Optical and IR observations of SAX J1808.4-3658 in outburst

ATel #515; N. Rea (SRON/OAR), V. Testa, G. L. Israel, A. Antonelli (OAR), P. G. Jonker (SRON/CfA), M. Mendez (SRON), S. Campana (OAB) and E. Molinari, G. Chincarini, F. M. Zerbi, M. Rodono', S. Covino, G. Tosti, P. Conconi, G. Cutispoto, L. Nicastro, E. Palazzi, F. Vitali, F. D'Alessio, E. Meurs, P. Goldoni on behalf of the REMIR/ROSS team
on 13 Jun 2005; 08:32 UT
Credential Certification: Nanda Rea (rea@mporzio.astro.it)

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We report on optical and infrared observations of the currently active transient millisecond pulsar SAXJ1808.4-3658 (see ATEL #505, #506, #507, #511, #513), performed with REM (Rapid Eye Mount), a 60-cm robotic telescope located at the La Silla Observatory (Chile).

Optical images were obtained using ROSS, the REM Optical Slitless Spectrograph (field of view of 10'x10' and a pixel size of 0.575"), on 2005 June 5, 6, 7, and 8, using a V, R, and I band filter.
Our photometric results are relative to those of Giles, Hill & Greenhill 1999 (MNRAS 304, 47).
SAX J1808.4-3658 optical counterpart was detected during all the observations. Its V, R, and I band magnitude is consistent with being constant during the observations within 2 sigma (See Table; errors are at 1 sigma confidence level). Our magnitudes are consistent with the 1998 outburst magnitudes reported by Giles et al. 1999.

Date-Obs   UT   t_exp     Vmag               Rmag               Imag         FWHM
=======================================================
05/05/05   01:22   60s   17.16+/-0.21   16.86+/-0.20   17.43+/-0.34       4.0"
06/05/05   01:08   60s   17.61+/-0.27   16.92+/-0.20   17.76+/-0.52       4.5"
07/06/05   01:05   60s   17.47+/-0.16   17.44+/-0.21   17.31+/-0.23       2.3"
08/06/05   00:58   60s   17.39+/-0.19   17.09+/-0.19   17.42+/-0.23       2.5"

Infrared observations were performed in the H band using the REMIR, the REM Infrared Camera (field of view of 10'x10' and a pixel size of 1.22"), on 2005 June 5, 6, 7, and 8 .
SAX J1808.4-3658 infrared counterpart was not detected in the H band. The 5 sigma magnitude upper limit on its non-detection is H>16.5 for all the observations.

Images for the four nights in V, R and I, and more details about the observations, can be found at http://www.mporzio.astro.it/~rea/saxj1808_rem.html
For further information on the REM telescope see http://golem.merate.mi.astro.it/projects/rem/

We plan to keep monitoring the source with REM in the next nights.

Optical and IR images of the REM observations