Crab Pulsar

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Crab Pulsar
Chandra-crab.jpg
The Crab Nebula, which contains the Crab Pulsar (the red star in the center). Image combines optical data from Hubble (in red) and X-ray images from Chandra (in blue).
Credit: NASA/CXC/ASU/J. Hester et al. [1]
Observation data
Epoch J2000       Equinox J2000
Constellation Taurus
Right ascension 05h 34m 31.95s [2]
Declination +22° 00′ 52.2″ [2]
Apparent magnitude  (V)16.65 [3]
Characteristics
Evolutionary stage Neutron star
U−B color index −0.45[ citation needed ]
B−V color index +0.47 [4]
Astrometry
Proper motion (μ)RA: −11.34 ± 0.06 [5]   mas/yr
Dec.: 2.65 ± 0.14 [5]   mas/yr
Parallax (π)0.53 ± 0.06  mas [5]
Distance approx. 6,200  ly
(approx. 1,900  pc)
Details
Radius 10[ citation needed ]  km
Luminosity 0.9  L☉
Temperature center (modeled): ~3×108 [6]  K,
surface: ~1.6×106  K
Rotation 33.5028583 ms [7]
Age 967[ citation needed ] years
Other designations
SNR G184.6-05.8, 2C 481, 3C 144.0, SN 1054A, 4C 21.19, NGC 1952, PKS 0531+219, PSR B0531+21, PSR J0534+2200, CM Tau
Database references
SIMBAD data

The Crab Pulsar (PSR B0531+21 or Baade's Star) is a relatively young neutron star. The star is the central star in the Crab Nebula, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054. [8] [9] [10] Discovered in 1968, the pulsar was the first to be connected with a supernova remnant. [11]

The sky seen in gamma-rays as seen by the Fermi Gamma-ray Space Telescope, reveals the Crab Pulsar as one of the brightest gamma-ray sources in the sky. 267641main allsky labeled HI.jpg
The sky seen in gamma-rays as seen by the Fermi Gamma-ray Space Telescope, reveals the Crab Pulsar as one of the brightest gamma-ray sources in the sky.

The Crab Pulsar is one of very few pulsars to be identified optically. The optical pulsar is roughly 20 kilometres (12 mi) in diameter and has a rotational period of about 33  milliseconds, that is, the pulsar "beams" perform about 30 revolutions per second. [6] The outflowing relativistic wind from the neutron star generates synchrotron emission, which produces the bulk of the emission from the nebula, seen from radio waves through to gamma rays. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the surrounding nebula, forming a termination shock. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar into the main body of the nebula. The period of the pulsar's rotation is increasing by 38  nanoseconds per day due to the large amounts of energy carried away in the pulsar wind. [12]

The Crab Nebula is often used as a calibration source in X-ray astronomy. It is very bright in X-rays, and the flux density and spectrum are known to be constant, with the exception of the pulsar itself. The pulsar provides a strong periodic signal that is used to check the timing of the X-ray detectors. In X-ray astronomy, "crab" and "millicrab" are sometimes used as units of flux density. A millicrab corresponds to a flux density of about 2.4×10−11  erg  s−1 cm−2 (2.4×10−14 W/m2) in the 2–10  keV X-ray band, for a "crab-like" X-ray spectrum, which is roughly power-law in photon energy: I ~ E−1.1.[ citation needed ] Very few X-ray sources ever exceed one crab in brightness.

Pulsed emission up to 1.5 TeV has been detected from the Crab pulsar [13] and together with the Vela Pulsar at 20 TeV are the only two known pulsar with emission in this energy range [14]

History of observation

X-ray picture of Crab Nebula, taken by Chandra Crab Nebula pulsar x-ray.jpg
X-ray picture of Crab Nebula, taken by Chandra

The Crab Nebula was identified as the remnant of SN 1054 by 1939. Astronomers then searched for the nebula's central star. There were two candidates, referred to in the literature as the "north following" and "south preceding" stars. In September 1942, Walter Baade ruled out the "north following" star, but found the evidence inconclusive for the "south preceding" star. [15] Rudolf Minkowski, in the same issue of The Astrophysical Journal as Baade, advanced spectral arguments claiming that the "evidence admits, but does not prove, the conclusion that the south preceding star is the central star of the nebula". [16]

