First X-ray source in Pictor

The first X-ray source in Pictor is unknown.
Pictor as a constellation
Pictor is a small and faint constellation in the southern sky. In equatorial coordinates, it extends from declination (Dec) −50° to −60°, and is located between the brilliant star Canopus and the Large Magellanic Cloud. It is number 59 in area of the celestial sphere and due to its small size may be likely to have about five astronomical X-ray sources of the first 840 or so discovered.
Astronomical X-ray source catalogs
As of December 1, 1969, none of the astronomical X-ray sources discovered by X-ray astronomy sounding rocket or balloon listed in "A Catalogue of Discrete Celestial X-ray Sources" is in Pictor. Nor was any X-ray source detected in the early seventies by the Vela series of satellites as a gamma-ray (or hard X-ray) burster.
2U 0544-39
During its first year of operation, the X-ray astronomy satellite Uhuru did not detect any X-ray source in Pictor, but it did detect 2U 0544-39 which is in the constellation Columba. However, in the third Uhuru catalog 3U 0510-44 has been reassigned to 2U 0544-39 (~9° apart) with a location in equatorial coordinates for the year 1950 (J1950) of maximum probability for 3U 0510-44 at right ascension declination . The area of its error box is 18.000 sq. degrees for an intensity of 2.0±0.5 counts/s.
Observations by Ariel 5 provided detections at 2A 0456-449 with 0.7±0.1 counts/s (~3.5° from 3U 0510-446).
Observations by OSO 7 at 1M 0513-401 recorded a count rate of 0.50±0.04 counts/s for the source: globular cluster NGC 1851, an X-ray burst source. Later, with Ariel 5, 3A 0512-401 was detected.
Using HEAO 1 A-1, 1H 0512-401 (NGC 1951) was detected. Pictor A is located at J1950 RA Dec .
The likely J2000 location for 3U 0510-44 is RA Dec . According to SIMBAD, the closest X-ray source is EXOSAT source EXSS 0509.5-4457. All of the nine X-ray sources within 1° of 3U 0510-44 are visibly dark X-ray sources.
Astronomical X-ray source
Pictor A is a Seyfert 1 galaxy that may have a black hole at its center which has emitted magnetized gas at extremely high speed. The bright spot at the right in the image is the head of the jet. As it plows into the tenuous gas of intergalactic space, it emits X-rays. Pictor A is X-ray source designated H 0517-456 and 3U 0510-44 (~2.4° apart), or, 1H 0507-459 and 3U 0510-44 at ~2° part. According to SIMBAD, none of the early X-ray sources observed by Uhuru, OSO 7, Ariel 5, or HEAO 1 in the vicinity of 3U 0510-44 is assigned to Pictor A.
In the image to the right are some sixty-five astronomical X-ray sources in the epoch J2000 error box for 3U 0510-44. The only dark nebula within the error box is denoted as 'HVCld' (a high-velocity cloud), not an X-ray source. Pictor A is just outside the error box near the Seyfert 1 galaxy at 05:16 and -46:00. The couple of blue ovals near the error box center is galaxy cluster ACO 3322 (Abell 3322).
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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