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The near-infrared counterpart to SWIFT J1842.5-1124

ATEL # 1720; M.A.P. Torres (CfA), D. Steeghs (Warick/CfA), P. G. Jonker (SRON/CfA), J. E. Greene (Princeton), K. N. Hainline (UCLA)
on 17 Sep 2008; 15:21 UT
Password Certification: Manuel Torres (

Subjects: Infra-Red, Binaries, Black Holes, Neutron Stars, Transients

We report on near-infrared follow-up observations of the field containing the currently active X-ray transient SWIFT J1842.5-1124 (ATel #1706, ATel #1716).

Our observations consist of a series of 10s Ks-band images totalling 270s on source and acquired on 2008 Sep 15 23:36 - 23:45 UT with the PANIC camera mounted on the 6.5m Baade telescope at Las Campanas Observatory. Sky conditions were good with a seeing of 0.4". Additional 3s exposures were obtained to derive an astrometric and absolute flux calibration of the data using 2MASS objects in the field of view. This delivered a positional RMS <0.15' and a zero-point accuracy of < 0.15 mag.

Our mosaic image (see finder) shows a bright point-like source at R.A (J2000)=18:42:17.44, Dec (J2000)=-11:25:03.95 consistent with the 0.6" Swift/UVOT position reported for the optical counterpart (Markwardt et al. 2008, ATel #1716). Pre-outburst K-band imaging is available from the UKIDSS survey obtained in September 2005 ( These show marginal evidence for a source at the above position indicating it was much fainter at the time and thus confirming it as the near-infared counterpart to SWIFT J1842.5-1124. PSF-fitting photometry of the PANIC images yields Ks=14.90 +/- 0.05 for the counterpart and from the UKIDSS imaging we estimate Ks ~ 17.4 or less during quiescence.

Finding chart for J1842.5

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