An ultraluminous X-ray source powered by an accreting neutron star


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 value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and 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 options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The X-ray light curve and pulsations from the region containing NuSTAR J095551+6940.8.
Figure 2: The spin-up behaviour of NuSTAR J095551+6940.8.
Figure 3: The counterpart of NuSTAR J095551+6940.8.


  1. 1

    Roberts, T. P. X-ray observations of ultraluminous X-ray sources. Astrophys. Space Sci. 311, 203–212 (2007)

    Article  ADS  Google Scholar 

  2. 2

    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)

    CAS  Article  ADS  Google Scholar 

  3. 3

    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 

  4. 4

    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 

  5. 5

    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 

  6. 6

    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 

  7. 7

    Kouveliotou, C. et al. A new type of transient high-energy source in the direction of the Galactic Centre. Nature 379, 799–801 (1996)

    CAS  Article  ADS  Google Scholar 

  8. 8

    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 

  9. 9

    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 

  10. 10

    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 

  11. 11

    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 

  12. 12

    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)

    CAS  Article  ADS  Google Scholar 

  13. 13

    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)

    CAS  Article  ADS  Google Scholar 

  14. 14

    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)

    CAS  Article  ADS  Google Scholar 

  15. 15

    Ransom, S. M. New Search Techniques for Binary Pulsars. PhD thesis, Harvard Univ. (2001)

  16. 16

    Bildsten, L. et al. Observations of accreting pulsars. Astrophys. J. Suppl. Ser. 113, 367–408 (1997)

    Article  ADS  Google Scholar 

  17. 17

    Canuto, V., Lodenquai, J. & Ruderman, M. Thomson scattering in a strong magnetic field. Phys. Rev. D 3, 2303–2308 (1971)

    Article  ADS  Google Scholar 

  18. 18

    Pringle, J. E. & Rees, M. J. Accretion disc models for compact X-ray sources. Astron. Astrophys. 21, 1–9 (1972)

    ADS  Google Scholar 

  19. 19

    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 

  20. 20

    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 

  21. 21

    Goobar, A. et al. The rise of SN 2014J in the nearby galaxy M82. Astrophys. J. 784, L12 (2014)

    Article  ADS  Google Scholar 

  22. 22

    Davis, J. E. Event pileup in charge-coupled devices. Astrophys. J. 562, 575–582 (2001)

    Article  ADS  Google Scholar 

  23. 23

    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)

    CAS  Article  ADS  Google Scholar 

  24. 24

    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 

  25. 25

    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 

  26. 26

    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 

  27. 27

    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 

  28. 28

    Cash, W. Parameter estimation in astronomy through application of the likelihood ratio. Astrophys. J. 228, 939–947 (1979)

    Article  ADS  Google Scholar 

  29. 29

    Arnaud, K. A. XSPEC: the first ten years. Astron. Data Analysis Softw. Syst. 101, 17–20 (1996)

    ADS  Google Scholar 

  30. 30

    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 

  31. 31

    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)

    CAS  Article  ADS  Google Scholar 

  32. 32

    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 

  33. 33

    Titarchuk, L. Generalized Comptonization models and application to the recent high-energy observations. Astrophys. J. 434, 570–586 (1994)

    Article  ADS  Google Scholar 

  34. 34

    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)

    CAS  Article  ADS  Google Scholar 

Download references


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




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.

Extended Data Table 1 List of NuSTAR observations used in this analysis
Extended Data Table 2 Best-fit orbital parameters
Extended Data Table 3 Best fit period and period derivatives for individual NuSTAR observations
Extended Data Table 4 3–10 keV flux contributions for bright sources near the nucleus of M82

Related audio

Astronomer Jeanette Gladstone on the origins of some of the Universe’s brightest objects.

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

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).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.