J/ApJ/965/L10 Multiwavelength observations of the Be/XRB SXP 182 (Gaudin+, 2024)
Discovery of a rare eclipsing Be/X-ray binary system, Swift J010902.6-723710 =
SXP 182.
Gaudin T.M., Kennea J.A., Coe M.J., Monageng I.M., Udalski A.,
Townsend L.J., Buckley D.A.H., Evans P.A.
<Astrophys. J., 965, L10 (2024)>
=2024ApJ...965L..10G 2024ApJ...965L..10G
ADC_Keywords: Binaries, eclipsing; Binaries, X-ray; Photometry; Stars, Be;
Spectra, optical
Keywords: High mass x-ray binary stars ; Massive stars ; X-ray binary stars ;
High energy astrophysics ; Eclipsing binary stars
Abstract:
We report on the discovery of Swift J010902.6-723710, a rare eclipsing
Be/X-ray Binary system by the Swift SMC Survey (S-CUBED). Swift
J010902.6-723710 was discovered via weekly S-CUBED monitoring
observations when it was observed to enter a state of X-ray outburst
on 2023 October 10. X-ray emission was found to be modulated by a
182s period. Optical spectroscopy is used to confirm the presence of
a highly inclined circumstellar disk surrounding a B0-0.5Ve optical
companion. Historical UV and IR photometry is then used to identify
strong eclipse-like features reoccurring in both light curves with a
60.623 day period, which is adopted as the orbital period of the
system. Eclipsing behavior is found to be the result of a large
accretion disk surrounding the neutron star. Eclipses are produced
when the disk passes in front of the OBe companion, blocking light
from both the stellar surface and circumstellar disk. This is only the
third Be/X-ray binary to have confirmed eclipses. We note that this
rare behavior provides an important opportunity to constrain the
physical parameters of a Be/X-ray binary with greater accuracy than is
possible in noneclipsing systems.
Description:
In this paper, we report on the recent X-ray outburst that was
experienced by Swift J010902.6-723710.
The Swift-XRT first detected this source during the weekly Swift SMC
Survey (S-CUBED; Kennea+ 2018, J/ApJ/868/47) monitoring in March of
2020. Two more detections occurred in July and September of 2021.
Another deep 10ks Swift observation was operated in August of 2023.
The results of all XRT observations during the recent outburst are
shown in Figure 1. See Section 2.1.
Swift J010902.6-723710 has been observed 221 times by UVOT in the uvw1
band since 2016 as part of S-CUBED monitoring, which represents
approximately weekly coverage. See Section 2.2.
The OGLE project provides long-term I-band photometry with a cadence
of 1-3 days for sources in the Magellanic Clouds. From the X-ray
position the optical/IR counterpart to Swift J010902.6-723710 is
identified as 2MASS J01090226-7237101. It was observed continuously
for nearly three decades by OGLE. The I-band data from just the OGLE
IV project are shown in the top panel of Figure 3 for comparison with
the contemporaneous Swift UVOT and XRT data.
For the purpose of period analysis the whole of the 26.4yr of OGLE
data were used and first detrended using a simple polynomial --see
Figure 4.
See Section 2.3.
Swift J010902.6-723710 was observed with the Southern African Large
Telescope (SALT) with the Robert Stobie Spectrograph using different
settings. On 2023 November 3 (MJD60251.88) the PG0900 grating was used
(grating angle of 15.125°) with an exposure time of 1200s covering
a wavelength range of 4200-7250Å. The PG2300 grating was used on
2023 November 9 (MJD60257.87) and 2023 December 2 (MJD60280.85)
(grating angle of 48.875°) with an exposure time of 1200s covering
a wavelength range 6100-6900Å. An additional observation was taken
on 2023 November 9 (MJD60257.87) with the PG2300 grating (grating
angle of 30.5°) with an exposure time of 1500s covering a
wavelength range 3840-4915Å. Figure 8 shows the Ha emission line
profiles. See Section 2.4.
