ABSTRACT
We report on the discovery of Swift J004516.6–734703, a Be/X-ray binary system by the Swift SMC Survey, S-CUBED. Swift J004516.6–734703, or SXP 146.6, was found to be exhibiting a bright ...(∼1037 erg s−1) X-ray outburst on 2020 June 18. The historical UV and IR light-curves from OGLE and Swift/UVOT showed that after a long period of steady brightness, it experienced a significant brightening beginning around 2019 March. This IR/UV rise is likely the signature of the formation of a circumstellar disc, confirmed by the presence of strong an H α line in SALT spectroscopy, that was not previously present. Periodicity analysis of the OGLE data reveals a plausible 426 d binary period, and in X-ray a pulsation period of 146.6 s is detected. The onset of X-ray emission from Swift J004516.6–734703 is likely the signature of a Type-I outburst from the first periastron passage of the neutron star companion through the newly formed circumstellar disc. We note that the formation of the circumstellar disc began at the predicted time of the previous periastron passage, suggesting its formation was spurred by tidal interaction with the neutron star.
ABSTRACT
Swift J004929.5-733107 is an X-ray source in the Small Magellanic Cloud (SMC) that has been reported several times, but the optical counterpart has been unclear due to source confusion in a ...crowded region of the SMC. Previous works proposed MA93 302 as the counterpart, however we show here, using data obtained from the S-CUBED project, that the X-ray position is inconsistent with that object. Instead we propose a previously unclassified object which has all the indications of being a newly identified Be star exhibiting strong H α emission. Evidence for the presence of significant I-band variability strongly suggest that this is, in fact, a Be type star with a large circumstellar disc. Over 18 yr worth of optical monitoring by the OGLE project reveal a periodic modulation at a period of 413 d, probably the binary period of the system. A SALT optical spectrum shows strong Balmer emission and supports a proposed spectral classification of B1-3 III-IVe. The X-ray data obtained from the S-CUBED project reveal a time-averaged spectrum well fitted by a photon index Γ = 0.93 ± 0.16. Assuming the known distance to the SMC, the flux corresponds to a luminosity ∼1035 erg s−1. All of these observational facts suggest that this is confirmed as a Be star–neutron star X-ray binary (BeXRB) in the SMC, albeit one with an unusually long binary period at the limits of the Corbet Diagram.
ABSTRACT We report on optical follow-up observations of an X-ray source initially detected by the Einstein Probe mission. Our investigations categorize the source as an intermediate polar, a class of ...magnetic cataclysmic variables, exhibiting an orbital period of 3.7614(4) h and a white dwarf spin period of 3.97 min. The orbital period was identified through TESS observations, while our high-speed photometric data, obtained using the 1.9m and Lesedi 1.0m telescopes at the South African Astronomical Observatory, revealed both the spin and beat periods. Additionally, we present orbitally phase-resolved spectroscopic observations using the 1.9m telescope, specifically centred on the H β emission line, which reveal two emission components that exhibit Doppler variations throughout the orbital cycle.
ABSTRACT
SXP4.78 was originally discovered in 2000 as a pulsar in the Small Magellanic Cloud by the Rossi X-ray Timing Explorer, but it was not spatially located at that time. A new detection in 2018 ...with the Neil GehrelsSwift Observatory during a Type II outburst permitted its position to be accurately located and its optical counterpart to be identified. We report X-ray and optical monitoring covering epochs before and during the outburst. Using photometric data, we show the long-term variability of the Be disc where we present flux and colour changes associated with the disc growth and decay over a period of ∼6000 d. We show evidence of disc growth during the recent outburst through an increase in the H α equivalent width and photometric flux. Period analysis was performed using both optical photometric and spectroscopic data, but with no significant detection of an orbital period. A modest periodic signature of 2.65 d was detected from the Optical Gravitational Lensing Experiment (OGLE) I-band data, but we attribute that to the non-radial pulsations of the Be star. We also obtained a blue spectrum from the Southern African Large Telescope, which permits us to classify the spectral type as B0.5 IV–V.
ABSTRACT
In this paper we report on the optical and X-ray behaviour of the Be X-ray binary, SXP 91.1, during a recent type I outburst. We monitored the outburst using the Neil Gehrels Swift ...Observatory. These data were supported by optical data from the Southern African Large Telescope and the Optical Gravitational Lensing Experiment (OGLE) to show the circumstellar disc activity. Matter from this disc accretes on to the neutron star, giving rise to the X-ray outburst as seen in the synchronous evolution of the optical and X-ray light curves. Using data taken with OGLE we show that the circumstellar disc has exhibited stable behaviour over two decades. A positive correlation is seen between the colour and magnitude from the OGLE and massive compact halo object observations, which indicates that the disc is orientated at relatively low-inclination angles. From the OGLE and Swift data, we demonstrate that the system has shown relative phase offsets that have persisted for many years. The spin period derivative is seen to be at maximum spin-up at phases when the mass accretion rate is at maximum. We show that the neutron star in SXP 91.1 is an unusual member of its class in the sense that it has had a consistent spin period derivative over many years, with the average spin-up rate being one of the highest for known Small Magellanic Cloud pulsars. The most recent measurements of the spin-up rate reveal higher values than the global trend, which is attributed to the recent mass accretion event leading to the current outburst.
