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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
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 16 57 49.83[1]
Declination +35 20 32.6[1]
Apparent magnitude (V) 13.83[1]
Spectral typeDA[1]
Other designations
4U 1656+35, HZ Her
Database references
SIMBADdata

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.[2]

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.[3]


Intensity


This light curve of Her X-1 shows long term and medium term variability. Each pair of vertical lines delineate the eclipse of the compact object behind its companion star. In this case, the companion is a 2 Solar-mass star with a radius of nearly 4 times that of the Sun. This eclipse shows the 1.7-day orbital period of the system.
This light curve of Her X-1 shows long term and medium term variability. Each pair of vertical lines delineate the eclipse of the compact object behind its companion star. In this case, the companion is a 2 Solar-mass star with a radius of nearly 4 times that of the Sun. This eclipse shows the 1.7-day orbital period of the system.

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.[2]

Uhuru observations revealed the presence of X-ray pulsations in Her X-1 (1.2 s) and confirmed that it contains a rapidly rotating neutron star. Figure adapted from figures by E. Schreier, STScI, taken from Figure 7-2a in Charles and Seward.
Uhuru observations revealed the presence of X-ray pulsations in Her X-1 (1.2 s) and confirmed that it contains a rapidly rotating neutron star. Figure adapted from figures by E. Schreier, STScI, taken from Figure 7-2a in Charles and Seward.

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 figure shows 15-second samples of the raw counts (per 20.48 ms) observed in a 1973 sounding-rocket-borne exposure to three of the X-ray brightest binary sources in the Milky Way galaxy: Her X-1 (1.7 days), Cyg X-3 (0.2 day), and Cyg X-1 (5.6 days).
The figure shows 15-second samples of the raw counts (per 20.48 ms) observed in a 1973 sounding-rocket-borne exposure to three of the X-ray brightest binary sources in the Milky Way galaxy: Her X-1 (1.7 days), Cyg X-3 (0.2 day), and Cyg X-1 (5.6 days).
OSO 8 spectra of Hercules X-1.
OSO 8 spectra of Hercules X-1.

Discovery of Her X-1


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.[4] The original discovery of this periodically pulsating binary X-ray source occurred in November 1971.[5]


Location


The position of Her X-1 was uncertain due to the failure of the Uhuru star aspect sensors, having been reported[5] at J1950 RA 17h05m Dec 34°52' using Uhuru and at 16h56.7m Dec 35°35'[6] using OSO 7. However, there is only one weak X-ray source (2U 1735+43) within 10° of Her X-1.[7] 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.[8] 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.[8] 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[8] 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 Herculis had a light curve that matched Hercules X-1's, fixing Hercules X-1's position.


References


  1. "Her X-1". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 10 February 2018.
  2. Priedhorsky WC, Holt SS (1987). "Long-term cycles in cosmic X-ray sources". Space Sci. Rev. 45 (3–4): 291–348. Bibcode:1987SSRv...45..291P. doi:10.1007/BF00171997. S2CID 120443194.
  3. Podsiadlowski P, Rappaport S, Pfahl E (2001). "Evolutionary Binary Sequences for Low- and Intermediate-Mass X-ray Binaries". The Astrophysical Journal. 565 (2): 1107–1133. arXiv:astro-ph/0107261. Bibcode:2002ApJ...565.1107P. doi:10.1086/324686. S2CID 16381236.
  4. Schreier E, Levinson R, Gursky H, Kellogg E, Tananbaum H, Giacconi R (Mar 1972). "Evidence for the Binary Nature of Centaurus X-3 from UHURU X-Ray Observations". Astrophys. J. 172 (3): L79–L89. Bibcode:1972ApJ...172L..79S. doi:10.1086/180896.
  5. Tananbaum H, Gursky H, Kellogg EM, Levinson R, Schreier E, Giacconi R (1972). "Discovery of a Periodic Pulsating Binary X-Ray Source in Hercules from UHURU". Astrophys J. 174: L143–9. Bibcode:1972ApJ...174L.143T. doi:10.1086/180968.
  6. Clark GW, Bradt HV, Lewin WH, Schnopper HW, Sprott G (1972). "X-ray Astronomy: Uhuru Dominates Madrid Meeting". Nature. 237 (5355): 369–370. Bibcode:1972Natur.237..369A. doi:10.1038/237369a0. S2CID 4279721.
  7. Giacconi R, Murray S, Gursky H, Kellogg E, Schreier E, Tananbaum T (1972). "The UHURU catalog of X-ray sources". Astrophys J. 178: 281. Bibcode:1972ApJ...178..281G. doi:10.1086/151790.
  8. Doxsey R, Murthy GT, Rappaport S, Spencer J, Zaumen W (Aug 1972). "Radio Search for the Pulsing X-Ray Source in Hercules". Astrophys. J. 176 (8): L15–8. Bibcode:1972ApJ...176L..15D. doi:10.1086/181010.

На других языках

[de] Hercules X-1

Hercules X-1 ist ein Röntgenpulsar und eines der am besten untersuchten Objekte der Röntgenastronomie. Es handelt sich um ein Doppelsternsystem, bestehend aus dem veränderlichen Blauen Riesen HZ Herculis (siehe Benennung veränderlicher Sterne) und einem Pulsar (Neutronenstern). Die Periodizität der Röntgenemission – und damit die Rotationsperiode des Pulsars – beträgt 1,24 Sekunden, die Stärke seines Magnetfeldes (d. h. die magnetische Flussdichte) etwa 4,6 · 108 Tesla. Ferner variiert die Intensität der Röntgenemission mit einer Periode von 35 Tagen, was vermutlich auf eine (retrograde) Präzession der Akkretionsscheibe zurückzuführen ist. Die Umlaufzeit des Doppelsternsystems beträgt 1,7 Tage; infolge der Bedeckung des Pulsars durch HZ Herculis ist jeweils während 0,24 Tagen keine Röntgenstrahlung detektierbar.
- [en] Hercules X-1

[ru] Геркулес X-1

Геркулес X-1 (Hercules X-1, Her X-1, 4U1656+35) — рентгеновский двойной источник промежуточной мощности, впервые исследованный спутником Uhuru. Состоит из нейтронной звезды, на которую происходит аккреция вещества с обычной звезды (HZ Her), вероятно, вследствие заполнения звездой полости Роша.


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