An anomalous low-state from the globular cluster X-ray source X1732-304 (Terzan 1)

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During a BeppoSAX observation of the X-ray burst source X1732-304 located in the globular cluster Terzan 1 in 1999 April, the source was detected in an anomalously low-state with an X-ray luminosity of 1.4 x 10³3 erg/s, about 300 times fainter than the lowest previously reported measure of the persistent flux. The spectral shape and intensity of this low-state emission is similar to that of a number of neutron star soft X-ray transients in quiescence, being well fit by a 0.34 keV blackbody together with a power-law with a photon index of 1.0. These similarities suggest that the same mechanism, such as the inhibition of accretion due to the propeller effect, is also operating in X1732-304. Alternatively, the X1732-304 low-state may be due to obscuration of the line of sight to the central neutron star, with only scattered and/or reflected X-rays being detected. The possibility that the source detected by BeppoSAX is not X1732-304, but a nearby dim source of the cluster field (what would make the observed dimming of X1732-304 even more remarkable) is also discussed.