Orbital Decay in M82 X-2

Creators: Bachetti, Matteo; Heida, Marianne; Maccarone, Thomas; Huppenkothen, Daniela; Israel, Gian Luca; Barret, Didier; Brightman, Murray; Brumback, McKinley; Earnshaw, Hannah P.; Forster, Karl; Fürst, Felix; Grefenstette, Brian W.; Harrison, Fiona A.; Jaodand, Amruta D.; Madsen, Kristin K.; Middleton, Matthew; Pike, Sean N.; Pilia, Maura; Poutanen, Juri; Stern, Daniel; Tomsick, John A.; Walton, Dominic J.; Webb, Natalie; Wilms, Jörn

Abstract

M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star for 7 yr, measure the decay of the orbit (Ṗ_(orb) / P_(orb) ≈ -8 • 10⁻⁶ yr⁻¹), and argue that this orbital decay is driven by extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true, the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also strongly favors models where the accretor is a highly magnetized neutron star.

Additional Information

The authors wish to thank Victoria Grinberg, Włodek Kluźniak, and Alessandro Ridolfi for useful discussions, and the staff at the NuSTAR Science Operations Center at Caltech for the help in scheduling the observations and the frequent clock-correction file updates, which allowed a prompt analysis of the data. We would also wish to thank the anonymous referee, and the three referees of a previous submission, who provided very insightful feedback that led to a substantial improvement of the quality of the analysis. M.B. was funded in part by PRIN TEC INAF 2019 "SpecTemPolar!—Timing analysis in the era of high-throughput photon detectors". M.H. is supported by an ESO fellowship. G.L.I. and M.B. acknowledge funding from the Italian MIUR PRIN grant No. 2017LJ39LM. A.D.J. was funded in part by the Chandra grant No. 803-0000-716015-404H00-6100-2723-4210-40716015HH83121. J.P. was supported by the grant No. 14.W03.31.0021 of the Ministry of Science and Higher Education of the Russian Federation and the Academy of Finland grant No. 333112. D.J.W. acknowledges support from STFC in the form of an Ernest Rutherford Fellowship. H.P.E. acknowledges support under NASA Contract No. NNG08FD60C. All the analysis of this paper was done using open-source software, Astropy, Stingray, HENDRICS, PINT, emcee, corner, and scinum, and can easily be verified using the solutions in Tables 1 and 2. The implementation of the Pletsch & Clark (2015) method can be found in the github repository https://github.com/matteobachetti/ell1fit. Figures were produced using the Matplotlib library and the Veusz software. The data used for this work come from the NuSTAR and XMM-Newton missions and are usually held private for one year, and made public on the High Energy Astrophysics Science archive (HEASARC) and the XMM-Newton Science Archive (XSA) afterwards. NuSTAR is a Small Explorer mission led by Caltech and managed by the JPL for NASA's Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

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Resource type: Journal Article
Publisher: American Astronomical Society
Published in: Astrophysical Journal, 937(2), Art. No. 125, ISSN: 0004-637X.