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Gamma-Ray Bursts The Brightest Explosions Since the Big Bang. H. A. Bethe Lecture March 6, 2002 . Electromagnetic radiation – of which ordinary visible light is an example – can be characterized by its wavelength. Gamma-rays have
The Brightest Explosions Since the Big Bang
H. A. Bethe Lecture March 6, 2002
example – can be characterized by its wavelength. Gamma-rays have
the shortest wavelengths of all and are very penetrating. They pass easily
through a block of wood but not through the Earth’s atmosphere.
Consequently cosmic sources of gamma-rays can only be seen by
satellites, rockets, and high flying balloons that go above most of
the Earth’s atmosphere.
First Vela satellite pair launched 1963
Velar – to watch
The Vela 5 satellites were placed in orbit by the Advanced
Research Projects of the DoD and the AEC. Launched on
May 23, 1969 into high earth orbit (118,000 km), this pair
of satellites and their predecessors, Vela 4, discovered the
first gamma-ray bursts. The discovery was announced
by Klebesadel, Strong, and Olson (ApJ, 182, 85) in 1973.
The Vela 5 satellites functioned from July, 1969 to April, 1979
and detected a total of 73 gamma-ray bursts in the energy
range 150 – 750 keV (n.b, radiation is sometimes defined by its
energy measure in electron volts. 0.3 to 30 keV approximately is
x-rays. Greater than 30 keV is gamma-rays)
20 seconds but there is
wide variation both in time-
structure and duration.
Some last only hundredths
of a second. Others last
thousands of seconds.
bright flash of gamma-rays lasting typically about 20
seconds that comes from an unpredictable location in
Some, in gamma-rays, are as bright as the planet Venus.
Most are as bright as the visible stars. It is only because of
the Earth’s atmosphere and the fact that our eyes are not
sensitive to gamma-rays that keeps us from seeing them
With appropriate instrumentation, we see about one of
these per day at the Earth. They seem never to repeat from
the same source.
Yes, there are gamma-raysbut I don’t know where they
but I do know when ...
if there are more than one detectors.
If “1” hears the sound later than “2” the sound is somewhere
to the right.
uncertainty in distance –
a factor of one billion.
nb. 27, 42, 105, 126
(quakes, comets falling, thermonuclear runaways, etc.)
The expected distribution on the sky if Galactic neutron
stars were responsible should center around the Galactic equator.
Plane of the MilkyWay Galaxy
wilderness for twenty years ...
(1973 – 1993).
April 5, 1991 – June 4, 2000
Expected if haven’t
reached any edge yet
own Galaxy ..
We are not at the center
of our galaxy so we
should see more bursts
towards the center than
in the opposite direction,
What we really needed was source identifications.
conceived July, 1981, Santa Cruz
born Nov 4, 1996
died Nov 5, 1996
(Italian-Dutch X-ray astronomy mission)
MEC S and LECS (medium and lowenergy x-ray sensors, 1 arc min positions)
(2-30 keV; 20x20 degree FOV
angular resolution 5 arc min)
The scintillator anti-coincidence shields of the Phoswich detector
are able to detect gamma-rays 60-600 keV and get crude angular
Feb 28, 1997 (8 hr after GRB using MECS)
March 3, 1997 (fainter by 20)
Each square is about 6 arc min or 1/5 the moon’s diameter
William Hershel Telescope
Isaac Newton Telescope
Groot, Galama, von Paradijs, et al IAUC 6584, March 12, 1997
get a crude spectrum of the host galaxy. Estimate z = 0.5
March 10, 1997
Spectrum of the host galaxy of GRB 970228 obtained at the Keck 2 Telescope.
Prominent emission lines of oxygen and neon are indicated and show that the
galaxy is located at a redshift of z = 0.695. (Bloom, Djorgovski, and Kulkarni
(2001), ApJ, 554, 678. See also GCN 289, May 3, 1999.
of light years. Far, far outside our galaxy.
From the distance and brightness an energy can be
1.6 x 1052 erg in gamma rays alone
This is 13 times as much energy as the sun will radiate in
its ten billion year lifetime, but emitted in gamma-rays
in less than a minute. It is 2000 times as much as a
really bright supernova radiates in several months.
This shows the light curve as seen by BATSE starting at 9:46:56 UT on
January 23, 1999. The burst was seen simultaneously by the WFC on BeppoSax.
The position was promptly determined to a few degrees by BATSE and shortly
thereafter to 5 arc min by BeppoSax.
by Akerlof et al, located at Los Alamos, images a piece of the sky
16.5 degrees across. It is able to slew anywhere in the sky in about 10 s.
It was notified of GRB 990123 within 4 s of the onset and was taking data
22 s into the event. The first three ROTSE points are shown superimposed
on the BATSE light curve.
47 s, 5 s exposure
m = 11.82
22 s, 5 s exposure
72 s, 5 s exposure
m = 13.22
259 s, 75 s exposure
m = 14.0
447 s, 75 s exposure
m = 14.53
612 s, 75 s exposure
This ID was made 3 hours after the burst following a 5AM “wake-up” call to Palomar from Italy
GRB 990123 6 to 33 hours
after the burst and 34 to 64
hours after the burst.
