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Discovery of Pulsation Dropout and Turn-on during the High State of the Accreting X-Ray Pulsar LMC X-4

Brumback, McKinley C. and Hickox, Ryan C. and Bachetti, Matteo and Ballhausen, Ralf and Fürst, Felix S. and Pike, Sean and Pottschmidt, Katja and Tomsick, John A. and Wilms, Jörn (2018) Discovery of Pulsation Dropout and Turn-on during the High State of the Accreting X-Ray Pulsar LMC X-4. Astrophysical Journal Letters, 861 (1). Art. No. L7. ISSN 2041-8213. doi:10.3847/2041-8213/aacd13.

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Two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the luminous X-ray pulsar LMC X-4 in 2015 October and November captured several bright accretion flares from this source, which has a long history of stable pulse and superorbital behavior. We present a timing analysis of these data in which we detect a rapid pulse "turn-on" in association with the accretion flares, during which the source reaches super-Eddington luminosities. Pulsations, which are normally seen from this source, are found to only occur for approximately one hour before and during the bright flares. Beyond one hour before and after the flares, we find pulsations to be weak or nonexistent, with fractional rms amplitudes of less than 0.05. At the onset of the flare, the pulse profiles exhibit a phase shift of 0.25 cycles that could be associated with a change in the emission geometry. This increase in pulse strength occurring well before the flare cannot be explained by the propeller effect, and potentially offers a connection between the magnetic properties of pulsars that accrete close to their Eddington limits and ultra-luminous X-ray pulsars.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Brumback, McKinley C.0000-0002-4024-6967
Hickox, Ryan C.0000-0003-1468-9526
Bachetti, Matteo0000-0002-4576-9337
Fürst, Felix S.0000-0003-0388-0560
Pike, Sean0000-0002-8403-0041
Pottschmidt, Katja0000-0002-4656-6881
Tomsick, John A.0000-0001-5506-9855
Wilms, Jörn0000-0003-2065-5410
Additional Information:© 2018 The American Astronomical Society. Received 2018 April 26; revised 2018 June 11; accepted 2018 June 16; published 2018 June 28. We would like to thank the anonymous referee for comments that substantially improved this Letter. We would also like to thank the NuSTAR Galactic Binaries Science Team for comments and contributions. M.C.B. acknowledges support from NASA grant Nos. NNX15AV32G and NNX15AH79H. This research made use of NuSTARDAS, developed by ASDC (Italy) and Caltech (USA) and of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT (
Funding AgencyGrant Number
Subject Keywords:pulsars: individual (LMC X-4) – stars: neutron – X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20180627-093050466
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Official Citation:McKinley C. Brumback et al 2018 ApJL 861 L7
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87380
Deposited By: Tony Diaz
Deposited On:27 Jun 2018 16:51
Last Modified:15 Nov 2021 20:47

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