Aquila X-1

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Double star
Aquila X-1
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Eagle
Right ascension 19 h 11 m 16.05 s
declination + 00 ° 35 ′ 5.8 ″
Apparent brightness 14.82 - 19.4 mag
Typing
rel. Brightness
(J-band) 		15,783 likes
B − V color index 0.6 
U − B color index −0.4 
Spectral class K6V-M0V + pec (e)
Variable star type XND 
Astrometry
Radial velocity 56 ± 11/136 ± 4 km / s
distance (16,952 ± 2.3)  ly
(5,200 ± 0.7)  pc  
Physical Properties
Dimensions (1.4 / 0.76)  M ☉
Rotation time 18.95 h
Other names
and catalog entries
2MASS catalog 2MASS J19111604 + 0035058 [1]
Other names V * V1333 Aql, 2U 1908 + 00, X Aql X-1, 3A 1908 + 005, PBC J1911.2 + 0035, 3U 1908 + 00, X Aql XR-1, 1ES 1908 + 00.5, 1RXS J191116.2 + 003504 , 4U 1908 + 005, [BM83] X1908 + 005, H 1908 + 005, 2S 1908 + 005, 4U 1908 + 00, [JVH96] NGC 6760 3, INTREF 968, SWIFT J1911.2 + 0036, XB 1908 + 005, [KRL2007b] 357, 1M 1908 + 005, SWIFT J1911.2 + 0034, 1XRS 19087 + 005

Template: Infobox Star / Maintenance / MagJ

Aquila X-1 , also Aql X-1 , is called L ow M ass X -ray B inary ( LMXB , German low-mass X-ray binary star system ), was founded in 1973 by PK Kunte et al. discovered at TIFR , and is the brightest X-ray source in the constellation of eagles .

The system consists of a neutron star , the matter of a main sequence star of spectral type K4 accreted , and was first from the satellite Vela 5B observed which plotted this source 1969-1976 several outbreaks. The companion is a variable and was designated according to the IAU standards with V1333 Aql .

Observations

Aquila X-1 is one of the most active X-ray binary star systems. Despite its relatively bright optical companion star at rest, its detection was hindered by the presence of another nearby star in the foreground. With the infrared integral field spectrograph SINFONI of the 8.2 m telescope unit 4 (UT4, Yepun) of the VLT , Aquila X-1 could be clearly distinguished from the interfering star. The phase-resolved spectroscopy in the near infrared shows absorption characteristics of a companion star of the spectral class K4 ± 2, which moves with a projected speed of K 2 = 136 ± 4 km s −1 . Astronomers calculated the first dynamic solution and the associated basic parameters of Aquila X-1, the orbit inclination (36 ° ˂ i ˂ 47 °) and the distance (d = 6 ± 2 k pc ) to this prototype of a neutron star with a impose new restrictions on the temporary outbreak in the field of X-rays.

These so-called N Eutron S tar X - R ay T ransients (. NSXRTs, dt neutron stars with temporary X-ray bursts) form a subgroup of LMXBs. They spend most of their existence in a weak, calm state, but show occasional bursts where their X-ray brightness can increase up to 10 percent above the Eddington luminosity .

The observation of NSXRTs during an outbreak is suitable for accretion studies, but at the same time means that most of the system luminosity can be attributed to the compact components, which completely outshines the spectral characteristics of the companion stars and prevents dynamic solutions in the infrared range as well. On the other hand, the investigation of NSXRTs in their resting state, in which the contribution of the companion star to the total brightness is greater, depends strongly on the distance and the galactic extinction .

Aquila X-1 is a recurrent X-ray pulsar, which has both coherent X-ray pulses with a period of 1.8 ms and thermonuclear bursts. Despite recurring eruptions and a relatively accessible optical brightness in the resting phase of V = 21.6 m , a radial velocity study of the companion star was still missing. This was prevented by the short distance of less than 0.5 arc seconds of a nearby G9 ± 2V star of Aql X-1.

This star in the foreground is approx. 2 magnitudes brighter in the V-band than Aql X-1, but has a comparable brightness at wavelengths in the near infrared range. C. Chevalier et al. used the better spatial resolution inherent in near-infrared observations and adaptive optics techniques to obtain phase-resolved integral field spectroscopy (IFS) that clearly separated Aql X-1 and the foreground star.

