arXiv subjects

F. Haberl

Publications and source records attributed to F. Haberl.

At least 37 records · Page 2Linked to original sources

arXiv2024

Thermally emitting isolated neutron star candidates from the SRG/eROSITA All-Sky Survey

The SRG/eROSITA All-Sky Survey (eRASS) allows for the creation of a complete sample of X-ray dim isolated neutron stars (XDINSs), which will significantly facilitate the study of their population properties, evolution, and connection to other families of isolated neutron stars (INSs). In this work, we conduct a systematic search for XDINSs on the western Galactic hemisphere and discuss the resulting candidate sample. Consistently with the properties of the known XDINSs, we selected all eRASS sources possessing a soft X-ray spectral distribution and that are unlikely to be associated with optical or infrared sources. Our selection criteria allowed us to recover all known XDINSs and previously proposed candidates. In addition, we put forward 33 new candidate members for dedicated follow-up identification campaigns. We found the resulting candidate sample to be about 30-50% complete, mainly due to source confusion and the stringent cross-matching criteria adopted. The candidates of the sample presented here can be divided into two groups: 13 soft and 20 somewhat hard X-ray emitters. Interestingly, the thermal nature, spatial distribution, lack of known counterparts, and absence of significant flux variability of the candidates in the first group agree well with the properties of other confirmed thermally emitting INSs. For the candidates in the second group, the current observational data do not allow one to discern between rotation-powered or recycled pulsars, cataclysmic variables, or quiescent neutron stars in binary systems or even to rule out an extragalactic nature. On the basis of population synthesis and the estimated source completeness of the search, we expect that between one and three new XDINSs are among the already singled-out list of XDINS candidates - a long-sought increase in the proposed number of members of this elusive class of X-ray emitters.

astro-ph.HE↗

arXiv2024

The first all-sky survey of star-forming galaxies with eROSITA: Scaling relations and a population of X-ray luminous starbursts

We present a study of X-ray normal galaxies using data from the first all-sky scan of the eROSITA X-ray survey. eRASS1 provides the first unbiased X-ray census of normal galaxies allowing us to study the X-ray emission from XRBs and the hot ISM in the full range of stellar population parameters present in the local Universe. By combining the HECATE value-added galaxy catalogue with the eRASS1, we study the X-ray emission from normal galaxies as a function of their SFR, M$_{*}$, Metallicity, and stellar population age. After applying optical and mid-IR activity classification criteria, we constructed a sample of 18790 star-forming galaxies with measurements of their L$_{X}$. By stacking the X-ray data in SFR-M$_{*}$-distance bins we study the correlation between the average L$_{X}$ and stellar population parameters. We also present updated L$_{\rm{X}}$-SFR and L$_{\rm{X}}$/SFR-Metallicity scaling relations accounting for the scatter dependence on the SFR. We find that the integrated L$_{X}$ of the HEC-eR1 star-forming galaxies is significantly elevated with respect to that expected from the current scaling relations. The observed scatter is also significantly larger. This excess persists even when we measure the average L$_{X}$ of galaxies in SFR-M$_{*}$-distance and metallicity bins and it is stronger in lower SFRs. The excess is not the result of hot gas, LMXBs, background AGN, LLAGN (including TDEs), or stochastic sampling of the XRB XLF. We find that while the excess correlates with lower metallicity, its primary driver is the age of the stellar populations. Our analysis reveals a sub-population of X-ray luminous starbursts with high sSFRs, low metallicities, and young stellar populations. This population drives upwards the X-ray scaling relations for star-forming galaxies, and has important implications for understanding the population of XRBs in the local and high-z Universe.

astro-ph.GA↗

arXiv2024

Detection of pulsed X-ray emission from the isolated neutron star candidate eRASSU J131716.9-402647

