A very general and brief introduction to gamma-ray bursts (GRBs).

1. Gamma-Ray
Bursts
Salwa Shaglel

2. Outline
2
first
What Are Gamma-Ray
Bursts ?
- Gamma-Rays
- How Can We Detect
Gamma Rays ?
GRBs Energy
second
GRBs Types
third
Effects of GRBs on Earth
- Are They Going to Kill us ?
- Did Any GRBs Hit the Earth ?
last
August 17th,2017 GRB
and Gravitational
Wave Detection
last

3. 1- What Are Gamma-Ray Bursts ?
3
● The brightest electromagnetic
events in the universe.
● Extremely energetic explosions
observed in distant galaxies.
● Lasts from ten milliseconds to
several hours.
● Followed by slowly fading
emission at longer wavelengths
created by collisions between
the burst ejecta and interstellar
gas ( Afterglow ).

4. 4

5. 1.1 - Gamma-Rays
● Electromagnetic radiation
● Carry very high energy.
● A single gamma-ray photon is more
energetic than a million visible photons
combined !
● DANGEROUS ??
Form of Ionizing
Radiation, it can
break apart atomic
bonds.
5
E=hf

6. 1.2 - How Can We Detect
Gamma-Rays ?
● Our Atmosphere (Ozone Layer O3
) blocks
𝛾-rays.
● 𝛾-rays should be detected by spacecrafts.
● The discovery of 𝛾-ray bursts was during
the cold war, when the USA sent up spy
satellites to detect 𝛾-rays from soviet
nuclear tests!.
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7. 7
Distribution is
isotropic.

8. 2- Gamma-Ray Bursts Energy
● The source of GRBs are distant galaxies.
● Incredibly energetic.
8
☀
● Releasing more energy in a
second than the sun will, in its
entire ten billion years lifetime!
● Unlike other cosmic
explosions, which spread out
and fade, GRBs stay focused.

9. 9
GRB 080319B :
- Detected by swift satellite at
March 19, 2008.
- Peak apparent magnitude of 5.3.
- Remained visible to human eyes
for 30 seconds.
- Occurred about 7.5 billion years
ago.

10. “
10
3- Types of Gamma-Ray Bursts
Short 𝛾-Ray Bursts Long 𝛾-Ray Bursts
Ultra-Long 𝛾-Ray
Bursts
Last for a few
seconds
Last for a minute
Last more than
10,000 seconds
Source : merge of 2
neutron stars in a binary.
30% of GRBs
Associated with
kilonovae.
Source : star
formation/core-collapse
supernova/deaths of massive
stars.
More than 50%
Source : collapse of a blue
supergiant stars/new-born
magnetar.
So rare

11. 11
4- Effects of GRBs on Earth
● One GRB per day is
detected.
● Most of these GRBs
are harmless.
● Originated outside
the milky way.

12. ● A nearby GRB could be disastrous! It would totally cook the
surface of the earth.
● A distant GRB are also dangerous. It wouldn’t need to be directly
pointing to us, because it would be a hundred light years wide
by the time it reaches us washing over the solar system.
12

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● A GRB would overwhelm the ozone
layer.
● Exposed to deadly solar radiation.
● Our sattelites and power grids would
all be fried.
● Because of GRBs, only 10% of all
galaxies might be hospitable to life.

14. 4.1 - Are GRBs
Going to Kill
Us?
14
N0
NO
No
No
No
No
No
● In a galaxy like the milky
way, there may only be one
GRB per million years.
● 𝛾-rays travel at the speed of
light, we won’t know when
it’s headed to us until it
arrives!!

15. 15
4.2 -Did Any GRB Hit The
Earth ?
● A GRB may have hit the
earth about 1200 years ago.
● In 2012, scientists
discovered unusually high
levels of 2 particular
isotopes :
C Be
14
6
10
4

16. 16
1- Ancient Trees.
Tree rings of old Japanese
cedars.
2- Ancient Ice.
Layers of Antarctic Ice.

17. 17

18. 18
5- August 17th, 2017
Gamma-Ray Burst and Gravitational Waves Detection.
● on Aug. 17, 2017: Scientists from U.S. and European
collaborations detected a GRB that coincided with
a burst of gravitational waves, followed by
kilonova.
● LIGO, and Virgo team, detected gravitational
waves produced by the coalescence of two
neutron stars.
● Two seconds later: NASA's Fermi Gamma-ray
Space Telescope detected a short flash of X-rays
and gamma rays from the same location in the sky.

19. 19
● The gamma rays allow for a
precise localization of where the
gravitational waves are coming
from.
● The combined information from
gravitational and
electromagnetic radiation allows
scientists to probe the binary
neutron star system.

20. Credits
Special thanks to :
● ScienceDaily website.
● 2-days Gamma-Ray Bursts workshop at AUS
(2016)
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Thanks!
Any questions?
You can find me at U14220199@sharjah.ac.ae