title: An ultraluminous X-ray source powered by an accreting neutron star.
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 holes. Their X-ray luminosities in the 0.5-10 kiloelectronvolt energy band range from 10(39) to 10(41) ergs per second. 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 systems. The most challenging sources to explain are those at the luminous end of the range (more than 10(40) 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 × 10(39) ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 kiloelectronvolt range of 1.8 × 10(40) ergs per second. 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.
authors.affiliation: 1] Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France [2] CNRS, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France.
authors.forename: M
authors.initials: M
authors.lastname: Bachetti
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: F A
authors.initials: FA
authors.lastname: Harrison
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Walton
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
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authors.initials: BW
authors.lastname: Grefenstette
authors.affiliation: MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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authors.initials: D
authors.lastname: Chakrabarty
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: F
authors.initials: F
authors.lastname: Fürst
authors.affiliation: 1] Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France [2] CNRS, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France.
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authors.lastname: Barret
authors.affiliation: Physics Department, Columbia University, 538 West 120th Street, New York, New York 10027, USA.
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authors.lastname: Beloborodov
authors.affiliation: Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Boggs
authors.affiliation: DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark.
authors.forename: F E
authors.initials: FE
authors.lastname: Christensen
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Craig
authors.affiliation: Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: A C
authors.initials: AC
authors.lastname: Fabian
authors.affiliation: Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA.
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authors.initials: CJ
authors.lastname: Hailey
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
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authors.lastname: Hornschemeier
authors.affiliation: Department of Physics, McGill University, Montreal, Quebec H3A 2T8, Canada.
authors.forename: V
authors.initials: V
authors.lastname: Kaspi
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Kulkarni
authors.affiliation: Department of Physics, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: T
authors.initials: T
authors.lastname: Maccarone
authors.affiliation: Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, Michigan 48109-1042, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Miller
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: V
authors.initials: V
authors.lastname: Rana
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
authors.forename: D
authors.initials: D
authors.lastname: Stern
authors.affiliation: Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Tendulkar
authors.affiliation: Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
authors.forename: J
authors.initials: J
authors.lastname: Tomsick
authors.affiliation: 1] Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France [2] CNRS, Institut de Recherche en Astrophysique et Planétologie, 9, Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France.
authors.forename: N A
authors.initials: NA
authors.lastname: Webb
authors.affiliation: NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Zhang