GRB Physics Progenitors

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GRB Physics / Progenitors

• Nobuyuki Kawai
• Tokyo Tech

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GRB outstanding problems

• Long GRBs
• progenitors and environments
• launching ultra-relativistic jets
• highly efficient gamma-ray emission
• GRB subclasses
• Short GRBs
• X-ray flashes
• sub-luminous SN-GRBs

• distance
• population
• mechanism

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EDGE capabilites for GRB study

• Fast localization and pointing (cf. Swift)
• precise location ? ground follow-up
• Wide-band trigger (cf. BeppoSAX, HETE-2)
• Epeak (Spectral Energy Peak) determination
• Sensitivity for X-ray flashes and short hard GRBs
• Large effective area and moderate energy
  resolution (cf. XMM, Suzaku)
• faint subclass (short GRB, XRF, )
• spectral features
• Superior spectral resolution

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Long GRBs

• Distance (known for 25 of Swift GRB) z06.3
• Associated with death of massive stars
• 410 GRBs associated with core-collapse SN
• whats special? ( rate 0.2 of ordinary ccSN)
• Mass
• occur at regions with vigorous star formation
• Wolf-Rayet wind shell
• Rotation
• ALL theoretical models require rotation for
  launching jets
• no observational evidence
• Metallicity
• optical/UV absorption lines
• X-ray low-energy absorption

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GRB Environment
galaxy ISM
Molecular Cloud
H II Region
SN ejecta
WR Wind Shell
IGM
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NHI(optical) vs. NH(X-ray)

• No correlation
• Gas cloud ionized by GRB UV light
• HI cloud at gt3 pc

Watson et al. 2007
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NH in X-ray afterglow of GRB050904

• decrease with time
• ? photoionization
• Inconsistency with (lack of) optical extinction
• ? no carbon dust?
• EDGE can test Photoionization model

Campana et al. 2007
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Absorption spectroscopy of CSM

• absorption edges/lines
• ionization state
• time variable? density structure
• velocity (radiative acceleration?)
• need for independent redshift ? opt/NIR afterglow
• chemical composition
• progenitor wind shell or primordial molecular
  cloud
• comparison with optical absorption
• ? dust/gas ratio

OVII and O VIII of warm absorber
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Emission lines

• 3-4 s detections, significance questioned
• visible when non-thermal continuum is weak
• late phase (104 s)
• early afterglow or flares of sub-luminous events
• Best targets X-ray flashes and local SN-GRBs
• need triggers at low energies (?soft X-ray
  sensitivity)
• Possible mechanism
• Shock/cocoon breakouts
• fluorescence on SN ejecta
• Need independent (i.e. optical) redshifts for
  identification and velocity measurements

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Fe lines/RRC in late afterglow
GRB 970507 BeppoSAX, t30000s Piro et al. 1999
GRB 991214 Chandra, t9700 s Piro et al. 2000
GRB 970828 ASCA, T10000s Yoshida et al. 1999

• seen only at late limited time intervals (T0104
  s)
• statistical significance (3 s) questioned
• Fe emission line and/or radiative recombination
  edge
• requires 0.1 Msun of iron pre-ejected at 0.1 c

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Line emission in late X-Ray Afterglow of
GRB030227 by XMM
Watson et al. 2003

• line flux increase with time
• Si, S, Ar, Ca, but no Fe photoionized?
• statistical significance (3 s) questioned
• z1.36 no independent redshift measurements

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Early X-ray afterglow
Butler 2007

• gt70 X-ray afterglow of Swift GRBs
• 1000 spectra examined
• Mostly power-law, a few notable outliers

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Possible line detections in Swift afterglows
Butler 2007
GRB 060218 2 Fe-L lines, 4-s
GRB 050822 flare 5 lines (Si, S, Ar) 4.4-s
GRB 050714B flare 4 lines (Si, S, Ar, Ca) 4.2-s

• found in early afterglow of 4 GRBs with soft
  thermal continuum
• (sub-luminous class of GRB/XRF?)
• breakout of GRB shock or mildly relativistic
  cocoon (?)
• only GRB060218 has established redshift

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Break out of a relativistic jet from a WR star
beamed emission
off-axis emission (XRF?)
thermal emission (break out)
Zhang, Woosley Heger 2004
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Short GRBs

• first 3 SGRBs with X-ray afterglows (2005)
• in elliptical or at a region with little star
  formation
• ? old population
• ? NS-NS merger!
• However
• some SGRBs at high z
• Swift detection rate low
• many without X-ray afterglows
• ambiguous events what are they? heterogeneous?
• EDGE will provide more locations and afterglow
  light curves for faint afterglows (WFI)

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The first 3 short GRBs with afterglows
GRB 050509B (Subaru) z0.225 ?
GRB 050724 (VLT) z0.258
GRB 050709 (HST) z0.16

• Hosts at low z, sites of little star formation
• x 10-3 less luminous than typical long GRBs

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Remarks

• Need optical/NIR follow-up for position, spectra,
  and redshifts
• power thermal design for anti-sun pointing
• Soft X-ray response of WFM and/or GBD
• current goal is 5 keV for WFM LD
• cf 2 keV for HETE WXM
• easy to extend down to 2 keV if non-imaging
• WFI astrometry accuracy

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Swift GRBs (with redshifts) vs. Sun angle
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prepared by Taka Sakamoto
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Locations of HETE Short- and Long- Duration
Bursts in (T90,SE)-Plane
Donaghy, Lamb, Sakamoto, Norris, et al. (2006)
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Summary (1)

• Absorption spectroscopy of afterglows
• CSM density /metallicity profile ?progenitor
• mass loss history
• metallicity
• More detections/identification of subclass
• short GRBs
• XRFs, local SN-GRBs
• Emission lines
• if breakouts ? jet mechanism
• if SN ejecta ? supranova (SN preceding GRB)
• Others fireball physics, prompt emission
  mechanism,

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Summary (2)

• There is a huge discovery space for EDGE in GRB
  physics
• High resolution spectra of X-ray afterglow
• GRB subclasses (short, sub-luminous, soft)
• Interpretation of spectra may be ambiguous
• Velocity
• Ionization state
• Optical follow-up observations are complementary
  and extremely important
• redshift, location, abundance,
• Spacecraft and instrument design (thermal and
  power) must accommodate anti-sun pointing

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absorption spectroscopy of CSM
Warm absorber similar to WHIM absorption
Cold ISM

• OVII, OIII absorption lines/edges from CSM
  photoionized by GRB emission
• Time variable ?density and metallicity profile
  of CSM
• velocity shift due to radiative acceleration

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Metallicity GRB-DLA vs. QSO-DLA
Prochaska et al. 2007

• GRB DLAs have generally larger metallicities
  than cosmic mean