The object we call now SN 1006 which 1st appeared on May 1, 1006 A.D was the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude. It was far brighter than Venus and visible during the daytime for weeks, exceeding roughly sixteen times the brightness of Venus. Appearing between April 30 and May 1, 1006 AD in the constellation of Lupus. This "Guest Star" was described by Astronomers in China, Japan, Europe, and the Arab world and they all documented this spectacular sight. Some observers reported it was clearly visible in the daytime even though it was blazing about 7,200 light-years away from earth.
SN 1006's associated supernova remnant from this event was not identified until 1965, when Doug Milne and Frank Gardner used the Parkes radio telescope to demonstrate a connection to known radio source PKS 1459-41. This is located near the star Beta Lupi, displaying a 30 arcmin circular shell. X-ray and optical emission from this remnant have also been detected, and during 2010 the H.E.S.S. gamma-ray observatory announced the detection of very-high-energy gamma-ray emission from the remnant. No associated neutron star or black hole has been found, which is the situation expected for the remnant of a Type Ia supernova (a class of explosion believed to completely disrupt its progenitor star). A survey in 2012 to find any surviving companions of the SN 1006 progenitor found no subgiant or giant companion stars, indicating that SN 1006 was most likely a double degenerate progenitor, that is, the merging of two white dwarf stars. In simple words, astronomers think SN 1006 was a type Ia Supernova triggered by two white dwarfs. As these stars orbited each other, they lost energy in the form of gravitational waves and eventually collided, creating an epic blast even brighter than usual. Understanding these supercharged supernova is vital for astronomers who use the blasts as cosmic measurement tools.
Remnant SNR G327.6+14.6 has an estimated distance of 2.2 kpc. from Earth, making the true linear diameter approximately 20 parsecs.
Ralph Neuhäuser, an astrophysicist at Friedrich Schiller University Jena in Germany, was studying works by the Persian scientist Ibn Sina, known to most in the West as Avicenna. The prolific scholar, who lived from 980 to 1037, traveled widely and wrote on subjects ranging from astronomy to medicine.
One section of his multipart opus Kitab al-Shifa, or “Book of Healing,” makes note of a transient celestial object that changed color and “threw out sparks” as it faded away. According to Neuhäuser and his colleagues, this object—long mistaken for a comet—is really a record of SN 1006, which Ibn Sina could have witnessed when he lived in southern Uzbekistan. According to the team’s translation, Ibn Sina saw the supernova start out as a faint greenish yellow, twinkle wildly at its peak brightness, then become a whitish color before it ultimately vanished.
Early Guest
In addition to Ibn Sina’s record, Neuhäuser recently found another piece of evidence for SN 1006 in works by a historian named al-Yamani, from Sanaa, Yemen. The text suggests observers there witnessed the guest star’s arrival even earlier than thought, which would also affect modern understanding of its evolution.
Most experts put the first sightings of SN 1006 at about April 28 or 30, depending on how they convert the lunar calendrical systems used by the ancient observers, as well as the imprecision of the observer's own dating. But Neuhäuser's work suggests a date of April 17, plus or minus two days.
The al-Yamani texts record the supernova rising about a half hour after sunset. Given the star’s position in the sky, there are only a few dates when that could happen, and they fall in the middle of April.
Also, the texts mark when the supernova rose in the sky relative to the moon, and that corresponds with dates between April 15 and 18, based on known positions of the moon at the time. According to Neuhäuser, records from China, Japan, and Switzerland can be interpreted in ways that back up the earlier date.
Notes
Brad Schaefer, a professor of physics and astronomy at Louisiana State University, has studied the timing of historical supernovae. He agrees that ancient observations can be useful for working out when this supernova reached peak brightness.
But he’s not convinced that the color data from Ibn Sina will be as helpful. One issue is that the supernova was close to the horizon for Ibn Sina, so that the colors he reported might be just atmospheric effects.
He also cautions that anyone trying to weave together various records of the event will have to account for variations in the relative brightness from observer to observer: "So for example, one person compared it to the brightness of Mars, another one to Venus, and another person to the brightness of the quarter moon,” he says.
For his part, Neuhäuser thinks that the earlier observation from Yemen may ultimately be the more useful find for filling in pieces of the supernova's history, which may in turn help refine today’s astrophysical models.
"I try to investigate old historical observations to use in state-of-the-art astrophysical questions," he says.
Effect on Earth
Research has suggested that Type Ia supernovae can irradiate the Earth with significant amounts of gamma-ray flux, compared with the typical flux from the Sun, up to distances on the order of 1 kiloparsec. The greatest risk is to the Earth's protective ozone layer, producing effects on life and climate. While SN 1006 did not appear to have such significant effects, a signal of its outburst can be found in nitrate deposits in Antarctic ice.
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