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Detection of Reflection Features in the Neutron Star Low-mass X-Ray Binary Serpens X-1 with NICER

Ludlam, R. M. and Miller, J. M. and Arzoumanian, Z. and Bult, P. M. and Cackett, E. M. and Chakrabarty, D. and Dauser, T. and Enoto, T. and Fabian, A. C. and García, J. A. and Gendreau, K. C. and Guillot, S. and Homan, J. and Jaisawal, G. K. and Keek, L. and La Marr, B. and Malacaria, C. and Markwardt, C. B. and Steiner, J. F. and Strohmayer, T. E. (2018) Detection of Reflection Features in the Neutron Star Low-mass X-Ray Binary Serpens X-1 with NICER. Astrophysical Journal Letters, 858 (1). Art. No. L5. ISSN 2041-8213. doi:10.3847/2041-8213/aabee6.

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We present Neutron Star Interior Composition Explorer (NICER) observations of the neutron star (NS) low-mass X-ray binary Serpens X-1 during the early mission phase in 2017. With the high spectral sensitivity and low-energy X-ray passband of NICER, we are able to detect the Fe L line complex in addition to the signature broad, asymmetric Fe K line. We confirm the presence of these lines by comparing the NICER data to archival observations with XMM-Newton/Reflection Grating Spectrometer (RGS) and NuSTAR. Both features originate close to the innermost stable circular orbit (ISCO). When modeling the lines with the relativistic line model RELLINE, we find that the Fe L blend requires an inner disk radius of 1.4^(+0.2)_(-0.1) R_(ISCO) and Fe K is at 1.03^(+0.13)_(-0.03) R_(ISCO) (errors quoted at 90%). This corresponds to a position of 17.3^(+2.5)_(-1.2) km and 12.7^(+1.6)_(-0.4) km for a canonical NS mass (M_(NS) = 1.4 M⊙) and dimensionless spin value of a = 0. Additionally, we employ a new version of the RELXILL model tailored for NSs and determine that these features arise from a dense disk and supersolar Fe abundance.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ludlam, R. M.0000-0002-8961-939X
Cackett, E. M.0000-0002-8294-9281
Chakrabarty, D.0000-0001-8804-8946
Dauser, T.0000-0003-4583-9048
Enoto, T.0000-0003-1244-3100
Fabian, A. C.0000-0002-9378-4072
García, J. A.0000-0003-3828-2448
Guillot, S.0000-0002-6449-106X
Homan, J.0000-0001-8371-2713
Jaisawal, G. K.0000-0002-6789-2723
Malacaria, C.0000-0002-0380-0041
Markwardt, C. B.0000-0001-9803-3879
Steiner, J. F.0000-0002-5872-6061
Strohmayer, T. E.0000-0001-7681-5845
Additional Information:© 2018 The American Astronomical Society. Received 2018 March 26; revised 2018 April 12; accepted 2018 April 16; published 2018 May 2. R.M.L. acknowledges funding through a NASA Earth and Space Science Fellowship. A.C.F. acknowledges ERC Advanced grant 340442. E.M.C. gratefully acknowledges NSF CAREER award AST-1351222.
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipUNSPECIFIED
European Research Council (ERC)340442
Subject Keywords:accretion, accretion disks – stars: individual (Ser X-1) – stars: neutron – X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20180503-130325076
Persistent URL:
Official Citation:R. M. Ludlam et al 2018 ApJL 858 L5
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86211
Deposited By: Tony Diaz
Deposited On:03 May 2018 20:16
Last Modified:15 Nov 2021 20:36

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