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Optical brightening of IGR J00291+5934

ATel #1665; M. A.P. Torres (CfA), P. G. Jonker (SRON/CfA), C. Bassa (SRON), G. Nelemans (Nijmegen), D. Steeghs (Warwick/CfA)
on 16 Aug 2008; 17:03 UT
Credential Certification: Danny Steeghs (dsteeghs@cfa.harvard.edu)

Subjects: Infra-Red, Optical, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 1666, 1667, 1668, 1726, 1786

Following the recently reported X-ray outburst of the millisecond pulsar IGR J00291+5934 (ATel #1660,#1664), we acquired photometry of its optical counterpart using the Wide Field Camera mounted on the 2.5m Isaac Newton Telescope at La Palma. A series of 120s images were obtained in the r' and i'-bands on 2008 Aug 15 00:38-01:47 UT. The frames were photometrically calibrated using the standard star GD 246, achieving a zero-point error of less than 0.2 mag.

PSF photometry of the optical counterpart yields r'=18.07 +/- 0.04 and i'= 17.75 +/- 0.03. This indicates that IGR J00291+5934 has brightened by more than 4 magnitudes compared to its optical brightness during quiescence (R=23, I~22; Torres et al. 2008,ApJ,672,1079; Jonker,Torres & Steeghs 2008; arXiv:0802.2394; D'Avanzo et al. 2007,A&A,472,881). The amplitude of the current outburst at optical wavelengths is similar to that observed during the 2004 discovery outburst (Torres et al. 2008, Fox et al. 2004, Atel #354).

Additional observations of the source at optical and near-infrared wavelengths are encouraged given its brightness.