Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34

F M Vincentelli; P Casella; A Borghese; Y Cavecchi; G Mastroserio; L Stella; D Altamirano; M Armas Padilla; M C Baglio; T M Belloni; J Casares; V A Cúneo; N Degenaar; M Díaz Trigo; R Fender; T Maccarone; J Malzac; D Mata Sánchez; M Middleton; S Migliari; T Muñoz-Darias; K O’Brien; G Panizo-Espinar; J Sánchez-Sierras; D M Russell; P Uttley

doi:10.1093/mnras/stad2414

Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34

F M Vincentelli, P Casella, A Borghese, Y Cavecchi, G Mastroserio, L Stella, D Altamirano, M Armas Padilla, M C Baglio, T M Belloni, J Casares, V A Cúneo, N Degenaar, M Díaz Trigo, R Fender, T Maccarone, J Malzac, D Mata Sánchez, M Middleton, S MigliariT Muñoz-Darias, K O’Brien, G Panizo-Espinar, J Sánchez-Sierras, D M Russell, P Uttley

Research output: Contribution to journal › Article › peer-review

6 Citations (Scopus)

Abstract

We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM-Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than h and an inclination higher than 8°.

Original language	English
Pages (from-to)	2509-2518
Number of pages	10
Journal	Monthly Notices of the Royal Astronomical Society
Volume	525
Issue number	2
Early online date	25 Aug 2023
DOIs	https://doi.org/10.1093/mnras/stad2414
Publication status	Published - Oct 2023
Externally published	Yes

Funding

We thank the referee for the valuable comments which improved the quality and readability of the paper. This work benefited from the discussions done during the ISSI meeting in Bern ‘‘Looking at the disc-jet coupling from different angles”. FMV acknowledges support from the grant FJC2020-043334-I financed by MCIN/AEI/10.13039/501100011033 and Next Generation EU/PRTR. This work is supported by the Spanish Ministry of Science under grants PID2020–120323GB–I00, PID2021–124879NB-I00, and EUR2021–122010'. MB acknowledges financial contribution from grant PRIN-INAF 2019 no. 15. YC acknowledges support from the grant RYC2021-032718-I, financed by MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR. LS acknowledges financial contributions from ASI-INAF agreements 2017-14-H.O and I/037/12/0; from ‘iPeska’ research grant (PI Andrea Possenti) funded under the INAF call PRIN-SKA/CTA (resolution 70/2016), from PRIN-INAF 2019 no. 15 and from the Italian Ministry of University and Research (MUR), PRIN 2020 (prot. 2020BRP57Z) “GEMS”.

Funders	Funder number
European Union	I/037/12/0
National Institute for Astrophysics	2020BRP57Z
Ministero dell’Istruzione, dell’Università e della Ricerca
Ministry of Science, Innovation and Universities	RYC2021-032718-I, PID2020–120323GB–I00, EUR2021–122010, PID2021–124879NB-I00

Keywords

X-rays: binaries
accretion, accretion discs
stars: neutron

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1093/mnras/stad2414

Cite this

Vincentelli, F. M., Casella, P., Borghese, A., Cavecchi, Y., Mastroserio, G., Stella, L., Altamirano, D., Padilla, M. A., Baglio, M. C., Belloni, T. M., Casares, J., Cúneo, V. A., Degenaar, N., Trigo, M. D., Fender, R., Maccarone, T., Malzac, J., Sánchez, D. M., Middleton, M., ... Uttley, P. (2023). Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34. Monthly Notices of the Royal Astronomical Society, 525(2), 2509-2518. https://doi.org/10.1093/mnras/stad2414

Vincentelli, FM, Casella, P, Borghese, A, Cavecchi, Y, Mastroserio, G, Stella, L, Altamirano, D, Padilla, MA, Baglio, MC, Belloni, TM, Casares, J, Cúneo, VA, Degenaar, N, Trigo, MD, Fender, R, Maccarone, T, Malzac, J, Sánchez, DM, Middleton, M, Migliari, S, Muñoz-Darias, T, O’Brien, K, Panizo-Espinar, G, Sánchez-Sierras, J, Russell, DM & Uttley, P 2023, 'Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34', Monthly Notices of the Royal Astronomical Society, vol. 525, no. 2, pp. 2509-2518. https://doi.org/10.1093/mnras/stad2414

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title = "Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34",

abstract = "We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM-Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than h and an inclination higher than 8°.",

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doi = "10.1093/mnras/stad2414",

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T1 - Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34

AU - Vincentelli, F M

AU - Casella, P

AU - Borghese, A

AU - Cavecchi, Y

AU - Mastroserio, G

AU - Stella, L

AU - Altamirano, D

AU - Padilla, M Armas

AU - Baglio, M C

AU - Belloni, T M

AU - Casares, J

AU - Cúneo, V A

AU - Degenaar, N

AU - Trigo, M Díaz

AU - Fender, R

AU - Maccarone, T

AU - Malzac, J

AU - Sánchez, D Mata

AU - Middleton, M

AU - Migliari, S

AU - Muñoz-Darias, T

AU - O’Brien, K

AU - Panizo-Espinar, G

AU - Sánchez-Sierras, J

AU - Russell, D M

AU - Uttley, P

PY - 2023/10

Y1 - 2023/10

N2 - We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM-Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than h and an inclination higher than 8°.

AB - We report on the first simultaneous high-time resolution X-ray and infrared (IR) observations of a neutron star low mass X-ray binary in its hard state. We performed h of simultaneous observations of 4U 1728-34 using HAWK-I@VLT, XMM-Newton, and NuSTAR. The source displayed significant X-ray and IR variability down to sub-second time-scales. By measuring the cross-correlation function between the IR and X-ray lightcurves, we discovered a significant correlation with an IR lead of ms with respect to the X-rays. We analysed the X-ray energy dependence of the lag, finding a marginal increase towards higher energies. Given the sign of the lag, we interpret this as possible evidence of Comptonization from external seed photons. We discuss the origin of the IR seed photons in terms of cyclo-synchrotron radiation from an extended hot flow. Finally, we also observed the IR counterpart of a type-I X-ray burst, with a delay of s. Although some additional effects may be at play, by assuming that this lag is due to light travel time between the central object and the companion star, we find that 4U 1728-34 must have an orbital period longer than h and an inclination higher than 8°.

KW - X-rays: binaries

KW - accretion, accretion discs

KW - stars: neutron

UR - https://www.scopus.com/pages/publications/85171629295

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DO - 10.1093/mnras/stad2414

M3 - Article

SN - 0035-8711

VL - 525

SP - 2509

EP - 2518

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 2

ER -

Sub-second infrared variability from the archetypal accreting neutron star 4U 1728−34

Abstract

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Keywords

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