In late 1968, David H. Staelin and Edward C. Reifenstein III reported the discovery of two pulsating radio sources "near the crab nebula that could be coincident with it" using the 300-foot (91 m) Green Bank radio antenna. [17] They were given the designations NP 0527 and NP 0532. The period and location of the Crab Nebula pulsar NP 0532 was discovered by Richard V. E. Lovelace and collaborators on 10 November 1968, at the Arecibo radio observatory. [18]

A subsequent study by them, including William D. Brundage, also found that the NP 0532 source is located at the Crab Nebula. [19] A radio source was also reported coincident with the Crab Nebula in late 1968 by L. I. Matveenko in Soviet Astronomy . [20]

Optical pulsations were first reported by Cocke, Disney, and Taylor using the 36-inch (91 cm) telescope on Kitt Peak of the Steward Observatory of the University of Arizona. [21] This observation had a audio tape recording the pulses and this tape also recorded the voices of John Cocke, Michael Disney and Bob McCallister (the night assistant) at the time of the discovery. [22] Their discovery was confirmed by Nather, Warner, and Macfarlane. [23]

Light curve and slow motion picture of the pulsar located in the center of the Crab Nebula. Image taken with a photon counting camera on the 80cm telescope of the Wendelstein Observatory, Dr. F. Fleischmann, 1998 M1.gif
Light curve and slow motion picture of the pulsar located in the center of the Crab Nebula. Image taken with a photon counting camera on the 80cm telescope of the Wendelstein Observatory, Dr. F. Fleischmann, 1998

Jocelyn Bell Burnell, who co-discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see. [24] [25]

In 2007, it was reported that Charles Schisler detected a celestial source of radio emission in 1967 at the location of the Crab Nebula, using a United States Air Force radar system in Alaska designed as an early warning system to detect intercontinental ballistic missiles. This source was later understood by Schisler to be the Crab Pulsar, after the news of Bell Burnell's initial pulsar discoveries was reported. [24] However, Schisler's detection was not reported publicly for four decades due to the classified nature of the radar observations. [26]

The Crab Pulsar was the first pulsar for which the spin-down limit was broken using several months of data of the LIGO observatory. Most pulsars do not rotate at constant rotation frequency, but can be observed to slow down at a very slow rate (3.7×10−10 Hz/s in case of the Crab). This spin-down can be explained as a loss of rotation energy due to various mechanisms. The spin-down limit is a theoretical upper limit of the amplitude of gravitational waves that a pulsar can emit, assuming that all the losses in energy are converted to gravitational waves. No gravitational waves observed at the expected amplitude and frequency (after correcting for the expected Doppler shift) proves that other mechanisms must be responsible for the loss in energy. The non-observation so far is not totally unexpected, since physical models of the rotational symmetry of pulsars puts a more realistic upper limit on the amplitude of gravitational waves several orders of magnitude below the spin-down limit. It is hoped that with the improvement of the sensitivity of gravitational wave instruments and the use of longer stretches of data, gravitational waves emitted by pulsars will be observed in future. [27] The only other pulsar for which the spin-down limit was broken so far is the Vela Pulsar.

A slow-motion animation of the Crab Pulsar taken at 800 nm wavelength (near-infrared) using a Lucky Imaging camera from Cambridge University, showing the bright pulse and fainter interpulse. Crab Lucky video2.gif
A slow-motion animation of the Crab Pulsar taken at 800 nm wavelength (near-infrared) using a Lucky Imaging camera from Cambridge University, showing the bright pulse and fainter interpulse.

