Her X-1 Apparently Entering A New Anomalous Low State
ATel #228; Patricia Boyd (UMBC and GSFC) and Martin Still (USRA and GSFC)
on 31 Jan 2004; 20:41 UT
Credential Certification: Patricia T. Boyd (padi@dragons.gsfc.nasa.gov)
Subjects: X-ray, Request for Observations, Binary, Neutron Star, Pulsar
Her X-1 (= HZ Her) appears to be evolving towards another anomalous low state. RXTE ASM count rates have decreased steadily from 8 cts/s to 1 cts/s at the peak of the long-high state over the last six 35-day precession cycles. This would be the fourth such time Her X-1 has dropped into an anomalous low state, where the 35 day X-ray cycle turns off yet the 35 day optical cycle continues unabated. This event, combined with the times of the previously observed anomalous low states (in 1983, 1993 and 1999) suggest a 5-10 year recurrence time scale for the behavior. During the anomalous low state, the X-ray source appears as an ADC spectrum with additional Compton reflection from the companion star. Models for the phenomenon involve either mass transfer rate and/or accretion disk structure evolution. The pulse period, which is typically spinning-up in Her X-1, has been observed to spin down rapidly during previous anomalous low states. Pointed observations over energy bands from IR to hard X-rays are encouraged as the source evolves.
