Gamma-Ray Bursts: Things that REALLY Go Bang in the Night

Andy Fruchter

STScI

Primary Topics

• An Historical Introduction• The Beppo-Sax Era and Beyond• HST Images• The Astrophysics of the Bursts • The Nature of the Hosts

The Electromagnetic Spectrum

Gamma-rays observed in Gamma-Ray Bursts have about 10 to 100 times the energy of the X-rays

What is Redshift?

• Ever since the big bang the universe has expanded with time

• As the universe expands, so do the photons in it --- their wavelengths get longer, and thus they become redder

• Astronomers use “z” to characterize this effect -- with the relative size of the universe equal to 1/(1+z)

The Sky at Different Wavelengths

Radio

Infra-red

Gamma-Ray

The Vela Satellites:Protecting the Nation from Illicit GRBs

Designed to detect nuclear tests (in violation of the test ban treaty), the Vela satellites discovered GRBs

Demonstrating the Cosmic Origin of Gamma Ray Bursts

Compton Gamma-Ray Observatory

Taken from http://www.batse.msfc.nasa.gov/data/grb/skymap

BATSE GRB Sky Distribution

Beppo-Sax Localization

BeppoSAX X-ray images of GRB 990123

GRB 970228

STIS: 4 September 1997 NICMOS: 24 February 1998

GRB 970508

2 June 1997 5 July 1998

OT GRB970508

OT Spectrum of GRB 970508

Metzger et al. 1997

z=0.83

Chicken or Egg?(or Red Herring?)

GRB 980425 Error Circles SN 1998bw

What is a Hypernova?

• “Royal Ahold, the international food retailer, opened its first hypermarket in the Czech capital of Prague. 'Hypernova'… is open every day - including Sunday - from 9 to 9.”

• Sales to date are well above expectations.

• My thought, exactly.

Daddy, where do stars go when they die?

White Dwarf Neutron Star?

43+= oαα

cθΓ1

To Beam or Not To BeamTwo primary mechanisms predict a change in the behavior of the light curve when 1/Γ~ θc

1. Mésáros and Rees: Edge Effect =>

2. Rhoads; Sari and Piran: Physical Expansion =>

300Γ+≈+= θτθθ ct

csc

p−=α

GRB 990123

• The brightest SAX burst yet

• Detected in optical during gamma-ray burst, with

peak

• Keck and NOT spectroscopy find metal absorption

lines => z=1.6

• Resulting ergs

• OT faded by a factor of 4 million in two weeks

54102E ×=γ

9mV =

GRB 990123: The First Ten Minutes

ROTSE-1

GRB 990123 Going…......going….…....gone

+16 days +59 days +380 days

Are Gamma Ray Bursts “Searchlights”?

• The extreme energy needed to produce a GRB could be reduced dramatically if the bursts are collimated “searchlights”.

• Two predictions for collimated GRBs:– There should be “orphan afterglows”, and

– Afterglows of collimated GRBs should fade more rapidly at late times.

• There are now a number observations of rapid late time fading.

Beaming Statistics

Frail et al. 2001

What GRB 990123 Lacks:A SN of Its Own

• Not its fault: at z=1.6, NICMOS or ACS would have been required to detect the SN component

• Numerous bursts show a late-time red excess 0.5 to 1.0 mags fainter than SN1998bw -- only one convincing case of a missing SN (Price et al. 2002) -- and limit is only 1.5 mags > 1998BW.

• At least one burst (GRB 020410; Levan et al. 2003) has been discovered by the late-time excess

What 990123 Lacked:

Hjorth et al. 2003 (Nature, submitted)

GRB 03032/SN2003dh

A Galaxy on (nearly) Every Burst

GRB 000301c

6 March 2000 3 April 2000

HST/STIS UV Spectrum of GRB 000301c

Smette et al. (2000)

•Star•z<1•1<z<2•2<z•z undetermined•GRB

Neon Signs

Bloom et al. 1998

GRB 990510

Convolved to FWHM = 0.”3 Native Resolution

~1 Year After Burst

Vreeswijk et al. 2000

Gamma Ray Bursts and the Deaths of Massive Stars

Afterglow data suggests that …• GRBS occur in galaxies with active star

formation,• often in regions with a lot of gas, which is where

new stars form and where the most massive stars spend their entire brief lives.

• And may often (always?) have underlying SNeHowever, GRBs are so rare that only a tiny fraction

of massive star deaths could produce them.

Effects of Gamma Ray Bursts on their Environments

Gamma ray bursts are not nice neighbors.The high energy photons they produce can

evaporate interstellar dust grains up 100 light years away, and ionize interstellar gas out to may light years.

The ionized gas will fluoresce as it gradually recombines, and might be used to look for GRB remnants in nearby galaxies.

What if a GRB happened nearby?

• It could be spectacular: GRB 990123 reached 9th magnitude at a redshift z=1.6.

• A GRB in our Galaxy would ionize atmospheric gasses, creating NOx compounds which destroy ozone (Thorsett 1995).

• Volcanic eruptions, industrial emissions, etc can have similar effects.

• Once in 100 million years, a GRB might be close enough to be more dangerous than Mt. Pinatubo.

• An asteroid will probably get us first.

The Shape of Things to Come

• SWIFT, a NASA MidEx mission, is approved and should fly in September. Yield: 300 good positions per year?

• These will open the way for systematic study of afterglows, including the still-mysterious short bursts.

Tomorrow’s QuestionsUpcoming space missions, better coordinated

followup, and ongoing theoretical work all promise continued rapid progress in GRBs.

Specific questions:• Do the short GRBs have afterglows? Host galaxies?

Are they caused by the death of massive stars, merging neutron stars or ….?

• Do all long GRBs have associated supernovae?And, ultimately….• Is every GRB the birth of a new black hole?

Conclusions

• In all cases evidence is found that the GRB lies in a host galaxies.

• The optical transients display power-law decays for a substantial fraction of the time (in log time), and some display possible evidence of beaming or SNe, but no one model explains all variaitions form power-law decay

• The hosts are blue, have strong [OII] emission, and a steep luminosity function -- all indicating a high star-formation rate.

• GRBs may provide a unique probe of a high-redshift star-forming galaxies.

GRB 990712

Loveday, Tresse and Maddox (1999)

M*

α

Hi [OII]

Med [OII]Low [OII]

⎟⎟⎠

⎞⎜⎜⎝

⎛−⎟⎟

⎠

⎞⎜⎜⎝

⎛=

∗ *

exp)(L

L

L

LL

α

φ

A Galaxy without an (optical) Afterglow

The SED of GRB 980329

Fruchter (1998)

Through Every Cloud a GRB May Shine

From Galama and Wijers, 2000

Light Curve of GRB 990510

GRB 980405

SN1998bw

Luminosity Functions by Play Dough

Luminosity Functions by Play Dough

12.055.1 ±−=α

The Evidence Gets Beta

Chary, Becklin and Armus (2002)

(nearly) Every GRB Is Above Average

Berger et al. 2002

Through Every Cloud a GRB May Shine

From Galama and Wijers, 2000

From Fruchter, Krolik and Rhoads (2001)