ABSTRACT The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical

maximum for spherical infall (the Eddington limit) onto stellar-mass black holes1,2. Their X-ray luminosities in the 0.5–10 kiloelectronvolt energy band range from 1039 to 1041 ergs per

second3. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star

systems1,2. The most challenging sources to explain are those at the luminous end of the range (more than 1040 ergs per second), which require black hole masses of 50–100 times the solar

the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3–30 kiloelectronvolt range of 4.9 × 1039 ergs per second. The pulsating source

is spatially coincident with a variable source4 that can reach an X-ray luminosity in the 0.3–10 kiloelectronvolt range of 1.8 × 1040 ergs per second1. This association implies a luminosity

of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the

ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects. Access through your institution Buy or subscribe This is a

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EXPLOSIONS ON NEUTRON STARS REVEAL THE SPEED OF THEIR JETS Article 27 March 2024 GAMMA-RAY HEARTBEAT POWERED BY THE MICROQUASAR SS 433 Article 17 August 2020 OPTICAL AND ULTRAVIOLET PULSED

EMISSION FROM AN ACCRETING MILLISECOND PULSAR Article 22 February 2021 REFERENCES * Roberts, T. P. X-ray observations of ultraluminous X-ray sources. _Astrophys. Space Sci._ 311, 203–212

(2007) Article  ADS  Google Scholar  * Liu, J.-F., Bregman, J. N., Bai, Y., Justham, S. & Crowther, P. Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1.

_Nature_ 503, 500–503 (2013) Article  CAS  ADS  Google Scholar  * Feng, H. & Soria, R. Ultraluminous X-ray sources in the Chandra and XMM-Newton era. _New Astron. Rev._ 55, 166–183

(2011) Article  ADS  Google Scholar  * Feng, H., Rao, F. & Kaaret, P. Discovery of millihertz X-ray oscillations in a transient ultraluminous X-ray source in M82. _Astrophys. J._ 710,

L137–L141 (2010) Article  ADS  Google Scholar  * Skinner, G. K. et al. Discovery of 69 ms periodic X-ray pulsations in A0538–66. _Nature_ 297, 568–570 (1982) Article  ADS  Google Scholar  *

Lucke, R., Yentis, D., Friedman, H., Fritz, G. & Shulman, S. Discovery of X-ray pulsations in SMC X-1. _Astrophys. J._ 206, L25–L28 (1976) Article  ADS  Google Scholar  * Kouveliotou, C.

et al. A new type of transient high-energy source in the direction of the Galactic Centre. _Nature_ 379, 799–801 (1996) Article  CAS  ADS  Google Scholar  * Basko, M. M. & Sunyaev, R.

A. The limiting luminosity of accreting neutron stars with magnetic fields. _Mon. Not. R. Astron. Soc._ 175, 395–417 (1976) Article  ADS  Google Scholar  * Gnedin, Y. N. & Sunyaev, R. A.

The beaming of radiation from an accreting magnetic neutron star and the X-ray pulsars. _Astron. Astrophys._ 25, 233–239 (1973) CAS  ADS  Google Scholar  * Basko, M. M. & Sunyaev, R. A.

Radiative transfer in a strong magnetic field and accreting X-ray pulsars. _Astron. Astrophys._ 42, 311–321 (1975) ADS  Google Scholar  * Harrison, F. A. et al. The Nuclear Spectroscopic

Telescope Array (NuSTAR) high-energy X-ray mission. _Astrophys. J._ 770, 103–122 (2013) Article  ADS  Google Scholar  * Kaaret, P. et al. Chandra High-Resolution Camera observations of the

luminous X-ray source in the starburst galaxy M82. _Mon. Not. R. Astron. Soc._ 321, L29–L32 (2001) Article  CAS  ADS  Google Scholar  * Kaaret, P., Simet, M. G. & Lang, C. C. A 62 day

X-ray periodicity and an X-ray flare from the ultraluminous X-ray source in M82. _Astrophys. J._ 646, 174–183 (2006) Article  CAS  ADS  Google Scholar  * Kong, A. K. H., Yang, Y. J., Hsieh,

P. Y., Mak, D. S. Y. & Pun, C. S. J. The ultraluminous X-ray sources near the center of M82. _Astrophys. J._ 671, 349–357 (2007) Article  CAS  ADS  Google Scholar  * Ransom, S. M. _New

Search Techniques for Binary Pulsars._ PhD thesis, Harvard Univ. (2001) * Bildsten, L. et al. Observations of accreting pulsars. _Astrophys. J. Suppl. Ser._ 113, 367–408 (1997) Article  ADS

  Google Scholar  * Canuto, V., Lodenquai, J. & Ruderman, M. Thomson scattering in a strong magnetic field. _Phys. Rev. D_ 3, 2303–2308 (1971) Article  ADS  Google Scholar  * Pringle, J.

