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ATEL # 1090; M.A.P. Torres (CfA), P. Rodriguez-Gil (IAC), D. Steeghs (CfA/Warwick), J. M. Corral-Santana (IAC), J. Casares (IAC), P. G. Jonker (CfA/SRON)
on 31 May 2007; 14:05 UT
Password Certification: Danny Steeghs (email@example.com)
Subjects: Optical, X-ray, Binaries, Neutron Stars, Pulsars, Transients
Referred to by ATEL #: 1091
Following the recently reported decline of the X-ray flux from the millisecond pulsar HETE J1900.1-2455 (Galloway et al. 2007, ATel #1086), we acquired images of its optical counterpart using the Wide Field Camera mounted on the 2.5m Isaac Newton Telescope at La Palma. The images were obtained on 2007 May 29 4:10-4:33 UT and May 30 3:42-4:17 UT and photometrically calibrated using the standard stars SA 113-260 and BD+33 2642.
PSF photometry of a single 10 min r-band image acquired each night yields r=20.61 +/- 0.06 on May 29 and r= 20.24 +/- 0.03 on May 30. This indicates that HETE J1900.1-2455 has faded by more than 2 magnitudes compared to the optical brightness reported during outburst (R~18; Fox et al. 2005, ATel #526; Steeghs et al, ATel #543). The data also supports significant variability between our two epochs.
Additional observations of the source at optical and near-infrared wavelengths in support of the ongoing X-ray monitoring is planned.