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ATEL # 2233; M.A.P. Torres (CfA), P. G. Jonker (SRON/CfA), D. Steeghs (Warwick/CfA), I. Damjanov (Toronto Univ.), E. Caris, K. Glazebrook (Swinburne U. of Technology)
on 9 Oct 2009; 12:10 UT
Password Certification: Manuel Torres (email@example.com)
Subjects: Infra-Red, Binaries, Neutron Stars, Pulsars, Transients
We report follow-up observations confirming the near-infrared (NIR) counterpart to the newly discovered accreting millisecond pulsar IGR J17511-3057 (Baldoven et al. 2009, ATel #2196; Markwardt et al. 2009, ATel #2197). A Ks~18 mag candidate counterpart was suggested in Torres et al. (ATel #2216) on the basis of its coincidence with the Chandra localization of the X-ray source (Nowak et al. 2009, ATel #2215). The candidate counterpart is not present in UKIDSS pre-outburst imaging of the field containing IGR J17511-3057.
Our observations consist of a series of Ks-band images obtained with the 6.5m Magellan Baade telescope between 2009 Oct 7 00:08-00:21 UT using the PANIC camera and totaling 450s on source. The seeing was 0.5 arcsec during the observations. Photometric and astrometric scales were defined with the same 2MASS references used in ATel #2216.
The images show that the proposed counterpart candidate has faded significantly during the observations to Ks > 18.8 (3-sigma upper limit magnitude). This large photometric variability confirms the candidate reported in ATEL #2216 as the NIR counterpart to IGR J17511-3057.