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Gamma-ray Bursts and Their Afterglows

Gamma-ray Bursts and Their Afterglows. Lijin Huang (ASIAA). 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.

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Gamma-ray Bursts and Their Afterglows

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  1. Gamma-ray Bursts and Their Afterglows Lijin Huang (ASIAA)

  2. 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)

  3. radio Infrared UV optical X-ray γ -ray

  4. radio microwave Infrared optical UV X-ray

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

  6. 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 030329 : 2003/3/29 0ccurred

  7. Gamma-ray bursts • 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 )

  8. 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)

  9. 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

  10. Gamma-ray bursts • 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 )

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

  12. 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.

  13. 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.

  14. History of Gamma-ray bursts(2) • 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.

  15. 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%

  16. 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 radiation • More optical observations indicate that different behaviors in individual afterglow GRB 970228

  17. Magnitude ( bright to faint) Time since GRB triggered by Satellite

  18. 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

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

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

  21. Spectral evolution Temporal evolution Early time (m > c ) Fast cooling at t0 (m = c ) slow cooling Late time (m < c ) Fast cooling 0 = m = c : transition of fast and slow cooling at t0 a : the synchrotron self-absorption m : the injection or typical frequency c : the cooling frequency

  22. 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.

  23. 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

  24. Satellites and ground telescopes Satellite detect a GRB GCN System Ground telescopes And observers observers telescopes

  25. 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.

  26. 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

  27. Lulin Observatory • 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.

  28. 阿里山 中央大學 玉山~4,000 m 鹿林天文台~2,860 m 日月潭 阿里山

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

  30. 120m 0.6km climbing !!! NO ROAD !!! Good For Your Health

  31. Our observations and Data Analysis • Observational method : • Data analysis : • -- scripts for World Coordinate in images. • -- real time GRB information at website. • -- script for brightness measurement of afterglows.

  32. Observational results using LOT • 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)

  33. GRB observation with TAOS Telescopes

  34. TAOS Project(Taiwan-America Occultation Survey)

  35. TAOSA and TASOB

  36. Asteroid 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)

  37. Special Featuresof 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 : 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

  38. Probe early optical emission of GRBs • 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 T90 =520s T90 =110s

  39. TAOS 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 s

  40. TAOS EAFON

  41. TAOS

  42. Summary 1: Breakthroughs in GRB study • GRBs are cosmological : Isotropic distribution • Detection of afterglows in 1997 : GRB 970228 • Supernovae associated with long-duration GRBs (4) Optical afterglows of short/hard GRBs (5) Discovery of the canonical behavior of X-ray afterglows

  43. Summary 2: About GRB Afterglows • 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)

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

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