[vsnet-chat 311] Re: Early SN detection via neutrinos

[Alec Habig <habig@budoe.bu.edu>]

Fraser Farrell writes :
> 
> How accurate (and precise) a position would be provided by this
> system?  Would an Alarm Report read "possible SN in Centaurus" or
> "possible SN at RA 13h19m11s +/-5s  Dec -55d20'09" +/-02"  ?

From comparisons of timing between the neutrino arrival directions at
the various experiments, some position can be given.  However, with only
two experiments, that information will be poor.  Geometrically, two
timing points gives you a ring on the sky, whose width depends upon the
angle between the SN position and the two experiments.  That line could
be 10 degrees or so at best.

Once more experiments come on line, that produces the intersection of
two such cones, so we'd be able to say "SN between RA 13h19m and 13h45m,
Dec. between -55d and -50d".

Also, neutrino experiments are only sensitive to galactic (and LMC/SMC)
SNae.  That further narrows the search, in a painfully loose sort of
way.

If the large water cerenkov experiments (SuperK and SNO) can be talked
into providing the pointing information available from the measurement
of the nu->e scattering interactions, then we'd also have a couple of
cones on the sky of radius 10 degrees or so to add to the timing
information.  

> Would the system give any indication of expected visual magnitude?  Even
> an approximate guess would help; for example, a 50000-neutrino pulse
> should be a brilliant SN, but a 50-neutrino pulse would warn us to get
> the binoculars and starcharts out...

It will be in our galaxy, so star charts shouldn't be too faint.  
However, if the SN lies on the other side of a big cloud of dust, then
optical observers are simply out of luck.  Let's hope that mother nature
is kind.

We hope to include some estimate of the relative intensity of the
neutrino signal, however.  It will be a subjective scale, though, since
it's not the coincidence network's job to analyze the data from the
various experiments at the event level.  After any initial alert from
the coincidence network, the individual experiments should chime in with
more carefully analyzed reports which should help out.

> How many hours/days between the neutrino pulse and the visual outburst?
> Or is this piece of information one of the things you hope to discover
> from this project?

This varies widely with the progenitor star (and whose models you
believe).  SN1987A had a delay of about 1h40m (although this was modeled
after the fact, instead of being directly measured).  Some models of
other compact blue giant stars produce shock breakout times of as low as
35m.  Red Supergiants, though, are so extended that it'll be hours
before anything gets to the surface.  If Betelgeuse goes, we've got some
time to prepare for the show :)

Reconstruction of this time for SN1987A depended heavily upon chance
observations (both positive and negative) by an amateur astronomer
named Jones (apologies, I'm forgetting your first name right now!).  

If the world has warning and is out looking, we'll get a lot of
observations at early times, and be able to well determine the breakout
time.  This gives us a very good handle on what the progenitor was like.

> You should post any Alarm Report into vsnet-alert and the International
> Supernova Network (isn@mbox.queen.it).  A lot of astronomers and
> institutions subscribe to these two mailers.  On numerous occasions,
> these have spread some vital news worldwide before any official messages
> from CBAT.

Will do!

-- 
       Alec Habig, Boston University Particle Astrophysics Group
			   habig@budoe.bu.edu
		       http://hep.bu.edu/~habig/

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