Appearance of supernova burst

[chornedsnorkack]

How exactly does a supernova burst look like?

I gather that in 1987, no one noticed until some half a day
afterwards. They found a pair of old photos with one hour interval,
one before and one after burst. They did not have spectra.

But what is the light curve and spectrum of a supernova like if you
happen to stare at it right when it explodes? The first minutes, first
seconds, first parts of second?

Especially funny would be the burst of a supernova of a first kind.
For a presupernova of the first kind is a white dwarf with radius of
just a few thousands km. This means that at some moment it would begin
collapsing with speeds of around 10 000 km/s. Th initial developments
of magnitude and spectrum would occur over the timescale of tenths of
second after it exceeds the Chandrasekhar limit. And then, the collapse
would be stopped over a few kilometres at a speed of around 100 000
km/s. This means that the luminosity would increase by orders of
magnitude over tens of microseconds!

I have heard that while the Crab exploded in 1054 to magnitude -4 or
-6 and is of second kind, there is supposed to have been another
supernova slightly earlier, like 1004 or something, with
magnitude of -10 and supposedly of first kind.

How would it look? Given that the whole starlit sky has magnitude of
-5 while full moon is -12,7, the supernova would be 100 times brighter
than the rest of stars and just 10 times dimmer than the Moon. Would
the supernova have instantly cast shadows of the landscape provided it
burst at night without moonlight? And would it have produced an
instant difference in a heavily overcast night?

[StupendousMan]

How exactly does a supernova burst look like?


But what is the light curve and spectrum of a supernova like if you
happen to stare at it right when it explodes? The first minutes, first
seconds, first parts of second?



Well, that's hard to say exactly, since there are few observations
of supernovae within hours of the shock breakout. However, there
have been several events in recent years which have been caught
at very early times. For example, GRB 060218 was observed in
X-rays, the near UV, and the visible by the SWIFT spacecraft.
See the paper by Waxman et al.,

http://arxiv.org/abs/astro-ph/0702450

for measurements of the flux from this object starting within several
minutes of the shock breakout.



Especially funny would be the burst of a supernova of a first kind.
For a presupernova of the first kind is a white dwarf with radius of
just a few thousands km. This means that at some moment it would begin
collapsing with speeds of around 10 000 km/s. ....


Type Ia SNe involve thermonuclear reactions in a white dwarf,
not the collapse of a white dwarf.



I have heard that while the Crab exploded in 1054 to magnitude -4 or
-6 and is of second kind, there is supposed to have been another
supernova slightly earlier, like 1004 or something, with
magnitude of -10 and supposedly of first kind.


SN 1006 in Lupus was very bright, and recent X-ray and radio
measurements do imply that it was a Type Ia.



How would it look? Given that the whole starlit sky has magnitude of
-5 while full moon is -12,7, the supernova would be 100 times brighter
than the rest of stars and just 10 times dimmer than the Moon. Would
the supernova have instantly cast shadows of the landscape provided it
burst at night without moonlight? And would it have produced an
instant difference in a heavily overcast night?

Winkler et al.

http://arxiv.org/abs/astro-ph/0208415

suggest that the peak apparent magnitude might have
been around -7.5. Their paper includes a translation of an
account of the supernova's appearance, written by an Arab
astronomer. Perhaps you should read that.

[grant hutchison]

Venus at maximum magnitude (about -4.7) marks an approximate threshold for casting detectable shadows. You can see Venus shadows only if you look carefully at a bright surface in the absence of other light sources. I've seen them only once, cast on snow in the Cairngorm Mountains.
Brighter sources will cast shadows that are more readily detectible.

Grant Hutchison

[chornedsnorkack]

Venus at maximum magnitude (about -4.7) marks an approximate threshold for casting detectable shadows. You can see Venus shadows only if you look carefully at a bright surface in the absence of other light sources. I've seen them only once, cast on snow in the Cairngorm Mountains.
Brighter sources will cast shadows that are more readily detectible.


Which means that the supernovae of Lupus and Taurus should have been bright enough to cast shadows.

As for a supernova of the second kind... Large Magellanic Cloud is about 160 000 lightyears away. Sanduleak 69 202 was magnitude +12,2 before burst, it was seen at magnitude +5,1 at the first night, and reached +2,9 in about three months.

Imagine a similar supernova at about 6500 lightyears. It would be 7 magnitudes brighter, so +5,2 before burst, -4,1 at maximum, -1,9 in a few hours. And +5,2 means a naked eye star - though an inconspicuous one.

Was the Crab supernova a naked eye star before it burst?

[chornedsnorkack]

The question continues to attract attention, maybe someone could merge a recently posted thread here.

[Jens]

I think the intent of the OP was, if I just happened to be looking at a patch of dark sky and a supernova exploded, would I see it go to its brightest in a matter of seconds, or would it take hours or days for it to get to its brightest? My initial thought was that it would take some time, but reading around I've found some references that it might only be a question of minutes.