Other
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21536004i&link_type=abstract
American Astronomical Society, AAS Meeting #215, #360.04; Bulletin of the American Astronomical Society, Vol. 42, p.547
Other
Scientific paper
The HZ Herculis/Hercules X-1 (HZ Her/Her X-1) system is characterized by a great wealth of phenomena, such as 1.24-s X-ray pulsations, 1.7-day orbital period eclipses, and a unique, approximately 35-day long, X-ray flux cycle. Each 35-day cycle has two high X-ray flux states, which are separated by a low X-ray flux state.
X-ray absorption phenomena, simply referred to as dips, were first noticed in the system's light curve soon after the system's discovery, almost 40 years ago, and their properties have been documented, analyzed and debated ever since. We continue to investigate HZ Her/Her X-1's light curve dips using the entire Rossi X-ray Timing Explorer (RXTE) database on this system.
We found a total of 695, new, light curve dips scattered over 43 X-ray flux high states and 23 low states; 276 are low-state dips, whereas 417 occur during the high states. However, only about half these dips have a clearly defined start and end. None of these dips, for which a start and end can be specified, exceeds 4 hours. The shortest observed dip lasts about half a minute. The dip durations recorded by RXTE are in agreement with previous Ginga, EXOSAT and Tenma observations of Her X-1. The dip ingress lasts longer than the egress for more than half the dips observed by the RXTE.
We documented a total of 411 pre-eclipse dips, 130 anomalous dips, and 154 post-eclipse dips. The marching dip trend to earlier orbital phases, as the 35-day cycle progresses, is clearly confirmed. There is an indication that pre-eclipse dips last longer and are stronger than the other dips. Anomalous dips appear to be stronger than post-eclipse dips. There is strong indication that the spectral evolution of dips is related to the orbital phase and not to the 35-day cycle.
Igna Ciprian
Leahy Denis A.
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