Determination of the masses and inclination of the orbit

The companion of Aql X-1 - a K4 ± 2 dwarf star - is not large enough to fill its Roche volume during an orbital period of approx. 19 hours, and therefore no accretion would be expected. However, the frequent bursts observed in Aql X-1 require that the companion must be an evolved star that has expanded to its Roche limit R L = 1.5 ± 0.1 R ☉ . Taking this into account, the absolute brightness of the companion of Aql X-1 is calculated to be M K = 3.0 ± 0.8 m , which results in a distance of d = 6 ± 2 kpc. This result is consistent with the analysis of the thermonuclear X-ray bursts (d <6 kpc, Galloway et al. 2008).

The occurrence of both thermonuclear outbursts and pulsed X-rays indicate an accreting neutron star in Aql X-1, whose mass (M NS ) should be greater than 1.2 solar masses (M ☉ ). Similarly, the companion star has been classified as an evolved K4 ± 2 star. Assuming that its mass was not significantly increased during the development of the system, then M B  <0.76 M ☉ results , from which an upper limit for the mass ratio of

calculate.

Taking into account a conservative restriction of M NS <3 M ☉ , the inclination parameter is set to a range between 23 ° < i <53 °. On the other hand, photometric observations limit the orbit inclination to i > 36 °. A matching mass of the neutron star M NS = 1.4 M ☉ would thus require an inclination  i  = 42 ± 3 °.

Accretion rate and magnetic field strength

Neutron stars with magnetic fields in the order of magnitude of 10 7 to 10 9 Gauss (10 3 to 10 5 Tesla ) can prevent the formation of an accretion disk far away from the star's surface. The pressure exerted by the magnetic field lines can push out the inner radius of an accretion disc until its strength is approximately equal to the dynamic pressure exerted by the accretion disc . Although this model makes a clear prediction of the condition of an accretion disk around a neutron star, direct confirmation is difficult.

The slice is only cut off if the magnetic field is sufficiently strong and the accretion rate is low. An X- ray burst occurred during observation of Aql X-1 with NuSTAR that lasted less than 20 seconds. X-ray bursts, especially type I bursts, often result from unstable thermonuclear hydrogen or helium fusions in the surface layers of the neutron star after a critical mass has accumulated on the surface. During such eruptions, the radiation pressure can even exceed the Eddington limit, so that the burning layer lifts off the surface, whereby the photosphere of the neutron star expands.

The analysis of the outbreak observed by NuSTAR revealed that it must have been a helium flash , which was triggered by the unstable burning of a helium-rich layer on the surface of the neutron star. During this observation, the mass accretion rate of 5.2 × 10 −9 M ☉ per year and the inner radius of the accretion disk of 15 R G (approx. 34 km) could be derived from the luminosity. At this accretion rate, the boundary layer extends to R B ~ 7.8 R G due to changes in viscosity and rotation .

From these values, a magnetic field strength of B = (5 ± 2) × 10 8 Gauss could be calculated, which agrees with earlier estimates for Aql X-1. This eruption shows that matter from the accretion disk is still reaching the surface of Aql X-1. Since the disc is cut off at such a large distance by the strong magnetic field, the accretion material can only be conducted along the magnetic field lines via accretion columns to the pole caps.

