Transcript Slides from the fourth lecture

The Nearest Galaxies
LMC
February 22, 1987
Image Courtesty of Mike Bessell
SMC
SN 1987A (Type II)
Image Courtesty of David Mailn, AAO
The Next Type II Supernova?
Image Courtesty of Mike Bessell
Betelgeuse
Image Courtesty of Mike Bessell
Massive Stars
• Stars with masses greater than 8-10 Msun the stars are able
to fuse elements beyond Oxygen into heavier elements by
adding 4He to each nucleus.
• However, 56Fe has a minimum binding energy, when you
add an 4He to it, you get a nucleus heavier than the sum of
its parts, and so there is no energy release (energy is
consumed!)
• This leads to a situation where not only is there no longer
any heat being supplied by nuclear reactions (and these
supply pressure to counteract gravity), The core actually
starts to cool as 56Fe+4He reactions occur. The denser it gets,
the cooler it gets, and a runaway collapse occurs, where the
core of the star overcomes electron degeneracy, and
collapses to about 10 km where neutron degeneracy takes
over.
Core Collapse SNe
Forming Neutron Star
Oxygen nBurning
n
n Burning
n
Silicon
n
n
Iron Burning
n n
The Evolution of a SN II-P
transition
releaseray
ofto
shock
nebular
gamma
deposition
radioactive
adiabatic
cooling
reheating
shock
breakout
phase
deposited energy
16
18
20
0
50 100
SN 92ba
150
<1
>1
<1
H
>1
<1
H
>1
<1
H
>1
<1
H
>1
•progenitor loses mass?
Wolf Rayet
Binary Interaction
•progenitor surrounded by dense
Circumstellar Material?
massive star loses H envelope via
wind.
Stars seem to trap gamma rays on
radioactive tail indicating large mass...
Quite Rare
Wolf Rayet Stars?
associated with GRBs?
0
20
40
60
massive star loses envelope via
binary interaction.
Stars do not seem to trap gamma rays
on radioactive tail indicating low
mass...
If incomplete envelope loss IIb
If very complete envelope loss Ic
if just through Hydrogen, Ib
0
10
20
Filippenko
30
1992am
Single Stars (but 2 out of 3 binaries)
Lots of Iron………………………………….Iron Poor
10 solar masses
40
100
260
THE DISCOVERY
Gamma-Ray Bursts (GRBs) Short
(few seconds) bursts of 100keVfew MeV were discovered
accidentally by Klebesadal,
Strong, and Olson in 1967 using
the Vela satellites (defense
satellites sent to monitor the
outer space treaty).
 The discovery was reported for
the first time only in 1973.
 There was an “invite prediction”.
S. Colgate was asked to predict
• as a scientific excuse for
GRBs
the launch of the Vela Satellites
1970s….The Data-free years
(aka..Theorists run wild)
• 1974: The NY Texas Symposium
– Meegan - GRB distribution is isotropic.
– Ruderman - First theoretical review:
> 30 models (More models than bursts) None even remotely relevant today.
• During the late seventies a consensus formed
that GRBs originate on galactic neutron stars.
COMPTON-GRO results
 Duration 0.01-100s
 Two populations (long and short)
 ~ 1 BATSE burst per day
 Non thermal Spectrum
(very high energy tail, up to GeV,
500GeV?)
 Rapid variability (less than 10ms)
Compton-GRO
1991-2000: BATSE
 BATSE on Compton GRO (Fishman et. al.)
discovered that the
distribution of GRBs
is isotropic:
Number versus Brightness
shows cosmological effects
(few fainter ones than
Euclidean Space)
Two Classes of Events
Two populations of GRBs – short and
long
Anti-correlation with spectral hardness –
short and hard (Higher energy), long and
soft (lower energy).
Internal Shocks
Shocks between different
shells of the ejected
relativistic matter
D=cT
d=cdT
• dT=R/cg2=d/c
D/c=T
• The observed light curve
reflects the activity of the
“inner engine”.
• To produce internal shocks
the source must be active
and highly variable over a
“long” period.