In 2019 the Crab Nebula, and presumably therefore the Crab Pulsar, was observed to emit gamma rays in excess of 100  TeV, making it the first identified source of ultra-high-energy cosmic rays. [28]

In 2023, Very long baseline interferometry (VLBI) was used to conduct precision astrometry using the radio giant-pulse emission of the Crab Pulsar, thus measuring a precise distance to the Crab Pulsar. [5]

Related Research Articles

<span class="mw-page-title-main">Neutron star</span> Collapsed core of a massive star

A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses (M☉), possibly more if the star was especially metal-rich. Except for black holes, neutron stars are the smallest and densest known class of stellar objects. Neutron stars have a radius on the order of 10 kilometers (6 mi) and a mass of about 1.4 M☉. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.

<span class="mw-page-title-main">Supernova</span> Explosion of a star at its end of life

A supernova is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months.

<span class="mw-page-title-main">SN 1987A</span> 1987 supernova event in the constellation Dorado

SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately 51.4 kiloparsecs from Earth and was the closest observed supernova since Kepler's Supernova in 1604. Light and neutrinos from the explosion reached Earth on February 23, 1987 and was designated "SN 1987A" as the first supernova discovered that year. Its brightness peaked in May of that year, with an apparent magnitude of about 3.

<span class="mw-page-title-main">Supernova remnant</span> Remnants of an exploded star

A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.

Timeline of neutron stars, pulsars, supernovae, and white dwarfs

<span class="mw-page-title-main">Crab Nebula</span> Supernova remnant in the constellation Taurus

The Crab Nebula is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The common name comes from a drawing that somewhat resembled a crab with arms produced by William Parsons, 3rd Earl of Rosse, in 1842 or 1843 using a 36-inch (91 cm) telescope. The nebula was discovered by English astronomer John Bevis in 1731. It corresponds with a bright supernova recorded by Chinese astronomers in 1054 as a guest star. The nebula was the first astronomical object identified that corresponds with a historically-observed supernova explosion.

<span class="mw-page-title-main">Pulsar wind nebula</span> Nebula powered by the pulsar wind of a pulsar

A pulsar wind nebula, sometimes called a plerion, is a type of nebula sometimes found inside the shell of a supernova remnant (SNR), powered by winds generated by a central pulsar. These nebulae were proposed as a class in 1976 as enhancements at radio wavelengths inside supernova remnants. They have since been found to be infrared, optical, millimetre, X-ray and gamma ray sources.

<span class="mw-page-title-main">Einstein@Home</span> BOINC volunteer computing project that analyzes data from LIGO to detect gravitational waves

Einstein@Home is a volunteer computing project that searches for signals from spinning neutron stars in data from gravitational-wave detectors, from large radio telescopes, and from a gamma-ray telescope. Neutron stars are detected by their pulsed radio and gamma-ray emission as radio and/or gamma-ray pulsars. They also might be observable as continuous gravitational wave sources if they are rapidly spinning and non-axisymmetrically deformed. The project was officially launched on 19 February 2005 as part of the American Physical Society's contribution to the World Year of Physics 2005 event.

<span class="mw-page-title-main">Pulsar</span> Highly magnetized, rapidly rotating neutron star

A pulsar is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays.

<span class="mw-page-title-main">Millisecond pulsar</span> Pulsar with a rotational period less than about 10 milliseconds

A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading theory for the origin of millisecond pulsars is that they are old, rapidly rotating neutron stars that have been spun up or "recycled" through accretion of matter from a companion star in a close binary system. For this reason, millisecond pulsars are sometimes called recycled pulsars.

<span class="mw-page-title-main">SN 1181</span> Supernova in the constellation Cassiopeia

First observed between August 4 and August 6, 1181, Chinese and Japanese astronomers recorded the supernova now known as SN 1181 in eight separate texts. One of only five supernovae in the Milky Way confidently identified in pre-telescopic records, it appeared in the constellation Cassiopeia and was visible and motionless against the fixed stars for 185 days. F. R. Stephenson first recognized that the 1181 AD "guest star" must be a supernova, because such a bright transient that lasts for 185 days and does not move in the sky can only be a galactic supernova.

<span class="mw-page-title-main">Geminga</span> X-ray pulsar in the constellation Gemini

Geminga is a gamma ray and x-ray pulsar source thought to be a neutron star approximately 250 parsecs from the Sun in the constellation Gemini.

