Lijin Huang (ASIAA)

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What are Gamma-rays?Gamma-rays (γ) are a from of

electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions .

They consist of high energy photon with energies above 100 keV.

Gamma-rays coming from space are mostly absorbed by the Earth’s atmosphere

Gamma-ray observatories need to build above all or most of all of atmosphere (e.g. satellites or balloons)

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radio

optical

X-ray

Infrared

UV

γ -ray

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radio microwave Infrared

optical UV X-ray 5

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• Solar system : AU or light year

• Nearby galaxies: pc , kpc, Mpc

• distant galaxies: redshift (z)

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What are gamma-ray bursts(GRBs)?

GRBs are short and intense bursts of high energy photons.

Rate : 1-2 times/dayDuration time : 0.01 – 1000sDifferent behaviors in

individual burst.GRBs are named by the date

that it was triggered. e.g. GRB 030329 : 2003/3/29 0ccurred

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• Three classifications of GRBs : (1) Long GRBs : T90 > 2s, with soft high-energy spectra Related with “Massive stars”. (2) Short GRBs : T90 < 2s, with hard high-energy spectra Related with “NS-NS or NS-BH” merger.

(3) X-ray flashes (XRFs) : No gamma-ray emission, but have number of X-ray emission. The same origin with Long GRBs, but with different observational angle. T90: the duration time ( 5%-95% of counts in 50-300 keV)

Short ( hard )

Long ( soft )

Gamma-ray bursts

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Afterglows and supernovae (1)Several long-duration GRB afterglows

accompanied with late time bump (several days after the GRB occurred)

Spectral observations indicate the late time bump was signals from supernovae.

Direct clues : GRB 030329 (z=0.106)

Stanek et al. (2003)

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Afterglows and supernovae (2)More evidences : GRB 980425 /SN1998bw (z=0.0085,

Type Ic) GRB 031203 / SN2003lw (z=0.165,

Type Ic) GRB 060218 / SN 2006aj (z = 0.003,

Type Ic) Progenitors of some long-duration GRBs

are massive stars.

ESO184-G82 12

• Three classifications of GRBs : (1) Long GRBs : T90 > 2s, with soft high-energy spectra Related with “Massive stars”. (2) Short GRBs : T90 < 2s, with hard high-energy spectra Related with “NS-NS or NS-BH” merger.

(3) X-ray flashes (XRFs) : No gamma-ray emission, but have number of X-ray emission. The same origin with Long GRBs, but with different observational angle. T90: the duration time ( 5%-95% of counts in 50-300 keV)

Short ( hard )

Long ( soft )

Gamma-ray bursts

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0

obs

GRBsOn-axis

XRFsOff-axis

max

Orphan OAsOff-axis

No prompt -ray emission

Jet break

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History of Gamma-ray bursts(1)1967 – the first GRB was detected by U.S military

satellite, Vela. 1973 – 16 GRBs detected by the Vela were reported

by

Klebesadel et al.

Cosmological origin or Galactic origin ?1991 – the Compton Gamma-ray Observatory was

lunched. The instrument” Burst and Transient

Source Experiment (BASTE)” detected 2074 GRBs

in 9 years.15

The results of BASTEGRB sky distribution is isotropic.GRBs come from outside of Galaxy.Disprove the galactic neutron model.GRBs are cosmological distance scale.

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BeppoSAX (1996~ 2002): -- Be able to localize GRB positions(~50’).

-- GRB 970228 : the first GRB detected its X-ray and optical afterglow -- GRB 970508 : z= 0.835. GRBs are cosmological distances.

HETE-2 (2000 ~ ) : -- It was designed to detect and localize GRBs.

-- Be able to calculate coordinates (~20’) and send them to ground-base observers. -- GRB 030329 : the first GRB was discovered to be connected with supernova.

History of Gamma-ray bursts(2)

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History of Gamma-ray bursts(3)Swift satellite (2004- present) Can localize GRBs in 20-75s with accurate < 10’.

Three telescopes : BAT(γ-ray), XRT(x-ray), UVOT(optical) can perform quick simulations observations.

the farthest GRB : GRB 050904 (z=6.3) X-ray flash (XRF 060218) is associated with Type

Ic SNe Optical afterglows of short GRBs Canonical behaviors in X-ray afterglow detection rate : X-ray afterglow ~ 90% optical afterglow ~ 50%

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Afterglows of GRBs The first optical afterglow : GRB 970228 (X-

ray, optical)The optical light curve show a simple power-

law decay consistent with theoretical expectation mechanism may be synchrotron radiationMore optical observations indicate that

different behaviors in individual afterglow GRB 970228

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Time since GRB triggered by Satellite 20

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Afterglows and host galaxies

After GRB afterglows faded, most of the bursts are associated with underlying galaxies (Host galaxies).

