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RXTE PCA Detects the Millisecond Pulsar SAX J1808.4-3658 in Outburst

ATEL # 1728; C. B. Markwardt (CRESST/U.Md./NASA/GSFC) & J. H. Swank (NASA/GSFC)
on 22 Sep 2008; 2:48 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Craig B. Markwardt (

Subjects: X-ray, Request for Observations, Binaries, Neutron Stars, Pulsars, Transients
Referred to by ATEL #: 1732, 1733

Regular RXTE PCA monitoring observations on 2008-09-21 at 10:00 UT detected flux from the position of the accreting millisecond pulsar SAX J1808.4-3658. The 2-10 keV flux was 10 mCrab. This appears to be the beginning of a new transient outburst (the last one began in June 2005).

There is a small amount of on-source PCA data with high time resolution, but the pulsations were not detectable. However, in previous outbursts the typical pulsed amplitude was ~5%, which is near the detectability limit for the present small amount of data. More PCA observations are planned. Follow-up observations at other wavelengths are encouraged.

We thank D. Altamirano and R. Wijnands for pointing out this outburst in the scan data.

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R. E. Rutledge , Editor
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