Chandra HETG observations of SAX J1808.4-3658
ATel #517; D. K. Galloway, N. S. Schulz, D. Chakrabarty (MIT)
on 14 Jun 2005; 22:33 UT
Credential Certification: Duncan K. Galloway (duncan@space.mit.edu)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Referred to by ATel #: 524, 527
We report on an
observation of the presently active accretion-powered millisecond
pulsar SAX J1808.4-3658 (see ATels #505, #506, #507, #511, #513, #515)
with the High-Energy Transmission Grating Spectrograph (HETGS) aboard the Chandra X-ray Observatory.
The observation lasted for approximately 15 ks starting June 10 0232h
(UT), and was made in continuous clocking mode (which provides no
imaging capability, but avoids photon pileup for bright sources).
Preliminary analysis of the medium-energy grating spectra has revealed
an absorption feature at 21.6 angstrom, attributable to the resonance
line of (He-like) oxygen VII. We also found evidence for absorption
features around the neutral oxygen edge, which we tentatively identify
with 1s-2p
transitions of O I and O II in the ISM. No other narrow absorption or
emission features attributable to the source were identified in the medium-
or high-energy grating spectra.
We fitted the continuum with an absorbed blackbody and power law spectrum,
with a temperature of 0.67 keV and photon spectral index 2.03. The
absorbed 2-10 keV flux was 7.6e-10 ergs/cm2/s (about 33 mCrab).
No thermonuclear bursts were detected. Analysis continues, and a paper
with more detailed results is in preparation.