See also

Individual evidence

  1. ↑ a b c d V * V1333 Aql. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed June 4, 2019 .
  2. ↑ a b V1333 Aql. In: VSX. AAVSO , accessed June 4, 2019 .
  3. ↑ 2MASS J19111604 + 0035058. In: VizieR. Université de Strasbourg / CNRS , accessed June 6, 2019 .
  4. ↑ a b V * V1333 Aql. In: VizieR. Université de Strasbourg / CNRS , accessed June 6, 2019 .
  5. ↑ a b c d D. Mata Sánchez, et al .: The donor of Aquila X-1 revealed by high angular resolution near-infrared spectroscopy . In: MNRASL . August 26, 2016. arxiv : 1609.00392 . doi : 10.1093 / mnrasl / slw172 .
  6. ↑ Kunte et al .: Hard X Rays from the region of Aquila XR-1 . In: Nature Physical Science 245, 37-38 . September 17, 1973. doi : 10.1038 / physci245037a0 .
  7. ^ S. Campana, et al .: Mining the Aql X-1 long-term X-ray light curve . In: MNRAS , Volume 432, Issue 2, 21 June 2013, Pages 1695–1700 . May 1, 2013. arxiv : 1304.4033 . doi : 10.1093 / mnras / stt604 .
  8. ↑ Spectrograph for Integral Field Observations in the Near Infrared. In: ESO. European Southern Observatory , accessed June 5, 2019 .
  9. ↑ Muñoz-Darias et al .: Black hole-like hysteresis and accretion states in neutron star low-mass X-ray binaries . In: MNRAS , Volume 443, Issue 4, 1 October 2014, Pages 3270–3283 . August 7, 2014. doi : 10.1093 / mnras / stu1334 .
  10. ^ Mata Sánchez et al .: Mass constraints to Sco X-1 from Bowen fluorescence and deep near-infrared spectroscopy . In: MNRASL , Volume 449, Issue 1, 01 May 2015, Pages L1 – L5 . February 13, 2015. doi : 10.1093 / mnrasl / slv002 .
  11. ↑ P. Casella et al .: Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1 . In: The Astrophysical Journal Letters, Volume 674, Number 1 . January 10, 2008. doi : 10.1086 / 528982 .
  12. ^ Galloway et al .: Thermonuclear (Type I) X-Ray Bursts Observed by the Rossi X-Ray Timing Explorer . In: The Astrophysical Journal Supplement Series, Volume 179, Number 2 . June 12, 2008. doi : 10.1086 / 592044 .
  13. ^ A b Claude Chevalier: Magnitude, color and spectral type of AQL X-1 in quiescence . In: Astronomy and Astrophysics . 347, No. 1, July 1999, pp. L51-L54. arxiv : astro-ph / 9906278 . bibcode : 1999A & A ... 347L..51C .
  14. ^ Eggleton, PP: Approximations to the radii of Roche lobes . In: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 268, May 1, 1983, p. 368, 369. . May 1983. bibcode : 1983ApJ ... 268..368E . doi : 10.1086 / 160960 .
  15. ↑ Galloway, Duncan K. et al. 2008: Thermonuclear (Type I) X-Ray Bursts Observed by the Rossi X-Ray Timing Explorer . In: The Astrophysical Journal Supplement Series, Volume 179, Issue 2, pp. 360-422 (2008) . December 2008. bibcode : 2008ApJS..179..360G . doi : 10.1086 / 592044 .
  16. ↑ Kiziltan, B. et al. 2013: The Neutron Star Mass Distribution . In: The Astrophysical Journal, Volume 778, Issue 1, article id. 66, 12 pp. (2013) . November 2013. bibcode : 2013ApJ ... 778 ... 66K . doi : 10.1088 / 0004-637X / 778/1/66 .
  17. ↑ Kolb, U. et al. 2001: Mass estimates in short-period compact binaries . In: MNRAS , Volume 321, Issue 3, pp. 544-548. . March 2001. arxiv : astro-ph / 0009458 . bibcode : 2001MNRAS.321..544K . doi : 10.1046 / j.1365-8711.2001.04096.x .
  18. ↑ Welsh, WF et al. 2000: The Orbital Light Curve of Aquila X-1 . In: The Astronomical Journal , Volume 120, Issue 2, pp. 943-949. . August 2000. arxiv : astro-ph / 0004344 . bibcode : 2000AJ .... 120..943W . doi : 10.1086 / 301486 .
  19. ↑ a b Mukherjee, D. et al. 2015: The magnetic-field strengths of accreting millisecond pulsars . In: MNRAS , Volume 452, Issue 4, p. 3994-4012 . October 2015. arxiv : 1507.02138 . bibcode : 2015MNRAS.452.3994M . doi : 10.1093 / mnras / stv1542 .
  20. ↑ Pringle, JE; Rees, MJ: Accretion Disc Models for Compact X-Ray Sources . In: Astronomy and Astrophysics , Vol. 21, p. 1 (1972) . October 1972. bibcode : 1972A & A .... 21 .... 1P .
  21. ↑ a b Ashley L. King et al. 2016: Measuring A Truncated Disk in Aquila X-1 . In: High Energy Astrophysical Phenomena (astro-ph.HE) . February 24, 2016. arxiv : 1602.07664v1 . doi : 10.3847 / 2041-8205 / 819/2 / L29 .
  22. ↑ Parikh, A. et al. 2013: Nucleosynthesis in type I X-ray bursts . In: Progress in Particle and Nuclear Physics, Volume 69, p. 225-253. . March 2013. arxiv : 1211.5900 . bibcode : 2013PrPNP..69..225P . doi : 10.1016 / j.ppnp.2012.11.002 .