Context.
Using data from eROSITA, the soft X-ray instrument aboard Spectrum-Roentgen-Gamma (SRG), we report the discovery of two new hard transients, eRASSU J050810.4–660653 and eRASSt ...J044811.1–691318, in the Large Magellanic Cloud. We also report the detection of the Be/X-ray binary RX J0501.6–7034 in a bright state.
Aims.
We initiated follow-up observations to investigate the nature of the new transients and to search for X-ray pulsations coming from RX J0501.6–7034.
Methods.
We analysed the X-ray spectra and light curves from our
XMM-Newton
observations, obtained optical spectra using the South African Large Telescope to look for Balmer emission lines and utilised the archival data from the Optical Gravitational Lensing Experiment (OGLE) for the long-term monitoring of the optical counterparts.
Results.
We find X-ray pulsations for eRASSU J050810.4–660653, RX J0501.6–7034, and eRASSt J044811.1–691318 of 40.6 s, 17.3 s, and 784 s, respectively. The H
α
emission lines with equivalent widths of −10.4 Å (eRASSU J050810.4–660653) and −43.9 Å (eRASSt J044811.1–691318) were measured, characteristic for a circumstellar disc around Be stars. The OGLE
I
- and
V
-band light curves of all three systems exhibit strong variability. A regular pattern of deep dips in the light curves of RX J0501.6–7034 suggests an orbital period of ∼451 days.
Conclusions.
We identify the two new hard eROSITA transients eRASSU J050810.4–660653 and eRASSt J044811.1–691318 and the known Be/X-ray binary RX J0501.6–7034 as Be/X-ray binary pulsars.
Context.
The Magellanic Clouds host a large population of high-mass X-ray binary (HMXB) systems, and although the Large Magellanic Cloud (LMC) is an order of magnitude more massive than the Small ...Magellanic Cloud, there are significantly fewer known HMXBs in the former.
Aims.
We conducted a search for new HMXBs in
XMM-Newton
observations that were performed with the aim of investigating supernova remnant candidates in the supergiant shells LMC5 and LMC7. The three observed fields are located in regions that have not been widely explored in the X-ray band.
Methods.
We analysed the
XMM-Newton
data to look for sources with hard X-ray spectrum and their counterparts with optical colours and brightness values that are typical of HMXBs.
Results.
We report the discovery of three new Be/X-ray binaries, two of them showing pulsations in their X-ray flux. With a luminosity of 6.5 × 10
34
erg s
−1
, we see that XMMU J045315.1−693242 in LMC7 was relatively X-ray faint. The long-term OGLE
I
-band light curve of the
V
= 15.5 mag counterpart suggests a 49.6 day or 24.8 day orbital period for the binary system. Then, XMMU J045736.9−692727, which is also located in LMC7, was brighter, with a luminosity of 5.6 × 10
35
erg s
−1
and hard spectrum with a power-law photon index of 0.63. The X-ray flux revealed clear pulsations with a period of 317.7 s. We obtained optical high resolution spectra from the
V
= 14.2 mag counterpart using the SALT-HRS spectrograph. H
α
and H
β
were observed in emission with complex line profiles and equivalent widths of −8.0 Å and −1.3 Å, respectively. The
I
-band light curve obtained from OGLE shows a series of four strong outbursts followed by a sudden drop in brightness by more than 1 mag within 73–165 days and a recovery to the level from before the outbursts. RX J0524.2−6620, previously classified as X-ray binary candidate, is located at the eastern part of LMC5. We report the discovery of 360.7 s pulsations. During the
XMM-Newton
observation the luminosity was at ∼4 × 10
35
erg s
−1
and the source showed a hard spectrum with a power-law photon index of 0.78. The H
α
emission line profile obtained from SALT-HRS is characterised by two broad peaks with a separation corresponding to ∼178 km s
−1
, along with an equivalent width of −4.2 Å. The long-term OGLE
I
-band light curve of the
V
= 14.9 mag counterpart reveals a quasi-periodic flaring activity while the colour evolution during the flares follows a hysteresis loop with redder colour during the rise. Based on the modelling the H
α
line profiles measured from XMMU J045736.9−692727 and RX J0524.2−6620, we derived constraints on the size of the Be disks.
Conclusions.
Our discovery of two pulsars among three new Be/X-ray binaries increases the number of known HMXB pulsars in the LMC to 25.
Context.
