Her X-1
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Hercules |
| Right ascension | 16 57 49.83 |
| Declination | +35 20 32.6 |
| Apparent magnitude (V) | 13.83 |
| Spectral type | DA |
| Other designations | |
|
4U 1656+35, HZ Her
|
|
| Database references | |
| SIMBAD | data |
Hercules X-1 (Her X-1), also known as 4U1656+35, is a moderately strong X-ray binary source first studied by the Uhuru satellite. It is composed of a neutron star accreting matter from a normal star (HZ Her) probably due to Roche lobe overflow.
Her X-1 is the prototype for the massive X-ray binaries although it falls on the borderline, ~2 M☉, between high- and low-mass X-ray binaries.
An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate mass star.
The source exhibits complex time variability, pulsing with a period of 1.24 s due to the rotation of the neutron star, eclipsing every 1.70 days with the period of the binary orbit, and also varying with a 35-day period believed associated with the precession of the accretion disk. From observations, a twisted accretion disk, in retrograde precession, modulates the X-rays illuminating HZ Her and Earth.
The 1.24 second pulsar period associated with Her X-1 is immediately evident from the data. The sharp cut-off at ~24 keV in the flat spectrum observed for Her X-1 in this exposure provided the first reported evidence for radiative transfer effects to be associated with a highly magnetized plasma near the surface of a neutron star.
The actual announcement of the discovery of Hercules X-1 by Uhuru occurred at the 1971-72 Winter Meeting of the High-Energy Astrophysics Division AAS held in San Juan. The original discovery of this periodically pulsating binary X-ray source occurred in November 1971.
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