From Piran
dT
T
The Internal-External Fireball Model
g-rays
Inner
Engine
Relativistic
Wind
Internal
Shocks
Afterglow
External
Shock
OPTICAL FLASH
From Piran
1997: Afterglow Discovery
 The Italian/Dutch
satellite BeppoSAX
discovered x-ray
afterglow
on 28 February 1997
(Costa et. al. 97).
 Immediate discovery of
Optical afterglow
(van Paradijs et. al
97).
The Radio Afterglow of
GRB970508
(Frail et. al, 97).
 Variability:
 * Scintillations (Goodman, 97; Frail Kulkarni &
Waxman 97)
 Size after one month ~1017cm.
 Rising Spectrum at low frequencies:
 Self absorption (Katz & Piran, 97; Frail et al 97)
Size after one month ~ 1017cm.
 Relativistic Motion!!! (but g~2-3since this is a
long time after the explosion
Afterglow Theory
Hydrodynamics: deceleration of the
relativistic shell by collision with the surrounding medium (Blandford &
McKee 1976)
(Meszaros & Rees 1997, Waxman 1997, Sari 1997, Cohen, Piran & Sari 1998)
Radiation: synchrotron
(Sari, Piran & Narayan 98)
Clean, well defined problem.
Few parameters:
E, n, p, (fraction of energy in electrons and magnetic
fields)ee, eB
From Piran
initial
shell
ISM
Comparison with Observations
(Sari, Piran & Narayan 98; Wijers & Galama 98;
Granot, Piran & Sari 98; Panaitescu & Kumar 02)
Powerlaws in both
frequency
And in time are predicted,
unfortunately, they do not
predict well the powerlaw
indices…

n 
F (n , t )  F0 (t0 ,n 0 ) 
n 0 
Radio to X-ray
t 
 
 t0 

GRB 990123 - The
Prompt Optical Flash
ROTSE’s detection of a 9th magnitude prompt optical
flash z=1.6 (M_V=-36…as bright as the entire
Universe for 50seconds) … if isotropically emitted
The Initial Lorentz Factor
 The observations of early afterglow from
GRB 990123 lead to several independent
estimates of the initial Lorentz factor (Sari
&Piran, 1999):
 gi~200 (The most relativistic motion
known in the Universe)
From Piran
“Direct” Energy Measurements
In bursts with afterglow for which the host galaxy
was observed we could estimate the total energy
“directly” using the redshift of the host galaxy.
GRB970508
971214
z=0.865
3.418
5.5x1051
2.1x1053
980703
0.966
6x1052
990123
1.6
1.4x1054
000131
4.5
1.2x1054
000418
1.119
8.2x1052
000926
2.037
3x1053
1.4x1054=Mc2 all in gamma Rays!
The Resolution of the Energy Crisis
 Etot - The total energy
 eg - Fraction of Energy in gamma rays
 Egiso - Observed (iostropic) g-ray energy
Etot  eg Eg iso
-1
Beaming:
Eg- Actual
g-ray energy
Etot  e g Eg  e g
-1
-1

2
2
Eg iso
JETS and BEAMING
Particles remain
within initial cone
Radiation is
“beamed” into
a narrow cone
Particles spreads
sideways
quickly
Radiation
is “beamed”
into a
large cone
g-1
Jets with an opening angle  expand forwards until g-1 and
then expand sideways rapidly lowering quickly the observed
flux (Piran, 1995; Rhoads, 1997; Wijers et al, 1997; Panaitescu
& Meszaros 1998).
GRB 990510 Jet Break!
1  0.8522.18
tbreak = 1.2 days  jet
angle = 4o
From Harrison et al 1999
Revised Energy Estimates
• Frail et al, 01: Eg 5
1050ergs FWHM ~ 5
• GRBs release a constant
amount of energy
~1051 ergs – about
same as a SN
What makes a GRB?
• Occur in Galaxies which are
rapidly forming stars
• Rapidly rotating Massive
Stars…
– Collapsar Model (MacFayden
& Woosley)
– Big Star that rapidly rotate
should make blackholes and
shoot jets out in the same
way that a forming star does
SN 1998bw!
