View source for Crab Pulsar

{{Short description|Pulsar in the constellation Taurus}}
{{starbox begin|name=Crab Pulsar}}
{{Use dmy dates|date=March 2024}}
{{starbox image
 |image=[[Image:Chandra-crab.jpg|250px]]
 |caption=The Crab Nebula, which contains the Crab Pulsar (the red star in the center). Image combines optical data from [[Hubble Space Telescope|Hubble]] (in red) and X-ray images from [[Chandra X-ray Observatory|Chandra]] (in blue).
|credit=NASA/CXC/ASU/J. Hester et al.<ref>{{cite press release | url=http://hubblesite.org/newscenter/archive/releases/2002/24/image/a | title= Space Movie Reveals Shocking Secrets of the Crab Pulsar | publisher=[[NASA]] | date=19 September 2002 }}</ref>
}}
{{Starbox observe
 | epoch=J2000
 | ra={{RA|05|34|31.95}}<ref name=dr3>{{cite Gaia DR3|3403818172572314624}}</ref>
 | dec= {{DEC|+22|00|52.2}}<ref name=dr3/>
 | appmag_v=16.65<ref>{{citation|title=Optical Observations of Pulsars: the ESO Contribution |page=22|url=https://www.eso.org/sci/publications/messenger/archive/no.99-mar00/messenger-no99-22-26.pdf}} </ref>
 | constell=[[Taurus (constellation)|Taurus]]
}}
{{Starbox character
 | type=[[Neutron star]]
 | b-v=+0.47<ref>{{cite journal |last=Davidson|first=Kris|title=SPECTROPHOTOMETRY OF THE CRAB NEBULA AS A WHOLE|journal=The Astrophysical Journal|date=October 1987|volume=94|number=4| pages=967 | url=https://articles.adsabs.harvard.edu/pdf/1987AJ.....94..964D}}</ref>
 | u-b=−0.45{{citation needed|date=June 2022}}
}}
{{Starbox astrometry
 | prop_mo_ra=−11.34 ± 0.06<ref name=radio_parallax/>
 | prop_mo_dec=2.65 ± 0.14<ref name=radio_parallax/>
 | parallax = 0.53
 | p_error = 0.06
 | absmag_v = 5.26
 | parallax_footnote =<ref name="radio_parallax">{{cite journal |last1=Lin |first1=Rebecca |last2=van Kerkwijk |first2=Marten H. |last3=Kirsten |first3=Franz |last4=Pen |first4=Ue-Li |last5=Deller |first5=Adam T. |title=The Radio Parallax of the Crab Pulsar: A First VLBI Measurement Calibrated with Giant Pulses |journal=The Astrophysical Journal |date=1 August 2023 |volume=952 |issue=2 |pages=161 |doi=10.3847/1538-4357/acdc98|arxiv=2306.01617 |bibcode=2023ApJ...952..161L |doi-access=free 
}}</ref>
}}
{{Starbox detail
 | luminosity=0.9<!--computed for 2200pc, magnitude 16.5-->
 | temperature= center (modeled): {{val|3|e=8|p=~}}<ref name="ROSAT">{{cite book |last1=Becker |first1=W. |last2=Aschenbach |first2=B. |chapter=ROSAT HRI Observations of the Crab Pulsar An Improved Temperature Upper Limit for PSR 0531+21 |editor-last1=Alpar |editor-first1=M. A. |editor-last2=Kızıloğlu |editor-first2=Ü. |editor-last3=van Paradijs |editor-first3=J. |date=1995|title=The Lives of the Neutron Stars |work=Proceedings of the NATO Advanced Study Institute on the Lives of the Neutron Stars |volume=450 |page=47 |publisher=[[Kluwer Academic]] |arxiv=astro-ph/9503012 |bibcode=1995ASIC..450...47B |isbn=978-0-7923-324-6-6 |mode=cs2}}</ref> K,<br/>
surface: {{val|1.6|e=6|p=~}}
