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Evidence for Pulsar-like Emission Components in the Broadband ULX Sample

Walton, D. J. and Fürst, F. and Heida, M. and Harrison, F. A. and Barret, D. and Stern, D. and Bachetti, M. and Brightman, M. and Fabian, A. C. and Middleton, M. J. (2018) Evidence for Pulsar-like Emission Components in the Broadband ULX Sample. Astrophysical Journal, 856 (2). Art. No. 128. ISSN 1538-4357. doi:10.3847/1538-4357/aab610.

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We present broadband X-ray analyses of a sample of bright ultraluminous X-ray sources (ULX) with the goal of investigating the spectral similarity of this population to the known ULX pulsars, M82 X-2, NGC 7793 P13, and NGC 5907 ULX. We perform a phase-resolved analysis of the broadband XMM-Newton+NuSTAR data set of NGC 5907 ULX, finding that the pulsed emission from the accretion column in this source exhibits a similar spectral shape to that seen in both M82 X-2 and NGC 7793 P13, and that this is responsible for the excess emission observed at the highest energies when the spectra are fit with accretion disk models. We then demonstrate that similar "hard" excesses are seen in all ULXs in the broadband sample. Finally, for ULXs where the nature of the accretor is currently unknown, we test whether the hard excesses are all consistent with being produced by an accretion column similar to those present in M82 X-2, NGC 7793 P13, and NGC 5907 ULX. Based on the average shape of the pulsed emission, we find that in all cases a similar accretion column can successfully reproduce the observed data, consistent with the hypothesis that this ULX sample may be dominated by neutron star accretors. Compared to the known pulsar ULXs, our spectral fits for the remaining ULXs suggest that the non-pulsed emission from the accretion flow beyond the magnetosphere makes a stronger relative contribution than the component associated with the accretion column. If these sources do also contain neutron star accretors, this may help to explain the lack of detected pulsations.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Walton, D. J.0000-0001-5819-3552
Fürst, F.0000-0003-0388-0560
Heida, M.0000-0002-1082-7496
Harrison, F. A.0000-0003-2992-8024
Barret, D.0000-0002-0393-9190
Stern, D.0000-0003-2686-9241
Bachetti, M.0000-0002-4576-9337
Brightman, M.0000-0002-8147-2602
Fabian, A. C.0000-0002-9378-4072
Middleton, M. J.0000-0002-8183-2970
Additional Information:© 2018 The American Astronomical Society. Received 2018 February 1; revised 2018 March 2; accepted 2018 March 8; published 2018 April 2. The authors would like to thank the reviewer for positive feedback which helped to improve the final manuscript. D.J.W. and M.J.M. acknowledge support from STFC Ernest Rutherford fellowships, A.C.F. acknowledges support from ERC Advanced Grant 340442, and D.B. acknowledges financial support from the French Space Agency (CNES). This research has made use of data obtained with NuSTAR, a project led by Caltech, funded by NASA and managed by NASA/JPL, and has utilized the NUSTARDAS software package, jointly developed by the ASDC (Italy) and Caltech (USA). This work has also made use of data obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States, and with Suzaku, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). Facilities: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, XMM - Newton X-Ray Multimirror Mission satellite, Suzaku - Suzaku (ASTRO-EII).
Group:Space Radiation Laboratory, NuSTAR, Astronomy Department
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
European Research Council (ERC)340442
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Subject Keywords:stars: neutron – X-rays: binaries – X-rays: individual (NGC 5907 ULX)
Issue or Number:2
Record Number:CaltechAUTHORS:20180315-091957565
Persistent URL:
Official Citation:D. J. Walton et al 2018 ApJ 856 128
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85327
Deposited By: Joy Painter
Deposited On:20 Mar 2018 22:44
Last Modified:15 Nov 2021 20:27

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