Nessun titolo diapositiva

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Cosmology and physics with GRB spectra
Lorenzo Amati (INAF - IASF Bologna, Italy)
ESTREMO meeting - March 22th, 2006
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• Outline
• GRB spectra and energetics
• Cosmology with spectral-energy correlations
• GRB physics with spectral energy correlations
• GRB and SN physics with prompt X-ray spectra
• Some basic requirements

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GRB spectra and energetics
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• GRBs spectra
• smoothly broken power-law spectra typically
  described by the empirical Band function with
  parameters a low-energy index, b high-energy
  index, E0roll over energy
• Ep E0 x (2 a) peak energy of the nFn
  spectrum

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• .
• CGRO/BATSE (25-2000 keV) Ep values distibuted
  around 200 keV
• BeppoSAX (2-700 keV) and HETE-2 (2-400 keV)
  measurements show that the Ep distribution is
  broader and extending towards low energy than
  inferred from BATSE

Kippen et a., Woods Hole 2001, AIP Proc.
Sakamoto et al., ApJ, submitted
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• .
• substantial spectral evolution, typically hard
  to soft during the whole event
• in some cases, Ep tracks the light curve, in
  others it monotonically evolves from high to low
  values

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• .
• spectra of short GRBs tend to be harder than
  those of long GRBs

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GRBs energetics

• discovery of afterglow emission in 1997 -gt
  detection and spectroscopy of optical
  counterparts and host galaxies -gt GRB redshifts !
• all GRBs with measured redshift (more than 60)
  are long and (except for the peculiar GRB980425)
  lie at cosmological distances (z 0.10 6.3)

S. Klose

• from distance, fluence and spectrum, it is
  possible to estimate the radiated energy assuming
  isotropic emission, Eiso

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• the isotropic equivalent radiated energy spans
  over several orders of magnitude, from 1051
  (1049 when including XRF020903 and the 2
  peculiar sub-energetic events GRB980425 and
  GRB031203) up to more than 1054 erg

Amati 2006
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• assuming jet angles derived from the break time
  of the optical afterglow light curve, the
  collimation-corrected radiated energy is
  clustered around 1051 erg.

Bloom et al. , ApJ, 2001
Ghirlanda et al. , ApJ, 2004
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Standard scenario and basic physics

• ms time variability huge energy detection of
  GeV photons -gt plasma occurring
  ultra-relativistic (G gt 100) expansion (fireball)
  
• non thermal spectra -gt shocks synchrotron
  emission (SSM)
• fireball internal shocks -gt prompt emission
• fireball external shock with ISM -gt afterglow
  emission

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LONG
SHORT

• energy budget up to gt1054 erg
• long duration GRBs
• metal rich (Fe, Ni, Co) circum-burst environment
• GRBs occur in star forming regions
• GRBs are associated with SNe
• naturally explained collimated emission

• energy budget up to 1051 - 1052 erg
• short duration GRBs (lt 5 s)
• clean circum-burst environment
• GRBs in the outer regions of the host galaxy

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Cosmology with spectral - energy correlations
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The EP,i-Eiso (Amati) correlation
(Amati et al. 2002)

• based on a sample of 12 BeppoSAX GRBs with known
  z found a correlation between Ep,i Ep x (2a)
  and Eiso , highly significant (r 0.949, chance
  prob. 0.005)

Ep,i kEiso
(0.52/-0.06)
Amati et al. , AA, 2002
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Confirmation and extension of the Ep,i-Eiso
correlation

• by adding data from BATSE and HETE-2 of 10 more
  GRBs the correlation was confirmed and its
  significance increased

• HETE-2 data shows that the Ep,i Eiso
  correlation extends to XRFs, thus spanning 5
  orders of magnitude in Eiso and 3 orders of
  magnitude in Ep,i