 | rotation=33.5028583 [[millisecond|ms]]<ref name=atnf>[http://www.atnf.csiro.au/research/pulsar/psrcat/ ATNF Pulsar Catalogue] database [http://www.atnf.csiro.au/research/pulsar/psrcat/proc_form.php?version=1.60&?Name=Name&PMRA=PMRA&PMDec=PMDec&PX=PX&GL=GL&GB=GB&P0=P0&Dist=Dist&Dist_DM=Dist_DM&dist_dm1=dist_dm1&dist_amn=dist_amn&dist_amx=dist_amx&dist_a=dist_a&Assoc=Assoc&startUserDefined=true&c1_val=&c2_val=&c3_val=&c4_val=&sort_attr=jname&sort_order=asc&condition=&pulsar_names=B0531%2B21&ephemeris=short&coords_unit=raj%2Fdecj&radius=&coords_1=&coords_2=&style=Short+with+errors&no_value=*&fsize=3&x_axis=&x_scale=linear&y_axis=&y_scale=linear&state=query&table_bottom.x=51&table_bottom.y=36&expert=expert&db_file= entry]. See {{citation | last=Manchester | first=R. N. |display-authors=etal | date=2005 | title=The Australia Telescope National Facility Pulsar Catalogue | journal=Astronomical Journal | volume=129 | issue=4 | pages=1993–2006 |arxiv = astro-ph/0412641 | bibcode=2005AJ....129.1993M | doi=10.1086/428488| s2cid=121038776 }}</ref>
 | age=8,142{{citation needed|date=June 2022}}
 | radius_km=10{{citation needed|date=June 2022}}
}}
{{Starbox catalog
 | names= [[Supernova remnant|SNR]] G184.6-05.8, [[Second Cambridge Catalogue of Radio Sources|2C]] 481, [[Third Cambridge Catalogue of Radio Sources|3C]] 144.0,  SN 1054A, [[Fourth Cambridge Survey|4C]] 21.19, [[New General Catalogue|NGC]] 1952, PKS 0531+219, PSR B0531+21, PSR J0534+2200, CM Tau
}}
{{Starbox reference| Simbad=Crab_Pulsar}}
{{Starbox end}}
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 [[supernova remnant|remnant]] of the [[supernova]] [[SN 1054]], which was widely observed on Earth in the year 1054.<ref name=SN1054>[http://messier.seds.org/more/m001_sn.html Supernova 1054 – Creation of the Crab Nebula].</ref><ref name="PASP1942">{{citation | last=Duyvendak | first=J. J. L. | title=Further Data Bearing on the Identification of the Crab Nebula with the Supernova of 1054 A.D. Part I. The Ancient Oriental Chronicles | journal=Publications of the Astronomical Society of the Pacific | volume=54 | issue=318 | pages=91 | date=1942 | bibcode=1942PASP...54...91D | doi=10.1086/125409 | doi-access=free }}<br />{{citation | last1=Mayall|first1=N. U.| last2=Oort | first2=Jan Hendrik | author2-link=Jan Oort | title=Further Data Bearing on the Identification of the Crab Nebula with the Supernova of 1054 A.D. Part II. The Astronomical Aspects | journal=Publications of the Astronomical Society of the Pacific | volume=54 |issue=318| pages=95 | date=1942|bibcode=1942PASP...54...95M | doi=10.1086/125410 | doi-access=free }}</ref><ref>{{Citation | last=Brandt | first=K. | date=1983 | title=Ancient records and the Crab Nebula supernova | journal=The Observatory | volume=103 | pages=106 | bibcode=1983Obs...103..106B |display-authors=etal}}</ref> Discovered in 1968, the [[pulsar]] was the first to be connected with a [[supernova remnant]].<ref>{{citation | last1=Zeilik | first1=Michael | last2=Gregory | first2=Stephen A. | page=369 | title=Introductory Astronomy & Astrophysics | date=1998 | publisher=Saunders College Publishing | isbn=978-0-03-006228-5 | edition=4th }}</ref>
[[File:267641main_allsky_labeled_HI.jpg|thumb|left|The [[sky]] seen in [[Gamma ray|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 [[pulsar]]s to be identified optically. The [[optical pulsar]] is roughly {{convert|20|km|mi}} in diameter and has a [[rotation]]al period of about 33&nbsp;[[millisecond]]s, that is, the pulsar "beams" perform about 30&nbsp;revolutions per second.<ref name="ROSAT" /> 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&nbsp;[[nanosecond]]s per day due to the large amounts of energy carried away in the pulsar wind.<ref>[http://cass.ucsd.edu/archive/public/tutorial/SN.html Supernovae, Neutron Stars & Pulsars].</ref>