<span class="mw-page-title-main">Cygnus Loop</span> Supernova remnant in the constellation of Cygnus

The Cygnus Loop is a large supernova remnant (SNR) in the constellation Cygnus, an emission nebula measuring nearly 3° across. Some arcs of the loop, known collectively as the Veil Nebula or Cirrus Nebula, emit in the visible electromagnetic range. Radio, infrared, and X-ray images reveal the complete loop.

<span class="mw-page-title-main">Vela Pulsar</span> Multi-spectrum pulsar in the constellation Vela

The Vela Pulsar is a radio, optical, X-ray- and gamma-emitting pulsar associated with the Vela Supernova Remnant in the constellation of Vela. Its parent Type II supernova exploded approximately 11,000–12,300 years ago.

<span class="mw-page-title-main">VERITAS</span> Ground-based gamma-ray observatory

VERITAS is a major ground-based gamma-ray observatory with an array of four 12 meter optical reflectors for gamma-ray astronomy in the GeV – TeV photon energy range. VERITAS uses the Imaging Atmospheric Cherenkov Telescope technique to observe gamma rays that cause particle showers in Earth's atmosphere that are known as extensive air showers. The VERITAS array is located at the Fred Lawrence Whipple Observatory, in southern Arizona, United States. The VERITAS reflector design is similar to the earlier Whipple 10-meter gamma-ray telescope, located at the same site, but is larger in size and has a longer focal length for better control of optical aberrations. VERITAS consists of an array of imaging telescopes deployed to view atmospheric Cherenkov showers from multiple locations to give the highest sensitivity in the 100 GeV – 10 TeV band. This very high energy observatory, completed in 2007, effectively complements the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope due to its larger collection area as well as coverage in a higher energy band.

<span class="mw-page-title-main">IC 443</span> Supernova remnant in the constellation Gemini

IC 443 is a galactic supernova remnant (SNR) in the constellation Gemini. On the plane of the sky, it is located near the star Eta Geminorum. Its distance is roughly 5,000 light years from Earth.

<span class="mw-page-title-main">History of supernova observation</span> Ancient and modern recorded observations of supernovae explosions

The known history of supernova observation goes back to 1006 AD. All earlier proposals for supernova observations are speculations with many alternatives.

<span class="mw-page-title-main">PSR B1937+21</span> Pulsar in the constellation Vulpecula

PSR B1937+21 is a pulsar located in the constellation Vulpecula a few degrees in the sky away from the first discovered pulsar, PSR B1919+21. The name PSR B1937+21 is derived from the word "pulsar" and the declination and right ascension at which it is located, with the "B" indicating that the coordinates are for the 1950.0 epoch. PSR B1937+21 was discovered in 1982 by Don Backer, Shri Kulkarni, Carl Heiles, Michael Davis, and Miller Goss.

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is a consortium of astronomers who share a common goal of detecting gravitational waves via regular observations of an ensemble of millisecond pulsars using the Green Bank Telescope, Arecibo Observatory, the Very Large Array, and the Canadian Hydrogen Intensity Mapping Experiment (CHIME). Future observing plans include up to 25% total time of the Deep Synoptic Array 2000 (DSA2000). This project is being carried out in collaboration with international partners in the Parkes Pulsar Timing Array in Australia, the European Pulsar Timing Array, and the Indian Pulsar Timing Array as part of the International Pulsar Timing Array.

<span class="mw-page-title-main">IGR J11014−6103</span> Nebula in the constellation Carina

IGR J11014−6103, also called the Lighthouse Nebula, is a pulsar wind nebula trailing the neutron star which has the longest relativistic jet observed in the Milky Way.

