Observations of the high-mass X-ray binary 4U 2206+54 with the Swift Burst Alert Telescope ( BAT ) do not show modulation at the previously reported period of 9.6 days found from observations made with the Rossi X-ray Timing Explorer ( RXTE ) All-Sky Monitor ( ASM ) .
Instead , the strongest peak in the power spectrum of the BAT light curve occurs at a period of 19.25 \pm 0.08 days , twice the period found with the RXTE ASM .
The maximum of the folded BAT light curve is also delayed compared to the maximum of the folded ASM light curve .
The most recent ASM data folded on twice the 9.6 day period show similar morphology to the folded BAT light curve .
This suggests that the apparent period doubling is a recent secular change rather than an energy-dependent effect .
The 9.6 day period is thus not a permanent strong feature of the light curve .
We suggest that the orbital period of 4U 2206+54 may be twice the previously proposed value .