Gamma-Ray Bursts Please press “1” to test your transmitter.

Which wavelength range probes the most violent events in the Universe? 1.Radio Waves 2.Gamma-Rays 3.X-Rays 4.Visible Light 5.Infrared Light

Gamma-Ray Bursts Short (~0.1 – 100 seconds) flashes of gamma-rays from random directions in the sky Wavelength Frequency, Energy

Mysterious Flashes of Gamma-Rays Discovered in 1967: Brighter than any other gamma- ray source in the sky, for a few seconds - minutes

Gamma-Ray Burst Missions Burst and Transient Search Experiment (BATSE) on the Compton Gamma-Ray Observatory:

Two Types of Gamma-Ray Bursts Long GRBs (duration > 2 s) Short GRBs (duration < 1 s)

GRB Light Curves Long GRBs (duration > 2 s)Short GRBs (duration < 1 s) Two different types of GRBs: Long and short bursts Time Brightness

General Properties of GRBs Random distribution in the sky Approx. 1 GRB per day observed No repeating: Only one single burst, and it’s gone! Galactic Plane Galactic Longitude Galactic Latitude

BeppoSAX (1996 – 2003) First identification of X-ray and optical counterparts (afterglows) of gamma-ray bursts in 1997

Afterglows of GRBs Most GRBs have gradually decaying afterglows in X-rays, some also in optical and radio. X-ray afterglow of GRB (GRBs are named by their date: Feb. 28, 1997) On the day of the GRB3 days after the GRB

Optical afterglow of GRB (May 10, 1999) Optical afterglows of GRBs are extremely difficult to localize: Very faint (~ 18 – 20 mag.); decaying within a few days. 1 day after GRB2 days after GRB

A GRB Afterglow Observed at the MDM Observatory

If an optical afterglow of a GRB has an apparent visual magnitude of 19, how many times fainter is it than the faintest object visible to the bare eye? *2.512 ≈ 37 3.(2.512) 13 ≈ 158,583 4.(2.512) 19 ≈ 39,844, = 10 26

Optical Afterglows of GRBs Optical afterglow of GRB (Hubble Space Telescope) GRBs are found in spiral arms of distant host galaxies (half-way across the Universe!) Host Galaxy Optical Afterglow

Energy Output of GRBs Observed brightness combined with large distance implies huge energy output of GRBs Energy equivalent to the entire mass of the sun (E = mc 2 ), converted into gamma-rays in just a few seconds! 10,000,000,000,000,000,000,000,000,000 (10 28 ) Hydrogen bombs!

Beaming GRBs are most likely not emitting isotropically (i.e. with the same intensity in all directions), but are beamed.

If GRBs are actually beamed, then the total energy that they emit is … compared to isotropic emission (i.e. equal energy output in all directions). 1.smaller 2.equal 3.larger 4.Depends on the duration of the GRB. 5.Depends on the photon frequency at which most of the energy is radiated away.

GRBs are actually emitting less energy than implied for isotropic emission. If we assume isotropic emission, the GRB would have to emit the same energy in all directions. For beamed GRBs, it’s only along the beams => Less total energy

If GRBs are actually beamed, then the total number of GRBs occurring in the Universe is … compared to what we would infer for isotropic emission. 1.smaller 2.equal 3.larger 4.Depends on the duration of the GRB. 5.Depends on the photon frequency at which most of the energy is radiated away.

There must be more GRB sources than implied for isotropic emission. If GRBs emitted isotropically, we would basically observe all GRBs, irrespective of their orientation. For beamed GRBs, we only observe those GRBs which are beamed towards us => There must be more sources that we don’t see as GRBs.

Current Gamma-Ray Burst Missions Swift Gamma-Ray Burst Explorer: Launched 2004 Gamma-Ray Burst Monitor X-ray Telescope Optical/UV telescope

The Swift Gamma-Ray Burst Mission

Current Gamma-Ray Burst Missions Fermi Gamma-Ray Space Telescope (Launched August 2008): GLAST Burst monitor (GBM)

Multi-Wavelength View of Gamma-Ray Bursts Gamma-Rays X-Rays Visible

How do massive stars (> 8 solar masses) end their lives? 1.The core collapses to a white dwarf, and the rest of the star explodes in a supernova explosion. 2.The core collapses into a neutron star, and the rest of the star explodes in a supernova explosion. 3.The core collapses into a white dwarf, and the rest of the star explodes to form a planetary nebula. 4.The core collapses into a neutron star, and the rest of the star explodes to form a planetary nebula. 5.The gradually use up their Hydrogen fuel and never ignite Helium burning.

Origin of GRBs Hypernova: There’s no consensus about what causes GRBs. Several models have been suggested, e.g.: Supernova explosion of a very massive (> 25 M sun ) star Iron core collapse forming a black hole; Material from the outer shells accreting onto the black hole Accretion disk => Jets => GRB!

Origin of GRBs Black-hole – neutron-star merger: Black hole and neutron star (or 2 neutron stars) orbiting each other in a binary system Neutron star will be destroyed by tidal effects; neutron star matter accretes onto black hole => Accretion disk => Jets => GRB! Model works probably only for short GRBs.

Origin of Short GRBs Black-hole – neutron-star merger

Origin of Short GRBs Neutron-star – neutron-star merger