The X-ray source eRASSU J131716.9-402647 was recently identified from observations with Spectrum Roentgen Gamma (SRG)/eROSITA as a promising X-ray dim isolated neutron star (XDINS) candidate on the premise of a soft energy distribution, absence of catalogued counterparts, and a high X-ray-to-optical flux ratio. Here, we report the results of a multi-wavelength observational campaign with XMM-Newton, NICER and the FORS2 instrument at the ESO-VLT. We found in both the XMM-Newton and NICER data that the X-ray emission is strongly pulsed at a period of $12.757$ s (pulsed fraction $p_\mathrm{f} = (29.1 \pm 2.6)$% in the 0.2-2 keV band). The pulse profile is double-humped, and the pulsed fraction increases with energy. The XMM-Newton and NICER epochs allow us to derive a 3$σ$ upper limit of $\dot{P}\leq 8\times 10^{-11}$ s s$^{-1}$ on the spin-down rate of the neutron star. The source spectrum is well described by a purely thermal continuum, either a blackbody with $kT\sim95$ eV or a magnetised neutron star atmosphere model with $kT \sim 35$ eV. Similarly to other thermally emitting isolated neutron stars, we found in either case strong deviations from the continuum, a broad absorption feature at energy $\sim260$ eV and a narrow one around $590$ eV. The FORS2 instrument at ESO-VLT has not detected the optical counterpart ($m_\mathrm{R}>27.5$ mag, $5σ$ detection limit), implying an X-ray-to-optical flux ratio of $10^4$ at least. The properties of eRASSU J131716.9-402647 strongly resemble those of a highly magnetised isolated neutron star and favour an XDINS or high-B pulsar nature.

astro-ph.HE↗

arXiv2024

eRASSUJ060839.5-704014: A double degenerate ultra-compact binary in the direction of the LMC

Context. During four all-sky surveys (eRASS1--4), eROSITA, the soft X-ray instrument aboard Spektrum-Roentgen-Gamma (SRG) detected a new supersoft X-ray source, eRASSU J060839.5-704014, in the direction of the Large Magellanic Cloud (LMC). Methods. We arranged follow-up observations in the X-ray and optical wavelengths and further searched in archival observations to reveal the nature of the object. Results. We discover pulsations at ~374 s with a pulse profile consistent with 100% modulation. We identify two other periodicities in the eROSITA data, which we establish as aliases due to the sampling of the eROSITA light curve. We identify a multi-wavelength counterpart to the X-ray source in UVW1 and g, r, i, and z images obtained by the optical/UV monitor on XMM-Newton and the Dark Energy Camera at the Cerro Tololo Inter-American Observatory. The timing and spectral characteristics of the source are consistent with a double degenerate ultra-compact binary system in the foreground of the LMC. eRASSU J060839.5-704014 belongs to a rare class of AM CVns, which are important to study in the context of progenitors of SN Ia and for persistent gravitational wave detection. Conclusions. We identify eRASSU J060839.5-704014 as a new double degenerate ultra-compact binary located in the foreground of the LMC.

astro-ph.HE↗

arXiv2024

The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere

The eROSITA telescope array aboard the Spektrum Roentgen Gamma (SRG) satellite began surveying the sky in December 2019, with the aim of producing all-sky X-ray source lists and sky maps of an unprecedented depth. Here we present catalogues of both point-like and extended sources using the data acquired in the first six months of survey operations (eRASS1; completed June 2020) over the half sky whose proprietary data rights lie with the German eROSITA Consortium. We describe the observation process, the data analysis pipelines, and the characteristics of the X-ray sources. With nearly 930000 entries detected in the most sensitive 0.2-2.3 keV energy range, the eRASS1 main catalogue presented here increases the number of known X-ray sources in the published literature by more than 60%, and provides a comprehensive inventory of all classes of X-ray celestial objects, covering a wide range of physical processes. A smaller catalogue of 5466 sources detected in the less sensitive but harder 2.3-5 keV band is the result of the first true imaging survey of the entire sky above 2 keV. We show that the number counts of X-ray sources in eRASS1 are consistent with those derived over narrower fields by past X-ray surveys of a similar depth, and we explore the number counts variation as a function of the location in the sky. Adopting a uniform all-sky flux limit (at 50% completeness) of F_{0.5-2 keV} > 5 \times 10^{-14}$ erg\,s$^{-1}$\,cm$^{-2}$, we estimate that the eROSITA all-sky survey resolves into individual sources about 20% of the cosmic X-ray background in the 1-2 keV range. The catalogues presented here form part of the first data release (DR1) of the SRG/eROSITA all-sky survey. Beyond the X-ray catalogues, DR1 contains all detected and calibrated event files, source products (light curves and spectra), and all-sky maps. Illustrative examples of these are provided.

