Gamma Ray Bursts and LIGO Emelie Harstad University of Oregon HEP Group Meeting Aug 6, 2007

Outline ● What are GRBs? ● GRB detection, types, and light curves ● GRB progenitors ● LIGO's interest in GRBs – GWs from GRBs – Targeted search using GRBs – Etc...

What are GRBs? ● Most luminous events in the universe since the Big Bang. ● Energy output erg/s (comparable to E emitted by Milky Way over 100 yrs.) ● Flashes of high energy photons (~MeV) which 'light up' the sky ~3 times per day. ● Lasting to 10 3 seconds (followed by longer wavelength afterglows). ● Isotropic distribution

Satellite Detection of GRBs ● 1969: Vela (first discoverd GRBs) ● 1991: Compton Gamma-Ray Observatory / BATSE – Showed isotropic/cosmological distribution ● 1997: Beppo-SAX – Detected x-ray afterglows –> accurate sky positions –> optical and radio observations –> red-shift measurements ● 2000: HETE-2 ● 2002: INTEGRAL ● 2004: Swift / BAT / XRT / UVOT – Early afterglows – Detected first short GRB afterglow

GRB Types and Light Curves ● Light curves vary in shape, number of peaks, decay rate, peak luminosity, etc. ● Fall into 2 general categories: – Short (<2ms) – Long (>2ms) ● Third category possibly exists – GRB – Long duration (~102 s) – Temporal lag and peak luminosity of short GRB – No associated SNe

GRB Jets ● GRBs thought to be beamed because of jet breaks in afterglow light curves. ● Due to relativistic beaming ( G ~1/ q ) and deceleration of ejected matter. ● Reduces total energy requirement of GRB by a few orders of magnitude ( q ~5-20). Articles/Archive/sabl/2005/August/0 5-GRB-supernovae.html

Short GRB Progenitors ● Found on outskirts of elliptical type galaxies where star formation is low ● Afterglows show no association with supernovae ● NS-NS or NS-BH inspirals are most likely candidates ● Merger results in black hole or hypermassive NS surrounded by accretion torus –> relativistically expanding fireball – > gamma rays

Long GRB Progenitors ● Found in active star-forming regions in galaxies ● Several afterglow light curves directly linked to supernovae ● Massive star collapse –> supernova, or 'failed supernova' (hypernovae, collapsar) ● Supernova results in BH with accretion disk –> expanding fireball –> gamma rays html

Fireball Shock Scenerio

What is it to LIGO? ● The same objects that produce GRBs will also produce gravitational waves. ● Interferometric gravitational detectors are designed to detect GWs by sensing differences in arm lengths: ● Binary systems have large non-spherical kinetic energy and coalese in LIGO peak sensitivity band. ● Supernovae develop non-spherical mass distributions (particularly if spinning) which can significantly contribute to non-spherical kinetic energy.