E. & Rees, M. J. Accretion disc models for compact X-ray sources. _Astron. Astrophys._ 21, 1–9 (1972) ADS  Google Scholar  * Ghosh, P. & Lamb, F. K. Accretion by rotating magnetic

neutron stars. III — Accretion torques and period changes in pulsating X-ray sources. _Astrophys. J._ 234, 296–316 (1979) Article  ADS  Google Scholar  * Weisskopf, M. C. et al. An overview

of the performance and scientific results from the Chandra X-ray observatory. _Publ. Astron. Soc. Pacif._ 114, 1–24 (2002) Article  ADS  Google Scholar  * Goobar, A. et al. The rise of SN

2014J in the nearby galaxy M82. _Astrophys. J._ 784, L12 (2014) Article  ADS  Google Scholar  * Davis, J. E. Event pileup in charge-coupled devices. _Astrophys. J._ 562, 575–582 (2001)

Article  ADS  Google Scholar  * Evans, P. A. et al. Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs. _Mon. Not. R. Astron. Soc._ 397,

1177–1201 (2009) Article  CAS  ADS  Google Scholar  * Houck, J. C. & Denicola, L. A. ISIS: an Interactive Spectral Interpretation System for high resolution X-ray spectroscopy. _Astron.

Data Analysis Softw. Syst._ 216, 591–594 (2000) ADS  Google Scholar  * Blandford, R. & Teukolsky, S. A. Arrival-time analysis for a pulsar in a binary system. _Astrophys. J._ 205,

580–591 (1976) Article  ADS  Google Scholar  * Edwards, R. T., Hobbs, G. B. & Manchester, R. N. TEMPO2, a new pulsar timing package — II. The timing model and precision estimates. _Mon.

Not. R. Astron. Soc._ 372, 1549–1574 (2006) Article  ADS  Google Scholar  * Scargle, J. D. Studies in astronomical time series analysis. II — Statistical aspects of spectral analysis of

unevenly spaced data. _Astrophys. J._ 263, 835–853 (1982) Article  ADS  Google Scholar  * Cash, W. Parameter estimation in astronomy through application of the likelihood ratio. _Astrophys.

J._ 228, 939–947 (1979) Article  ADS  Google Scholar  * Arnaud, K. A. XSPEC: the first ten years. _Astron. Data Analysis Softw. Syst._ 101, 17–20 (1996) ADS  Google Scholar  * Mitsuda, K. et

al. Energy spectra of low-mass binary X-ray sources observed from TENMA. _Astron. Soc. Jpn_ 36, 741–759 (1984) CAS  ADS  Google Scholar  * Ranalli, P., Comastri, A., Origlia, L. &

Maiolino, R. A deep X-ray observation of M82 with XMM-Newton. _Mon. Not. R. Astron. Soc._ 386, 1464–1480 (2008) Article  CAS  ADS  Google Scholar  * Mewe, R., Gronenschild, E. H. B. M. &

van den Oord, G. H. J. Calculated X-radiation from optically thin plasmas. V. _Astron. Astrophys. Suppl. Ser._ 62, 197–254 (1985) CAS  ADS  Google Scholar  * Titarchuk, L. Generalized

Comptonization models and application to the recent high-energy observations. _Astrophys. J._ 434, 570–586 (1994) Article  ADS  Google Scholar  * Kalberla, P. M. W. et al. The

Leiden/Argentine/Bonn (LAB) survey of Galactic HI. Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections. _Astron. Astrophys._ 440, 775–782 (2005)

Article  CAS  ADS  Google Scholar  Download references ACKNOWLEDGEMENTS This work was supported by NASA (grant no. NNG08FD60C), and made use of data from the Nuclear Spectroscopic Telescope

Array (NuSTAR) mission, a project led by Caltech, managed by the Jet Propulsion Laboratory and funded by NASA. We thank the NuSTAR operations, software and calibration teams for support with

execution and analysis of these observations. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. M.B. thanks the Centre National

d’Études Spatiales (CNES) and the Centre National de la Recherche Scientifique (CNRS) for support. Line plots were done using Veusz software by J. Sanders. AUTHOR INFORMATION AUTHORS AND

AFFILIATIONS * Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France, M. Bachetti, D.

