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last change 2006 April 24, R. Arlt
X-ray astronomy

RBS 825 - X-raying a gravitational lens

AIP astronomers have observed the unusual gravititational lens RBS 825 (also known as SDSS 1004+4112) with the X-ray satellite XMM-Newton. Gravitational lensing occurs when the observer sees a background light source almost perfectly aligned with a massive object in the foreground. Due to bending of the light by the gravitation of the foreground object, the source can appear distorted or even be split into multiple images.

Due to gravitational lensing by a foreground galaxy cluster, the distant quasar RBS 825 is split into 4 images, separated by up to 14 arcseconds (Figure 1) angular distance. This is the widest image splitting observed so far and it was possible to resolve the 4 lensed images with the X-ray telescopes of the XMM-Newton satellite. Surprisingly the optically brightest image A is relatively faint in X-rays and hardly visible in the XMM image (Figure 2). However, gravitational lensing should affect both optical and X-ray light in the same way. The probable reason for the dimming of image A in X-rays is additional gravitational lensing by the stars in a galaxy on the line of sight. This so-called mircolensing seems to zoom into an off-nuclear region of the quasar, but weakens the emission from the X-ray emitting core.

Lamer, G., Schwope, A., Wisotzki, L., Christensen, L.: Strange magnification pattern in the large separation lens SDSS J1004+4112 from optical to X-rays. Accepted for Astronomy & Astrophys.


Scientific contact
Dr. Georg Lamer
Astrophysikalisches Institut Potsdam
An der Sternwarte 16
D-14482 Potsdam
(0331) 7499 287

Press contact
Shehan Bonatz
(0331) 7499 469


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Gravitational lens in the optical light
Optical image of the gravitational lens RBS 825 (Subaru telescope). The yellow circles mark the 4 images of the background quasar. Also visible are the galaxies of the cluster of galaxies, whose mass is responsible for the lensing effect.

X-ray image of the gravitational lens
X-ray image of RBS 825 taken with XMM-Newton. The lensed images are marked with circles. The optically brightest image A is hardly visible in X-rays.


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