1. Sco-X1search : S2 results
C Messenger
on behalf of LSC-PULG
LIGO Scientific Collaboration Meeting
UMich, 4th – 5th June 2005
LIGO-G Z

2. Outline Astrophysical scenario Data Analysis Pipeline S2 results
Data-set selection
Parameter space
F-statistic Search
Coincidence test
Injections
Upperlimits
Work in progress and future plans
UMich LSC Meeting, 4th – 5th June 2005

3. Astrophysical Scenario
Conjecture for LMXBs: GWs are the limiting physics that prevents NSs from being spun-up to the braking frequency
Two models:
Density fluctuations – “mountain” on neutron star (Bildsten, 1998; Ushomirsky, Cutler, Bildsten, 2000; Cutler, 2002)
fgw = 2 frot
R-modes (Andersson et al, 1999; Wagoner, 2002)
fgw = 4/3 frot
(from Cutler and Thorne 2000)
Sco-X1 is a LMXB in an ~18 hr and approximately circular orbit.
Expected GW amplitude is ~10-26
UMich LSC Meeting, 4th – 5th June 2005

4. Data analysis pipeline
Data-set selection
Template bank generation
F-statistic Search
Coincidence test
Chi-squared test
Injections & Upperlimits
This is a wide parameter space search !!!
UMich LSC Meeting, 4th – 5th June 2005

5. S2 results : Data-set selectionH1
LLO
LHO
Tstart
Tend
# SFT
198
332
Tspan
18535
20302
Tobs
11880
19920
frequency
Sh1/2
Data-set selected based on sensitivity factor
Factor in the noise floor across the search band & sky position sensitivity
Limited to 6 hour maximum observation span (Tcomp a Tspan5)
UMich LSC Meeting, 4th – 5th June 2005

6. S2 results : Parameter Space
2+1 dimensional parameter space
2 orbital parameters (Projected Semi-Major axis & Periapse passage)
+ Intrinsic GW emission frequency
Orbital period NOT a search parameter for coherent observation times < 1 week
Spin down NOT a search parameter for coherent observation times < 1 month
Time of periapsis
Projected Semi-Major Axis
Projected Semi-Major Axis {1.44 +/ sec} at 1 sigma
Time of periapsis { /- 299 GPS sec} at 1 sigma (phase in the orbit)
Frequency range split into 2 bands {474 +/- 10 & 614 +/- 10 Hz} (from QPO observations)
METRIC used to place filters in orbital parameter space (frequency projected out) & frequency space (independent of orbital parameters)
UMich LSC Meeting, 4th – 5th June 2005

7. S2 results : F-statistic search
L Hz
L Hz
H Hz
H Hz
The F-statistic part of the analysis is identical to the isolated pulsar search + binary demodulation.
The F-Statistic in the presence of Gaussian noise should be c24 distributed
We have “good” and “bad” bands.
The “bad” bands deviate significantly from the expected distribution in the tails resulting in statistically unlikely large values.
Usually due to large “spikes” not removed by the running median.
UMich LSC Meeting, 4th – 5th June 2005

8. S2 results : Coincidence test
The method involves finding orbital templates that could be common closest filters to a possible signal.
Have to search a finite range of frequencies around possible event frequency.
Factor of 1.4
+/- 20 bins 2F
Number of frequency bins
Observation span
frequency
UMich LSC Meeting, 4th – 5th June 2005

9. S2 results : Candidate Events
Proj Semi-Major Axis
Proj Semi-Major Axis
Time of periapse passage
The parameter space contains features after coincidence appearing as planes of events at constant frequency.
Event densities in orbital parameter space show no structure
Time of periapse passage
frequency
UMich LSC Meeting, 4th – 5th June 2005

10. S2 results : Injections & ULs
Frequentist upper limits are obtained via signal injections into the dataset h0
Confidence h0
frequency
Upperlimits are ~4x1022 in both bands.
Coincidence analysis helps us in the case where one detector is “clean” and one detector is “not clean”.
UL’s around the 60 Hz power line harmonic at 480 Hz are dominated by very large loudest events inconsistent with Gaussian statistics.
UMich LSC Meeting, 4th – 5th June 2005

11. Work in Progress & future plans
S2 paper in initial draft form (FINISH SOON).
This coherent pipeline is clearly not the way to search for GW’s from Sco-X1 (but we knew that).
An incoherent approach (Virginia Re, Greg Mendell) is the way forward and is currently being tested.
The coherent pipeline is currently suitable to place limits on accreting msec X-ray binary pulsars: the parameter space is much smaller allowing far longer observation times (Dominic Kasprzyk).
UMich LSC Meeting, 4th – 5th June 2005