All Figures

$\begin{figure} \par\includegraphics[width=15cm]{2693f1.eps}\end{figure}$ Figure 1: The Compton Gamma-Ray Observatory (CGRO) and one of the 8 BATSE detector modules (drawings courtesy of the National Space Science and Technology Centre, Huntsville, AL, USA).
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In the text

$\begin{figure} \par\includegraphics[width=15cm]{2693f2.eps}\end{figure}$ Figure 2: a) This shows the relative scale of the Earth, its atmosphere (up to 125 km) and the virtual BATSE volume for the GEANT4 polarisation sensitive simulations. b) BAMM contains detailed structural, geometrical and material infomation for BATSE, EGRET, COMPTEL, OSSE and the CGRO spacecraft. Cut-aways of the BATSE module (top right) and the whole CGRO (bottom right) show the internal detail. To illustrate the crucial components that will deflect or absorb gamma-ray photons, some external volumes have been made transparent.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm]{2693f3.eps}\end{figure}$ Figure 3: All BATSE triggers plotted to identify the six most suitable candidates for polarimetry. Triggers 2151 and 5614 were initially selected with the remainder discarded due to their particularly long and structured lightcurves.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm]{2693f4.eps}\end{figure}$ Figure 4: The simulated angular distribution of gamma-ray flux reflected off the Earth's atmosphere during GRB 930131 and GRB 960924 for 100% polarised and unpolarised fluxes. Contours are the 0, 5, 10, 15, 20 and 25 mean counts per pixel ( $4.5^{\circ }\times 4.5^{\circ }$ ) for $5\times 10^{7}$ incident GRB photons. This pixelated distribution is used as the input to BAMM.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm]{2693f5new.eps}\end{figure}$ Figure 5: The spectra of the albedo component of GRB 930131 and GRB 960924. The dotted lines represent the domain in which the data is compared: 31-98 keV (LAD CONT channels 3-6). These limits equate to 67% and 62% of the albedo flux respectively.
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In the text

$\begin{figure} \par\includegraphics[width=16cm]{2693f6.eps}\end{figure}$ Figure 6: A comparison of the fitted simulated count-rates with the LAD CONT data for GRB 930131. The CONT data is shown as a dashed line, the error on that count is shown as solid lines. The best fit for each polarisation angle is shown with the relevant counting error from the Monte Carlo. LAD3 and LAD4 simulations are expected to match the recorded data, independent of polarisation. LAD1 and LAD2 are sensitive to polarisation in the GRB's prompt flux and will show an improvement in fit for angles that corresponds to the burst polarisation angle.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm]{2693f7.eps}\end{figure}$ Figure 7: For GRB 930131, the Z statistic (solid line) for each of the best fits from Fig. 6. The statistic becomes significant (95% confidence) between polarisation angles of 163 $^{\circ }$ and 9 $^{\circ }$ and this corresponds to a high (>90%) degree of polarisation (dashed line). The Earth's North/South equivalent angle is at 5 $^{\circ }$ , see Sect. 4.4.1.
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In the text

$\begin{figure} \par\includegraphics[width=16cm]{2693f8.eps}\end{figure}$ Figure 8: A comparison of the fitted simulated count-rates with the LAD CONT data for GRB 960924. The CONT data is shown as a dashed line, the error on that count is shown as solid lines. The best fit for each polarisation angle is shown with the relevant counting error from the Monte Carlo. LAD6 simulations are expected to match the recorded data, independent of polarisation. LAD2 and LAD4 are sensitive to polarisation in the GRB's prompt flux and will show an improvement in fit for the specific angle that the burst is polarised to. LAD0 is largely insensitive to polarisation and so should be consistent with the CONT data regardless of polarisation.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm]{2693f9.eps}\end{figure}$ Figure 9: For GRB 960924, the Z statistic (solid line) for each of the best fits from Fig. 8. The statistic becomes significant (95% confidence) between polarisation angles of 58 $^{\circ }$ and 64 $^{\circ }$ and this corresponds to a high (100%) degree of polarisation (dashed line). The Earth's North/South equivalent angle is at 47 $^{\circ }$ , see Sect. 4.4.1.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{2693f10.eps}\end{figure}$ Figure 10: A comparision between using a 12 layered graded atmospheric model and a constant density and composition integrated model. The incident photon energy is 200 keV. The upper plot shows the back-scatter rate with altitude and the lower two histograms show the albedo zenith distribution.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{2693f11.eps}\end{figure}$ Figure 11: The CONT data for GRB 930131 is compared to the simulations with $\Pi$ restricted to a range of maximum values between 0% and 100%. The confidence levels in the Z statistic are shown.
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In the text