The [[Crab Nebula]] is often used as a [[calibrator star|calibration source]] in [[X-ray astronomy]]. It is very bright in [[X-ray]]s, and the [[flux density]] and [[Electromagnetic spectrum|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 {{val|2.4|e=-11|u=[[erg]]&nbsp;s<sup>−1</sup>&nbsp;cm<sup>−2</sup>}} ({{val|2.4|e=-14|u=W/m<sup>2</sup>}}) in the 2–10&nbsp;[[kiloelectronvolt|keV]] X-ray band, for a "crab-like" X-ray spectrum, which is roughly power-law in photon energy: ''I''&nbsp;~&nbsp;''E''<sup>−1.1</sup>.{{citation needed|date=April 2013}}
Very few X-ray sources ever exceed one crab in brightness.

Pulsed emission up to 1.5 [[Teraelectronvolt|TeV]] has been detected from the Crab pulsar.<ref>{{Cite journal |last1=The H.E.S.S. Collaboration |display-authors=etal |last2=Aharonian |first2=F. |last3=Benkhali |first3=F. Ait |last4=Aschersleben |first4=J. |last5=Ashkar |first5=H. |last6=Backes |first6=M. |last7=Martins |first7=V. Barbosa |last8=Batzofin |first8=R. |last9=Becherini |first9=Y. |last10=Berge |first10=D. |last11=Bernlöhr |first11=K. |last12=Bi |first12=B. |last13=Böttcher |first13=M. |last14=Boisson |first14=C. |last15=Bolmont |first15=J. |date=5 October 2023 |title=Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts |url=https://www.nature.com/articles/s41550-023-02052-3 |journal=Nature Astronomy |volume=7 |issue=11 |pages=1341–1350 |language=en |doi=10.1038/s41550-023-02052-3 |issn=2397-3366|arxiv=2310.06181 }}</ref> The only other known pulsar with emission in this energy range is the [[Vela Pulsar]] at 20 TeV.<ref>{{Cite journal |last1=The H.E.S.S. Collaboration |last2=Aharonian |first2=F. |last3=Benkhali |first3=F. Ait |last4=Aschersleben |first4=J. |last5=Ashkar |first5=H. |last6=Backes |first6=M. |last7=Martins |first7=V. Barbosa |last8=Batzofin |first8=R. |last9=Becherini |first9=Y. |last10=Berge |first10=D. |last11=Bernlöhr |first11=K. |last12=Bi |first12=B. |last13=Böttcher |first13=M. |last14=Boisson |first14=C. |last15=Bolmont |first15=J. |date=5 October 2023 |title=Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts |url=https://www.nature.com/articles/s41550-023-02052-3 |journal=Nature Astronomy |volume=7 |issue=11 |pages=1341–1350 |language=en |doi=10.1038/s41550-023-02052-3 |issn=2397-3366|arxiv=2310.06181 }}</ref>

==History of observation==
[[File:Crab Nebula pulsar x-ray.jpg|thumb|left|[[X-ray]] picture of [[Crab Nebula]], taken by [[Chandra X-ray Observatory|Chandra]]]]
The [[Crab Nebula]] was identified as the remnant of SN 1054 by 1939. [[Astronomer]]s 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.<ref>{{Citation |last=Baade | first=Walter | title=The Crab Nebula |journal=Astrophysical Journal |volume=96 |pages=188 | date=1942 |bibcode=1942ApJ....96..188B |doi=10.1086/144446}}</ref>
[[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".<ref>{{Citation | last=Minkowski | first=Rudolf | title=The Crab Nebula |journal=Astrophysical Journal |volume=96 | pages=199 | date=1942 | bibcode=1942ApJ....96..199M | doi=10.1086/144447| doi-access=free }}</ref>

<!--It appears that it may have been Staelin, D. H., and Reifenstein, E. C., IAU Circ. No. 2110 (1968) or Richards, D., IAU Circ. No. 2114 (1968) (with a period) that is the true first published source for a pulsar but since there's no electronic online version to confirm, the Science article should remain the source for now.-->
In late 1968, [[David H. Staelin]] and Edward C. Reifenstein III reported the discovery of two rapidly varying radio sources "near the crab nebula that could be coincident with it" using the {{convert|300|foot|adj=on}} [[Green Bank Telescope|Green Bank radio antenna]].<ref>{{Citation | last1=Staelin | first1=David H. | last2=Reifenstein, III | first2=Edward C. | title=Pulsating radio sources near the Crab Nebula | journal=Science | volume=162 | pages=1481–3 | date=1968 |doi=10.1126/science.162.3861.1481 | pmid=17739779 | issue=3861 | jstor=1725616 |bibcode = 1968Sci...162.1481S| s2cid=38023534 }}</ref> They were given the designations NP 0527 and NP 0532. The period of 33 milliseconds 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|Arecibo Radio Observatory]].<ref name="Lovelace1968">[https://ui.adsabs.harvard.edu/abs/1968IAUC.2113....1L/abstract "Pulsar NP 0532 Near Crab Nebula"] Lovelace, R. V. E. , Sutton, J. M. , Craft, H. D. 1968, IAU Circ., No. 2113, #1</ref> <ref name = "Comella1969">[https://ui.adsabs.harvard.edu/abs/1969Natur.221..453C/abstract "Crab nebula pulsar NP 0532"] 1969, J. M. Comella, H. D. Craft, R. V. E. Lovelace, J. M. Sutton, G. L. Tyler, ''Nature'' 221 (5179), 453-454.</ref> The discovery of the pulsar with such a short period proved that pulsars are rotating neutron stars (not pulsating white dwarfs, as many scientists suggested). Soon after the discovery of the Crab Pulsar, David Richards discovered (using the Arecibo Telescope) that it spins down and, therefore, loses its rotational energy. [[Thomas Gold]] has shown that the pulsar's spin-down power is sufficient to power the Crab Nebula.

