Gamma ray burst triggered searches in the S2, S3, S4 runs of LIGO Soumya D. Mohanty On behalf of the LIGO Science Collaboration

Relevant astrophysics Central engine: GRBs come in two classes –Long soft (LSB): Stellar core collapse to Black Holes or magnetars for anomalously long and soft bursts, e.g., , 1998bw (980425) –Short hard (SHB): NS-NS, NS-BH, BH-WD mergers following GW driven inspiral Distance scales: –LSB should follow massive Star formation rate  pdf of observed redshifts peaks at z > 1 –SHB pdf should peak at closer redshifts (  0.5)

Detection Rate/upper limits Analysis pipelines developed for both direct coincidence and population signature searches Direct detection –LSB: about 1/yr for adv. LIGO (kobayashi, Meszaros, 2003) –SHB: ? (papers by Kalogera et al) –Very low redshift X-ray Flashes (D  100 Mpc): once in 3 to 5 years Upper limits on E GW – (XRF) and S2: 340 M ๏ c 2 ; sub-solar possible with initial LIGO ( was at 35 Mpc) –GRB population average (Finn, Mohanty, Romano, 1999): sub- solar on LSBs possible with adv. LIGO

GRBs during S2, S3, S4 runs 39 GRBs (with 2 SHBs): –HETE-2, INTEGRAL, Swift triggers obtained via GCN notices –22 GRBs were well localized on the sky 35 GRBs had the two Hanford detectors in lock More …

Cross-correlation based search Cc statistic –Definition of cc –Max. over cc (max. over abs(cc) for LHO and LLO) Parameters of the search –Integration length 100 ms –Search length 180 sec (-60 to +20 sec )

Significance

Binomial test

Upper limits

Search for population signature Max. Likelihood ratio detection statistic –Prior information about redshifts, directions and astrophysics not taken into account yet –Sum-max statistic Non-parametric version (rank-sum test) significance: 0.64 –Cannot reject null hypothesis (no GWs associated with the S2, S3, S4 GRB sample)

Constraints on population properties Joint pdf of population parameters determines the distribution of the sum-max statistic –Population parameters: redshift, E GW, inclination (beaming) –Frequentist confidence belt S2,S3,S4: only H1,H2 cross-correlation used –Single source parameter: observed matched filtering snr TO BE REPLACED BY RECENTLY CHANGED CF BELTS

Population model Standard candle model Redshift distribution prediction from Bromm, Loeb, 2002 –Z peak = 1.8 (for Swift) 90% confidence level upper limit on E GW is 2.4  10 4 M ๏ c 2

LIGO/GEO S5 run Isabel to fill in

Summary Search for GWs associated with GRBs conducted over S2, S3, S4 data; upper limits obtained (individual/population) Analysis pipelines in place Better understanding of how to combine multiple triggers: exploring parametric/non-parametric approaches S5 results for population upper limits may be 10 to 20 times better Many possibilities for enhancing sensitivity: shorter search lengths, coherent network analysis,…