The Small Magellanic Cloud (SMC) hosts many known high-mass X-ray binaries (HMXBs), and all but one (SMC X-1) have a Be companion star. Through the calibration and verification phase of ...eROSITA on board the Spektrum-Roentgen-Gamma (SRG) spacecraft, the Be/X-ray binary XMMU J010429.4-723136 was in the field of view during observations of the supernova remnant, 1E0102.2-7219, used as a calibration standard.
Aims.
We report timing and spectral analyses of XMMU J010429.4-723136 based on three eROSITA observations of the field, two of which were performed on 2019 November 7-9, with the third on 2020 June 18-19. We also reanalyse the OGLE-IV light curve for that source in order to determine the orbital period.
Methods.
We performed a Lomb-Scargle periodogram analysis to search for pulsations (from the X-ray data) and for the orbital period (from the OGLE data). X-ray spectral parameters and fluxes were retrieved from the best-fit model.
Results.
We detect, for the first time, the pulsations of XMMU J010429.4-723136 at a period of -164 s, and therefore designate the source as SXP 164. From the spectral fitting, we derive a source flux of ~1 × 10
−12
erg s
−1
cm
−2
for all three observations, corresponding to a luminosity of ~4 × 10
35
erg s
−1
at the distance of the SMC. Furthermore, reanalysing the OGLE light curve, including the latest observations, we find a significant periodic signal that we believe is likely be the orbital period; at 22.3 days, this is shorter than the previously reported values. The
Swift/XRT
light curve, extracted from two long monitorings of the field and folded at the same period, suggests that a modulation is also present in the X-ray data.
The VLT-FLAMES survey of massive stars Lennon, D. J.; Dufton, P. L.; Villaseñor, J. I. ...
Astronomy and astrophysics (Berlin),
09/2022, Letnik:
665
Journal Article
Recenzirano
Context.
NGC 2004#115 was classified as a single lined Be spectroscopic binary in the Large Magellanic Cloud. Its H
α
morphology is reminiscent of the Galactic systems LB-1 and HR 6819, both of which ...are proposed as either Be+BH or Be+stripped He-star systems.
Aims.
Multi-epoch optical spectra of NGC 2004#115 are used to determine if this binary can be explained by either of these two scenarios, and hence shed additional light on these interesting systems.
Methods.
VLT-FLAMES and SALT-HRS data covering a baseline of ∼20 years were analyzed to determine radial velocities and orbital parameters, while non-LTE model atmospheres were used to determine stellar parameters and the relative brightness of the system components. Archive MACHO,
Gaia
, and
XMM-Newton
data provide additional constraints on the system.
Results.
NGC 2004#115 is found to be a triple system consisting of an inner binary with a period
P
= 2.92 d, eccentricity
e
∼ 0.0, and mass function
f
= 0.07
M
⊙
. The only firmly detected star in this inner binary is a B2 star, the primary, with a projected rotational velocity (
v
e
sin
i
) of 10 km s
−1
and a luminosity of log
L
/
L
⊙
= 3.87. It contributes ∼60% of the total
V
-band light, with the tertiary contributing the other ∼40% of the light, while the secondary is not detected in the optical spectrum. The possibility that the primary is a low mass inflated stripped star is excluded since its Roche radius would be smaller than its stellar radius in such a compact system. A main sequence star of mass 8.6
M
⊙
is therefore inferred; however, the assumption of synchronous rotation leads to a secondary mass in excess of 25
M
⊙
, which would therefore be a black hole. The tertiary is detected as a fainter blended component to the hydrogen and helium lines, which is consistent with a slightly less massive B-type star, though with
v
e
sin
i
∼ 300 km s
−1
. The data do not permit the characterization of the outer period, though it likely exceeds 120 days and is therefore in a stable configuration. The disk-like emission is variable, but may be associated with the inner binary rather than the rapidly rotating tertiary.
XMM-Newton
provides an upper limit of 5 × 10
33
ergs s
−1
in the 0.2–12 keV band which is consistent with, though not constraining, the system hosting a quiescent B+BH binary. A number of caveats to this scenario are discussed.
Ongoing all-sky surveys by the eROSITA and the
Mikhail Pavlinsky
ART-XC telescopes on board the Spectrum-Roentgen-Gamma (SRG) mission have already revealed over a million of X-ray sources. One of ...them, SRGA J124404.1–632232/SRGU J124403.8–632231, was detected as a new source in the third (of the planned eight) consecutive X-ray surveys by ART-XC. Based on the properties of the identified optical counterpart, it was classified as a candidate X-ray binary. We report on the follow-up observations of this source with the Nuclear Spectroscopic Telescope Array, the
Neil Gehrels Swift
Observatory, and the Southern African Large Telescope, which allowed us to unambiguously confirm the initial identification and establish SRGU J124403.8–632231 as a new X-ray pulsar with a spin period of ~538 s and a Be-star companion, making it one of the first Galactic X-ray pulsars discovered by the SRG.
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