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Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1

Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1
Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1
We report the discovery of an episode of coherent millisecond X-ray pulsation in the neutron star low-mass X-ray binary Aql X-1. The episode lasts for slightly more than 150 seconds, during which the pulse frequency is consistent with being constant. No X-ray burst or other evidence of thermonuclear burning activity is seen in correspondence with the pulsation, which can thus be identified as occurring in the persistent emission. The pulsation frequency is 550.27 Hz, very close (0.5 Hz higher) to the maximum reported frequency from burst oscillations in this source. Hence we identify this frequency with the neutron star spin frequency. The pulsed fraction is strongly energy dependent, ranging from <1% (3-5 keV) to >10% (16-30 keV). We discuss possible physical interpretations and their consequences for our understanding of the lack of pulsation in most neutron star low-mass X-ray binaries. If interpreted as accretion-powered pulsation, Aql X-1 might play a key role in understanding the differences between pulsating and non-pulsating sources.
stars, binaries general, pulsars, individual (Aql X-1), stars neutron, x-rays binaries
0004-637X
L41-L44
Casella, P.
8dc7f5b0-354e-4329-b225-5cc2124801a6
altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
patruno, A.
61450a42-2fa8-4ca1-a0af-44f2dfe14fcc
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
van der Klis, M.
d3635ef2-91fc-4d3a-b453-ac2861a9edb3
Casella, P.
8dc7f5b0-354e-4329-b225-5cc2124801a6
altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
patruno, A.
61450a42-2fa8-4ca1-a0af-44f2dfe14fcc
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
van der Klis, M.
d3635ef2-91fc-4d3a-b453-ac2861a9edb3

Casella, P., altamirano, D., patruno, A., Wijnands, R. and van der Klis, M. (2008) Discovery of Coherent Millisecond X-Ray Pulsations in Aquila X-1. The Astrophysical Journal, 674 (1), L41-L44. (doi:10.1086/528982).

Record type: Article

Abstract

We report the discovery of an episode of coherent millisecond X-ray pulsation in the neutron star low-mass X-ray binary Aql X-1. The episode lasts for slightly more than 150 seconds, during which the pulse frequency is consistent with being constant. No X-ray burst or other evidence of thermonuclear burning activity is seen in correspondence with the pulsation, which can thus be identified as occurring in the persistent emission. The pulsation frequency is 550.27 Hz, very close (0.5 Hz higher) to the maximum reported frequency from burst oscillations in this source. Hence we identify this frequency with the neutron star spin frequency. The pulsed fraction is strongly energy dependent, ranging from <1% (3-5 keV) to >10% (16-30 keV). We discuss possible physical interpretations and their consequences for our understanding of the lack of pulsation in most neutron star low-mass X-ray binaries. If interpreted as accretion-powered pulsation, Aql X-1 might play a key role in understanding the differences between pulsating and non-pulsating sources.

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0708.1110v2.pdf - Author's Original
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Published date: February 2008
Keywords: stars, binaries general, pulsars, individual (Aql X-1), stars neutron, x-rays binaries
Organisations: Physics & Astronomy

Identifiers

Local EPrints ID: 358792
URI: https://eprints.soton.ac.uk/id/eprint/358792
ISSN: 0004-637X
PURE UUID: c1ac56d0-f955-459e-9924-d66d6c90f8cd
ORCID for D. altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 14 Oct 2013 13:04
Last modified: 06 Jun 2018 12:23

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