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Radius expansion bursts from the neutron star transient XTE J1701-462; a new distance estimate

ATEL # 1183; Dacheng Lin, Jeroen Homan, Ron Remillard (MIT/MKI), Rudy Wijnands,
on 16 Aug 2007; 13:54 UT
Password Certification: Jeroen Homan (

Subjects: X-ray, Neutron Stars, Transients

A detailed spectral analysis of the second and third type-I X-ray bursts from the neutron star transient XTE J1701-462 (detected on July 20 and July 25, see also ATel #1165) reveals clear photospheric radius expansion in both of them. The bursts show radius expansion for about 2-3 seconds, with the color temperature decreasing from ~2.5 keV to ~1.6 keV and the radius increasing from ~10 km to 20-25 km. During the expansion phase the bolometric flux peaked at a value close to 4.0e-8 erg/s/cm^2. As reported in ATel #1144 the first X-ray burst from XTE J1701-462, which was detected on July 17, did not show evidence for photospheric radius expansion.

The peak fluxes from the radius expansion bursts can be used to estimate the distance of XTE J1701-462. Using the empirically determined Eddington luminosity for radius expansion bursts (Kuulkers et al. 2003, A&A, 399, 663) we derive a distance of 8.9 kpc with an uncertainty of ~10%. Alternatively, using equation 6 from Galloway et al. (2006, astro-ph/0608259), which gives a more theoretically motivated estimate for the Eddington luminosity, and assuming a 1.4 solar-mass neutron star with a radius of 10 km, we obtain 7.4 kpc (for H-poor bursts) or 5.7 kpc (for H-rich bursts).

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