References

  1. ↑ "Space Movie Reveals Shocking Secrets of the Crab Pulsar" (Press release). NASA. 19 September 2002.
  2. 1 2 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv: 2208.00211 . Bibcode:2023A&A...674A...1G. doi: 10.1051/0004-6361/202243940 . S2CID   244398875. Gaia DR3 record for this source at VizieR.
  3. ↑ Optical Observations of Pulsars: the ESO Contribution (PDF), p. 22
  4. ↑ Davidson, Kris (October 1987). "SPECTROPHOTOMETRY OF THE CRAB NEBULA AS A WHOLE". The Astrophysical Journal. 94 (4): 967.
  5. 1 2 3 4 Lin, Rebecca; van Kerkwijk, Marten H.; Kirsten, Franz; Pen, Ue-Li; Deller, Adam T. (1 August 2023). "The Radio Parallax of the Crab Pulsar: A First VLBI Measurement Calibrated with Giant Pulses". The Astrophysical Journal. 952 (2): 161. arXiv: 2306.01617 . Bibcode:2023ApJ...952..161L. doi: 10.3847/1538-4357/acdc98 .
  6. 1 2 Becker, W.; Aschenbach, B. (1995), "ROSAT HRI Observations of the Crab Pulsar An Improved Temperature Upper Limit for PSR 0531+21", in Alpar, M. A.; Kızıloğlu, Ü.; van Paradijs, J. (eds.), The Lives of the Neutron Stars, vol. 450, Kluwer Academic, p. 47, arXiv: astro-ph/9503012 , Bibcode:1995ASIC..450...47B, ISBN   978-0-7923-324-6-6 {{cite book}}: |work= ignored (help)
  7. ↑ ATNF Pulsar Catalogue database entry. See Manchester, R. N.; et al. (2005), "The Australia Telescope National Facility Pulsar Catalogue", Astronomical Journal, 129 (4): 1993–2006, arXiv: astro-ph/0412641 , Bibcode:2005AJ....129.1993M, doi:10.1086/428488, S2CID   121038776
  8. ↑ Supernova 1054 – Creation of the Crab Nebula.
  9. ↑ Duyvendak, J. J. L. (1942), "Further Data Bearing on the Identification of the Crab Nebula with the Supernova of 1054 A.D. Part I. The Ancient Oriental Chronicles", Publications of the Astronomical Society of the Pacific, 54 (318): 91, Bibcode:1942PASP...54...91D, doi: 10.1086/125409
    Mayall, N. U.; Oort, Jan Hendrik (1942), "Further Data Bearing on the Identification of the Crab Nebula with the Supernova of 1054 A.D. Part II. The Astronomical Aspects", Publications of the Astronomical Society of the Pacific, 54 (318): 95, Bibcode:1942PASP...54...95M, doi: 10.1086/125410
  10. ↑ Brandt, K.; et al. (1983), "Ancient records and the Crab Nebula supernova", The Observatory, 103: 106, Bibcode:1983Obs...103..106B
  11. ↑ Zeilik, Michael; Gregory, Stephen A. (1998), Introductory Astronomy & Astrophysics (4th ed.), Saunders College Publishing, p. 369, ISBN   978-0-03-006228-5
  12. ↑ Supernovae, Neutron Stars & Pulsars.
  13. ↑ The H.E.S.S. Collaboration; Aharonian, F.; Benkhali, F. Ait; Aschersleben, J.; Ashkar, H.; Backes, M.; Martins, V. Barbosa; Batzofin, R.; Becherini, Y.; Berge, D.; Bernlöhr, K.; Bi, B.; Böttcher, M.; Boisson, C.; Bolmont, J.; et al. (5 October 2023). "Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts". Nature Astronomy. arXiv: 2310.06181 . doi:10.1038/s41550-023-02052-3. ISSN   2397-3366.
  14. ↑ The H.E.S.S. Collaboration; Aharonian, F.; Benkhali, F. Ait; Aschersleben, J.; Ashkar, H.; Backes, M.; Martins, V. Barbosa; Batzofin, R.; Becherini, Y.; Berge, D.; Bernlöhr, K.; Bi, B.; Böttcher, M.; Boisson, C.; Bolmont, J. (5 October 2023). "Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts". Nature Astronomy. arXiv: 2310.06181 . doi:10.1038/s41550-023-02052-3. ISSN   2397-3366.