$\begin{figure} \par\includegraphics[width=8cm]{2693f12.eps}\end{figure}$ Figure 12: The CONT data for GRB 960924 is compared to the simulations with $\Pi$ restricted to a range of maximum values between 0% and 100%. The confidence levels in the Z statistic are shown.
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In the text

$\begin{figure} \par\includegraphics[width=15cm]{2693f1.eps}\end{figure}$	Figure 1: The Compton Gamma-Ray Observatory (CGRO) and one of the 8 BATSE detector modules (drawings courtesy of the National Space Science and Technology Centre, Huntsville, AL, USA).
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$\begin{figure} \par\includegraphics[width=8.6cm]{2693f3.eps}\end{figure}$	Figure 3: All BATSE triggers plotted to identify the six most suitable candidates for polarimetry. Triggers 2151 and 5614 were initially selected with the remainder discarded due to their particularly long and structured lightcurves.
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$\begin{figure} \par\includegraphics[width=8.5cm]{2693f4.eps}\end{figure}$	Figure 4: The simulated angular distribution of gamma-ray flux reflected off the Earth's atmosphere during GRB 930131 and GRB 960924 for 100% polarised and unpolarised fluxes. Contours are the 0, 5, 10, 15, 20 and 25 mean counts per pixel ( $4.5^{\circ }\times 4.5^{\circ }$ ) for $5\times 10^{7}$ incident GRB photons. This pixelated distribution is used as the input to BAMM.
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$\begin{figure} \par\includegraphics[width=8.5cm]{2693f5new.eps}\end{figure}$	Figure 5: The spectra of the albedo component of GRB 930131 and GRB 960924. The dotted lines represent the domain in which the data is compared: 31-98 keV (LAD CONT channels 3-6). These limits equate to 67% and 62% of the albedo flux respectively.
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$\begin{figure} \par\includegraphics[width=8.8cm]{2693f7.eps}\end{figure}$	Figure 7: For GRB 930131, the Z statistic (solid line) for each of the best fits from Fig. 6. The statistic becomes significant (95% confidence) between polarisation angles of 163 $^{\circ }$ and 9 $^{\circ }$ and this corresponds to a high (>90%) degree of polarisation (dashed line). The Earth's North/South equivalent angle is at 5 $^{\circ }$ , see Sect. 4.4.1.
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$\begin{figure} \par\includegraphics[width=8.8cm]{2693f9.eps}\end{figure}$	Figure 9: For GRB 960924, the Z statistic (solid line) for each of the best fits from Fig. 8. The statistic becomes significant (95% confidence) between polarisation angles of 58 $^{\circ }$ and 64 $^{\circ }$ and this corresponds to a high (100%) degree of polarisation (dashed line). The Earth's North/South equivalent angle is at 47 $^{\circ }$ , see Sect. 4.4.1.
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$\begin{figure} \par\includegraphics[width=8cm]{2693f10.eps}\end{figure}$	Figure 10: A comparision between using a 12 layered graded atmospheric model and a constant density and composition integrated model. The incident photon energy is 200 keV. The upper plot shows the back-scatter rate with altitude and the lower two histograms show the albedo zenith distribution.
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$\begin{figure} \par\includegraphics[width=8cm]{2693f11.eps}\end{figure}$	Figure 11: The CONT data for GRB 930131 is compared to the simulations with $\Pi$ restricted to a range of maximum values between 0% and 100%. The confidence levels in the Z statistic are shown.
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$\begin{figure} \par\includegraphics[width=8cm]{2693f12.eps}\end{figure}$	Figure 12: The CONT data for GRB 960924 is compared to the simulations with $\Pi$ restricted to a range of maximum values between 0% and 100%. The confidence levels in the Z statistic are shown.
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