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Register a new userSupernova of 1006 (G327.6+14.6)
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Authors
Satoru Katsuda
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SN 1006 (G327.6+14.6) was the brightest supernova (SN) witnessed in human history. As of one thousand years later, it stands out as an ideal laboratory to study Type Ia SNe and shocks in supernova remnants (SNRs). The present state of knowledge about SN 1006 is reviewed in this article. No star consistent with a surviving companion expected in the traditional single-degenerate scenario has been found, which favors a double-degenerate scenario for the progenitor of SN 1006. Both unshocked and shocked SN ejecta have been probed through absorption lines in ultraviolet spectra of background sources and thermal X-ray emission, respectively. The absorption studies suggest that the amount of iron is < 0.16 M_sun, which is significantly less than the range for normal SNe Ia. On the other hand, analyses of X-ray data reveal the distribution of shocked ejecta to be highly asymmetric especially for iron. Therefore, most of iron might have escaped from the ultraviolet background sources. Another important aspect with SN 1006 is that it was the first SNR in which synchrotron X-ray emission was detected from shells of the remnant, providing evidence that electrons are accelerated up to ~100 TeV energies at forward shocks. The bilateral symmetry of the synchrotron emission (bright in northeastern and southwestern limbs) is likely due to a polar cap geometry. The broadband (radio, X-ray, and gamma-ray) spectral energy distribution suggests that the gamma-ray emission is predominantly leptonic. At the northwestern shock, evidence for extreme, but less than mass proportional, temperature non-equilibration has been found by optical, ultraviolet, and X-ray observations.
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The recently published Yemeni observing report about SN 1006 from al-Yamani clearly gives AD 1006 Apr $17 pm 2$ (mid-Rajab 396h) as first observation date. Since this is about 1.5 weeks earlier than the otherwise earliest reports (Apr 28 or 30) as discussed so far, we were motivated to investigate an early sighting in more depth. We searched for additional evidences from other areas like East Asia and Europe. We found that the date given by al-Yamani is fully consistent with other evidence, including: (a) SN 1006 rose several times half an hour after sunset (al-Yamani), which is correct for the location of Sana in Yemen for the time around Apr 17, but it would not be correct for late Apr or early May; (b) the date (3rd year, 3rd lunar month, 28th day wuzi, Ichidai Yoki) for an observation of a guest star in Japan is inconsistent (there is no day wuzi in that lunar month), but may be dated to Apr 16 by reading wuwu date rather than a wuzi date; (c) there is observational evidence that SN 1006 was observed in East Asia early or mid April; for the second half of April, a bad weather (early monsoon) period is not unlikely -- there is a lack of night reports; (d) the observer in St. Gallen reported to have seen SN 1006 for three months, which must have ended at the very latest on AD 1006 Jul 10, given his northern location, so that his observations probably started in April. We conclude that the correctly reported details give quite high confidence in the fully self-consistent report of al-Yamani, so that the early discovery date should be considered seriously.
We present two Arabic texts of historic observations of supernova SN 1006 from Yemen as reported by al-Yamani and Ibn al-Dayba (14th to 16th century AD). An English translation of the report by the latter was given before (Stephenson & Green 2002), but the original Arabic text was not yet published. In addition, we present for the first time the earlier report, also from Yemen, namely by al-Yamani in its original Arabic and with our English translation. It is quite obvious that the report by Ibn al-Dayba is based on the report by al-Yamani (or a common source), but the earlier report by al-Yamani is more detailed and in better (Arabic) language. We discuss in detail the dating of these observations. The most striking difference to other reports about SN 1006 is the apparent early discovery in Yemen in the evening of 15th of Rajab of the year 396h (i.e. AD 1006 Apr 17 pm 2 on the Julian calendar), as reported by both al-Yamani and Ibn al-Dayba. i.e. about 1.5 weeks earlier than the otherwise earliest known reports. We also briefly discuss other information from the Yemeni reports on brightness, light curve, duration of visibility, location, stationarity, and color.
We present the results from deep X-ray observations (~400 ks in total) of SN 1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg, Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components is in good agreement with that predicted by a standard model of Type Ia supernovae (SNe). The spatially resolved analysis reveals that the distribution of the O-burning and incomplete Si-burning products (Si, S, and Ar) is asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively uniform in the SNR interior. The peak position of the former is clearly shifted by 5 (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNRs geometric center. Using the SNR age of ~1000 yr, we constrain the velocity asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is also significantly higher in the southeast region than in the northwest region. Given that the non-uniformity is observed only among the heavier elements (Si through Fe), we argue that SN 1006 originates from an asymmetric explosion, as is expected from recent multi-dimensional simulations of Type Ia SNe, although we cannot eliminate the possibility that an inhomogeneous ambient medium induced the apparent non-uniformity. Possible evidence for the Cr K-shell line and line broadening in the Fe K-shell emission is also found.
We present here an Arabic report about supernova 1006 (SN 1006) written by the famous Persian scholar Ibn Sina (Lat. Avicenna, AD 980-1037), which was not discussed in astronomical literature before. The short observational report about a new star is part of Ibn Sinas book called al-Shifa, a work about philosophy including physics, astronomy, and meteorology. We present the Arabic text and our English translation. After a detailed discussion of the dating of the observation, we show that the text specifies that the transient celestial object was stationary and/or tail-less (a star among the stars), that it remained for close to three months getting fainter and fainter until it disappeared, that it threw out sparks, i.e. it was scintillating and very bright, and that the color changed with time. The information content is consistent with the other Arabic and non-Arabic reports about SN 1006. Hence, it is quite clear that Ibn Sina refers to SN 1006 in his report, given as an example for transient celestial objects in a discussion of Aristotles Meteorology. Given the wording and the description, e.g. for the color evolution, this report is independent from other reports known so far.
We present the deepest optical spectrum acquired to date of Balmer-dominated shocks in the NW rim of SN 1006. We detect the broad and narrow components of H-alpha, H-beta and H-gamma and report the first detection of the He I 6678 emission line in this supernova remnant. We may have detected, at the 1.5-sigma level, faint He II 4686 emission. We measure a full width half maximum of 2290 +/- 80 km/s in the broad component H-alpha line, with broad-to-narrow flux ratios of 0.84^+(0.03)_(-0.01) and 0.93^(+0.18)_(-0.16) in H-alpha and H-beta, respectively. To match these observations, our nonradiative shock models require a low degree of electron-proton equilibration at the shock front, T_e/T_p <= 0.07, and a shock speed of 2890 +/- 100 km/s. These results agree well with an earlier analysis of ultraviolet lines from SN 1006. The He I/H-alpha and He I/He II flux ratios also indicate low equilibration. Furthermore, our models match the observations for mostly ionized (~ 90%) preshock H and mostly neutral (>~ 70%) preshock He, respectively. We conclude that the high H ionization fraction cannot be explained by either photoionization from the reverse shock or relic ionization from EUV photons released in the 1006 A.D. supernova. The most plausible explanation appears to be photoionization from the Galactic Lyman continuum.
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