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Candidate near-infrared counterpart to SAX J1753.5-2349

ATEL # 2526; M.A.P. Torres (CfA), P. G. Jonker (SRON/CfA), D. Steeghs (Warick/CfA), J. Chaname (Carnegie/DTM)
on 31 Mar 2010; 0:17 UT
Password Certification: Manuel Torres (

Subjects: Infra-Red, Binaries, Neutron Stars, Transients
Referred to by ATEL #: 2540

We report on near-infrared follow-up observations of the field containing the currently active X-ray transient SAX J1753.5-2349 (Chenevez et al. ATel #2505).

Our observations consist of a series of 15s Ks-band images totalling 450s on source and acquired on 2010 Mar 27 09:19 - 09:31 UT with the PANIC camera mounted on the 6.5m Baade telescope at Las Campanas Observatory. The observations were performed during good sky conditions and with 0.35" seeing. Additional 3s exposures were acquired to derive an astrometric and absolute flux calibration of the data using 2MASS objects in the field of view. This delivered a positional RMS < 0.1" and a photometric zero point accuracy of ~ 0.1 mag.

We searched for counterpart candidates within the 2.3" Swift X-ray position for SAX J1753.5-2349 (Starling & Evans 2008, ATel #1814). To do this we compared our data to pre-outburst imaging obtained in 2007 May and available from the UKIDSS survey ( Our mosaic image shows a Ks = 15.63 +/- 0.01 mag point-like source at R.A (J2000)=17:53:31.89, Dec (J2000)=-23:49:14.8. The UKIDSS images show no evidence for this object, indicating it was much fainter at the time. We estimate Ks > 17.8.

We consider this variable source the likely near-infrared counterpart to SAX J1753.5-2349.

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