The x-ray source is clearly
fading. Each grid box is
12 x 15 arc min. The error in
position is then about 1.5 arc
February 8, 1999, the one on the right March 23, 1999. Each picture
is 3.2 arc seconds on a side. Three orbits of HST time were used for
the first picture; two for the second – hence the somewhat reduced
using the Keck Telescopes gives a redshift of 1.61.
Given the known brightness of the burst (in gamma-rays) this
distance implies an energy of over several times 1054 erg.
About the mass of the sun turned into pure energy.
Had this burst occurred on the far side of our Galaxy,
at a distance of 60,000 light years, it would have been
as bright – in gamma-rays – as the sun. This is ten billion
times brighter than a supernova and equivalent to seeing a
one hundred million trillion trillion megaton explosion.
promptly localized by various satellites
(starting in 1997).
X-ray afterglows had been detected from 40 and
optical afterglows from 28.
Red shifts (distances) were determined for about 21.
Typical values are z ~1. The largest is 3.42 (GRB 971214)
corresponding to emission when the universe was
about 15% its present age.
5% of the mass of the sun turned to pure
energy according to E = mc2
If the energy were
beamed to 0.1% of the
sky, then the total
energy could be
1000 times less
Nothing seen down here
for every one that we do see. About 1000 in fact.
Quasar 3C273 as seen by the
Chandra x-ray Observatory
Artist’s conception of SS433 based on observations
Microquasar GPS 1915
in our own Galaxy – time sequence
and time scales for GRBs correct the beam must
be “relativistic”, that is it must travel at very close
to the speed of light.Otherwise the bursts would be much softer and
last much longer.
of light that it emits its radiation in a small angle along its
direction of motion. The angle is inversely proportional to the
This offers a way of measuring the beaming angle. As the
beam runs into interstellar matter it slows down.
an opening angle of
about 5 degrees.
with known redshifts and afterglow
Using the angles inferred from
this sort of analysis of the
afterglows, Frail et al find that
an inverse correlation exists
between the apparent energy of
the burst and this angle.
Correcting for the fact that the
burst is beamed to a small part of the sky, they find a typical
energy in gamma-rays is
5 x 1050 erg. For a reasonable
conversion efficiency between
explosion energy and gamma-rays (20%), the total jet energy is about
2 x 1051, not so different from
an ordinary supernova.
and its Immediate Surroundings
black hole pairs
Strengths: a) Known event
b) Plenty of angular momentum
c) Rapid time scale
d) High energy
e) Well developed numerical models
Weaknesses: a) Outside star forming regions
b) Beaming and energy may be inadequate
for long bursts
But this model may still be good for a class of bursts called
the “short hard” bursts for which we have no counterpart information
collapses to a neutron star and the energy released explodes
the rest of the star.
But what if the explosion fizzled? What if the iron core
collapsed to an object too massive to be a neutron star –
a black hole.
A star without rotation would then simply disappear....
But what if the star had too much rotation to all go
down the (tiny) black hole?
If supernovae are the observational signal that a
neutron star has been born, what is the event that
signals the birth of a black hole?
axis of the black hole, by a
variety of possible processes,
energy is deposited.
The exact mechanism for
extracting this energy either
from the disk or the rotation
of the black hole is fascinating
physics, but is not crucial
to the outcome, so long as the
energy is not contaminated by
too much matter.
7.6 s after core collapse; high viscosity case.
NTT image (May 1, 1998) of SN 1998bw in
the barred spiral galaxy ESO 184-G82[Galama et al, A&A S, 138, 465, (1999)]
WFC error box (8') for GRB 980425
and two NFI x-ray sources. The IPN
error arc is also shown.
1) Were the two events the same thing?
2) Was GRB 980425 an "ordinary" GRB
(distance from here to the Galactic center) would give
as much energy to the earth in 10 seconds as the sun –
equivalent to a 200 megaton explosion.
Does it matter having an extra sun in the sky for
Probably not. This is spread all over the surface of
the earth and the heat capacity of the Earth’s atmosphere
is very high. Gamma-rays would deposit their energy
about 30 km up. Some bad nitrogen chemistry would happen.
Noticeable yes, deadly to all living things – No.
Distance Events Megatons Results
(kpc) /10 by
* Depends on uncertain efficiency for conversion of energetic electrons to optical light
Atkins et al. (2000), Astrophysical Journal Letters,533, L119
Large watertight detector near Los Alamos.
Threshold about 100 GeV (gamma-rays with 100,000 times more energy and shorter
wavelength than “ordinary” GRB energies)
Fluence of this burst in BATSE was1.5 x 10-7 erg cm-2.
100 times more energy in TeV radiation??
Sensitive to GRBs in the
energy range 20 MeV to 300 GeV
Scheduled for launch by NASA
detector follows the paths of
electron-positron pairs created
Will the high energy emission
of GRBs be their dominant emission?
October 6, 2000