Amati, ChJAA, 2003
Amati, MemSAIT, 2004
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• analysis of the most updated sample of GRBs with
  firm estimates of z and Ep,i (43 events) gives a
  chance probability for the Ep-Eiso correlation lt
  10-9
• Swift GRBs with known z and Ep,i are fully
  consistent with the correlation
• remark the correlation is highly significant
  but characterized by a sample variance
  s(logEp,i) 0.15

Amati 2006
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The Ep,i Eg and Ep,i Eiso tb correlations
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• by substituting Eiso with the collimation
  corrected energy Eg the correlation still holds,
  with a lower dispersion and a steeper slope of
  0.7 (Ghirlanda et al. 2004, Dai et al. 2004)

Nava et al.. , AA, 2005
Dai et al., ApJ, 2004
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• very recently, Liang et al. (2005) performed a
  multi-variable correlation analysis between
  various observables of prompt and afterglow
• they found a tight correlation between Epi, Eiso
  and tb
• with respect to Ep,i Eg correlation it has the
  advantage of being model independent
• differently from the Ep,i-Eiso correlation, the
  Ep,i-Eg and Ep,i-Eiso-tb correlations can be used
  for only a fraction of events (a firm estimate of
  tb is needed)

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• use of the Ep,i-Eg and Ep,i-Eiso-tb
  correlations for the estimate of cosmological
  parameters, in a way similar to SN Ia

Ghisellini et al., NCIM, 2005
Ghirlanda et al.,ApJ, 2004
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• use of the Ep,i-Eg and Ep,i-Eiso-tb
  correlations for the estimate of cosmological
  parameters, in a way similar to SN Ia

Liang Zhang,ApJ, 2005
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• use of the Ep,i-Eg and Ep,i-Eiso-tb
  correlations for the estimate of cosmological
  parameters, in a way similar to SN Ia

Ghisellini et al. 2005
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• cautions / problems
• based on a still low number of events (and the
  Ep,i-Eg requires assumptions on the density and
  distribution of the circum-burst environment and
  on the kinematic to radiated energy conversion
  efficiency)
• differently from the Ep,i-Eiso correlation, the
  Ep,i-Eg and Ep,i-Eiso-tb correlations can be used
  for only a fraction of events (a firm estimate of
  tb is needed)

c) circularity problem d) physics
underlying these correlations still not
settled d) outliers, lack of jet breaks in Swift
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GRB physics with spectral - energy correlations
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• GRB prompt emission models

• physics of prompt emission still not settled -gt
  various scenarios SSM internal shocks,
  IC-dominated internal shocks, external shocks,
  photospheric emission dominated models, kinetic
  energy dominated fireball , poynting flux
  dominated fireball)
• e.g., Ep,i ? G-2 L1/2 tn-1 for syncrotron
  emission from a power-law
  distribution of electrons generated in an
  internal shock, Ep,i ? G Tpk ? G2 L-1/4 for
  comptonized thermal emission from the photosphere
  
• to be combined with the general assumption L ?
  Gb

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• more in general, Ep,i ? GM and Eiso ? GN , with
  M and N varying in each scenario and for
  different set of parameters within each scenario
  -gt positive correlation between Ep,i Eiso and
  its slope constrain parameters ranges in each
  scenario

• also the extension of the correlation puts
  constraints on prompt emission models, showing
  that the distribution of Ep,i is much broader
  than thought before (e.g. zhang Meszaros 2002,
  Asano Kobayashi 2004)

Zhang Meszaros, ApJ, 2002
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• jet and GRB/XRF unification models

• the validity of the Ep,i Eiso correlation from
  the brightest GRBs to XRFs puts severe
  constraints on jet and GRB/XRF unification models
• uniform jet -gt majority of GRBs with jet angles
  lt 1
• universal structured jet -gt too many XRFs
• new hypothesis quasi-universal structured jet
  Fisher-shape jet

structured
uniform
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• Ep,i Eiso correlation and off-axis scenarios
• when the viewing angle exceeds the jet opening
  angle both Ep,i and Eiso decrease dramatically
  and we observe normal GRBs as very soft and weak
  events (i.e. XRFs), due to relativistic beaming
  and Doppler effects

