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Discovery of a 205.89 Hz accreting millisecond x-ray pulsar in the globular cluster NGC 6440

Discovery of a 205.89 Hz accreting millisecond x-ray pulsar in the globular cluster NGC 6440
Discovery of a 205.89 Hz accreting millisecond x-ray pulsar in the globular cluster NGC 6440
We report on the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with RXTE on 2009 August 30, October 1 and October 28, during the decays of 4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequency, we find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and a projected semimajor axis of 6.22 lt-ms. Based on the mass function, we estimate a lower limit to the mass of the companion to be 0.0067 M ? (assuming a 1.4 M ? neutron star). This new pulsar shows the shortest outburst recurrence time among AMXPs (~1 month). If this behavior does not cease, this AMXP has the potential to be one of the best sources in which to study how the binary system and the neutron star spin evolve. Furthermore, the characteristics of this new source indicate that there might exist a population of AMXPs undergoing weak outbursts which are undetected by current all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs, while no AMXPs have been detected in any other globular cluster.
2041-8205
L58-L62
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Patruno, A.
61450a42-2fa8-4ca1-a0af-44f2dfe14fcc
Heinke, C. O.
50442ec4-8a45-4aa5-b425-28d0c896dc08
Markwardt, C.
42b907ed-dbe4-4e4f-b80b-554ec69bcb0e
Strohmayer, T. E.
491eee42-6b4e-4dcc-a7cd-2a36ac992a7d
Linares, M.
cea3a79a-1831-4a7f-be41-3bf3b7b25383
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
van der Klis, M.
d3635ef2-91fc-4d3a-b453-ac2861a9edb3
Swank, J. H.
c509010a-a8fb-4f59-981a-18025617f727
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Patruno, A.
61450a42-2fa8-4ca1-a0af-44f2dfe14fcc
Heinke, C. O.
50442ec4-8a45-4aa5-b425-28d0c896dc08
Markwardt, C.
42b907ed-dbe4-4e4f-b80b-554ec69bcb0e
Strohmayer, T. E.
491eee42-6b4e-4dcc-a7cd-2a36ac992a7d
Linares, M.
cea3a79a-1831-4a7f-be41-3bf3b7b25383
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
van der Klis, M.
d3635ef2-91fc-4d3a-b453-ac2861a9edb3
Swank, J. H.
c509010a-a8fb-4f59-981a-18025617f727

Altamirano, D., Patruno, A., Heinke, C. O., Markwardt, C., Strohmayer, T. E., Linares, M., Wijnands, R., van der Klis, M. and Swank, J. H. (2010) Discovery of a 205.89 Hz accreting millisecond x-ray pulsar in the globular cluster NGC 6440. The Astrophysical Journal Letters, 712 (1), L58-L62. (doi:10.1088/2041-8205/712/1/L58).

Record type: Article

Abstract

We report on the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with RXTE on 2009 August 30, October 1 and October 28, during the decays of 4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequency, we find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and a projected semimajor axis of 6.22 lt-ms. Based on the mass function, we estimate a lower limit to the mass of the companion to be 0.0067 M ? (assuming a 1.4 M ? neutron star). This new pulsar shows the shortest outburst recurrence time among AMXPs (~1 month). If this behavior does not cease, this AMXP has the potential to be one of the best sources in which to study how the binary system and the neutron star spin evolve. Furthermore, the characteristics of this new source indicate that there might exist a population of AMXPs undergoing weak outbursts which are undetected by current all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs, while no AMXPs have been detected in any other globular cluster.

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Published date: 2010
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 358799
URI: https://eprints.soton.ac.uk/id/eprint/358799
ISSN: 2041-8205
PURE UUID: f578e911-7f5b-42a6-b273-d217b9cc466c
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 14 Oct 2013 13:32
Last modified: 06 Jun 2018 12:23

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