°.
===1H 0833+153===
1H 0833+153 may be Abell 689, which is ROSAT RX J0837.4+1458, 19' from 1H 0833+153, according to SIMBAD. The X-ray luminosity of Abell 689 is dominated by a BL Lac. The visible spectrum of this central galaxy shows only uncertain absorption features and a very blue continuum. The galaxy has an unusually blue, unresolved core, a 40-mJy Green Bank 4.85-GHz survey source coincident with the galaxy, a not significantly extended X-ray source, and a tentative radio flux at 1.4 GHz of 146 mJy.
A689 is one of the most luminous clusters known but as of 2008 has yet to be observed by Chandra or XMM. It is bright enough to be included in many cluster surveys, but is often excluded because of possible point source contamination by a BL Lac object.<ref name=Maughan/>
===1H 0856+108===
Although this X-ray source may be another visibly dark X-ray source, SIMBAD questions that this source may be IRAS 08599+1102. The J2000 position of 1H 0856+108 is RA Dec .
===1H 0908+289===
Likely to be another visibly dark X-ray source. The J2000 position is RA Dec . ROSAT has detected at least five X-ray sources within 1° of 1H 0908+289.
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.

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