Barret & N. A. Webb * CNRS, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France, M. Bachetti, D. Barret & N.

A. Webb * Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, 91125, California, USA F. A. Harrison, D. J. Walton, B. W.

Grefenstette, F. Fürst, S. R. Kulkarni, V. Rana & S. P. Tendulkar * MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, 02139,

Massachusetts, USA D. Chakrabarty * Physics Department, Columbia University, 538 West 120th Street, New York, New York 10027, USA, A. Beloborodov * Space Sciences Laboratory, University of

California, Berkeley, 94720, California, USA S. E. Boggs & J. Tomsick * DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark, F.

E. Christensen * Lawrence Livermore National Laboratory, Livermore, 94550, California, USA W. W. Craig * Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA,

UK, A. C. Fabian * Columbia Astrophysics Laboratory, Columbia University, New York, 10027, New York, USA C. J. Hailey * NASA Goddard Space Flight Center, Greenbelt, 20771, Maryland, USA A.

Hornschemeier & W. W. Zhang * Department of Physics, McGill University, Montreal, Quebec H3A 2T8, Canada, V. Kaspi * Department of Physics, Texas Tech University, Lubbock, 79409, Texas,

USA T. Maccarone * Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, Michigan 48109-1042, USA, J. M. Miller * Jet Propulsion Laboratory, California Institute of

Technology, Pasadena, 91109, California, USA D. Stern Authors * M. Bachetti View author publications You can also search for this author inPubMed Google Scholar * F. A. Harrison View author

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author inPubMed Google Scholar CONTRIBUTIONS M.B., reduction and timing analysis of the NuSTAR observations, interpretation of results, manuscript preparation; F.A.H., interpretation of

results, manuscript preparation; D.J.W., NuSTAR and Chandra spectroscopy, point source analysis; B.W.G., NuSTAR image analysis; D.C., accretion torque analysis, interpretation; F.F.,

verification of timing analysis, interpretation; D.B., A.B., A.C.F., A.H., V.M.K., T.M., J.T., interpretation of results and manuscript review; S.B., F.C., W.W.C., C.J.H., D.S., S.P.T.,

N.W., W.W.Z., manuscript review. CORRESPONDING AUTHORS Correspondence to M. Bachetti or F. A. Harrison. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial

interests. EXTENDED DATA FIGURES AND TABLES EXTENDED DATA FIGURE 1 X-RAY SOURCES IDENTIFIED BY CHANDRA IN THE CENTRAL REGION OF M82. A, Chandra image of the central region of M82 from the

observation taken coincident with NuSTAR ObsID 006. The yellow circle shows the 70″ radius region used to extract NuSTAR fluxes. Within this region, 24 discrete X-ray point sources are

identified, including X-1 and X-2. B, Expanded view of the crowded central region of A. Yellow crosses indicate the locations of identified point sources. We have used, where possible, the

numbering from ref. 13 (sources up to no. 15). After this we assign our own numerical identification (note that sources 4 and 10 from ref. 13 are not detected in this observation). EXTENDED

DATA FIGURE 2 SWIFT IMAGING OF THE REGION CONTAINING M82 X-1 AND M82 X-2. A, B, In greyscale are images obtained via Swift automated processing over the 5–10 keV band for all of the

observations during early February (A; 2014 February 04 through 2014 February 11) and mid-March (B; 2014 March 7 through 2014 March 11). The early February observations have 68.5 ks of

exposure (mostly because of the increased cadence of observations due to the Swift monitoring of SN 2014J), while the mid-March snapshot has 1.8 ks of exposure. The images are 1.5 arcmin on

a side and have been smoothed with a 2-pixel (4 arcsecond) Gaussian kernel (circle at lower left). The location of X-1 and X-2 are shown by the crosses in both panels. The late-time

observation clearly shows a reduction in the flux from X-1 and that the flux is dominated by X-2. RELATED AUDIO ASTRONOMER JEANETTE GLADSTONE ON THE ORIGINS OF SOME OF THE UNIVERSE’S

BRIGHTEST OBJECTS. POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3 RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE

CITE THIS ARTICLE Bachetti, M., Harrison, F., Walton, D. _et al._ An ultraluminous X-ray source powered by an accreting neutron star. _Nature_ 514, 202–204 (2014).

https://doi.org/10.1038/nature13791 Download citation * Received: 24 June 2014 * Accepted: 06 August 2014 * Published: 08 October 2014 * Issue Date: 09 October 2014 * DOI:

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