Publication Date:
2016-04-14
Description:
As part of the Chandra Galactic Bulge Survey (GBS), we present a catalogue of optical sources in the GBS footprint. This consists of two regions centred at Galactic latitude b = 1 $_{.}^{\circ}$ 5 above and below the Galactic Centre, spanning ( l x b ) = (6° x 1°). The catalogue consists of two or more epochs of observations for each line of sight in r ', i ' and H α filters. The catalogue is complete down to r ' = 20.2 and i ' = 19.2 mag; the mean 5 depth is r ' = 22.5 and i ' = 21.1 mag. The mean root-mean-square residuals of the astrometric solutions is 0.04 arcsec. We cross-correlate this optical catalogue with the 1640 unique X-ray sources detected in Chandra observations of the GBS area, and find candidate optical counterparts to 1480 X-ray sources. We use a false alarm probability analysis to estimate the contamination by interlopers, and expect ~10 per cent of optical counterparts to be chance alignments. To determine the most likely counterpart for each X-ray source, we compute the likelihood ratio for all optical sources within the 4 X-ray error circle. This analysis yields 1480 potential counterparts (~90 per cent of the sample). 584 counterparts have saturated photometry ( r ' ≤ 17, i ' ≤ 16), indicating these objects are likely foreground sources and the real counterparts. 171 candidate counterparts are detected only in the i ' band. These sources are good qLMXB and CV candidates as they are X-ray bright and likely located in the Bulge.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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