• extension to XRFs of the Ep,i-Eiso correlation
  Yamazaki et al. (2004)
• dg(1 - bcos(qv - Dq))-1
• DEp ? d , DEiso ? d(1a) -gt DEp ? DEiso(1a)
• a12.3 -gt Ep(qv) ? Eiso(qv)0.50.3

• other scenarios based on viewing angle include
  ring shaped fireball (Eichler Levinson 2004),
  multi component jets / subjets (e.g. Toma et al.
  2005) cannonball model (Dar, Dado, De Rujula)

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• the Ep,i Eiso correlation, the GRB/SN
  connection and sub-energetic GRBs

• the Ep and Eiso values of the GRB/SN prototype
  event GRB980425/SN1998bw (z0.008) are
  inconsistent with the correlation
• it has been claimed that this is true also for
  the other sub-energetic event GRB031203 /
  SN2003lw, but ISGRI Ep lower limit is debated,
  based on dust echo measured by XMM

• the other GRB/SN events (e.g. GRB030329
  /SN2003dh) are consistent with the Ep,i-Eiso
  correlation
• GRB060218 / SN2006aj is consistent !

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• the most common explanations for the (apparent
  ?) sub-energetic nature of GRB980425 and
  GRB031203 and their violation of the Ep,i Eiso
  correlation are based on peculiar viewing
  conditions (e.g. Yamazaki et al. 2003,
  Ramirez-Ruiz et al. 2005)

• double-peak interpretation (e.g. Dado and Dar
  2004) in GRB980425 and GRB031203 we are seeing
  the high energy peak due to Compton up-scatter of
  UV photons by CR electrons accelerated by SN jets

• in general possible use of the Ep,i Eiso
  plane to identify sub-classes ?

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• Ep,i Eiso correlation and short GRBs

• only very recently, redshift estimates for short
  GRBs (1 by HETE-2, 3 by Swift) were available (in
  the range 0.16-0.72)
• estimates of both Ep,i and Eiso are available
  for GRB050709 (HETE-2) and GRB051221 (Swift) and
  are inconsistent with Ep,i-Eiso correlation
  holding for long GRBs
• low Eiso values and high lower limits to Ep,i
  indicate inconsistency also for the other three
  short GRBs
• furher evidence for a different nature of short
  GRBs

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• Ep,i Eiso correlation as a tool

• use of the Ep,i Eiso to construct GRB
  redshift estimators (es. Atteia, 2003)
  pseudo-redshift of HETE-2 bursts published in
  GCN
• use of the Ep,i Eiso correlation to infer the
  star formation rate (SFR) evolution ,
  e.g.Yonetoku et al., 2004 , Firmani et al. 2004)
• use of the Ep,i Eiso correlation to infer the
  jet angle probability distribution (e.g. Liang et
  al. 2004, Bosnjak et al 2004)
• Ep,i Eiso correlation is often used in GRB
  synthesis simulations as an input or a required
  output

Atteia, AA, 2003
Liang et al. 2004
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GRB and SN physics with prompt emission X-ray
spectra
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Extending to X-rays from BATSE

• major contribution came in the 90s from the
  NASA BATSE experiment (25-2000 keV) onboard CGRO
  (1991-2000)
• based on NaI scintillator detectors 8 units
  covering a 4p FOV

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Extending to X-rays to BeppoSAX

• BeppoSAX
• NFI (X-ray focusing telescopes, 0.1-10 keV PDS,
  15-200 keV)
• WFC (2 units, proportional counters coded mask,
  FOV 20x20 each unit, 2-28 keV)
• GRBM (4 units, CsI scintillators, large FOV, GRB
  triggering, 40-700 keV)
• WFC and GRBM co-aligned

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Extending to X-rays and HETE-2

