LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY - LIGO - CALIFORNIA INSTITUTE OF TECHNOLOGY MASSACHUSETTS INSTITUTE OF TECHNOLOGY

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1 LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY - LIGO - CALIFORNIA INSTITUTE OF TECHNOLOGY MASSACHUSETTS INSTITUTE OF TECHNOLOGY Document Type LIGO-T W 2007/05/17 Validation of the S5 V3 LHO calibrations for GRB Evan Goetz, Eiichi Hirose, Michael Landry Distribution of this draft: LIGO Scientific Collaboration California Institute of Technology Massachusetts Institute of Technology LIGO Project - MC LIGO Project - NW E California Blvd 175 Albany Street Pasadena CA Cambridge, MA Phone (626) Phone (617) Fax (626) Fax (617) info@ligo.caltech.edu info@ligo.mit.edu WWW: Processed with L A TEX on 2007/05/17

2 Abstract We describe validation of the S5 V3 calibration of the LIGO Hanford interferometers during the epoch including GRB As of this writing, the current S5 calibration version is V3. Final V3 epochs for both H1 and H2 were expected to still be representative of the H1 and H2 instruments on the date of GRB (gps time ). Through a series of cross checks of the state of the machines, and comparisons with the quasi-independent calibration procedure autocalibrator, this is shown to be the case. 1 Introduction Both H1 and H2 were locked and in science mode during GRB We have plotted strainequivalent noise curves for H1 and H2, using roughly 55s of DARM ERR data centered on gps time (GRB070201). These curves correspond to binary neutron star inspiral ranges of 15.6Mpc (H1) and 6.8Mpc (H2), respectively. The calibration employed here for both H1 and H2 is S5 V3. Strain equivalent noise (Hz 1/2 ) GRB Noise curves H2 H Figure 1: Strain equivalent noise curves for H1 and H2 for 55s around the gps event time of GRB H2 Calibration Validation of the H2 calibration for GRB is slightly more complicated than H1, owing to a filter modification prior to the Feb 1 event. We thus deal with H2 first in this document, and then follow with H1. The S5 H2 V3 calibration comprises three distinct calibration epochs, listed in Table 1. The duration of the third epoch is given as nine 9 s, or indefinite. This indicates the calibration is expected then to apply to GRB However, there was an H2 filter modification made on 22 January 2007, necessitating a check on this epoch to ensure its validity at the time of the GRB. page 2 of 7

3 epoch start (gps) epoch duration (s) OLG measurement (gps) V3 and V4 model comparisons Table 1: S5 H2 V3 epoch parameters. An official calibration run was performed for H2 on 23 January 2007 during the commissioning break. We made a V4 model from the results of this calibration run and compare it to the V3 model to understand any changes in the DARM loop that were made during the commissioning break period. Figure 2 shows the comparison of V3 and V4 versions of the DARM model. The differences between V3 and V4 versions of the H2 calibration are less than 1 percent in magnitude and less than 1 degree in phase between 10 Hz and 7 khz, a good indication that the filter module change has not significantly impacted the calibration and the V3 calibration is still valid at the time of the Feb 1 GRB. Figure 2: Comparison of the V3 and V4 versions of the DARM model for H Autocalibrator comparisons As an additional cross-check, we compare autocalibrations (typically made weekly to bi-weekly) against propogated V3 calibration, in order to look for systematic shifts that suggest the V3 calibration is out of date. Autocalibrations rely on the same DC calibrations that are employed by page 3 of 7

4 the official method, but use a physical transfer function (as opposed to a model), and thus all other components of the calibration are independent. Two autocalibrations bracket the Feb 1 GRB: that of Jan 29, 2007, and Feb 6, 2007 (this for both H2 and H1). Shown in Figures 3 and 5 below are strain curves from the two autocalibration measurements, and the strains produced from the V3 calibration for the same AS Q data use by the autocalibrator. Agreement is more readily judged in the linear ratios Figures 4 and 6. Both ratios show a slight (about 4-5) percent systematic to more sensitive autocalibrations. As this i) is within calibration error, ii) is conservative with respect to the V3 calibration, iii) may demonstrate some problem with the autocalibration sweep templates, we believe the systematic to be small enough such that the offical calibration is acceptable. We have begun testing the autocalibrator procedure in effort to identify the nature of the systematic, and will shortly prove whether or not it resides in the autocalibrator as suspected H2 Official and Acal strains official V3 cal autocal new f r es srd Strain (1/ Hz) Figure 3: Comparison of H2 29 Jan 07 autocalibrator spectrum with official calibration method. 2.3 Factors check 2.4 Conlog check We checked the Conlog differences for LSC, ASC, SUS, PSL and IO subsystems between the V3 model time for H2 (gps= ) and the time of GRB (gps= ). The state of the instrument shows nothing out of the ordinary at the time of the GRB (i.e. there were no gain changes in the DARM loop or filters not in place). The Conlog differences are mostly due to alignment differences and servo offsets (SUS and ASC). A few example of channels that had changes are H2:SUS RM LLYAW GAIN and H2:LSC-AS3 I OFFSET. The input matrix element (AS Q to DARM ERR) is slightly different between the fiducial calibration time and the time of the GRB, but this is a dynamical parameter in the LSC loop to cancel changes in optical gain over time. page 4 of 7

