According to IAUC No. 6778, Y. Sano (Hokkaido, Japan) discovered a possible supernova in UGC 4107.
07h 57m 02s.82 (J2000.0)
+49o 33' 40".2
(10" E, 20" S of the center of UGC 4107)
1997 Nov. 25.582 16.7 (Sano)
26.81 16.1 (Kushida)
IAUC also tells that the spectrum taken by P. Garnavich et al. shows unusual, only broad features. For a detail, see the corresponding IAUC issue. Follow-up observations are encourged.
Regards,
Taichi Kato
SN1997ef (in UGC 4107)
(Re: vsnet-alert 1358)
According to IAUC 6783, Sano's object in UGC 4107 has been confirmed to be a supernova showing a peculiar spectrum. For a detail, see the corresponding IAUC issue. The observations by the BAO team indicate that the supernova is still rising. Follow-up observations are encouraged.
Regards,
Taichi Kato
(Hypernova article by H. Yamaoka, published in "2002 Special Bulletin of M 1 Group", see also introduction in SN 2002ap list)
Hypernovae: more energetic explosion than normal SNe
H. Yamaoka (Kyushu University, Japan)
The search for the supernovae (SNe) has always a possibility of the discovery of a object in the other category. It would be a comet (like C/1998 Y2 (Li) and C/1999 E1 (Li) by the Lick Observatory SN Search), or a Galactic cataclysmic variable (like KL Draconis, which was originally announced as SN 1998di). Hypernovae, however, are not in the other category but of the subclass of supernovae, which are the whole destruction of stars at their end of the life.
The most impressive example of hypernovae is SN 1998bw. It was discovered by the ESO team, who were seeking the optical counterpart of the gamma-ray burst occured on Apr. 25, 1998. The spectrum of this object has some broad lines, which suggested that it is expanding with a high velocity, or, in the other word, exploding. The expansion velocity of this object reached 30000 km/s, i.e., 10 % of the speed of light.
It does not resemble, however, to that of any known class of supernovae. The hydrogen lines are absent, thus it would be classified as type I. But no silicon line (typical for SN Ia) nor helium line (strong in SN Ib) are observed. Such supernovae are classified as SN Ic, but SN 1998bw did not resemble to the typical SNe Ic, such as SN 1994I in Messier 51. Then, this "supernova" is now classified as "peculiar type Ic". The expanding velocity and the light curve suggests that the explosion was occured sometime during Apr. 21-27, which supports the association of this SN with the gamma-ray burst.
The other striking characteristics of SN 1998bw was its luminosity; it was more luminous than typical SNe Ia which are thought to be most luminous class among SNe. The energy source of SNe after explosion is a decay of the radioactive nuclei (mostly Nickel 56) produced during the explosion, so the amount of such matters would be larger in this object than the normal SNe. The light curve shows a slow evolution, which suggests that the large amount of material is ejected.
On these basis, a "hypernova" model is constructed (Iwamoto et al., 1998, Nature). Very massive star (having 40 solar mass or more at birth) evolved losing its hydrogen-rich envelope and helium layer, then finally the gravitational core collapse occured. If the energy supplied by the collapse is 30 times larger than the typical core-collapse SNe, the amount of the produced radioactive nuclei are 10 times larger than a typical core collapser, or slightly larger than in a typical SN Ia. It also explains the higher expansion velocity. The central remnant would be a blackhole, which may ejected the "gamma-ray burst" during the collapse.
Such hypernovae were searched from the previously discovered SNe. Then, from the resemblance of the spectrum and the light curve, it is now considered that SN 1997ef is also a hypernova though the coincident gamma-ray burst was not detected. This SN was discovered by Japanese amateur Yasuo Sano. You may be the next discoverer of hypernova! I hope your SN search and observation will reveal the new aspect of SN science.
B, V and I-band images taken at Ouda Station
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