• HETE-2 extending the sample of X-ray rich GRBs
  and XRFs

• FREGATE NaI crystal scintillators, 6-400 keV,
  FOV 3 sterad
• WXM 2 units, gas proportional counters 1-D
  codedmask, 2-25 keV , localization of few arcmin
• SXC 2 units, CCD 1-D coded mask. 0.5 10
  keV, 30 arcsec
• accurate localization (few arcmin) and fast
  position dissemination
• study of prompt emission down to X-rays

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Extending to X-rays light curves

• pulse width as a function of energy test of
  SSM
• spectral lag luminosity relation

Frontera et al., ApJS, 2000
Piro et al./Feroci et al. , AA, 1997/2001
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Extending to X-rays spectra

• many GRB spectra are consistent with syncrotron
  shock emission models down to X-rays
• the extension to few keV allow a better estimate
  of low energy index and of Ep

BATSE (Tavani, ApJ, 1995)
BeppoSAX (Amati et al., 2001)
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Extending to X-rays deviations from SSM

• a fraction of GRB time resolved spectra are
  inconsistent with optically thin synchrotron
  emission (i.e. a gt -0.67)

From BATSE data
From BeppoSAX
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Extending to X-rays deviations from SSM

• possible explanations quasi-saturated
  comptonization, thermal component, Compton
  drags, synchrotron emission with small pitch
  angle, syncrotron self-absorption )

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Extending to X-rays thermal component

• evidences for a thermal component (from
  fireball photosphere ? SN ???)

BATSE
BeppoSAX
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Extending to X-rays absorption features

• BeppoSAX detection of a transient absorption
  feature in the first 13 s of GRB990705.

Amati et al., Science, 2000
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Transient absorption feature in GRB990705 two
possible interpretations

• K absorption edge of neutral Fe within a shell of
  material around the GRB site, photo-ionized by
  the GRB photons (Amati et al. 2000).
  Consequences
• i. X-ray redshift (0.860.17) of the burst
  source, which was later confirmed by the optical
  redshift of the GRB host galaxy (Le Floch et al.
  2002)
• ii. Iron relative abundance A/Asun75,
  typical of supernova explosions.
• iii. A large mass of Fe, unless Fe is
  clumped and a clump is along the line of sight
  (Boettcher et al. 2001).

Amati et al. 2000
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• Absorption line due resonant scattering of GRB
  photons off H-like Fe (transition 1s-2p, Erest
  6.927 keV) (Lazzati et al. 2001).
• Consequences
• a) The redshift is still consistent with
  that of the HG
• b) Fe mass required 0.2 Msun
• c) Fe relative abundance 10

Lazzati et al. 2001

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Variable intrinsic absorption in the prompt
emission of GRB980329 and GRB 000528
Frontera et al. 2000

• Variable NH from 2.5 x 1023 cm-2 to a value
  compatible with 1x1022 cm-2 which was observed
  during the late afterglow phase (Frontera et al.
  2000) (Galactic value1x1021 cm-2 ).
• The NH time behaviour is explained (Lazzati
  Perna 2001) if the GRB event occurs in overdense
  regions within molecular clouds (Bok globules)
• Variable NH detected also in GRB000528

Lazzati Perna 2001
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Extending to X-rays X-Ray Flashes

• BeppoSAX discovers X-Ray Flashes (XRF) GRBs
  with only X-ray emission
• distribution of spectral peak energies has a low
  energy tails

Amati et al. Science, 2000
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Extending to X-rays X.Ray Flashes

• normal GRBs, XRRs and XRFs are found to be in
  the ratio 111
• recent XRF redshift estimates z in the 0.1 1
  range
• GRBs, XRRs and XRFs form a continuum in the Ep
  fluence plane evidence of a common origin
• most likely explanation inefficient internal
  shocks due to low contrast of DG between
  colliding shells with respect to fireball bulk G

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Extending to X-rays Swift

• Swift NASA mission dedicated to GRB studies
  launched 20 Nov. 2004 USA / Italy / UK consortium
• main goals afterglow onset, connection
  prompt-afterglow, substantially increase of
  conunterparts detection at all wavelengths (and
  thus of redshift estimates)

• payload BAT (CZTcoded mask, 15-350 keV, wide
  FOV, arcmin ang. res.), XRT (X-ray optics, 0.3-10
  keV, arcsec ang.res.), UVOT (sub-arcsec ang.res.
  mag 24 in 1000 s)
• spacecraft automatic slew to target source in
  1 - 2 min.

