Review Committee Meeting Monday 17 April 2006 09:00 PST / 12:00 EST
Minutes: Monday 17 April 2006 09:00 PST / 12:00 EST
Agenda and Contact Info
Today's meeting with focus on issues of relating upper limits on strain
to radiated energies.
- Energetics for Untriggered Searches
- Energetics for Triggered Searches: GRBs. See discussion in Sec. VIIA
of GRB030329 paper: [ PDF ]
- Energetics for Triggered Searches: SGR analysis. See technical note:
[ PDF ]
AccuConference teleconferencing service:
Phone: 1-800-704-9896, participant code: 038621#
International callers ++1-404-920-6472 with same code
- Also see Keith Riles's technical report
[ PDF ].
- Central issue: hrss is not meaningful to our audience. They want
"solar masses radiated" and "megaparsecs".
- In Patrick Sutton's presentation: Best hrss limit for LTA was
6e-22 Hz^-1/2 for the 153 Hz SG (isotropic sky distribution) which yields
an energy if the source was radiating isotropically but linearly polarized
- Why assume isotropic linearly polarized radiation? Would expect
patterns of linearly polarized radiation to be far from isotropic. Why
choose this as a benchmark? Suggestion: isotropic radiation with equal
power in both polarizations. Factor of 2 different in energy. Do we
care about factors of 2?
- There are other assumptions. Assumed relationship between hrss and
energy is only true for SG waveform.
- Another issue: cannot translate an upper bound on hrss to a bound
on energy. Can always have a source that radiates lots of energy but
none of it is detectable (poorly oriented). That would be consistent
with observations. Similarly, a source that radiates almost no energy
would also be consistent with observations. Need to use some knowledge
or model of source to get a true energy bound -- this may not be appropriate
for searches for unmodelled bursts! Perhaps we should not try to have
a true energy bound but rather a characteristic energy corresponding to
our search sensitivity. Similarly, perhaps should use hrss50% rather than
- If we don't care about factors of 2 then perhaps we should say things
like E ~ 1 solar mass at D ~ 10^2 Mpc rather than E = 1 solar mass at D = 75
- Luca's document: Similar to Keith's (isotropic emission of linearly
polarized waves but now have a known value for polarization-averaged F+^2).
Is this more similar to GRB case (where direction to source is known) or
to the untriggered case (where we don't want to assume any particular
emission pattern or source inclination). Note: we don't know the inclination
of the NS but perhaps we could hypothesize an emission pattern based on
the mode we think is excited based on QPO observations.
- Again: perhaps there should be a factor of 2 for the second
- Section 4 of Luca's document. May not be well motivated. Eq. (10)
is fine if you will be averaging over polarization angles or if you
assume uncorrelated h+ and hx waveforms, but otherwise would expect it
to be of the form:
(hrss90%)^2 = F+^2 h+rss^2 + 2 F+ Fx (h+ hx)rss + Fx^2 hxrss^2
Particularly maliciously chosen h+ and hx signals could give a null signal.
Additional reasonable assumptions about the source can probably clear this
- Some precendence in energy statements from the GRB030329 paper.
Here an "optimistic" model is chosen (with a quadrupolar emission pattern
and zero inclination -- i.e., view the source along the axis so that
we are receiving circularly polarized waves). Note: situation is not
so clean-cut: for the GRB030329 case we had only H1-H2 so linearly polarized
simulations were sufficient. Now we also have some limits coming from
H1-L1 so we would need circularly polarized simulations for these.
Do we want to continue to do what was done before or change somehow so that
all the searches (triggered and untriggered) have energy statements with
- What meaning is really wanted? A "sensitivity" style statement of the
form: "we would hope to see a source at XX Mpc if it radiated XX Msun"?
Or something more in the form of a bound: "a such-and-such source that
radiates XX Msun of radiation would have to be farther than XX Mpc or else
it would produce hrss greater than hrss90%"? Latter type of statement might
be harder to make with any sort of rigor.
- Let's put some proposals together and circulate to burst group email
list and have the discussion off-line. Perhaps there can be some sort of
condensation on a particular proposal or on a couple of proposals by
tomorrow's burst group meeting.
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