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
Credential Certification: Jeroen Homan (jeroen@space.mit.edu)
Subjects: X-ray, Neutron Star, Transient
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).