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Extending to X-rays Swift

• new features seen by Swift in X-ray afterglow
  light curves initial very steep decay, early
  breaks, flaresmay occurr all together or only
  some of them

-3
( 1 min t hours )
-0.7
105 106 s
- 1.3
-2
102 103 s
104 105 s
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Extending to X-rays Swift

• initial steep decay in some cases matches end
  of prompt emission continuation of prompt
  emission ?
• in other cases inconsistent with prompt
  emission mini break due to patchy shell, IC
  up-scatter of the reverse shock sinchrotron
  emission ?
• may also be due to missed flare

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Extending to X-rays Swift

• flat decay probably refreshed shocks, due
  either to

• Long duration ejection (t tflat )
• Short ejection (t t?), but with range of ?

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Extending to X-rays Swift

• Flares could be due to
• Refreshed shocks
• IC from reverse shock
• External density bumps
• Continued ctrl. engine activity late internal
  shocks
• in some cases, missed part of a flare can
  explain early steep decay

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Some requirements for the Wide Field Imager
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Requirements energy band and sensitivity of main
GRB instruments
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(No Transcript)
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Requirements spectral-energy corr.

• due to the broad and smooth roll-over that
  characterizes GRBs spectra, the estimate of Ep
  can be significantly affected by detectors
  energy band (data truncation effect) and
  sensitivity as a function of energy
• indeed, in several cases, for simultaneously
  detected events, BATSE (25-2000 keV), BeppoSAX
  (2-700 keV), HETE-2 (2-400 keV), Swift/BAT
  (15-350 keV) and Konus-Wind (15-5000 keV) provide
  significantly different values of Ep !
• if the energy band is not large enough, a fit
  with the Band function does not allow to
  constrain all the parameters and often a cut-off
  power-law is adopted (e.g. for HETE-2 and
  Swift/BAT)
• if the energy band is narrow, a fit with a
  power-law is usually acceptable (e.g. about 80
  of BAT spectra )

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Requirements X-ray spectroscopy, XRFs, flares, SN

• BATSE missed most XRFs, intensively studied by
  BeppoSAX and HETE-2
• X-ray transient absorption features detectable
  only when etending energy band down to a few keV
• photospheric emission observable only at few keV
  
• new phenomenology (flares, steep decay,
  counter-break, early break) could be discovered
  by Swift only because it pointed in few tens of
  second with XRT (0-1-10 keV)
• high sensitivity X-ray observations of prompt
  emission allowed Swift also to detect SN shock
  break-out in GRB060218/SN2006aj (very recent
  Campana et al. 2006, Nature)

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Requirements conclusions

• for spectral-energy correlations (cosmology
  GRB physics idenification of different classes
  of GRBs) an energy band from a few keV to at
  least 500-600 keV is required moderate energy
  resolution (e.g. that of a NaI, CsI or BGO
  scintillator) is enough
• for X-ray spectroscopy (features, photosphere,
  SN, XRFs, flares) an energy band down to 1-2 keV
  is required, with good energy resolution (e.g.
  that of a CdTe or CZT detector, 5-10 at 6 keV)
• sensitivity is more important in the X-ray
  domain (low S/N ) than in the hard X-ray domain
  (high S/N)
• e.g. a sophisticated X-ray camera (e.g. CZT
  coded mask operating in the 1 - 2keV to 150 keV
  plus a simple and smaller soft gamma detector
  (e.g. a scintillator operating in 50 -1000 keV)
  fast (e.g. 100 s) pointing with X-ray telescope.

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THE END