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The ultraluminous X-ray source NGC 1313 X-2 - Its optical counterpart and environment

Grise, F; Pakull, MW; Soria, R; Motch, C; Smith, IA; Ryder, SD; Bottcher, M; (2008) The ultraluminous X-ray source NGC 1313 X-2 - Its optical counterpart and environment. ASTRON ASTROPHYS , 486 (1) 151 - 163. 10.1051/0004-6361:200809557.

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Abstract

NGC 1313 X-2 is one of the brightest ultraluminous X-ray sources in the sky, at both X-ray and optical wavelengths; therefore, quite a few studies of available ESO VLT and HST data have appeared in the literature. Here, we present our analysis of VLT/FORS1 and HST/ACS photometric data, confirming the identification of the B similar to 23 mag blue optical counterpart. We show that the system is part of a poor cluster with an age of 20 Myr, leading to an upper mass limit of some 12 M-circle dot for the mass donor. We attribute the different results with respect to earlier studies to the use of isochrones in the F435W and F555W HST/ACS photometric system that appear to be incompatible with the corresponding Johnson B and V isochrones. The counterpart exhibits significant photometric variability of about 0.2 mag amplitude, both between the two HST observations and during the one month of monitoring with the VLT. This includes variability within one night and suggests that the light is dominated by the accretion disk in the system and not by the mass donor.

Type:Article
Title:The ultraluminous X-ray source NGC 1313 X-2 - Its optical counterpart and environment
DOI:10.1051/0004-6361:200809557
Keywords:galaxies : individual : NGC 1313, accretion,accretion disks, black hole physics, galaxies : star clusters, X-rays : binaries, X-rays : individuals : NGC 1313 X-2, MASS BLACK-HOLES, RED GIANT BRANCH, QUASI-PERIODIC OSCILLATIONS, THEORETICAL ISOCHRONES, PHOTOMETRIC SYSTEMS, EVOLUTIONARY TRACKS, DISTANCE INDICATOR, SOURCE POPULATION, ACCRETION DISKS, GALAXY NGC-1313
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Space and Climate Physics

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