astro-ph.HE↗

arXiv2024

The MeerKAT 1.3 GHz Survey of the Small Magellanic Cloud

We present new radio continuum images and a source catalogue from the MeerKAT survey in the direction of the Small Magellanic Cloud (SMC). The observations, at a central frequency of 1.3 GHz across a bandwidth of 0.8 GHz, encompass a field of view ~7 x 7 degrees and result in images with resolution of 8 arcsec. The median broad-band Stokes I image Root Mean Squared noise value is ~11 microJy/beam. The catalogue produced from these images contains 108,330 point sources and 517 compact extended sources. We also describe a UHF (544-1088 MHz) single pointing observation. We report the detection of a new confirmed Supernova Remnant (SNR) (MCSNR J0100-7211) with an X-ray magnetar at its centre and 10 new SNR candidates. This is in addition to the detection of 21 previously confirmed SNRs and two previously noted SNR candidates. Our new SNR candidates have typical surface brightness an order of magnitude below those previously known, and on the whole they are larger. The high sensitivity of the MeerKAT survey also enabled us to detect the bright end of the SMC Planetary Nebulae (PNe) sample - point-like radio emission is associated with 38 of 102 optically known PNe, of which 19 are new detections. Lastly, we present the detection of three foreground radio stars amidst 11 circularly polarised sources, and a few examples of morphologically interesting background radio galaxies from which the radio ring galaxy ESO 029-G034 may represent a new type of radio object.

astro-ph.GA↗

arXiv2023

O Corona, where art thou? eROSITA's view of UV-optical-IR variability-selected massive black holes in low-mass galaxies

Finding massive black holes (MBHs, $M_{BH}\approx10^4-10^7 M_{\odot}$) in the nuclei of low-mass galaxies ($M_{*}\lessapprox10^{10} M_{\odot}$) is crucial to constrain seeding and growth of black holes over cosmic time, but it is particularly challenging due to their low accretion luminosities. Variability selection via long-term photometric ultraviolet, optical, or infrared (UVOIR) light curves has proved effective and identifies lower-Eddington ratios compared to broad and narrow optical spectral lines searches. In the inefficient accretion regime, X-ray and radio searches are effective, but they have been limited to small samples. Therefore, differences between selection techniques have remained uncertain. Here, we present the first large systematic investigation of the X-ray properties of a sample of known MBH candidates in dwarf galaxies. We extracted X-ray photometry and spectra of a sample of $\sim200$ UVOIR variability-selected MBHs and significantly detected 17 of them in the deepest available \emph{SRG}/eROSITA image, of which four are newly discovered X-ray sources and two are new secure MBHs. This implies that tens to hundreds of LSST MBHs will have SRG/eROSITA counterparts, depending on the seeding model adopted. Surprisingly, the stacked X-ray images of the many non-detected MBHs are incompatible with standard disk-corona relations, typical of active galactic nuclei, inferred from both the optical and radio fluxes. They are instead compatible with the X-ray emission predicted for normal galaxies. After careful consideration of potential biases, we identified that this X-ray weakness needs a physical origin. A possibility is that a canonical X-ray corona might be lacking in the majority of this population of UVOIR-variability selected low-mass galaxies or that unusual accretion modes and spectral energy distributions are in place for MBHs in dwarf galaxies.

