Gamma Ray Burst Heterogeneity

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Richard S Sternberg - 27 Sep 2007 11:42 GMT

[[Mod. note -- I apologise for the delay in this posting's appearance.
Richard S. Sternberg <richard@NOSPAMrssternberg.org> E-mailed it to me
on 18.Sept.2007, but I was travelling and had with limited internet
access at the time. -- jt]]

I've watched YA (yet another) History Channel popularizer program,
and the scientists here know that always brings me back to an
exploration of the hypothesis I've asked about before. I have YA
technical question to ask the group.

The television program explains that studies from the Dutch gamma ray
satellite led to confirming observations of long GRB afterglow in the
visible light band. Measurement of the redshift in those afterglows
led to confirmation that long GRBs are uniformly distant from us,
fairly uniformly around .8 redshift, or thousands of light years
away, about half-way across the observable universe. As such, the
consensus of scientists conclude, the energy released is so
unimaginably great that it would be around the energy level of
converting the entire universe into gamma rays. Further observations
suggest that the best hypothesis for factoring down the energy level
is a collimated beacon from a collapsar.

But, my question steps back a bit to the first step of these
observations. Isn't the consistency of the long distance to long GRBs
a clear violation of the principle of homogeneity? Is there some
explanation in the Big Bang Theory why the super neutron stars that
are theorized to become collapsars are all so far away?

Alternatively, if GRBs (or, at least, some GRBs) are the result of
boundary collisions as the Big Bang overtook matter-energy in a
larger external Universe, wouldn't the energy from collisions at or
near the time of the BB be significantly time-stretched, such that
they would appear to be further away than they were? Isn't this
difference testable? If the GRBs are all from the edge of the
observable universe, couldn't we use the data from redshifts in
surrounding afterglow to map the phenomenon? If the result is
homogenous, wouldn't that be the null hypothesis (for me) and tend to
prove that it's just a kind of star going nova? If the result is a
multi-dimensional shape, what can that shape be other than the shape
of the boundary of the Big Bang or a projection from it?

As a second question, does anyone here know whether the findings from
the Swift satellite, monitored by Penn State, have yet provided
enough data on short GRBs to determine a curve of distances based on
redshifts in the afterglows? Do we know the range of distances and
the normality and kurtosis of the curve of those distances? If we
have the data, is it homogenous?

Does anyone know to whom I might write or call to pursue this line of
thought?

TIA!

-- Richard S. Sternberg, Esq.
richard@NOSPAMrssternberg.org

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Kent Paul Dolan - 28 Sep 2007 08:23 GMT

> The television program explains that studies from
> the Dutch gamma ray satellite led to confirming
[quoted text clipped - 5 lines]
> away, about half-way across the observable
> universe.

Probably then you meant "billions of light years
away", not "thousands".

> Further observations suggest that the best
> hypothesis for factoring down the energy level is
> a collimated beacon from a collapsar.

> But, my question steps back a bit to the first
> step of these observations. Isn't the consistency
[quoted text clipped - 3 lines]
> the super neutron stars that are theorized to
> become collapsars are all so far away?

If you model the situation in your mind, maybe, just
maybe, the "uniformity" of the distance isn't so
strange.

For sources much farther away, the received energy
might be below the threshold of easy detection.

For sources much closer, the combination of smaller
numbers of them in a smaller volume, and the
"collimated beam" not yet having spread enouugh to
have a very large area to intersect our vicinity,
might mean that in general they aren't going to hit
our detectors very often.

That would leave a shell of "most likely to be
detected" sources, even IF homogeneity were still
the real situation.

Yes, I absolutely refuse to do the math to see if
either of those intuitions makes numerical sense.

xanthian.

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David M. Palmer - 28 Sep 2007 08:40 GMT

> The television program explains...
> ... long GRBs are uniformly distant from us,
> fairly uniformly around .8 redshift, or thousands of light years
> away, about half-way across the observable universe.

They are not all at the same redshift. Television lies.

> As a second question, does anyone here know whether the findings from
> the Swift satellite, monitored by Penn State, have yet provided
> enough data on short GRBs to determine a curve of distances based on
> redshifts in the afterglows? Do we know the range of distances and
> the normality and kurtosis of the curve of those distances? If we
> have the data, is it homogenous?

The data is available at
http://swift.gsfc.nasa.gov/docs/swift/archive/grb_table/
which lets you select the columns of the data table, including redshift.

And yes, there is a large range in redshifts.

There are a lot of selection effects, so going from the distribution of
redshifts to the history of GRB production rates is a big job, fraught
with uncertainty.

Signature

David M. Palmer dmpalmer@email.com (formerly @clark.net, @ematic.com)

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Evert - 29 Sep 2007 19:27 GMT

> The television program explains that studies from the Dutch gamma ray
> satellite led to confirming observations of long GRB afterglow in the

To set the record properly straight: BeppoSAX was an Italian-Dutch
mission, not Dutch only (but the Dutch did discover the first GRB
afterglow).

> But, my question steps back a bit to the first step of these
> observations. Isn't the consistency of the long distance to long GRBs
> a clear violation of the principle of homogeneity? Is there some
> explanation in the Big Bang Theory why the super neutron stars that
> are theorized to become collapsars are all so far away?

Nothing about the Big Bang theory, but it appears that the progenitors
of long-GRBs (collapsars indeed: massive stars), prefer a low-
metallicity environment: the further back in time you go, the lower
the amount of metals wil be, so GRBs will tend to be found at higher
redshift. It even looks like (but that's yet not really statistically
confirmed) long GRBs follow a different formation curve than the
general star-formation curve, peaking at larger redshift.
Other than that, there are also observational biases, which may lead
to a somewhat underestimate of GRBs at certain redshift (although
that's accountable), and the Universe is of course simply larger at
redshift 1 than at current.

There are about a dozen redshifts for short bursts, not enough for all
the details. There are indeed closer-by (suiting the picture of binary
compact-object mergers, which need some time to merge), at redshifts
in the range of 0.2 - 1 (although there are a few claims for z > 1,
but hard to secure).

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Evert - 29 Sep 2007 19:28 GMT

> For sources much closer, the combination of smaller
> numbers of them in a smaller volume, and the
> "collimated beam" not yet having spread enouugh to
> have a very large area to intersect our vicinity,
> might mean that in general they aren't going to hit
> our detectors very often.

That argument doesn't really work, because it assumes the beam ("jet")
travels all the way from there to here, spreading al the time.
The jet is, in fact, not even a light year long when first spotted,
and certainly much smaller in diameter: it is the photons produced in
the jet that we see, and these travel straight on towards Earth.
The thing that matters here is the jet *pointing* in our direction,
and whether the energy/outflow speed at the sides tapers off, meaning
the jet edges would be harder to see. But whether that is true or
not, the problem of the jet pointing in our direction is the same
locally or at high redshift.

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Space Forum / Astronomy / September 2007

Gamma Ray Burst Heterogeneity