A subsequent study by them, including William D. Brundage, also found that the NP 0532 source is located at the Crab Nebula.<ref>{{Citation |last1=Reifenstein, III |first1=Edward C. | last2=Staelin | first2=David H. | last3=Brundage | first3=William D. | title=Crab Nebula Pulsar NPO527 | date=1969 | journal=[[Physical Review Letters]] | volume=22 | issue=7 | pages=311 | doi=10.1103/PhysRevLett.22.311 | bibcode=1969PhRvL..22..311R}}</ref> A radio source was also reported coincident with the Crab Nebula in late 1968 by L. I. Matveenko in ''[[Soviet Astronomy]]''.<ref>{{Citation | last=Matveenko | first=L. I. | title=Position of a Source of Small Angular Size in the Crab Nebula |journal=Soviet Astronomy |volume=12 |pages=552 | date=1968 | bibcode=1968SvA....12..552M}}</ref>

Optical pulsations were first reported by Cocke, Disney, and Taylor using the {{convert|36|inch|cm|adj=on}} telescope on Kitt Peak of the Steward Observatory of the University of Arizona.<ref>{{Citation | last1=Cocke | first1=W. J. | last2=Disney | first2=M. | last3=Taylor | first3=D. J. | title=Discovery of Optical Signals from Pulsar NP 0532 |journal=Nature |volume=221 |issue=5180 |date=1969 | doi=10.1038/221525a0 | pages=525 |bibcode = 1969Natur.221..525C| s2cid=4296580 }}</ref> This observation had an [[Tape recorder|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.<ref>{{Cite web |title=Moments of Discovery - A pulsar Discovery |url=https://history.aip.org/exhibits/mod/pulsar/pulsar1/01.html |access-date=2024-03-14 |website=history.aip.org}}</ref> Their discovery was confirmed by [[Ed Nather|Nather]], [[Brian Warner (astronomer)|Warner]], and Macfarlane.<ref>{{Citation |last1=Nather |first1=R. E. |title=Optical Pulsations in the Crab Nebula Pulsar |date=1969 |journal=[[Nature (journal)|Nature]] |volume=221 |issue=5180 |pages=527 |bibcode=1969Natur.221..527N |doi=10.1038/221527a0 |last2=Warner |first2=B. |last3=Macfarlane |first3=M. |author-link=Ed Nather |author-link2=Brian Warner (astronomer) |s2cid=4295264}}</ref>

[[File:M1.gif|thumb|left|[[Light curve]] and slow motion [[Image|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 (astronomy)|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&nbsp;Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see.<ref name="Brumfiel">{{Citation | author=Brumfiel | title=Air force had early warning of pulsars | journal=Nature | volume=448 |pages=974–975 | date=2007 | doi=10.1038/448974a | pmid=17728726 | issue=7157 |bibcode = 2007Natur.448..974B| doi-access=free }}</ref><ref name="Bell Burnell">"Beautiful Minds: Jocelyn Bell Burnell", BBC television documentary broadcast 7 April 2010.</ref>

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|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.<ref name="Brumfiel" /> However, Schisler's detection was not reported publicly for four decades due to the classified nature of the radar observations.<ref>{{cite journal |last1=Schisler |first1=Charles |title=An Independent 1967 Discovery of Pulsars |journal=AIP Conference Proceedings |date=2008 |volume=983 |pages=642–645 |doi=10.1063/1.2900320 |bibcode=2008AIPC..983..642S |url=https://pubs.aip.org/aip/acp/article/983/1/642/620966/An-Independent-1967-Discovery-of-Pulsars}}</ref>

