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Optical detection of the anomalous X-ray pulsar 1E 1048.1-5937 following a glitch

ATEL # 1071; Z. Wang, C. G. Bassa, V. M. Kaspi, R. Dib, C. Tam (McGill)
on 10 May 2007; 17:50 UT
Password Certification: Z. Wang (

Subjects: Optical, Neutron Stars, Pulsars

Following the sudden spin-up and increase in the X-ray flux of the anomalous X-ray pulsar 1E 1048.1-5937 at the end of March (Dib et al. 2007; ATEL #1041) and the subsequent brightening of the near-IR counterpart by ~1.5 magnitude in the Ks band (Wang et al. 2007; ATEL #1044), we report a similar brightening at optical wavelengths. We were awarded a DDT optical imaging observation from European Southern Observatory (ESO), and observed the field of 1E 1048.1-5937 on 2007 May 8, UT 00:01, at I band, using the optical camera FORS2 on the Very Large Telescope. The exposure was 46 min and the seeing 0.5 arcsec. We detected the optical counterpart identified by Durant & van Kerkwijk (2005, ApJ, 627, 376), and found I =24.9+/-0.2 mag. It is interesting to note that like the brightening in Ks band, the source in I band was 1.3 (+/-0.4) mag brighter than in 2003 June (Durant & van Kerkwijk 2005). This may suggest that the optical and near-IR emissions from this AXP are related. Further optical observations are encouraged.

We thank ESO for granting us this DDT observation and Ferdinando Patat at the Users Support Department of ESO for making the data accessible to us right after the observation.

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