GRBs are associated with stellar objects.Afterglow position, especially optical

afterglows, could provide accurate GRB hosts

Afterglow Host galaxy

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Morphology of GRB hosts Compact, irregular, spiral or merger-

driven

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How does afterglow from Proposed by Sari & Prain in 1997.Gamma-ray : Internal shocks Afterglow : External shocks

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Spectral evolution

a : the synchrotron self-absorptionm : the injection or typical frequencyc : the cooling frequency

Early time (m > c )

Late time (m < c )

Temporal evolution

0 = m = c : transition of fast and slow cooling at t0

Fast cooling

slow cooling

Fast cooling

at t0 (m = c )

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Study GRB afterglowsImportance -- Understand their origin, mechanism, and

environments . -- The connection between GRBs and SNe -- Can GRB used for cosmological candle ?Difficulty -- Cannot forecast the GRB position, we thus need the

pointing of satellite. -- GRB never repeat at same position -- Fast decay in brightness of afterglows No easy for long term monitoring.

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What afterglows tell us ?From optical light curve -- temporal evolution and spectral evolution

Test GRB models and constrain physical parameters

Accurate position of afterglows -- indentify host galaxies

understand environment of GRB origins From afterglow spectrum, photometric redshift -- estimate distance of GRBs

estimate total energy, luminosity of GRBs

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Satellite detect a GRB

GCN System

Ground telescopesAnd observers

telescopes observers

Satellites and ground telescopes

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East-Asia GRB follow-up Observation Network (EAFON)

Advantages in East-AsiaA blank in the East Asia The follow-up are

expected to provide valuable observations for GRB field.

Different positions of sites To reduce the risk of weather. Allow the cover range to up Dec~ -40 deg Complete multi-band light curves.

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• Telescopes (1) WIDGET – 4 optical cameras, each camera with F.O.V. ~ 60d x 60d . (2) KISO observatory (1.05m) - Optical camera(50’x50’) - Infrared camera (20’x20’). (3) LOT (1.0m) – F.O.V~ 11’ x 11’ - Optical camera (4) Beijing (0.8 m & 2m) – robotic 0.8m (10’x 10’) - 2m telescope spectroscopy (5) CFHT (3.6m) - WIRcam F.O.V ~20.5’x 20.5’ (6) Mt. Lemon (1.0m) - Optical camera

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Located at central part of Taiwan.Height ~ 2862 m Lulin One-meter telescope (LOT)CCD : PI1300 and Ap8 (F.O.V.~ 11’x11’)Filter : U,B,V,R,I and some narrow band filters.

Lulin Observatory

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鹿林天文台~2,860 m

玉山 ~4,000 m

中央大學

阿里山

阿里山

日月潭

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照片由中央大學提供 ( 拍攝時間 :2007年八月 )

Lulin ObservatoryLulin Observatory

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!!! NO ROAD !!!!!! NO ROAD !!!

Good For Your HealthGood For Your Health

120m120m

0.6km climbing

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• Observational method :

Our observations and Data Analysis

• Data analysis : -- scripts for World Coordinate in images. -- real time GRB information at website. -- script for brightness measurement of afterglows.

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• 42 TOO observations were performed. • Response time : 24mins~ 20.4 hrs• Detected 15 afterglows• 6 refereed papers. Additional work keeps going and mounting.(1) Optical Afterglow Observations of the Unusual Short-Duration Gamma-ray Bursts GRB 040924. (Huang et al. 2005)(2) Multicolor Shallow decay and Chromatic Breaks in the GRB 050319 Optical Afterglow (Huang et al. 2007)(3) When do Internal Shocks End and External Shock Begin? Early-Time Broadband Modeling of GRB 051111 (Bulter et al. 2005)(4) Very early multicolor observation of the GRB 041006 rebrighting afterglow (Urata et al. 2007)(5) Extensive multiband study of the X-ray rich GRB 050408. A likely off-axis event with an intense energy injection (A de Ugarte Postigo et al. 2007)(6) A multi band study of optically dark GRB 051028 (Urata et al. 2007,PASJ, accepted)

Observational results using LOT

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GRB observation with TAOS Telescopes

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TAOS ProjectTAOS Project(Taiwan-America Occultation Survey)

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TAOSA and TASOB

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Asteroid EventsAsteroid Events

A bright star HIP 079407 (MV = 8.80) was occulted by an asteroid (51) Nemausa (MV = 11.9, diameter = 150 km) with a occultation duration around 5 seconds at around 18:55 21st Feb. 2004 (UTC). (TAOS A observation is shown above.)