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{{e|-10}}&nbsp;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 wave]]s. No [[Gravity|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]].<ref>{{Citation |title=Beating the spin-down limit on gravitational wave emission from the Crab pulsar |date=2008 |author1=The LIGO Scientific Collaboration |last2=Abbott |first2=B. |last3=Abbott |first3=R. |last4=Adhikari |first4=R. |last5=Ajith |first5=P. |last6=Allen |first6=B. |last7=Allen |first7=G. |last8=Amin |first8=R. |last9=Anderson |first9=S. B. |last10=Anderson |first10=W. G. |last11=Arain |last12=Araya |first12=M. |last13=Armandula |first13=H. |last14=Armor |first14=P. |last15=Aso |first15=Y. |last16=Aston |first16=S. |last17=Aufmuth |first17=P. |last18=Aulbert |first18=C. |last19=Babak |first19=S. |last20=Ballmer |first20=S. |last21=Bantilan |last22=Barish |first22=B. C. |last23=Barker |first23=C. |last24=Barker |first24=D. |last25=Barr |first25=B. |last26=Barriga |first26=P. |last27=Barton |first27=M. A. |last28=Bastarrika |first28=M. |last29=Bayer |first29=K. |last30=Betzwieser |first30=J. |doi=10.1086/591526 |volume=683 |issue=1 |pages=L45–L50 |journal=Astrophys. J. |arxiv=0805.4758 |bibcode = 2008ApJ...683L..45A|s2cid=250871270 |display-authors=29 }}<br/>
And erratum in {{citation |title=none |journal=Astrophys. J. |volume=706 |issue=1 |pages=L203–L204 |doi=10.1088/0004-637X/706/1/L203 |bibcode = 2009ApJ...706L.203A|year=2009 |arxiv=0805.4758 |last1=Abbott |first1=B. |last2=Abbott |first2=R. |last3=Adhikari |first3=R. |last4=Ajith |first4=P. |last5=Allen |first5=B. |last6=Allen |first6=G. |last7=Amin |first7=R. |last8=Anderson |first8=S. B. |last9=Anderson |first9=W. G. |last10=Arain |first10=M. A. |last11=Araya |first11=M. |last12=Armandula |first12=H. |last13=Armor |first13=P. |last14=Aso |first14=Y. |last15=Aston |first15=S. |last16=Aufmuth |first16=P. |last17=Aulbert |first17=C. |last18=Babak |first18=S. |last19=Ballmer |first19=S. |last20=Bantilan |first20=H. |last21=Barish |first21=B. C. |last22=Barker |first22=C. |last23=Barker |first23=D. |last24=Barr |first24=B. |last25=Barriga |first25=P. |last26=Barton |first26=M. A. |last27=Bastarrika |first27=M. |last28=Bayer |first28=K. |last29=Betzwieser |first29=J. |last30=Beyersdorf |first30=P. T. |display-authors=1 }}</ref> The only other pulsar for which the spin-down limit was broken so far is the [[Vela Pulsar]].
[[Image:Crab Lucky video2.gif|upright=1.2|thumb|left|A slow-motion animation of the Crab Pulsar taken at 800&nbsp;nm [[wavelength]] (near-infrared) using a [[Lucky Imaging]] camera from [[University of Cambridge|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 ray]]s in excess of 100&nbsp;[[Electronvolt|TeV]], making it the first identified source of [[ultra-high-energy cosmic ray]]s.<ref>{{cite journal |last1=Amenomori |first1=M. |title=First detection of photons with energy beyond 100 TeV from an astrophysical source |journal=Phys. Rev. Lett. |volume=123 |issue=5 |pages=051101 |date=13 June 2019 |url=https://inspirehep.net/record/1739844?ln=en |access-date=8 July 2019|bibcode=2019PhRvL.123e1101A |arxiv=1906.05521 |doi=10.1103/PhysRevLett.123.051101 |pmid=31491288 |s2cid=189762075 }}</ref>

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.<ref name=radio_parallax/>

{{Clear}}

==References==
{{commons category|Crab Pulsar}}
{{Reflist|2}}

{{Stars of Taurus}}
{{Portal bar|Astronomy|Stars|Outer space}}

{{DEFAULTSORT:Crab Pulsar}}
[[Category:Crab Nebula]]
[[Category:Objects with variable star designations|Tauri, CM]]
[[Category:Optical pulsars]]
[[Category:Taurus (constellation)]]