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Absence of nebular He{\sc ii} $λ$4686 constrains the UV emission from the ultraluminous X-ray pulsar NGC~1313~X--2

Absence of nebular He{\sc ii} $λ$4686 constrains the UV emission from the ultraluminous X-ray pulsar NGC~1313~X--2
Absence of nebular He{\sc ii} $λ$4686 constrains the UV emission from the ultraluminous X-ray pulsar NGC~1313~X--2
While much has been learned in recent decades about the X-ray emission of the extragalactic Ultraluminous X-ray sources (ULXs), their radiative output in the UV band remains poorly constrained. Understanding of the full ULX spectral energy distribution (SED) is imperative to constrain the accretion flow geometry powering them, as well as their radiative power. Here we present constraints on the UV emission of the pulsating ULX (PULX) NGC~1313~X--2 based on the absence of nebular {He{\sc ii} λ4686} emission in its immediate environment. To this end, we first perform multi-band spectroscopy of the ULX to derive three realistic extrapolations of the SED into the unaccessible UV, each predicting varying levels of UV luminosity. We then perform photo-ionization modelling of the bubble nebula and predict the {He{\sc ii} λ4686} fluxes that should have been observed based on each of the derived SEDs. We then compare these predictions with the derived upper limit on {\heii} from MUSE data, which allows us to infer a UV luminosity LUV≲1×1039 erg/s in the PULX NGC~1313~X--2. Comparing the UV luminosity inferred with other ULXs, our work suggests there may be an intrinsic difference between hard and soft ULXs, either related to different mass-transfer rates and/or the nature of the accretor. However, a statistical sample of ULXs with inferred UV luminosities is needed to fully determine the distinguishing features between hard and soft ULXs. Finally, we discuss ULXs ionising role in the context of the nebular {He{\sc ii} λ4686} line observed in star-forming, metal-poor galaxies.
astro-ph.HE
1365-2966
Gúrpide, Andrés
97591ff3-cd37-41e9-8dd1-a818fa382092
Segura, Noel Castro
0dee6349-38d9-4a0e-b389-df77063638d5
Soria, Roberto
5c123193-2dcd-49b7-a20d-4ddbf878a886
Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad
Gúrpide, Andrés
97591ff3-cd37-41e9-8dd1-a818fa382092
Segura, Noel Castro
0dee6349-38d9-4a0e-b389-df77063638d5
Soria, Roberto
5c123193-2dcd-49b7-a20d-4ddbf878a886
Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad

Gúrpide, Andrés, Segura, Noel Castro, Soria, Roberto and Middleton, Matthew (2024) Absence of nebular He{\sc ii} $λ$4686 constrains the UV emission from the ultraluminous X-ray pulsar NGC~1313~X--2. Monthly Notices of the Royal Astronomical Society. (In Press)

Record type: Article

Abstract

While much has been learned in recent decades about the X-ray emission of the extragalactic Ultraluminous X-ray sources (ULXs), their radiative output in the UV band remains poorly constrained. Understanding of the full ULX spectral energy distribution (SED) is imperative to constrain the accretion flow geometry powering them, as well as their radiative power. Here we present constraints on the UV emission of the pulsating ULX (PULX) NGC~1313~X--2 based on the absence of nebular {He{\sc ii} λ4686} emission in its immediate environment. To this end, we first perform multi-band spectroscopy of the ULX to derive three realistic extrapolations of the SED into the unaccessible UV, each predicting varying levels of UV luminosity. We then perform photo-ionization modelling of the bubble nebula and predict the {He{\sc ii} λ4686} fluxes that should have been observed based on each of the derived SEDs. We then compare these predictions with the derived upper limit on {\heii} from MUSE data, which allows us to infer a UV luminosity LUV≲1×1039 erg/s in the PULX NGC~1313~X--2. Comparing the UV luminosity inferred with other ULXs, our work suggests there may be an intrinsic difference between hard and soft ULXs, either related to different mass-transfer rates and/or the nature of the accretor. However, a statistical sample of ULXs with inferred UV luminosities is needed to fully determine the distinguishing features between hard and soft ULXs. Finally, we discuss ULXs ionising role in the context of the nebular {He{\sc ii} λ4686} line observed in star-forming, metal-poor galaxies.

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2405.13714v1 - Accepted Manuscript
Available under License Creative Commons Attribution.
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Accepted/In Press date: 22 May 2024
Additional Information: 11 Figures
Keywords: astro-ph.HE

Identifiers

Local EPrints ID: 492116
URI: http://eprints.soton.ac.uk/id/eprint/492116
ISSN: 1365-2966
PURE UUID: d212da50-adc4-4fe7-980b-766fe9ee097b

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Date deposited: 17 Jul 2024 16:31
Last modified: 17 Aug 2024 04:01

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Contributors

Author: Andrés Gúrpide
Author: Noel Castro Segura
Author: Roberto Soria

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