A bright star HIP 050535 (MV = 8.46) was occulted by an asteroid (1723) Klemola (MV = 15.7, diameter = 31 km) with a occultation duration around 1 seconds at around 12:10 5th Jun. 2004 (UTC). (Observed by both TAOS A & B running in synchronous mode)

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Special Features of TAOS project

Four robotic telescopes (50cm, F/1.9 Cassegrain)2k x 2 k CCD Camera (EEV CCD 42-40)Field of View ~ 1.7 degree x 1.7 degreePixel size ~ 3 “Filter : 5000-7000 A (near R band )Observational Mode – Zipper mode (0.2 sec exposure) - Stare mode Nearly real-time processing /correlation among

telescopes Response to GCN (GRB Coordinate Network) alert in 1 min

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Two components of optical emission during the first

few minutes (Vestrand et al. 2006)

(a) The prompt optical emission

Correlated with prompt gamma-ray emission.

Could probe isolated jet from the surrounding medium

(b) The early optical afterglow emission

Uncorrelated with prompt gamma-ray emission Strongly depends on the nature of medium

Probe early optical emission of Probe early optical emission of GRBsGRBs

T90 =520s T90 =110s

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TAOS GRB observations in 2006-2007TAOS GRB observations in 2006-2007

(1) GRB 071010B Duration : 35s Afterglows : XT, OT Redshift : 0.947 Response telescopes :

TAOSA(1s),TAOSB(5s),TAOSD(25s)

Response time : 52s after trigger 38s after alert Fastest response in this event Time coverage : 63-230 s

(2) GRB 071112C Duration : 15s

Afterglows : XT, OT

Redshift : 0.823

Response telescopes : TAOSA(1s),TAOSB(5s)

Response time :

94s after trigger

41s after alert

Time coverage : 94-4000 s44

EAFON

TAOS

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TAOS

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(1) GRBs are cosmological : Isotropic distribution

(2) Detection of afterglows in 1997 : GRB 970228(3) Supernovae associated with long-duration GRBs

(4) Optical afterglows of short/hard GRBs (5) Discovery of the canonical behavior of X-ray

afterglows

Summary 1: Breakthroughs in GRB study

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Power-law evolution synchrotron emission

Detection rate : X-ray afterglows > 90% Optical/IR afterglows ~ 50% Radio afterglows ~ 20%

Before the Swift era, afterglow light curves are well described by several power-law components

The swift events show complicated evolution (e.g. flares, shallow decay)

Summary 2: About GRB Afterglows

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Importance of Optical Afterglow monitoring Breaks yield important information about the ejecta.Study these breaks would helpful to examine standard model and understand GRB ejecta: (1) Passing through spectral (1) Passing through spectral frequency breaksfrequency breaks emission mechanism (2) Multiple components(2) Multiple components Additional energy injection Different emission regions (3) Geometrical effect(3) Geometrical effect Jet

Harrison et al 1999

Jet break

~ -1~ -1 ~ -2~ -2

Break pointBreak point ~ 1/~ 1/

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Expected Spectrum from standard model (1998)

Synchrotron Shock Model (SSM) with electron cooling

Electron energy distribution

Synchrotronabsorption

Cooling a : self-absorption frequencym : injection frequency of electrons c : cooling frequencySari et al. 1998

• Fast cooling -- early GRB stage -- m > c

-- All the electron will have cooling • Slow cooling -- afterglow stage -- partly electron m > c

-- only the electron > c will have cooling •Afterglow evolution

ttF ),(

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Expected light curve from standard model

Fast cooling

Fast cooling

• 0 is critical frequency.

0 = c (t0) = m (t0) transition from fast cooling to slow cooling

slow cooling• < 0

t0 < tm < tc

Evolution : BFGH

• > 0

t0 > tm > tc

Evolution : B CDH

The standard model well explained to the afterglow evolution before the swift era (Nov. 2004).

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