The soft component in the X-ray spectrum of 4U 1700-37

Details The soft component in the X-ray spectrum of 4U 1700-37 The soft component in the X-ray spectrum of 4U 1700-37

Aug 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...288..796h&link_type=abstract

Astronomy and Astrophysics 288, 796-802 (1994)

Astronomy and Astrophysics

Astrophysics

13

Stars: Atmospheres, Stars: Binaries: Eclipsing, Stars: Early Type, Stars: Supergiants, X-Rays: Stars

Scientific paper

We report on ROSAT all-sky survey and Ginga observations of the supergiant X-ray binary 4U 1700-37. The survey light curve from August 1990 covered the time around eclipse egress of the neutron star and shows little flux to at least orbital phase 0.26, indicating high absorption suppressing the soft X-rays. After phase 0.37 intensity variations up to a factor of 20 are seen, probably caused by variations in absorption. The X-ray spectrum in the ROSAT PSPC band can be modeled with thermal Bremsstrahlung, consistent with the soft component seen during a first Ginga observation of 4U 1700-37 in April 1990 and the second Ginga observation in April 1991 reported here. During the second Ginga observation, performed around eclipse of the hard X-ray source, the temperature for a thermal Bremsstrahlung model increases near eclipse egress from 0.47keV before eclipse to 0.74keV after eclipse. This suggests a temperature distribution in an extended, soft X-ray emitting region around the neutron star with higher temperatures in front of the neutron star and lower temperatures in a long tail trailing it. Although the soft 1-5keV flux shows short term variations (with lower amplitude than during the ROSAT observations) it is not correlated with the hard X-ray flux from the neutron star. Combining the two Ginga observations the spectral analysis yields an upper limit of 38.6deg for the eclipse semi-angle which is smaller than previously derived from intensity measurements in the 1-20keV band. This is of importance for the determination of the system parameters and for deriving the density structure of the stellar wind from the column density profile.

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