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Intermittent millisecond x-ray pulsations from the neutron star x-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440

Intermittent millisecond x-ray pulsations from the neutron star x-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440
Intermittent millisecond x-ray pulsations from the neutron star x-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440
We report on intermittent X-ray pulsations with a frequency of 442.36 Hz from the neutron-star X-ray binary SAX J1748.9-2021 in the globular cluster NGC 6440. The pulsations were seen during both 2001 and 2005 outbursts of the source, but only intermittently, appearing and disappearing on timescales of hundreds of seconds. We find a suggestive relation between the occurrence of type-I X-ray bursts and the appearance of the pulsations but the relation is not strict. This behavior is very similar to that of the intermittent accreting millisecond X-ray pulsar HETE J1900.1-2455. The reason for the intermittence of the pulsations remains unclear. However it is now evident that a strict division between pulsating and non-pulsating does not exist. By studying the Doppler shift of the pulsation frequency we determine an orbit with a period of 8.7 hrs and an projected semi major axis of 0.39 lightsec. The companion star might be a main-sequence or a slightly evolved star with a mass of ~1 Msun. Therefore, SAX J1748.9-2021 has a longer period and may have a more massive companion star than all the other accreting millisecond X-ray pulsars except for Aql X-1.
0004-637X
L45-L48
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Casella, P.
8dc7f5b0-354e-4329-b225-5cc2124801a6
Patruno, A.
61450a42-2fa8-4ca1-a0af-44f2dfe14fcc
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
van der Klis, M.
d3635ef2-91fc-4d3a-b453-ac2861a9edb3
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Casella, P.
8dc7f5b0-354e-4329-b225-5cc2124801a6
Patruno, A.
61450a42-2fa8-4ca1-a0af-44f2dfe14fcc
Wijnands, R.
382893ee-0e03-45e3-9321-db8b9fc74914
van der Klis, M.
d3635ef2-91fc-4d3a-b453-ac2861a9edb3

Altamirano, D., Casella, P., Patruno, A., Wijnands, R. and van der Klis, M. (2008) Intermittent millisecond x-ray pulsations from the neutron star x-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440. The Astrophysical Journal, 674 (1), L45-L48. (doi:10.1086/528983).

Record type: Article

Abstract

We report on intermittent X-ray pulsations with a frequency of 442.36 Hz from the neutron-star X-ray binary SAX J1748.9-2021 in the globular cluster NGC 6440. The pulsations were seen during both 2001 and 2005 outbursts of the source, but only intermittently, appearing and disappearing on timescales of hundreds of seconds. We find a suggestive relation between the occurrence of type-I X-ray bursts and the appearance of the pulsations but the relation is not strict. This behavior is very similar to that of the intermittent accreting millisecond X-ray pulsar HETE J1900.1-2455. The reason for the intermittence of the pulsations remains unclear. However it is now evident that a strict division between pulsating and non-pulsating does not exist. By studying the Doppler shift of the pulsation frequency we determine an orbit with a period of 8.7 hrs and an projected semi major axis of 0.39 lightsec. The companion star might be a main-sequence or a slightly evolved star with a mass of ~1 Msun. Therefore, SAX J1748.9-2021 has a longer period and may have a more massive companion star than all the other accreting millisecond X-ray pulsars except for Aql X-1.

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Published date: 2008
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 358795
URI: https://eprints.soton.ac.uk/id/eprint/358795
ISSN: 0004-637X
PURE UUID: 9df04e11-1136-45e1-a13e-9a9b62cc871e
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 14 Oct 2013 13:09
Last modified: 30 Jun 2018 00:29

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