Very low luminosities from the accretion-driven millisecond X-ray pulsar SAX J1808.4-3658 during quiescence

Abstract

We have observed the millisecond X-ray pulsar SAX J1808.4-3658 on three occasions during its 2000 outburst with the BeppoSAX satellite. The source was highly variable and erratic during this outburst, and by coincidence we obtained data only during times when the source had very low luminosities. During our observations, we detected four faint sources. The source closest to the position of SAX J1808.4-3658 is still ~1.6' away. This source can only be identified with SAX J1808.4-3658 if we assume that the BeppoSAX positional reconstruction is not completely understood. We also reanalyzed a BeppoSAX observation taken in March 1999 when the source was in quiescence and during which the source was thought to have been detected (Stella et al. 2000). Based on the similarities (position and luminosity) of this source with the above mentioned source ~1.6' away from SAX J1808.4-3658, it is possible that they are the same source. If this source is not the millisecond pulsar, then during all BeppoSAX observations of SAX J1808.4-3658 (the 2000 outburst ones and the 1999 quiescent one), the millisecond pulsar was not detected. A reanalysis of the ASCA quiescent data of SAX J1808.4-3658 (Dotani, Asai, & Wijnands 2000) confirms that during this observation the source was securely detected in quiescence. We discuss our results for SAX J1808.4-3658 in the context of the quiescent properties of low-mass X-ray binary transients.

Accepted for publication by ApJ Main Journal, 30 January 2002

References in corpus (5)

• New Evidence for Black Hole Event Horizons from Chandra
• The first outburst of SAX J1808.4-3658 revisited
• Time-Variable Emission from Transiently Accreting Neutron Stars In Quiescence due to Deep Crustal Heating
• The Optical Counterpart of the Accreting Millisecond Pulsar SAX J1808.4-3658 in Outburst: Constraints on the Binary Inclination
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• The Optical Counterpart to SAX J1808.4-3658 in Quiescence: Evidence of an Active Radio Pulsar?
• A Search for Pulsars in Quiescent Soft X-Ray Transients. I
• An observational review of accretion-driven millisecond X-ray pulsars
• Chandra observations of the bursting X-ray transient SAX J1747.0-2853 during low-level accretion activity
• The quiescent X-ray properties of the accreting millisecond X-ray pulsar and eclipsing binary Swift J1749.4-2807
• A XMM-Newton observation during the 2000 outburst of SAX J1808.4-3658
• New results on neutron star low mass transients in the quiescence
• Probing Strong Field $f(R)$ Gravity and Ultra-Dense Matter with the Structure and Thermal Evolution of Neutron Stars