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ATEL # 2169; E.Ratti (SRON), D.Steeghs (Warwick), P.G.Jonker (SRON/Utrecht)
on 21 Aug 2009; 16:50 UT
Password Certification: Danny Steeghs (firstname.lastname@example.org)
Subjects: Optical, Binaries, Neutron Stars, Pulsars, Soft Gamma-ray Repeaters
We report on optical imaging near the recently announced Chandra position of the Soft Gamma Repeater SGR 0418+5729 (ATEL #2159).
We acquired four 300s r-band images of the field containing SGR 0418+5729 on 2009-08-16, using the ACAM imager mounted at the 4.2 m William Herschel Telescope on La Palma. Observations of a nearby field containing SDSS calibrated stars were obtained for the absolute photometric calibration while astrometry was performed against 2MASS sources, resulting in an accuracy of ~0.1" on both RA and Dec.
No source is detected within the 95% confidence error-circle reported by Woods et al. (Atel #2159) down to a limit of r=24. PSF photometry reveals that the nearest object is detected at a magnitude r = 22.7 +/- 0.1 and center coordinates RA=04:18:34.0, Dec=57:32:23.5. This source is consistent with the near-infrared source reported by Wachter et al. (Atel #2164) but given its ~1.37" distance from the Chandra HRC position (which is boresight corrected using the same 2MASS astrometric frame used here) is not expected to be a viable counterpart.
Optical r-band image of the field near SGR0418+5729