Objects:
-------------------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------------------
01 09 02.28 -72 37 10.3 Swift J010902.6-723710 = SXP 182
-------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig1.dat 63 29 XRT light curve for Swift J010902.6-723710 from
August 2023 to present, combining data from
S-CUBED observations and follow-up TOOs
fig3.dat 88 2817 OGLE IV, Swift UVOT, and Swift XRT light curves
for Swift J010902.6-723710
fig4.dat 28 5766 The whole and de-trended OGLE data set covering
26 years
fig8.dat 22 12632 The SALT spectral observations
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See also:
J/MNRAS/353/601 : 2dF survey of the Small Magellanic Cloud (Evans+, 2004)
J/AJ/127/1531 : Star formation history of SMC (Harris+, 2004)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJS/208/9 : Intrinsic colors & temperatures of PMS stars (Pecaut+, 2013)
J/A+A/574/A33 : BVRI photometry of high-mass X-ray binaries (Reig+, 2015)
J/A+A/586/A81 : High-mass X-ray binaries in the SMC (Haberl+, 2016)
J/ApJ/868/47 : 1st year of the Swift SMC Survey (S-CUBED) (Kennea+, 2018)
J/ApJ/904/13 : Radial velocity for 10 giant EBs (Graczyk+, 2020)
J/AcA/74/241 : OGLE-IV MC eclipsing & ellipsoidal binaries (Glowacki+, 2024)
Byte-by-byte Description of file: fig1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Type Observation type (1)
9- 19 F11.5 d MJD [60129.9/60353.11] Modified Julian Date
21- 27 F7.5 d E_MJD [0.0002/0.31] Upper uncertainty in MJD
29- 35 F7.5 d e_MJD Lower uncertainty in MJD
37 A1 --- l_Lum Upper limit flag on Lum
38- 45 E8.2 10-7W Lum [5.8e+35/1.6e+37] The 0.3-10keV X-ray luminosity
in erg/s (2)
47- 54 E8.2 10-7W E_Lum [/3.25e+36]? Upper uncertainty in Lum
56- 63 E8.2 10-7W e_Lum [/2.71e+36]? Lower uncertainty in Lum
--------------------------------------------------------------------------------
Note (1): Observation type as follows:
S-CUBED = The Swift SMC Survey (Kennea+ 2018, J/ApJ/868/47)
TOO = Target of Opportunity
Note (2): To convert to flux, one simply has to divide
the data by a factor of 4.6142e+47.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Source Data source (1)
6- 16 F11.5 d MJD [5346.93/60305] Modified Julian Date
(MJD=JD-2400000.5 for XRT and UVOT;
or JD-2450000 for OGLE)
18- 24 F7.5 d E_MJD [0/0.17] Upper uncertainty in MJD
26- 32 F7.5 d e_MJD Lower uncertainty in MJD
35- 42 E8.2 mag mag [13.7/17.1]? Observed magnitude from Source
44- 51 E8.2 mag E_mag [0.003/0.1]? Upper uncertainty in mag
53- 60 E8.2 mag e_mag ? Lower uncertainty in mag
62 A1 --- l_CR Upper limit flag on CR
63- 70 E8.2 --- CR [0.012/0.46]? Observed XRT count rate from Source
72- 79 E8.2 --- E_CR [0.003/0.08]? Upper uncertainty in CR
81- 88 E8.2 --- e_CR ? Lower uncertainty in CR
--------------------------------------------------------------------------------
Note (1): Data source as follows:
OGLE = Optical Gravitational Lensing Experiment IV I band photometry.
UVOT = Swift/UVOT UVW1 filter photometry.
XRT = Swift/XRT 0.3-10keV X-ray count rate.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fig4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Type Data type (1)
5- 15 F11.5 d JD [627.92/10248.7] Julian Date of observation;
JD-2450000
17- 22 F6.3 mag mag [-0.2/17.11] OGLE IV I band magnitude of Type
24- 28 F5.3 mag e_mag [0/0.02] Uncertainty in mag (2)
--------------------------------------------------------------------------------
Note (1): Data type as follows:
Org = Original OGLE data set, no de-trending applied.
DT = OGLE data set with a simple polynomial de-trending applied.
Note (2): The detrended photometry has no uncertainty and thus is zero.
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Byte-by-byte Description of file: fig8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.2 d MJD [60251.88/60280.85] Modified Julian Date of the
observation (1)
10- 16 F7.2 0.1nm lambda [3843.56/7263.62] Wavelength; Angstroms
18- 22 F5.2 --- NFlux [0.57/1.75] Normalized flux
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Note (1): Date as follows:
60251.88 = November 3, 2023 using the PG0900 grating. This data
covers a wavelength range of 4200-7250 angstroms.
60257.87 = November 9, 2023 using the PG2300 grating. There is a blue
component that was taken over a wavelength range of
3840-4915 angstroms and a red component with a wavelength
range of 6100-6900 angstroms.
60280.85 = December 2, 2023 using the PG2300 grating. This data
covers a wavelength range of 6100-6900 angstroms.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Aug-2026