An anomalous low-state from the globular cluster X-ray source X 1732-304 (Terzan 1)
Abstract
During a BeppoSAX observation of the X-ray burst source X 1732-304 located in the globular cluster Terzan 1 in April 1999, the source was detected in an anomalous low-state with an X-ray luminosity of 1.4 x 10(33) erg s(-1) , 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 +/-(1.0}_{1.3) . These similarities suggest that the same mechanism, such as the inhibition of accretion due to the propeller effect, is also operating in X 1732-304. Alternatively, the X 1732-304 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 X 1732-304, but a nearby dim source of the cluster field (what would make the observed dimming of X 1732-304 even more remarkable) is also discussed.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1999
- DOI:
- 10.48550/arXiv.astro-ph/9907067
- arXiv:
- arXiv:astro-ph/9907067
- Bibcode:
- 1999A&A...349..819G
- Keywords:
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- ACCRETION;
- ACCRETION DISKS;
- STARS: INDIVIDUAL: X 1732-304;
- STARS: NEUTRON;
- GALAXY: GLOBULAR CLUSTERS: INDIVIDUAL: TERZAN 1;
- X-RAYS: GENERAL;
- Astrophysics
- E-Print:
- 7 Latex pages, 6 figures, Accepted for publication in Astronomy &