OVI E0'386 keV EW0'13 eV

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ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
Detecting WHIM in GRB spectra

• Corsi, L. Piro WHIM Working Group

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Summary

• Why GRBs?
• Updated simulations (Viel 2006) - that include
  OVII k-?, OVII k-?, OVIII and FeXVII - tested on
  a typical GRB spectrum
• Number distribution of bright GRBs

ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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GRBs energy and distances
The brightest (Liso1053-54 erg/s) and most
distant sources in the Universe (z 0.16 - 6.3)
sufficiently bright and distant to be good
candidates as background sources to detect WHIM
absorption features

• Mean redshift
• ltzgt 2.8
• Prompt fluence
• ltF15-150 keVgt 2.4?10-6 erg cm-2
• ? 80 of GRBs have X-ray afterglows with fluences
  around 10-1000 of the prompt fluence
• 2.4x10-7 erg cm-2 lt F 0.3-10 keV lt 2.4x10-5
  erg cm-2

(OBrien et al. 2006)
(Jackobsson et al. 2005)
ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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WHIM absorption features line _at_0.5 keV on a
background GRB afterglow
ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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WHIM absorption features from the hydro simulation
We have considered 5 line of sights generated
from the output of the new hydrodynamical
simulation (Viel 2006) and computed the EW, the
mean Energy and the ?. An example LOS 1
OVII k-?
OVII k-?
OVIII
FeXVII
ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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(No Transcript)
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ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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Distribution

• 1 filament with EW ? 0.1eV ( 50 km/s) in OVII
  k-? up to z0.5 (i.e. 2 per unit z) in agreement
  with what expected from Viel et al. (2003). From
  Hellsten et al. about 10 per unit z
• 1 filament with EW ? 1/3 x 0.1eV ( 17 km/s) in
  OVIII up to z0.5 (i.e. 2 per unit z). From Viel
  et al. 2003 0.6 per unit redshift. From Hellsten
  et al. about 10 per unit z
• The same filament gives OVIII line with a mean EW
  of about 1/3 of the OVII k-a one and FeXVII line
  with EW of about ½ the OVII k-a .

ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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Detecting WHIM in GRB spectra

• A routine to include the model in XSPEC has been
  developed. It is now available on the web page
  (tested for XSPEC11). Multiplicative model. The
  user can select the LOS and the ION. Applying
  more times the model one can simulate the whole
  spectrum
• Convolved with 2 eV resolution matrix
• The background source spectrum is a typical GRB
  one absorbed power-law with photon index 2,
  NH2e20 cgs, fluence of 4e-6 cgs between 60 s and
  60 ks.

ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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OVII k-? z0.062 EW0.33 eV
OVII k-? z0.46 eV EW 0.11 eV
Fe XVII z0.062 EW0.21 eV
OVII k-? z0.062 EW0.18 eV
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OVII k-? z0.46 EW0.093 eV
OVII k-? z0.26 EW0.095 eV
OVII k-? z0.36 EW0.089 eV
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Fe XVII z0.35 EW0.35 eV
OVII k-? z0.061 EW0.19 eV
- 10
- 20
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OVII k-? z0.16 EW0.12 eV
OVII k-? z0.1 EW0.19 eV
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How many afterglows?

• We are interested in the logN-logS of GRB X-ray
  afterglows (Sfluence)
• Method 1 derive it directly from afterglow
  observations, assuming that the sample is
  unbiased so that one can normalize the observed
  distribution to 1000 GRB/yr (expected GRB rate in
  all the sky)
• Method 2 adopt an afterglow-to-prompt ratio and
  use the logN-logS of the prompt
• 2a - use the prompt X (better than
  gamma-rays because stronger correlation with
  X-ray afterglow)
• 2b - use the prompt gamma (logN-logS better
  sampled vs prompt X)

ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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X-ray afterglow fluence distribution comparing
methods 1-2a/b
F. Fiore, first Rome meeting
1000 GRB yr-1
Using the mean value for the ratio prompt X-ray
fluence / X-ray afterglow flux _at_ 11 hrs and the
WFC logN-logS, we can compute the number of
bursts per yr observable with a FOV of 3sr
100 sec
ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5
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Conclusions

• In ¼ of the sky
• we expect to see about 10 GRBs per year having
  an X-ray afterglow fluence of the order of 4e-6
  cgs ? typical case detection of OVII k-? lines
  best case detection of OVII k-? lines plus
  FeXVII or OVII k-?
• we expect to see about 3 GRBs per year having an
  X-ray afterglow fluence of the order of 1e-5 cgs
  ? typical case detection of 2 IONs, OVII k-?
  OVII k-? / FeXVII / OVIII best case detection
  of all of the 4.

ESTREMO/WFXRT Meeting on scientific requirements
Bologna, 2006 May 4-5