The Nearest GalaxiesThe Nearest GalaxiesLMC

SMC

February 22, 1987February 22, 1987

Image Courtesty of Mike Bessell

SN 1987A (Type II)

Image Courtesty of David Mailn, AAO

The Next Type II Supernova? 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.

Oxygen BurningSilicon BurningIron Burning

Forming Neutron Star

Core Collapse SNe Core Collapse SNe

The Evolution of a SN II-P

SN 92ba

shock breakoutadiabatic coolingrelease of shock deposited energyradioactive reheatinggamma ray deposition

16

18

20

0 50 100 150

transition to nebularphase

>1<1

>1<1

H

Vel increasing

>1<1

H

vmax

<1

H

>1

<1

H

>1

•progenitor loses mass?Wolf RayetBinary 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 RareWolf 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 IIbIf very complete envelope loss Icif just through Hydrogen, Ib

Filippenko

0 10 20 30

1992am

Single Stars (but 2 out of 3 binaries)Lots of Iron…

……

……

……

……

……

……

.Iron P

oor

10 solar masses 40 100 260

THE DISCOVERY

Gamma-Ray Bursts (GRBs) Short (few seconds) bursts of 100keV- few 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 There was an “invite prediction”. S. Colgate was prediction”. S. Colgate was asked to predict GRBs as a asked to predict GRBs as a scientific excuse for the scientific excuse for the launch of the Vela Satelliteslaunch of the Vela Satellites

•

1970s….The Data-free years 1970s….The Data-free years (aka..Theorists run wild)(aka..Theorists run wild)

• 1974: The NY Texas Symposium1974: 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.

Duration 0.01-100sTwo populations (long and

short)

~ 1 BATSE burst per dayNon thermal Spectrum

(very high energy tail, up to GeV, 500GeV?)

Rapid variability (less than 10ms)

COMPTON-GRO resultsCOMPTON-GRO results

Compton-GRO

1991-2000: BATSE 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 thanEuclidean Space)

Two Classes of EventsTwo populations of GRBs – short and long

Anti-correlation with spectral hardness – short and hard (Higher energy), long and soft (lower energy).

• =R=R//cc==//cc//cc=T=T

• The observed light curve The observed light curve reflects the activity of the reflects the activity of the “inner engine”. “inner engine”.

• To produce internal shocks To produce internal shocks the source must be active the source must be active and highly variable over a and highly variable over a

“long” period.“long” period.

=cT=cT

==cT

Internal ShocksInternal ShocksShocks between different Shocks between different shells of the ejected shells of the ejected relativistic matterrelativistic matter

TT

From Piran

InnerEngine

Relativistic Wind

The Internal-External Fireball ModelThe Internal-External Fireball Model

ExternalShock

Afterglow

InternalShocks

-rays

OPTICAL FLASHOPTICAL FLASH

From Piran

1997: Afterglow Discovery 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 AfterglowThe Radio Afterglow of of GRB970508 GRB970508 (Frail et. al, 97).(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 since this is a long time after the explosion

Afterglow TheoryAfterglow Theory

Hydrodynamics: deceleration of therelativistic 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)e, B

initialinitialshellshell ISMISM

From Piran

Comparison with Comparison with ObservationsObservations

(Sari, Piran & Narayan 98; Wijers & (Sari, Piran & Narayan 98; Wijers & Galama 98; Granot, Piran & Sari 98; Galama 98; Granot, Piran & Sari 98;

Panaitescu & Kumar 02)Panaitescu & Kumar 02)

Radio to X-rayRadio to X-ray

Powerlaws in both frequencyAnd in time are predicted, unfortunately, they do not predict well the powerlaw indices…

00000 ),(),(

t

ttFtF

GRB 990123 - TheGRB 990123 - ThePrompt Optical FlashPrompt 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 FactorThe Initial Lorentz Factor The observations of early afterglow

from GRB 990123 lead to several independent estimates of the initial Lorentz factor (Sari &Piran, 1999):

i~200 (The most relativistic motion known in the Universe)

From Piran

““Direct” Energy Direct” Energy MeasurementsMeasurements

In bursts with afterglow for which the host galaxy In bursts with afterglow for which the host galaxy was observed we could estimate the total energy was observed we could estimate the total energy “directly” using the redshift of the host galaxy.“directly” using the redshift of the host galaxy.

GRB970508

z=0.865 5.5x1051

971214 3.418 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=Mc2 all in gamma Rays!

The Resolution of the Energy The Resolution of the Energy CrisisCrisis Etot - The total energy

- Fraction of Energy in gamma rays Eiso-Observed (iostropic) ray energy

isotot EE 1

isotot EEE 2

211

Beaming:Beaming:EE- Actual - Actual ray energyray energy

JETS and BEAMINGJETS and BEAMING

Jets with an opening angle expand forwards until and then expand sideways rapidly lowering quickly the observed flux (Piran, 1995; Rhoads, 1997; Wijers et al, 1997; Panaitescu & Meszaros 1998).

Particles spreadssidewaysquickly

Radiationis “beamed”into a large cone

Particles remainwithin initial cone

Radiation is “beamed” intoa narrow cone

GRB 990510 - GRB 990510 - Jet Break!Jet Break!

tbreak = 1.2 days jet angle = 4o

FromFrom Harrison et al 1999Harrison et al 1999

Revised Energy EstimatesRevised Energy Estimates

• Frail et al, 01: E 5 1050ergs FWHM ~ 5

• GRBs release a GRBs release a constant amount constant amount of energy ~10of energy ~105151 ergs – about ergs – about same as a SNsame 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 relativisticEjecta…But 10000 times fainter than normal GRBs

Berger et al.

Berger et al.

Matheson et al.

GRB 030329SSO 40inch observations

Rates and Rates and DistancesDistances

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?

• 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!

GRB 020405

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 Neutron-Star 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-VaseyComments: 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 long-duration 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 undoubtedly help to further clarify the progenitor picture.

GRB 050505b: Keck/Subaru

Kulkarni et al.

Berger et al.

GRB 050724

Keck Laser Guide Star AO

Kulkarni & Cameron

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, 050724Comparison 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 GRBs as Beacons for the UniverseUniverse

• 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

Si IV

C IVO I

Ly

Berger et al. personalcommunication

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 Swiftto feed SALT or other facilities.