Very Energetic SN, Within hours of GRB
Brightest Radio SN ever –
Measurements indicate relativistic
Ejecta…
But 10000 times fainter than
normal GRBs
Berger et al.
Berger et al.
GRB 030329
SSO 40inch observations
Matheson et al.
Rates and Distances
 One long GRBs per 104 (/0.1)-2 years per
galaxy.
Beaming factor
 One observable long burst per year at D~600
Mpc (z~0.1) if you could cover entire sku
 Should be one mis-directed burst per year at
D~135 (/0.1) 2/3 Mpc (z=0.03).
Do all GRBs Have SNe?
GRB 020405
• Collapsar models allow jet
to be produced, where the
shock will not have enough
energy to disrupt star,
(whole shooting match
goes into Black Hole)
• Presently, there is no GRB
observed as faint as the
faintest Hypernovae – but
some are close!
GRB010921
What are Short-Hard Bursts
• Counts verus brightness tests indicated they
occur at lower redshift then long-soft bursts
and have less energy.
• Best guess for last decade has been NeutronStar Neutron Star mergers.
The Frenetic Pace of GRB-science
• Mon 09 May 05 04:00:33
UT
– BAT Position +12h 36m 13s
+29d 00' 01" +/- 3’
• Mon 09 May 05 04:04:01
UT
– BAT light curve
• 05/05/09 05:03:23 UT
– Reported as a Short Hard
Burst – 1st one for SWIFT
• 05/05/09 06:29:23 UT
– XRT position 12:36:13.6
+28:58:58.6 +/- 6”
• 05/05/09 06:44:52 GMT
– Nothing in Rband down to 21st mag from La Palma
• 05/05/09 07:21:27 GMT
– Bloom et al. Noted there is a big 2mass Elliptical near the XRT
position using WIYN+Paritel
• 05/05/09 07:38:23 GMT
– Frail and Soderberg No radio with VLA
• 05/05/09 08:44:13 GMT
– Bloom et al. report Point source in XRT position
• 05/05/09 09:22:11 GMT
– Prochaska report z of big galaxy from Keck-I z=0.22
– The spectral features are consistent with an early type galaxy with
no ongoing star formation. If the association is confirmed, this
would be the first GRB host that is an early-type, hinting that
GRBs of short duration may be due to progenitors that are
unrelated to current and on-going star formation.
• 05/05/09 09:36:49 GMT
•
– Cenko et al (Keck-II) Inside the XRT error circle, we find four
sources, three of which are marginal detections to 26th
magnitude in g,r
5/10/2005 18:20:00 GMT
– HST triggered
• 24 May 2005 18:27:28 GMT
– Closing in on a Short-Hard Burst Progenitor: Constraints from Early-Time
Optical Imaging and Spectroscopy of a Possible Host Galaxy of GRB 050509b
– Authors: J. S. Bloom, J. X. Prochaska, D. Pooley, C. H. Blake, R. J. Foley, S.
Jha, E. Ramirez-Ruiz, J. Granot, A. V. Filippenko, S. Sigurdsson, A. J. Barth,
H.-W. Chen, M. C. Cooper, E. E. Falco, R. R. Gal, B. F. Gerke, M. D. Gladders,
J. E. Greene, J. Hennanwi, L. C. Ho, K. Hurley, B. P. Koester, W. Li, L. Lubin,
J. Newman, D. A. Perley, G. K. Squires, W. M. Wood-Vasey
Comments: ApJ, in press. 35 pages, 9 figures
– The localization of the short-duration, hard-spectrum GRB 050509b was a
watershed event. Thanks to the nearly immediate relay of the GRB position by
Swift, we began imaging the GRB field 8 minutes after the burst and
continued for the following 8 days. No convincing optical/infrared candidate
afterglow or supernova was found for the object. We present a re-analysis of
the XRT afterglow and find an absolute position that is ~4" to the west of the
XRT position reported previously. Close to this position is a bright elliptical
galaxy with redshift z=0.2248, about 1' from the center of a rich cluster of
galaxies. Based on positional coincidences, the GRB and the bright elliptical
are likely to be physically related. We thus have discovered evidence that at
least some short-duration, hard-spectra GRBs arise at cosmological distances.