5 Ratio of H2 Off. cal/autocal, w0=.764 propogated V3 cal/reformed autocal Figure 4: Ratio of H2 29 Jan 07 official calibration to autocalibrator output. 3 H1 Calibration There were no changes in filters or gains between the V3 calibration measurement and the time of GRB A new model is not implicitly necessary because the state of the instrument is essentially the same as during the V3 official calibration measurements. Thus the validation is considered simpler and did not necessitate a separate V4 measurement specifically for GRB The four H1 V3 calibration epochs are noted in Table 1 below. epoch start (gps) epoch duration (s) OLG measurement (gps) Table 2: S5 H1 V3 epoch parameters. 3.1 Autocalibrator comparisons Autocalibrator comparisons for Jan 29 and Feb 6 were made for H1, in a similar fashion to that described above for H2. While no significant mean systematic is observed, one as a function of frequency (about ±5%) is indeed present. This may or may not reside within the 4km autocalibrator setup - investigations are also underway. The error is however within the error of the two calibrations, and thus again we claim the V3 calibration sufficient for current analyses of the GRB event. page 5 of 7

6 H2 Official and Acal strains official V3 cal autocal new f r es srd Strain (1/ Hz) Figure 5: Comparison of H2 6 Feb 07 autocalibrator spectrum with official calibration method. 3.2 Factors check 3.3 Conlog check We checked the Conlog differences between the V3 model time for H1 (gps= ) and the time of GRB (gps= ). The state of the instrument shows nothing out of the ordinary at the time of the GRB (i.e. there were no gain changes or filters not in place). As for H2, nearly all the Conlog differences are due to alignment changes and offsets. Examples of channels with different settings are H1:ASC-QPDX 1 OFFSET and H1:SUS-ETMX LRYAW GAIN. Also, as with H2, the intput matrix element for AS Q to DARM ERR is slightly different due to changing optical gain. 4 Response functions For completeness, we plot here the V3 DARM ERR response functions, and the compare them to their V2 counterparts. Figure 11 is a plot of the H1 V3 response function (fourth and final epoch), while Figure 12 compares this function with the V2 response function from its (second and) final epoch. Figure 13 is a plot of the H2 V3 response function (third and final epoch), while Figure 14 compares this function with the V2 response function from its (second and) final epoch. 5 Conclusions The H1 and H2 V3 calibrations (final epochs) are sufficiently representative of the working state of the machines on Feb 1, 2007 to be employed in data analyses of GRB Some sytematics were noted in comparisons with autocalibrator output: we will continue to investigate these effects page 6 of 7

7 Ratio of H2 Off. cal/autocal, w0=.764 propogated V3 cal/reformed autocal Figure 6: Ratio of H2 6 Feb 07 official calibration to autocalibrator output H1 Official and Acal strains official V3 cal reformed autocal, w0=.767 srd Strain (1/ Hz) Figure 7: Comparison of H1 29 Jan 07 autocalibrator spectrum with official calibration method. The dip at 60Hz is an artifact of the autocalibrator measurement. and they are suspected to reside in the existing LHO autocal setup (such as swept sine template amplitudes which may be saturating the actuation chain). page 7 of 7

8 Ratio of H1 Off. cal/autocal, w0=.761 propogated V3 cal/reformed autocal Figure 8: Ratio of H1 29 Jan 07 official calibration to autocalibrator output H1 Official and Acal strains official V3 cal reformed autocal, w0=.767 srd Strain (1/ Hz) Figure 9: Comparison of H1 6 Feb 07 autocalibrator spectrum with official calibration method. The dip at 60Hz is an artifact of the autocalibrator measurement. page 8 of 7

9 Ratio of H1 Off. cal/autocal, w0=.761 propogated V3 cal/reformed autocal Figure 10: Ratio of H1 6 Feb 07 official calibration to autocalibrator output. Resp. mag. (m/ct) Resp. phase (deg) H1 Reference response function Figure 11: V3 response function for H1 DARM ERR. page 9 of 7

10 Figure 12: Comparison of DARM ERR V3 reference response function to the V2 reference response function for H1. Resp. mag. (m/ct) Resp. phase (deg) H2 Reference response function Figure 13: V3 response functions for H2 DARM ERR. page 10 of 7

11 Figure 14: Comparison of DARM ERR V3 reference response function to the V2 reference response function for H2. page 11 of 7