  15. ↑ Baade, Walter (1942), "The Crab Nebula", Astrophysical Journal, 96: 188, Bibcode:1942ApJ....96..188B, doi:10.1086/144446
  16. ↑ Minkowski, Rudolf (1942), "The Crab Nebula", Astrophysical Journal, 96: 199, Bibcode:1942ApJ....96..199M, doi: 10.1086/144447
  17. ↑ Staelin, David H.; Reifenstein, III, Edward C. (1968), "Pulsating radio sources near the Crab Nebula", Science, 162 (3861): 1481–3, Bibcode:1968Sci...162.1481S, doi:10.1126/science.162.3861.1481, JSTOR   1725616, PMID   17739779, S2CID   38023534
  18. ↑ IAU Circ. No. 2113, 1968.
  19. ↑ Reifenstein, III, Edward C.; Staelin, David H.; Brundage, William D. (1969), "Crab Nebula Pulsar NPO527", Physical Review Letters , 22 (7): 311, Bibcode:1969PhRvL..22..311R, doi:10.1103/PhysRevLett.22.311
  20. ↑ Matveenko, L. I. (1968), "Position of a Source of Small Angular Size in the Crab Nebula", Soviet Astronomy, 12: 552, Bibcode:1968SvA....12..552M
  21. ↑ Cocke, W. J.; Disney, M.; Taylor, D. J. (1969), "Discovery of Optical Signals from Pulsar NP 0532", Nature, 221 (5180): 525, Bibcode:1969Natur.221..525C, doi:10.1038/221525a0, S2CID   4296580
  22. ↑ "Moments of Discovery - A pulsar Discovery". history.aip.org. Retrieved 14 March 2024.
  23. ↑ Nather, R. E.; Warner, B.; Macfarlane, M. (1969), "Optical Pulsations in the Crab Nebula Pulsar", Nature , 221 (5180): 527, Bibcode:1969Natur.221..527N, doi:10.1038/221527a0, S2CID   4295264
  24. 1 2 Brumfiel (2007), "Air force had early warning of pulsars", Nature, 448 (7157): 974–975, Bibcode:2007Natur.448..974B, doi: 10.1038/448974a , PMID   17728726
  25. ↑ "Beautiful Minds: Jocelyn Bell Burnell", BBC television documentary broadcast 7 April 2010.
  26. ↑ Schisler, Charles (2008). "An Independent 1967 Discovery of Pulsars". AIP Conference Proceedings. 983: 642–645. Bibcode:2008AIPC..983..642S. doi:10.1063/1.2900320.
  27. ↑ The LIGO Scientific Collaboration; Abbott, B.; Abbott, R.; Adhikari, R.; Ajith, P.; Allen, B.; Allen, G.; Amin, R.; Anderson, S. B.; Anderson, W. G.; Arain; Araya, M.; Armandula, H.; Armor, P.; Aso, Y.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Ballmer, S.; Bantilan; Barish, B. C.; Barker, C.; Barker, D.; Barr, B.; Barriga, P.; Barton, M. A.; Bastarrika, M.; Bayer, K.; et al. (2008), "Beating the spin-down limit on gravitational wave emission from the Crab pulsar", Astrophys. J., 683 (1): L45–L50, arXiv: 0805.4758 , Bibcode:2008ApJ...683L..45A, doi:10.1086/591526, S2CID   250871270
    And erratum in Abbott, B.; et al. (2009), Astrophys. J., 706 (1): L203–L204, arXiv: 0805.4758 , Bibcode:2009ApJ...706L.203A, doi:10.1088/0004-637X/706/1/L203 {{citation}}: CS1 maint: untitled periodical (link)
  28. ↑ Amenomori, M. (13 June 2019). "First detection of photons with energy beyond 100 TeV from an astrophysical source". Phys. Rev. Lett. 123 (5): 051101. arXiv: 1906.05521 . Bibcode:2019PhRvL.123e1101A. doi:10.1103/PhysRevLett.123.051101. PMID   31491288. S2CID   189762075 . Retrieved 8 July 2019.
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