However, while GRB 050509b was underluminous compared to longduration GRBs, we demonstrate that the ratio of the blast-wave energy to the
gamma-ray energy is consistent with that of long-duration GRBs. Based on
this analysis, on the location of the GRB (40 +- 13 kpc from a bright galaxy),
on the galaxy type (elliptical), and the lack of a coincident supernova, we
suggest that there is now observational consistency with the hypothesis that
short-hard bursts arise during the merger of a compact binary. We limit the
properties of a Li-Paczynski ''mini-supernova.'' Other progenitor models are
still viable, and additional rapidly localized bursts from the Swift mission will
GRB 050505b: Keck/Subaru
Kulkarni et al.
GRB 050724
Berger et al.
Keck Laser Guide Star AO
Kulkarni & Camer
GRB050813
After the dust has settled + 4 more
bursts
•
•
•
•
•
3/4 bursts at z<0.3
3/4 bursts elliptical
1/4 bursts spirals
optical afterglow in 2 out of 5 cases, but
No supernova to very faint level in all cases
Summary: 050509b, 050709, 050724
Comparison to Long-Soft Bursts
Conclusions
• Short hard bursts occur in spiral and elliptical
galaxies (cf SN Ia)
• The energy release of short hard bursts is
smaller than those of long duration bursts
(duration of engine)
• Median redshift of detectable sample is 0.2
Ramifications
• Short time scale of events indicates small size (ct <
50ms=15000km) of Engine
• No supernova light indicates very small ejected mass with
almost no radioactive output
• No star formation eliminates any massive star progenitors
• Lack of afterglow indicates very clean interstellar medium
–
–
–
–
–
–
Best Guess is a Neutron Star – Neutron Star/Blackhole merger.
Gives reasonable agreement with the rates
Gives right time scale for energy release
Occurs in right galaxies
Has right amount of energy
No expected supernova – just afterglow if enough interstellar
medium
GRBs as Beacons for the
Universe
• Long Soft GRBs should follow the star
formation rate.
• LS-GRBs and their afterglow can be
detected even from Z~10.
• Some LS-GRBs are from Z>5 ???
• LS-GRBs are ideal beacons to explore the
early universe – at the time of “first light”.
How-bright is bright...
Gamma Ray Bursts are the Brightest Objects in the Universe
(e.g. GRB990123 MR=-36 mag)
Associated with explosions of Massive stars
Their underlying continuum is smooth power law
Useful beacons for probing very high-z galaxies and
re-ionisation (i.e. Gunn-Peterson effect)
Studying Normal Galaxies at z>4
GRB050505 GRB050730
Ly 
Si IV
OI
C IV
Berger et al. personal
communication
Chen et al. 2005
GRB050904
• SWIFT GRB –
• No r/i detection with Palomar 60inch at
– t+3h33m R > 20.
– t+3h49m i > 19.7
• Bright J=17.5 object seen with SOAR @ 3 hrs
• Subsequent photometry sees it in i
(barely),z,and Y, J,H,K.
A Missed Opportunity
• Labour Day Holiday USA
• Spectrum taken at 3.5 days
(Z=21.5) showed z=6.28
• At 10 minutes, was J=13, or
MJ=-35.9
• At 100 minutes was still
J=16.5 or MJ=-32.4
But there are still more
outhere
Opportunities for South Africa.
South Africa owns this time zone for the southern sky. Need to
coordinate smaller telescopes with the SALT. SALT at a
disadvantage because it must wait for GRB to transit into
observable ring, but there will still be opportunities.
Two Key Science areas
•What are objects which explode into GRBs (need spectroscopy of
z<0.5 objects at regular intervals between t=5 to 50 days)
•Spectroscopy of objects at 5<z<7. Got to get onto them when they
are young. Follow up the objects we find in Australia? (Need red
arm of the spectrograph)
•How many GRBs as a function of z. Get redshifts of GRBs and their
host galaxies.
Other Considerations:
In next 3 years, Swift with provide GRBs over ¼ of useful
sky for optical/IR follow-up. No real planned mission post Swift
to feed SALT or other facilities.