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Discovery of millihertz quasi-periodic oscillations in the X-ray binary EXO 0748−676

Discovery of millihertz quasi-periodic oscillations in the X-ray binary EXO 0748−676
Discovery of millihertz quasi-periodic oscillations in the X-ray binary EXO 0748−676

We report the discovery of millihertz quasi-periodic oscillations (mHz QPOs) from the bursting, high-inclination atoll neutron star low-mass X-ray binary (NS LMXB) EXO 0748−676 with the Rossi X-ray Time Explorer (RXTE). This class of QPO, originally discovered in three NS LMXBs, has been interpreted as a consequence of a special mode of nuclear burning on the NS surface. Using all the RXTE archival observations of the source, we detected significant (>3σ) mHz QPOs in 11 observations. The frequency of the oscillations was between ∼5 and ∼13 mHz. We also found a decrease of the QPO frequency with time in two occasions; in one of these the oscillations disappeared with the onset of an X-ray burst, similar to what was reported in other sources. Our analysis of the X-ray colours revealed that EXO 0748−676 was in a soft spectral state when it exhibited the QPOs. This makes EXO 0748−676 the sixth source with mHz oscillations associated with marginally stable burning, and the second one that shows a systematic frequency drift. Our results suggest that the mechanism that produces the drift might always be present if the mHz QPOs are observed in the so-called intermediate state.

Accretion, Accretion discs, Stars: individual: EXO 0748−676, Stars: neutron, X-rays: binaries
1745-3925
L74-L79
Mancuso, G.C.
59acaddd-cafd-4960-ba78-3665c0f30dcb
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
García, F.
a48757e1-56fb-477f-a28c-0ac649bd857c
Lyu, M.
6b2e28ac-079d-49f1-baeb-edd2c1b1de68
Méndez, M.
5cc6f759-dae2-488a-9cc2-cff89f4eca72
Combi, J.A.
b7b2bd53-d3d0-41b6-a2f3-13da7e34bdaa
Díaz-Trigo, M.
04422ade-9ae6-434c-98bc-50d0ac75e19e
in’t Zand, J.J.M.
92e32435-6102-46a2-8c50-05ee17a0df17
Mancuso, G.C.
59acaddd-cafd-4960-ba78-3665c0f30dcb
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
García, F.
a48757e1-56fb-477f-a28c-0ac649bd857c
Lyu, M.
6b2e28ac-079d-49f1-baeb-edd2c1b1de68
Méndez, M.
5cc6f759-dae2-488a-9cc2-cff89f4eca72
Combi, J.A.
b7b2bd53-d3d0-41b6-a2f3-13da7e34bdaa
Díaz-Trigo, M.
04422ade-9ae6-434c-98bc-50d0ac75e19e
in’t Zand, J.J.M.
92e32435-6102-46a2-8c50-05ee17a0df17

Mancuso, G.C., Altamirano, D., García, F., Lyu, M., Méndez, M., Combi, J.A., Díaz-Trigo, M. and in’t Zand, J.J.M. (2019) Discovery of millihertz quasi-periodic oscillations in the X-ray binary EXO 0748−676. Monthly Notices of the Royal Astronomical Society: Letters, 486 (1), L74-L79. (doi:10.1093/mnrasl/slz057).

Record type: Article

Abstract

We report the discovery of millihertz quasi-periodic oscillations (mHz QPOs) from the bursting, high-inclination atoll neutron star low-mass X-ray binary (NS LMXB) EXO 0748−676 with the Rossi X-ray Time Explorer (RXTE). This class of QPO, originally discovered in three NS LMXBs, has been interpreted as a consequence of a special mode of nuclear burning on the NS surface. Using all the RXTE archival observations of the source, we detected significant (>3σ) mHz QPOs in 11 observations. The frequency of the oscillations was between ∼5 and ∼13 mHz. We also found a decrease of the QPO frequency with time in two occasions; in one of these the oscillations disappeared with the onset of an X-ray burst, similar to what was reported in other sources. Our analysis of the X-ray colours revealed that EXO 0748−676 was in a soft spectral state when it exhibited the QPOs. This makes EXO 0748−676 the sixth source with mHz oscillations associated with marginally stable burning, and the second one that shows a systematic frequency drift. Our results suggest that the mechanism that produces the drift might always be present if the mHz QPOs are observed in the so-called intermediate state.

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Accepted/In Press date: 22 April 2019
e-pub ahead of print date: 10 May 2019
Published date: 1 June 2019
Keywords: Accretion, Accretion discs, Stars: individual: EXO 0748−676, Stars: neutron, X-rays: binaries

Identifiers

Local EPrints ID: 432339
URI: http://eprints.soton.ac.uk/id/eprint/432339
ISSN: 1745-3925
PURE UUID: 43d4c7e3-1d60-43b8-b3f2-3d18479bc602
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

Catalogue record

Date deposited: 11 Jul 2019 16:30
Last modified: 26 Nov 2021 03:02

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Contributors

Author: G.C. Mancuso
Author: D. Altamirano ORCID iD
Author: F. García
Author: M. Lyu
Author: M. Méndez
Author: J.A. Combi
Author: M. Díaz-Trigo
Author: J.J.M. in’t Zand

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