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Sco X-1 revisited with Kepler, MAXI and HERMES: outflows, time-lags and echoes unveiled

Sco X-1 revisited with Kepler, MAXI and HERMES: outflows, time-lags and echoes unveiled
Sco X-1 revisited with Kepler, MAXI and HERMES: outflows, time-lags and echoes unveiled
Sco X-1 has been the subject of many multiwavelength studies in the past, being the brightest persistent extrasolar X-ray source ever observed. Here, we revisit Sco X-1 with simultaneous short cadence Kepler optical photometry and Monitor of All-sky X-ray Image X-ray photometry over a 78 d period, as well as optical spectroscopy obtained with High Efficiency and Resolution Mercator Echelle Spectrograph (HERMES). We find Sco X-1 to be highly variable in all our data sets. The optical fluxes are clearly bimodal, implying the system can be found in two distinct optical states. These states are generally associated with the known flaring/normal branch X-ray states, although the flux distributions associated with these states overlap. Furthermore, we find that the optical power spectrum of Sco X-1 differs substantially between optical luminosity states. Additionally we find rms-flux relations in both optical states, but only find a linear relation during periods of low optical luminosity. The full optical/X-ray discrete correlation function displays a broad ≈12.5 h optical lag. However, during the normal branch phase, the X-ray and optical fluxes are anticorrelated, whilst being correlated during the flaring branch. We also performed a Cepstrum analysis on the full Kepler light curve to determine the presence of any echoes within the optical light curve alone. We find significant echo signals, consistent with the optical lags found using the discrete cross-correlation. We speculate that whilst some of the driving X-ray emission is reflected by the disc, some is absorbed and re-processed on the thermal time-scale, giving rise to both the observed optical lags and optical echoes.
accretion, accretion discs, X-rays: binaries, X-rays: individual: Sco X-1
0035-8711
3857-3867
Scaringi, S.
88701970-a1b9-41fe-bf55-886716ee3374
Maccarone, T.J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Hynes, R.I.
f6158bd7-6589-436a-86e0-c43a779cdd0b
Körding, E.
2fb1638c-4392-4acc-83ea-78e0eb9c078b
Ponti, G.
1e60398d-fc61-4f6e-be2e-e6b31c2d3623
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Britt, C.T.
91612ea1-45fc-4047-a119-8d89662a4b3b
van Winckel, H.
401a1bb9-f441-48cc-8b23-38c53b28dd1d
Scaringi, S.
88701970-a1b9-41fe-bf55-886716ee3374
Maccarone, T.J.
c2f1d87b-e2ef-4e33-b09f-a2861d917ea8
Hynes, R.I.
f6158bd7-6589-436a-86e0-c43a779cdd0b
Körding, E.
2fb1638c-4392-4acc-83ea-78e0eb9c078b
Ponti, G.
1e60398d-fc61-4f6e-be2e-e6b31c2d3623
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Britt, C.T.
91612ea1-45fc-4047-a119-8d89662a4b3b
van Winckel, H.
401a1bb9-f441-48cc-8b23-38c53b28dd1d

Scaringi, S., Maccarone, T.J., Hynes, R.I., Körding, E., Ponti, G., Knigge, C., Britt, C.T. and van Winckel, H. (2015) Sco X-1 revisited with Kepler, MAXI and HERMES: outflows, time-lags and echoes unveiled. Monthly Notices of the Royal Astronomical Society, 451 (4), 3857-3867. (doi:10.1093/mnras/stv1216).

Record type: Article

Abstract

Sco X-1 has been the subject of many multiwavelength studies in the past, being the brightest persistent extrasolar X-ray source ever observed. Here, we revisit Sco X-1 with simultaneous short cadence Kepler optical photometry and Monitor of All-sky X-ray Image X-ray photometry over a 78 d period, as well as optical spectroscopy obtained with High Efficiency and Resolution Mercator Echelle Spectrograph (HERMES). We find Sco X-1 to be highly variable in all our data sets. The optical fluxes are clearly bimodal, implying the system can be found in two distinct optical states. These states are generally associated with the known flaring/normal branch X-ray states, although the flux distributions associated with these states overlap. Furthermore, we find that the optical power spectrum of Sco X-1 differs substantially between optical luminosity states. Additionally we find rms-flux relations in both optical states, but only find a linear relation during periods of low optical luminosity. The full optical/X-ray discrete correlation function displays a broad ≈12.5 h optical lag. However, during the normal branch phase, the X-ray and optical fluxes are anticorrelated, whilst being correlated during the flaring branch. We also performed a Cepstrum analysis on the full Kepler light curve to determine the presence of any echoes within the optical light curve alone. We find significant echo signals, consistent with the optical lags found using the discrete cross-correlation. We speculate that whilst some of the driving X-ray emission is reflected by the disc, some is absorbed and re-processed on the thermal time-scale, giving rise to both the observed optical lags and optical echoes.

Full text not available from this repository.

More information

e-pub ahead of print date: 29 June 2015
Published date: 21 August 2015
Keywords: accretion, accretion discs, X-rays: binaries, X-rays: individual: Sco X-1

Identifiers

Local EPrints ID: 429993
URI: http://eprints.soton.ac.uk/id/eprint/429993
ISSN: 0035-8711
PURE UUID: a879d35f-62b1-4ad1-9cb6-54488a70fc11

Catalogue record

Date deposited: 09 Apr 2019 16:30
Last modified: 09 Apr 2019 16:30

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