Re: Swift Data rules out beamed theory


"sean" <jaymoseley@xxxxxxxxxxx> writes:

George Dishman wrote:
sean wrote:
...
George dishman wrote in an earlier article...


Take care Sean, I'm not saying the spectra
are definitive or unambiguous, I haven't seen
many and I can't remember the papers I saw to
check whether they were SWIFT grism spectra or
ground based folllow-ups. What I am saying is
that Lyman break data are pefectly valid as a
rough indicator which when combined with ground
data, which is also valid, has allowed the
redshift of many GRBs to be deterined. It may
be less than half as you say, but even that
contains many which are definitely at high
redshift so I think that rules out your local
source idea.

George

If I can respond with some of the latest data from
GRB research. Here are 2 recent gcn posts.
The first claims to supply Lyman break evidence in
optical spectra.

No it doesn't. What it says is quite clear:

"We observed the optical transient of GRB 060512
... under POOR OBSERVING CONDITIONS ...

We report a break in the continuum around 4800A
and bluewards which, IF IDENTIFIED as the onset
of the Lyman-alpha forest, indicates a redshift in the
range z ~ 2.7-2.9. The signal-to-noise is TOO LOW to
allow identification of further lines."

(My emphasis)
Im aware of the seeing conditions in that gcn. After all I posted it
here.
But let me put it this way. If they didnt think that their observation
indicated z ~ 2.7-2.9 then why did they post that in their gcn?

As it turns out, it was a data reduction error, as you can read about
in Starling et al. (GCN #5149):

"In both the TNG and the VLT spectra we see no break in the continuum
emission and no obvious features in either absorption or emission."

There is some more discussion about the possible solutions in that GCN.

However, even if there wasn't a data reduction error, there will
occasionally be cases of low significance features where the
interpretation is not clear. That of course does *not* invalidate
other cases with highly significant redshift indicators.


No Matter what spin you try to put on this the plain fact of it is that

they observed a spectra and felt there was strong enough indication
to merit a gcn posting saying there is a Lyman break at 4800A. If there

was no evidence of a break Im sure they would not have mentioned it.
And that contradicts the other gcn redshift. Thats called ambiguity,

No. See above. As George quite correctly points out, the authors
originally said, "*IF*" the break-like feature could be identified as
the onset of the Ly-alpha forest, then z ~ 2.7-2.9. Please, clear
your head of conspiratorial "spin" theories for just a second and look
at the conditional, "IF." GCN's are for rapid dissemination of new
results, so speculation like that is allowed, and in fact welcomed.
Since afterglows fade quickly, it's better to know about something
interesting (but perhaps wrong) now, than it is to wait three months
for the correct result.

Please, come back when you have a real contradiction.

CM
.

Relevant Pages

  • Re: Swift Data rules out beamed theory
    ... redshift of many GRBs to be deterined. ... Here are 2 recent gcn posts. ... optical spectra. ... As it turns out, it was a data reduction error, as you can read about ...
    (sci.astro)
  • Re: Swift Data rules out beamed theory
    ... redshift of many GRBs to be deterined. ... optical spectra. ... Im aware of the seeing conditions in that gcn. ... spectra only of a suspected host galaxy is studied. ...
    (sci.astro)