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Integral looks at Earth to seek source of cosmic radiation

13 February 2006

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ESA's Integral gamma-ray observatory has been observing Earth during a period spanning from 24 January to 9 February 2006. The main purpose of the observations has been to study the high-energy diffuse background radiation known as 'cosmic X-ray background' (CXB), by analysis of the decrease of its isotropic flux (not varying with distance or direction) while Earth passes in front of Integral's field of view. High-energy emission from the atmosphere, due to reflections of the CXB, interaction with cosmic rays and aurorae, have also been observed.

Credits: ESA

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This preliminary gamma-ray image has been taken by the SPI spectrometer on board Integral, during the Earth observation campaign (January-February 2006). The dark central part represents the Earth disc (about 5-7 degrees in diameter) transiting in the instrument's field of view (2.5 deg), that explains the blurred Earth rim in the image. The cosmic X-ray background radiation in the vicinity of Earth is characterised by a strong emission of high-energy (hard) X-rays.

Credits: (c) CESR and SPI team

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This simulation shows the passage of Earth through the field of view of Integral's IBIS/ISGRI gamma-ray imager, during the observations performed on 24 and 25 January 2006. The North Pole is indicated by a cross on Earth's disc, and the time on the top right corner is given in hours and minutes UTC. Earth is occulting the diffuse cosmic X-ray background (CXB), but its atmosphere is also emitting X-rays both through reflection of the CXB and through interaction with cosmic rays.

The occultation of the CXB resulted in one of the 'lightcurves' recorded by IBIS/ ISGRI (around 30-40 keV energy range), and here indicated by the dotted line. The asymmetry of the curve is due to the decreasing size of Earth as seen by Integral moving away from the planet on its orbit, and to enhanced cosmic-ray induced emission closer to the North Pole.

Credits: (c) ISDC and IBIS team

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These preliminary X-ray images were taken by Integral's JEM-X instrument in two separate slots of the Earth observation campaign, in late January (top row) and early February 2006 (bottom row).

The four images in each row correspond to different energy intervals. The plot shows the image of Earth against the diffuse cosmic X-ray background, as the JEM-X field of view sweeps across it (fixed stars would make stripes in this representation). The most remarkable thing to note is the bright spot visible at the two bottom left images, presumably indicating a northern auroral X-ray emission.

Credits: (c) DSRI and JEM-X team

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