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Observations of the Ultra-compact X-Ray Binary 4U 1543-624 in Outburst with NICER, INTEGRAL, Swift, and ATCA

Ludlam, R. M. and Shishkovsky, L. and Bult, P. M. and Miller, J. M. and Zoghbi, A. and Strohmayer, T. E. and Reynolds, M. and Natalucci, L. and Miller-Jones, J. C. A. and Jaisawal, G. K. and Guillot, S. and Gendreau, K. C. and García, J. A. and Fiocchi, M. and Fabian, A. C. and Chakrabarty, D. and Cackett, E. M. and Bahramian, A. and Arzoumanian, Z. and Altamirano, D. (2019) Observations of the Ultra-compact X-Ray Binary 4U 1543-624 in Outburst with NICER, INTEGRAL, Swift, and ATCA. Astrophysical Journal, 883 (1). Art. No. 39. ISSN 1538-4357.

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We report on X-ray and radio observations of the ultra-compact X-ray binary 4U 1543−624 taken in August 2017 during an enhanced accretion episode. We obtained Neutron Star Interior Composition Explorer (NICER) monitoring of the source over a ~10 day period during which target-of-opportunity observations were also conducted with Swift, INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), and the Australia Telescope Compact Array. Emission lines were measured in the NICER X-ray spectrum at ~0.64 keV and ~6.4 keV that correspond to O and Fe, respectively. By modeling these line components, we are able to track changes in the accretion disk throughout this period. The innermost accretion flow appears to move inwards from hundreds of gravitational radii (R_g = GM/c^2) at the beginning of the outburst to <8.7 R g at peak intensity. We do not detect the source in radio, but are able to place a 3σ upper limit on the flux density at 27 μJy beam^(−1). Comparing the radio and X-ray luminosities, we find that the source lies significantly away from the range typical of black holes in the L_r-L_x plane, suggesting a neutron star primary. This adds to the evidence that neutron stars (NSs) do not follow a single track in the L_r-L_x plane, limiting its use in distinguishing between different classes of NSs based on radio and X-ray observations alone.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ludlam, R. M.0000-0002-8961-939X
Zoghbi, A.0000-0002-0572-9613
Strohmayer, T. E.0000-0001-7681-5845
Natalucci, L.0000-0002-6601-9543
Miller-Jones, J. C. A.0000-0003-3124-2814
Jaisawal, G. K.0000-0002-6789-2723
Guillot, S.0000-0002-6449-106X
García, J. A.0000-0003-3828-2448
Fiocchi, M.0000-0001-5697-6019
Fabian, A. C.0000-0002-9378-4072
Chakrabarty, D.0000-0001-8804-8946
Cackett, E. M.0000-0002-8294-9281
Bahramian, A.0000-0003-2506-6041
Altamirano, D.0000-0002-3422-0074
Additional Information:© 2019 The American Astronomical Society. Received 2019 June 18; revised 2019 July 26; accepted 2019 July 31; published 2019 September 18. This work was supported by NASA through the NICER mission and the Astrophysics Explorers Program, and made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC). The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. R.M.L. acknowledges partial funding from a NASA Earth and Space Science Fellowship. E.M.C. gratefully acknowledges support through CAREER award number AST-1351222. M.F. acknowledges ASI financial/programmatic support via ASI-INAF agreement n. 2013-025.R1 and ASI-INAF N. 2017-14-H.0. J.A.G. acknowledges support from Chandra Theory grant TM8-19003X and from the Alexander von Humboldt Foundation. J.C.A. M.-J. is the recipient of an Australian Research Council Future Fellowship (FT 140101082), funded by the Australian Government.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Australian GovernmentUNSPECIFIED
NASA Earth and Space Science FellowshipUNSPECIFIED
Agenzia Spaziale Italiana (ASI)2013-025.R1
Agenzia Spaziale Italiana (ASI)2017-14-H.0
Alexander von Humboldt FoundationUNSPECIFIED
Australian Research CouncilFT 140101082
Subject Keywords:accretion, accretion disks – stars: neutron
Issue or Number:1
Record Number:CaltechAUTHORS:20190918-140450734
Persistent URL:
Official Citation:R. M. Ludlam et al 2019 ApJ 883 39
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98739
Deposited By: Tony Diaz
Deposited On:18 Sep 2019 21:29
Last Modified:09 Mar 2020 13:18

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