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NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371

Ludlam, R. M. and Miller, J. M. and Barret, D. and Cackett, E. M. and Coughenour, B. M. and Dauser, T. and Degenaar, N. and García, J. A. and Harrison, F. A. and Paerels, F. (2019) NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371. Astrophysical Journal, 873 (1). Art. No. 99. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20190225-075539902

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Abstract

Atoll sources are accreting neutron star (NS) low-mass X-ray binaries. We present a spectral analysis of four persistent atoll sources (GX 3+1, 4U 1702−429, 4U 0614+091, and 4U 1746−371) observed for ~20 ks each with NuSTAR to determine the extent of the inner accretion disk. These sources range from an apparent luminosity of 0.006–0.11 of the Eddington limit (assuming the empirical limit of 3.8 × 10^(38) erg s^(−1)). Broad Fe emission features shaped by Doppler and relativistic effects close to the NS were firmly detected in three of these sources. The position of the disk appears to be close to the innermost stable circular orbit (ISCO) in each case. For GX 3+1, we determine R_(in) = 1.8^(+0.2)_(−0.6) R_(ISCO) (90% confidence level) and an inclination of 27°–31°. For 4U 1702−429, we find a R_(in) = 1.5^(+1.6)_(−0.4) R_(ISCO) and inclination of 53°–64°. For 4U 0614+091, the disk has a position of R_(in) = 1.3^(+5.4)_(−0.2) R_(ISCO) and inclination of 50°–62°. If the disk does not extend to the innermost stable circular orbit, we can place conservative limits on the magnetic field strength in these systems in the event that the disk is truncated at the Alfvén radius. This provides the limit at the poles of B ≤ 6.7 × 10^8 G, 3.3 × 10^8 G, and 14.5 × 10^8 G for GX 3+1, 4U 1702−429, and 4U 0614+091, respectively. For 4U 1746−371, we argue that the most plausible explanation for the lack of reflection features is a combination of source geometry and strong Comptonization. We place these sources among the larger sample of NSs that have been observed with NuSTAR.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/ab0414DOIArticle
https://arxiv.org/abs/1902.00520arXivDiscussion Paper
ORCID:
AuthorORCID
Ludlam, R. M.0000-0002-8961-939X
Barret, D.0000-0002-0393-9190
Cackett, E. M.0000-0002-8294-9281
Dauser, T.0000-0003-4583-9048
García, J. A.0000-0003-3828-2448
Harrison, F. A.0000-0003-2992-8024
Additional Information:© 2019 The American Astronomical Society. Received 2018 July 12; revised 2019 January 30; accepted 2019 January 31; published 2019 March 7. We thank the referee for their comments that have improved this work. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (Caltech, USA). R.M.L. is funded through a NASA Earth and Space Science Fellowship. E.M.C. gratefully acknowledges NSF CAREER award AST-1351222. We thank J. van den Eijnden for verifying the unabsorbed flux of IGR J17062−6143.
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funders:
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipUNSPECIFIED
NSFAST-1351222
Subject Keywords:accretion, accretion disks – stars: neutron – stars: individual (GX 3+1, 4U 1746-371, 4U 1702-429, 4U 0614+091) – X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20190225-075539902
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190225-075539902
Official Citation:R. M. Ludlam et al 2019 ApJ 873 99
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93193
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:25 Feb 2019 16:05
Last Modified:03 Oct 2019 20:51

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