Gamma Ray Bursts

1

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

2
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...

3
What are GRBs?

• Most luminous events in the universe since the
  Big Bang.
• Energy output 1051-1054 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 10-3 to 103 seconds (followed by longer
  wavelength afterglows).
• Isotropic distribution

4
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 gt accurate sky
  positions gt optical and radio observations gt
  red-shift measurements
• 2000 HETE-2
• 2002 INTEGRAL
• 2004 Swift / BAT / XRT / UVOT
• Early afterglows
• Detected first short GRB afterglow

http//heasarc.gsfc.nasa.gov/docs/swift/swift.html
5
GRB Types and Light Curves

• Light curves vary in shape, number of peaks,
  decay rate, peak luminosity, etc.
• Fall into 2 general categories
• Short (lt2ms)
• Long (gt2ms)
• Third category possibly exists GRB 060614
• Long duration (102 s)
• Temporal lag and peak luminosity of short GRB
• No associated SNe

http//imagine.gsfc.nasa.gov/docs/science/know_l1/
grb_profiles.html
6
GRB Jets

• GRBs thought to be beamed because of jet breaks
  in afterglow light curves.
• Due to relativistic beaming (G1/q) and
  deceleration of ejected matter.
• Reduces total energy requirement of GRB by a few
  orders of magnitude (q5-20).

http//www.lbl.gov/Science-Articles/Archive/sabl/2
005/August/05-GRB-supernovae.html
http//www.mpe.mpg.de/jcg/grb060814.html
7
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 gt relativistically
  expanding fireball
  gt gamma
  rays

http//www.astro.exec.ac.uk/people/dprice/research
/nsmag/
8
Long GRB Progenitors

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

http//imagine.gsfc.nasa.gov/docs/science/know_l1/
bursts.html
9
Fireball Shock Scenerio
http//www.oamp.fr/ECLAIRS/01home/home.htm
10
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.