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Catalogue XRT results for GRB 091018

Data were analysed using HEASOFT version 6.29

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Summary Information

RA:02h 08m 44.47sLC breaks:2
Dec:-57° 32′ 53.9′′LC type:Oddball.
Err:1.4′′NH,intr.:2.50×1021 cm-2
Gal long:284.081Redshift0.971
Gal lat:-56.660Γ1.9
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Jump to: Light curve | Spectra | Compare to other bursts.

If you use any of these data, please cite Evans et al. (2009), which describes how these products were created (see the usage policy for more information).

Light curve

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This light curve comes from the light curve repository (if you use it, please cite Evans et al [2007, 2009]. Flares, marked by cross-hatched regions, are identified automatically, but may have been manually corrected. These are excluded from the fit. Any power-law breaks added to the fit must be required at the 4-σ level (according to an f-test) to be included in the best-fit. Details of all fits attempted are given below the plot. For more information see the light curve fitting documentation.

Fitted light curve of GRB 091018

Fit Details

Nbreaksχ2dofCommentsImage
0573133Image of this fit
1181131Break required.

(1.74e-31 % probability of chance improvement)
Image of this fit
2152129Break required.

(1.15e-03 % probability of chance improvement).
This is the best fit.
Image of this fit
3135127Break significance <4-σ
(0.07 % probability of chance improvement)
Image of this fit
4128125Break significance <4-σ
(0.04 % probability of chance improvement)
Image of this fit

There are no flares ignored from this fit.

The best-fitting light curve has 2 breaks.

Click on the number of breaks in the table to the right to change which fit is plotted above and detailed below.

Currently showing the best fit.

α10.45 (+0.06, -0.09)
Tb,1538 (+94, -129) s
α21.14 (+0.03, -0.03)
Tb,24.16 (+1.36, -0.69) × 104 s
α31.51 (+0.15, -0.11)

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Spectra

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Spectra have been created for each power-law segment in the best fitting light curve (shown above). Times of flaring have not been removed, however this makes little difference to most spectra (see Fig 7/8c of Evans et al. 2009). For more information see the time-resolved spectroscopy documentation.

Jump to: phase1|phase2|phase3

phase1 spectrum (T0 + 67 to 538 s)

Download spectral files for phase1 spectrum.

Plots to download

WT and PC mode spectra of GRB 091018

WT mode. Mean photon arrival: T0+105 s

NH (Galactic)3.07 × 1020 cm-2
NH (intrinsic)9.7 (+12.9, -9.7) × 1020 cm-2
z of absorber0.971
Photon index1.95 (+0.15, -0.15)
Flux (0.3-10 keV)
(Observed)
4.1 (+0.4, -0.4) × 10-10 erg cm-2 s-1
Flux (0.3-10 keV)
(Unabsorbed)
4.7 (+0.4, -0.4) × 10-10 erg cm-2 s-1
Counts to flux (obs)3.24 × 10-11 erg cm-2 ct-1
Counts to flux (unabs)3.65 × 10-11 erg cm-2 ct-1
W-stat (dof)
What's this?
264.39 (303)
Spectrum exposure80 s

PC mode. Mean photon arrival: T0+324 s

NH (Galactic)3.07 × 1020 cm-2
NH (intrinsic)1.5 (+1.5, -1.4) × 1021 cm-2
z of absorber0.971
Photon index1.77 (+0.15, -0.14)
Flux (0.3-10 keV)
(Observed)
2.62 (+0.28, -0.25) × 10-10 erg cm-2 s-1
Flux (0.3-10 keV)
(Unabsorbed)
2.92 (+0.25, -0.23) × 10-10 erg cm-2 s-1
Counts to flux (obs)3.71 × 10-11 erg cm-2 ct-1
Counts to flux (unabs)4.13 × 10-11 erg cm-2 ct-1
W-stat (dof)
What's this?
279.40 (281)
Spectrum exposure388 s

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phase2 spectrum (T0 + 538 to 41591 s)

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Plots to download

PC mode spectrum of GRB 091018

PC mode. Mean photon arrival: T0+12150 s

NH (Galactic)3.07 × 1020 cm-2
NH (intrinsic)2.6 (+1.1, -1.0) × 1021 cm-2
z of absorber0.971
Photon index1.94 (+0.10, -0.10)
Flux (0.3-10 keV)
(Observed)
7.8 (+0.5, -0.5) × 10-12 erg cm-2 s-1
Flux (0.3-10 keV)
(Unabsorbed)
9.3 (+0.5, -0.5) × 10-12 erg cm-2 s-1
Counts to flux (obs)3.39 × 10-11 erg cm-2 ct-1
Counts to flux (unabs)4.05 × 10-11 erg cm-2 ct-1
W-stat (dof)
What's this?
339.46 (388)
Spectrum exposure11.6 ks

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phase3 spectrum (T0 + 41593 to 787293 s)

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PC mode spectrum of GRB 091018

PC mode. Mean photon arrival: T0+118069 s

NH (Galactic)3.07 × 1020 cm-2
NH (intrinsic)3.1 (+2.4, -2.1) × 1021 cm-2
z of absorber0.971
Photon index1.86 (+0.20, -0.19)
Flux (0.3-10 keV)
(Observed)
2.33 (+0.32, -0.28) × 10-13 erg cm-2 s-1
Flux (0.3-10 keV)
(Unabsorbed)
2.76 (+0.29, -0.27) × 10-13 erg cm-2 s-1
Counts to flux (obs)3.57 × 10-11 erg cm-2 ct-1
Counts to flux (unabs)4.22 × 10-11 erg cm-2 ct-1
W-stat (dof)
What's this?
176.77 (234)
Spectrum exposure85.2 ks

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Comparison with other bursts

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Parameter distributions

The plots below show the probability density functions of the temporal and time-averaged spectral parameters for all GRBs, with the data for GRB 091018 shown on in colour. Click the images for larger versions.

For all plots, the solid vertical lines mark the values for this GRB, and the dashed lines the 1-σ uncertainties. For α and Tb, the colour changes for each phase. For the spectral parameters, the WT fits are shown in blue and the PC in red. These figures correspond to Figs. 5,6, 7a and 8a of Evans et al. (2009). See the PDF documentation for more information.

Temporal indicesBreak TimesNHSpectral indices
Comparison of decay indices Comparison of light curve break times Comparison of intrinsic column densities Comparison of spectral energy indices

Closure Relationships

The plots below show (α, β) scatter plots for each of the different types/phases of light curves (see light-curve types), since GRB 091018 is of type, "Oddball," which has no scatter plots of its own. GRB 091018 is shown in colour, with each light curve phase, or XRT mode marked by a different colour. α and β are the temporal and spectral energy power-law indices respectively. The shaded regions mark those allowed by the standard closure relationships. These figures correspond to Fig. 10 of Evans et al. (2009). See the closure relationship documentation for more information.

No break
Comparison of nobreak closures
One-break, steep first
Steep phase
One-break, steep first
Shallow phase
Comparison of One-break, steep first, steep phase closuresComparison of One-break, steep first, shallow phase closures
One-break, shallow first
Shallow phase
One-break, shallow first
Steep phase
Comparison of One-break, shallow first, shallow phase closuresComparison of One-break, shallow first, steep phase closures
Canonical
Steep phase
Canonical
Plateau
Canonical
'Normal'
Canonical
Post jet-break
Comparison of Canonical, steep phase closuresComparison of Canonical, plateau phase closuresComparison of Canonical, normal phase closuresComparison of Canonical, post jet-break phase closures

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