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Title: LONG-TERM EVOLUTION OF THE MAIN-ON STATES IN HERCULES X-1

Rossi X-ray Timing Explorer All-sky Monitor (RXTE ASM) observations and American Association of Variable Star Observers (AAVSO) optical data were used for a time-series analysis of the long-term activity of Her X-1. The problem of measuring the long-term evolution of the X-ray intensity in the light curve which consists only of separated intense spikes was addressed. For this purpose, the fluence of each Main-On state was determined. The fluences vary generally (not only in the transitions into/from anomalous low states (ALSs)) by tens of percent on timescales of at least several epochs of the cycle length of the superorbital cycle (but without any stable cycle) while irradiation of the donor producing the optical modulation remains considerably more stable. ALS1 and ALS2 are extensions of the tail in the statistical distribution of these fluences. In this interpretation, the variations of the fluences are caused by the changes of the structure of the inner disk region, which produces variable obscuration of the beams (emitting in the ASM band) at the neutron star. A small change of obscuration of these beams by the inner disk region suffices to change the fluences largely. However, the irradiation of the donor is changed significantly less becausemore » this inner disk region (which emits beyond the ASM band and acts as the occulting region of the beams) also irradiates the donor.« less
Authors:
 [1]
  1. Astronomical Institute, The Czech Academy of Sciences, 25165 Ondřejov (Czech Republic)
Publication Date:
OSTI Identifier:
22520209
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 150; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; DIAGRAMS; IRRADIATION; MODULATION; NEUTRON STARS; TIME-SERIES ANALYSIS; VARIABLE STARS; VARIATIONS; VISIBLE RADIATION