Swift J004427.3−734801 – a probable Be/white dwarf system in the Small Magellanic Cloud

ABSTRACT Swift J004427.3−734801 is an X-ray source in the Small Magellanic Cloud (SMC) that was first discovered as part of the Swift S-CUBED programme in 2020 January. It was not detected in any of the previous 3 yr worth of observations. The accurate positional determination from the X-ray data has permitted an optical counterpart to be identified that has the characteristics of an O9V−B2III star. Evidence for the presence of an infrared excess and significant I-band variability strongly suggests that this is an OBe-type star. Over 17 yr worth of optical monitoring by the OGLE (Optical Gravitational Lensing Experiment) project reveals periods of time in which quasi-periodic optical flares occur at intervals of ∼21.5 d. The X-ray data obtained from the S-CUBED project reveal a very soft spectrum, too soft to be that from accretion on to a neutron star or black hole. It is suggested here that this is a rarely identified Be star–white dwarf binary in the SMC.

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A new super-soft X-ray source in the Small Magellanic Cloud: Discovery of the first Be/white dwarf system in the SMC?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201117789 ◽

2012 ◽

Vol 537 ◽

pp. A76 ◽

Cited By ~ 19

Author(s):

R. Sturm ◽

F. Haberl ◽

W. Pietsch ◽

M. J. Coe ◽

S. Mereghetti ◽

...

Keyword(s):

White Dwarf ◽

Magellanic Cloud ◽

Small Magellanic Cloud ◽

X Ray

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The Spectrum of Smc X-1

Publications of the Astronomical Society of Australia ◽

10.1017/s132335800001393x ◽

1974 ◽

Vol 2 (5) ◽

pp. 286-289

Author(s):

B. A. Peterson ◽

N. V. Vidal

Keyword(s):

Magellanic Cloud ◽

Small Magellanic Cloud ◽

Optical Counterpart ◽

X Ray

The variable X-ray source in the direction of the Small Magellanic Cloud (SMC), SMC X-1 (2U 0115-73) was discovered by Leong et al. (1971). X-ray eclipses with a period of 3.8927 ± 0.0010 days were subsequently reported by Schreier et al. (1972). Identification of the X-ray source with SK 160, star number 160 in the list of Sanduleak (1968), was proposed by Webster et al. (1972) on the basis of the similarity of its spectrum with that of the optical counterpart of Cyg X-1.

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Searching for New Be/X–ray Binaries in the SMC: the case of 1SAXJ0103–7209, XTEJ0055–724, RXJ0052–7319, XTEJ0111–7317 and 2E0050–7247

International Astronomical Union Colloquium ◽

10.1017/s0252921100056736 ◽

2000 ◽

Vol 175 ◽

pp. 681-684

Author(s):

S. Covino ◽

G.L. Israel ◽

V.F. Polcaro ◽

S. Campana ◽

S. Mereghetti ◽

...

Keyword(s):

Magellanic Cloud ◽

Optical Observations ◽

Small Magellanic Cloud ◽

Optical Counterpart ◽

X Ray ◽

X Ray Binaries

AbstractWe obtained X–ray (ROSAT, BeppoSAX and ASCA) and optical observations of a sample of newly discovered X–ray pulsars. We here report on the discovery of the likely optical counterpart of five of them in the Small Magellanic Cloud: 1SAXJ0103–7209, XTEJ0055–724, RXJ0052–7319, XTEJ0111–7317 and 2E0050–7247.

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Discovery of an ∼30-yr-duration post-nova pulsating supersoft source in the Large Magellanic Cloud

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2922 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2007-2014

Author(s):

G Vasilopoulos ◽

F Koliopanos ◽

T E Woods ◽

F Haberl ◽

M D Soraisam ◽

...

Keyword(s):

White Dwarf ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

X Ray ◽

Short Period ◽

Type Ia ◽

Nuclear Burning ◽

Soft Spectrum ◽

Binary Evolution ◽

First Time

ABSTRACT Supersoft X-ray sources (SSS) have been identified as white dwarfs accreting from binary companions and undergoing nuclear burning of the accreted material on their surface. Although expected to be a relatively numerous population from both binary evolution models and their identification as type Ia supernova progenitor candidates, given the very soft spectrum of SSSs relatively few are known. Here we report on the X-ray and optical properties of 1RXS J050526.3−684628, a previously unidentified accreting nuclear-burning white dwarf located in the Large Magellanic Cloud (LMC). XMM–Newton observations enabled us to study its X-ray spectrum and measure for the first time short-period oscillations of ∼170 s. By analysing newly obtained X-ray data by eROSITA, together with Swift observations and archival ROSAT data, we have followed its long-term evolution over the last 3 decades. We identify 1RXS J050526.3−684628 as a slowly evolving post-nova SSS undergoing residual surface nuclear burning, which finally reached its peak in 2013 and is now declining. Though long expected on theoretical grounds, such long-lived residual-burning objects had not yet been found. By comparison with existing models, we find that the effective temperature and luminosity evolution are consistent with an ∼0.7 M⊙ carbon–oxygen white dwarf accreting ${\sim} 10^{-9}~\rm {M}_{\odot }$ yr−1. Our results suggest that there may be many more undiscovered SSSs and ‘missed’ novae awaiting dedicated deep X-ray searches in the LMC and elsewhere.

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