Hercules X-1
Encyclopedia
Hercules 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.
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.
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.
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.
star aspect sensors, having been reported at J1950 RA
17h05m Dec
34°52' using Uhuru and at 16h56.7m Dec
35°35' using OSO 7
. However, there is only one weak X-ray source (2U 1735+43) within 10° of Her X-1. But four radio sources: (1) RA
16h56m50.75s Dec
35°14'33±3" of a double point source separated by 17±2" and a stellar image 13±3" from the centroid, (2) RA
16h57m10.65s Dec
35°21'35±3" within 6±3" of the stellar image, (3) RA
16h57m35.72s Dec
35°15'19±3" with no star visible on the Palomar Sky Survey print, and (4) RA
16h58m39.17s Dec
35°10'53±3" were found near the overlap of Uhuru and OSO 7 positions. At that time the search could not discover the radio counterpart of Her X-1 if its radio emission were analogous to its 36-day periodic X-ray behavior, although there was no compelling astrophysical reason for the two fluxes to be correlated. The four sources above were observed during several eclipse phases of the X-ray star. No radio eclipses were detected that corresponded. At that time Doxsey specified that (1) repeated radio searches, especially during the high X-ray luminosity state of Her X-1, should be made and (2) there was a clear need for a better position determination for Her X-1.
In 1973, Bahcall and Bahcall determined that HZ Hercules had a light curve that matched Hercules X-1's, fixing Hercules X-1's position.
X-ray binary
X-ray binaries are a class of binary stars that are luminous in X-rays.The X-rays are produced by matter falling from one component, called the donor to the other component, called the accretor, which is compact: a white dwarf, neutron star, or black hole.The infalling matter releases...
source first studied by the Uhuru
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
satellite.
It is composed of a neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
accreting matter from a normal star (HZ Her) probably due to Roche lobe
Roche lobe
The Roche lobe is the region of space around a star in a binary system within which orbiting material is gravitationally bound to that star. If the star expands past its Roche lobe, then the material can escape the gravitational pull of the star. If the star is in a binary system then the material...
overflow.
Intermediate-mass X-ray binary (IMXB)
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.
Intensity
The source exhibits complex time variability, pulsing with a periodOrbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
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.
Discovery of Her X-1
The actual announcement of the discovery of Hercules X-1 by UhuruUhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
occurred at the 1971-72 Winter Meeting of the High-Energy Astrophysics Division AAS held in San Juan
San Juan, Puerto Rico
San Juan , officially Municipio de la Ciudad Capital San Juan Bautista , is the capital and most populous municipality in Puerto Rico, an unincorporated territory of the United States. As of the 2010 census, it had a population of 395,326 making it the 46th-largest city under the jurisdiction of...
. The original discovery of this periodically pulsating binary X-ray source occurred in November 1971.
Location
The position of Her X-1 was uncertain due to the failure of the UhuruUhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
star aspect sensors, having been reported at J1950 RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
17h05m Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
34°52' using Uhuru and at 16h56.7m Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
35°35' using OSO 7
OSO 7
OSO 7 is the seventh in the series of American Orbiting Solar Observatory satellites launched by NASA between 1962 and 1975...
. However, there is only one weak X-ray source (2U 1735+43) within 10° of Her X-1. But four radio sources: (1) RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
16h56m50.75s Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
35°14'33±3" of a double point source separated by 17±2" and a stellar image 13±3" from the centroid, (2) RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
16h57m10.65s Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
35°21'35±3" within 6±3" of the stellar image, (3) RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
16h57m35.72s Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
35°15'19±3" with no star visible on the Palomar Sky Survey print, and (4) RA
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
16h58m39.17s Dec
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
35°10'53±3" were found near the overlap of Uhuru and OSO 7 positions. At that time the search could not discover the radio counterpart of Her X-1 if its radio emission were analogous to its 36-day periodic X-ray behavior, although there was no compelling astrophysical reason for the two fluxes to be correlated. The four sources above were observed during several eclipse phases of the X-ray star. No radio eclipses were detected that corresponded. At that time Doxsey specified that (1) repeated radio searches, especially during the high X-ray luminosity state of Her X-1, should be made and (2) there was a clear need for a better position determination for Her X-1.
In 1973, Bahcall and Bahcall determined that HZ Hercules had a light curve that matched Hercules X-1's, fixing Hercules X-1's position.