TY - JOUR
T1 - Physical changes during Z-track movement in Sco X-1 on the flaring branch
AU - Barnard, R
AU - Church, Michael
AU - Balucinska-Church, Monika
PY - 2003/7/1
Y1 - 2003/7/1
N2 - We present results of a detailed study of X-ray flaring in the Z-track source Sco X-1 in a highly super-Eddington state made using high quality Rossi-XTE data from the PCA and HEXTE instruments. The emission model successfully used to explain the dipping LMXB, and other classes of LMXB in recent years, was applied to study the physical evolution along the Z-track which remains a major problem. This model consists of blackbody emission from the neutron star plus Comptonized emission from an extended accretion disk corona. As found in earlier work, major changes take place in the neutron star blackbody emission with kT increasing in flaring, and the blackbody radius R-BB increasing substantially to a maximum value of 9.4 +/- 0.6 km, consistent with the radius of the neutron star, after which RBB decreases. Thus this result is a measurement of neutron star radius. The behaviour of Sco X-1 in flaring is compared with our previous results for the strong flaring that takes place in the bright dipping, flaring LMXB X 1624-490. Remarkably, during movement along the Normal Branch towards the apex with the Flaring Branch, the luminosities of both spectral components decrease, suggesting the possibility that (M)over dot may decrease on the Normal Branch, contrary to the widely-held view that (M)over dot increases monotonically along the Z-track. During flaring, we detect for the first time an increase of the Comptonization cut-off energy which may suggest heating of the ADC plasma by the neutron star flare. The energy of a broad Gaussian line at similar to6.4 keV does not change, but the intensity of the line increases in flaring suggesting either an increase in ADC size in flaring or the effects of irradiation by the neutron star.
AB - We present results of a detailed study of X-ray flaring in the Z-track source Sco X-1 in a highly super-Eddington state made using high quality Rossi-XTE data from the PCA and HEXTE instruments. The emission model successfully used to explain the dipping LMXB, and other classes of LMXB in recent years, was applied to study the physical evolution along the Z-track which remains a major problem. This model consists of blackbody emission from the neutron star plus Comptonized emission from an extended accretion disk corona. As found in earlier work, major changes take place in the neutron star blackbody emission with kT increasing in flaring, and the blackbody radius R-BB increasing substantially to a maximum value of 9.4 +/- 0.6 km, consistent with the radius of the neutron star, after which RBB decreases. Thus this result is a measurement of neutron star radius. The behaviour of Sco X-1 in flaring is compared with our previous results for the strong flaring that takes place in the bright dipping, flaring LMXB X 1624-490. Remarkably, during movement along the Normal Branch towards the apex with the Flaring Branch, the luminosities of both spectral components decrease, suggesting the possibility that (M)over dot may decrease on the Normal Branch, contrary to the widely-held view that (M)over dot increases monotonically along the Z-track. During flaring, we detect for the first time an increase of the Comptonization cut-off energy which may suggest heating of the ADC plasma by the neutron star flare. The energy of a broad Gaussian line at similar to6.4 keV does not change, but the intensity of the line increases in flaring suggesting either an increase in ADC size in flaring or the effects of irradiation by the neutron star.
KW - stars : individual : Sco X-1
KW - accretion, accretion disks
KW - binaries : close
KW - X rays : stars
KW - stars : neutron
UR - http://www.scopus.com/inward/record.url?scp=0038079833&partnerID=8YFLogxK
U2 - 10.1051/0004-6361:20030539
DO - 10.1051/0004-6361:20030539
M3 - Article
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
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SN - 1432-0756
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SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
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SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
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SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
SN - 1432-0756
VL - 405
SP - 237
EP - 247
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
IS - 1
ER -