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\IBVShead{5663}{1 December 2005}

\IBVStitletl{Unsuccessful Optical Search for the 0.006223Hz Pulsar }{Frequency from the X-Ray Binary MX0656-072}

\IBVSauth{Bartolini, C.$^1$; Casares, J. V$^2$; Guarnieri, A.$^1$; Nanni, D.$^2$; Piccioni, A.$^1$; Terra, F.$^2$}

\IBVSinst{Dipartimento di Astronomia, Universit\'a di Bologna, via Ranzani 1, 40127 Bologna, Italy}
\IBVSinst{Monte Porzio Observatory, to be completed, Roma}
\IBVSinst{Instituto de Astrof\'{\i}sica de Canarias, V\'{\i}a L\'actea 
s/n E38200, La Laguna (Tenerife), Spain}


\SIMBADobjAlias{MXB 0656-072}{XTE J0658-073}
\IBVStyp{ HMXRB }
\IBVSkey{photometry}
\IBVSabs{Results from B and R CCD observations of the  X-ray Binary system}
\IBVSabs{MX0656-072 High Mass X-Ray Binaries are given.}
\IBVSabs{No optical pulsations was found from the X-Ray Pulsar.}


\begintext


The Be X-Ray binary MX0656-072 was discovered as an X-Ray pulsar  during the outburst of October 21, 2003 (Remillard et al., 2003), with a pulse period of $160.7$s (Morgan et al., 2003; Heindl et al., 2004). We observed the optical counterpart of this source in November 2003 with the OGS ESA telescope and the IAC CCD camera at the Iza\~na Observatory in Tenerife to verify if the 
pulsar signal could be observed also in the optical band.
We obtained 111 frames in B light with exposure time of $30$s on 
November 10 and 154 frames with exposure time of $20$s on November 14, 
2003; in the same night we got also 430 frames with exposure time of 
$10s$ in R light. 
To have the lowest possible frame transfer time we reduced the image field 
to a small square containing 4 objects: the target star and the three 
comparison stars indexed Figure~1. 
Separate calibration of the comparison objects was obtained in the same
nights using additional full field exposures.
We performed separate Discrete Fourier Transforms of the magnitudes 
computed with DAOPHOT from the data obtained in the three runs.
We repeated the temporal analysis on a file collecting all B images
of the two nights and on a second file collecting all images of the
three nights after detrending the nightly mean magnitudes.
The frequency of $0.006223Hz$ = $537.64779c/d$, corresponding to 
the period of 160.7s, is absent in all our analyses, where the spectral
power near to the expected frequency results to be particularly low. 
Figure~2 shows, as example, the spectral power of the R stream
of 430 measures performed on November 14, 2003. 
This result is not surprising because, due to the high luminosity of the
Be companion star, the reprocessed signal could be diluted, the phase 
information could be destroyed by the large reprocessing area; or the 
X-ray beam could interact weakly with the companion and/or the 
accretion flux environment. 

\IBVSfig{10cm}{5663-f1.eps}{CCD image of the full observation field: 
the comparison stars are the objects 1, 2 and 3 in the lower central 
part of the image.}
\IBVSfigKey{5663-f1.eps}{MXB 0656-072}{finding chart}

\IBVSfig{10cm}{5663-f2.eps}{Fourier power spectrum of the observation 
run of November 14, 2003, performed with R filter, after prewhitening of 
the two lower frequencies}
\IBVSfigKey{5663-f2.eps}{MXB 0656-072}{periodogram}

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\references

Heindl W.A., Rothschild R.E., Coburn W., Staubert R., Wilms J., Kreykenbohm I., Kretschmar P., 2004, {\it AIP Conf. Proc.}, {\bf 714}, 323
% astro - ph/0403197

Morgan E., Remillard R., Swank J., 2003, {\it ATEL}, {\bf 199}

Remillard R., Marshall F., 2003, {\it ATEL}, {\bf 197}

\endreferences

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