Lijin Huang (ASIAA) 1

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) 2

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radio optical X-ray Infrared UV γ -ray 4

radio microwave Infrared optical UV X-ray 5

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Distance Units in Astronomy Solar system : AU or light year Nearby galaxies: pc, kpc, Mpc distant galaxies: redshift (z) 7

What are gamma-ray bursts(GRBs)? GRBs are short and intense bursts of high energy photons. Rate : 1-2 times/day Duration time : 0.01 – 1000s Different behaviors in individual burst. GRBs are named by the date that it was triggered. e.g. GRB : 2003/3/29 0ccurred 8

Three classifications of GRBs : (1) Long GRBs :  T 90 > 2s, with soft high-energy spectra  Related with “Massive stars”. (2) Short GRBs :  T 90 < 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. T 90 : the duration time ( 5%-95% of counts in keV) Short ( hard ) Long ( soft ) Gamma-ray bursts 9

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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 (z=0.106) Stanek et al. (2003) 11

Afterglows and supernovae (2) More evidences : GRB /SN1998bw (z=0.0085, Type Ic) GRB / SN2003lw (z=0.165, Type Ic) GRB / 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 :  T 90 > 2s, with soft high-energy spectra  Related with “Massive stars”. (2) Short GRBs :  T 90 < 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. T 90 : the duration time ( 5%-95% of counts in keV) Short ( hard ) Long ( soft ) Gamma-ray bursts 13

00  obs GRBs On-axis XRFs Off-axis  max Orphan OAs Off-axis No prompt  -ray emission Jet break 14

History of Gamma-ray bursts(1) 1967 – the first GRB was detected by U.S military satellite, Vela – 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 BASTE GRB sky distribution is isotropic. GRBs come from outside of Galaxy. Disprove the galactic neutron model. GRBs are cosmological distance scale. 16

BeppoSAX (1996~ 2002): -- Be able to localize GRB positions(~50’). -- GRB : the first GRB detected its X-ray and optical afterglow -- GRB : z=  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 : the first GRB was discovered to be connected with supernova. History of Gamma-ray bursts(2) 17

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 (z=6.3)  X-ray flash (XRF ) 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% 18

Afterglows of GRBs The first optical afterglow : GRB (X-ray, optical) The optical light curve show a simple power-law decay  consistent with theoretical expectation  mechanism may be synchrotron radiation More optical observations indicate that different behaviors in individual afterglow GRB

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 AfterglowHost galaxy 22

Morphology of GRB hosts Compact, irregular, spiral or merger-driven 23

How does afterglow from Proposed by Sari & Prain in Gamma-ray : Internal shocks Afterglow : External shocks 24

Spectral evolution a : the synchrotron self-absorption m : the injection or typical frequency c : the cooling frequency Early time ( m > c ) Late time ( m < c ) Temporal evolution 0 = m = c : transition of fast and slow cooling at t 0 Fast cooling slow cooling Fast cooling at t 0 ( m = c ) 25

Study GRB afterglows Importance -- 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. 26

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 27

Satellite detect a GRB GCN SystemGround telescopes And observers telescopes observers Satellites and ground telescopes 28

East-Asia GRB follow-up Observation Network (EAFON) Advantages in East-Asia A 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. 29

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 30

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 31

鹿林天文台 ~2,860 m 玉山 ~4,000 m 中央 大學 阿里山 日月潭日月潭 32

照片由中央大學提供 ( 拍攝時間 : 2007年八月 ) Lulin Observatory 33

!!! NO ROAD !!! Good For Your Health Good For Your Health 120m 0.6km climbing 34

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. 35

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 (Huang et al. 2005) (2) Multicolor Shallow decay and Chromatic Breaks in the GRB Optical Afterglow (Huang et al. 2007) (3) When do Internal Shocks End and External Shock Begin? Early-Time Broadband Modeling of GRB (Bulter et al. 2005) (4) Very early multicolor observation of the GRB rebrighting afterglow (Urata et al. 2007) (5) Extensive multiband study of the X-ray rich GRB 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 (Urata et al. 2007,PASJ, accepted) Observational results using LOT 36

GRB observation with TAOS Telescopes 37

TAOS Project TAOS Project (Taiwan-America Occultation Survey) 38

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TAOSA and TASOB 40

Asteroid Events A bright star HIP (M V = 8.80) was occulted by an asteroid (51) Nemausa (M V = 11.9, diameter = 150 km) with a occultation duration around 5 seconds at around 18:55 21st Feb (UTC). (TAOS A observation is shown above.) A bright star HIP (M V = 8.46) was occulted by an asteroid (1723) Klemola (M V = 15.7, diameter = 31 km) with a occultation duration around 1 seconds at around 12:10 5th Jun (UTC). (Observed by both TAOS A & B running in synchronous mode) 41

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 degree Pixel size ~ 3 “ Filter : 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 42

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 GRBs T 90 =520s T 90 =110s 43

TAOS GRB observations in (1) GRB B  Duration : 35s  Afterglows : XT, OT  Redshift :  Response telescopes : TAOSA(1s),TAOSB(5s),TAOSD(25s)  Response time : 52s after trigger 38s after alert  Fastest response in this event  Time coverage : s (2) GRB C  Duration : 15s  Afterglows : XT, OT  Redshift :  Response telescopes : TAOSA(1s),TAOSB(5s)  Response time : 94s after trigger 41s after alert  Time coverage : s 44

EAFON TAOS 45

TAOS 46

(1) GRBs are cosmological : Isotropic distribution (2) Detection of afterglows in 1997 : GRB (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 47

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 48

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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 breaks frequency breaks  emission mechanism (2) Multiple components  Additional energy injection  Different emission regions (3) Geometrical effect (3) Geometrical effect  Jet Harrison et al 1999 Jet break  ~ -1  ~ -2 Break point  ~ 1/  50

Expected Spectrum from standard model (1998) Synchrotron Shock Model (SSM) with electron cooling Electron energy distribution Synchrotron absorption Cooling a : self-absorption frequency m : injection frequency of electrons c : cooling frequency Sari et al 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 51

Expected light curve from standard model Fast cooling 0 is critical frequency.  0 = c (t 0 ) = m (t 0 )  transition from fast cooling to slow cooling < 0  t 0 < t m < t c  Evolution : B  F  G  H > 0  t 0 > t m > t c  Evolution : B  C  D  H The standard model well explained to the afterglow evolution before the swift era (Nov. 2004). 52