astro-ph.GA↗

arXiv2023

ATCA Study of Small Magellanic Cloud Supernova Remnant 1E 0102.2-7219

We present new and archival Australia Telescope Compact Array and Atacama Large Millimeter/submillimeter Array data of the Small Magellanic Cloud supernova remnant 1E 0102.2-7219 at 2100, 5500, 9000, and 108000 MHz; as well as Hi data provided by the Australian Square Kilometre Array Pathfinder. The remnant shows a ring-like morphology with a mean radius of 6.2 pc. The 5500 MHz image reveals a bridge-like structure, seen for the first time in a radio image. This structure is also visible in both optical and X-ray images. In the 9000 MHz image we detect a central feature that has a flux density of 4.3 mJy but rule out a pulsar wind nebula origin, due to the lack of significant polarisation towards the central feature with an upper limit of 4 per cent. The mean fractional polarisation for 1E 0102.2-7219 is 7 +- 1 and 12 +- 2 per cent for 5500 and 9000 MHz, respectively. The spectral index for the entire remnant is -0.61 +- 0.01. We estimate the line-of-sight magnetic field strength in the direction of 1E 0102.2-7219 of ~44 microG with an equipartition field of 65 +- 5 microG. This latter model, uses the minimum energy of the sum of the magnetic field and cosmic ray electrons only. We detect an Hi cloud towards this remnant at the velocity range of ~160-180 km s-1 and a cavity-like structure at the velocity of 163.7-167.6 km s-1. We do not detect CO emission towards 1E 0102.2-7219.

astro-ph.HE↗

arXiv2023

Discovery of a magnetar candidate X-ray pulsar in the Large Magellanic Cloud

During a systematic search for new X-ray pulsators in the XMM-Newton archive, we discovered a high amplitude ($PF\simeq86\%$) periodic ($P\simeq7.25\,\mathrm{s}$) modulation in the X-ray flux of 4XMM J045626.3-694723 (J0456 hereafter), a previously unclassified source in the Large Magellanic Cloud (LMC). The period of the modulation is strongly suggestive of a spinning neutron star (NS). The source was detected only during one out of six observations in 2018-2022. Based on an absorbed power-law spectral model with photon slope of $Γ\simeq 1.9$, we derive a 0.3-10 keV luminosity of $L_\mathrm{X}\simeq2.7\times10^{34}$ erg cm$^{-2}$ s$^{-1}$ for a distance of 50 kpc. The X-ray properties of J0456 are at variance with those of variable LMC X-ray pulsars hosted in high-mass X-ray binary systems with a Be-star companion. Based on SALT spectroscopic observations of the only optical object that matches the X-ray uncertainty region, we cannot completely rule out that J0456 is a NS accreting from a late-type (G8-K3) star, an as-yet-unobserved binary evolutionary outcome in the MCs. We show that the source properties are in better agreement with those of magnetars. J0456 may thus be second known magnetar in the LMC after SGR 0526-66.

astro-ph.HE↗

arXiv2023

Discovery of two promising isolated neutron star candidates in the SRG/eROSITA All-Sky Survey

We report the discovery of the isolated neutron star (INS) candidates eRASSU J065715.3+260428 and eRASSU J131716.9-402647 from the Spectrum Roentgen Gamma (SRG) eROSITA All-Sky Survey. Selected for their soft X-ray emission and absence of catalogued counterparts, both objects were recently targeted with the Large Binocular Telescope and the Southern African Large Telescope. The absence of counterparts down to deep optical limits (25 mag, 5$σ$) and, as a result, large X-ray-to-optical flux ratios in both cases strongly suggest an INS nature. The X-ray spectra of both sources are well described by a simple absorbed blackbody, whereas other thermal and non-thermal models (e.g. a hot-plasma emission spectrum or power law) are disfavoured by the spectral analysis. Within the current observational limits, and as expected for cooling INSs, no significant variation ($>2σ$) has been identified over the first two-year time span of the survey. Upcoming dedicated follow-up observations will help us to confirm the candidates' nature.

astro-ph.HE↗

arXiv2023

A helium-burning white dwarf binary as a supersoft X-ray source

Type Ia supernovae are cosmic distance indicators, and the main source of iron in the Universe, but their formation paths are still debated. Several dozen supersoft X-ray sources, in which a white dwarf accretes hydrogen-rich matter from a non-degenerate donor star, have been observed and suggested as Type Ia supernovae progenitors. However, observational evidence for hydrogen, which is expected to be stripped off the donor star during the supernova explosion, is lacking. Helium-accreting white dwarfs, which would circumvent this problem, have been predicted for more than 30 years, also including their appearance as supersoft X-ray sources, but have so far escaped detection. Here we report a supersoft X-ray source with an accretion disk whose optical spectrum is completely dominated by helium, suggesting that the donor star is hydrogen-free. We interpret the luminous and supersoft X-rays as due to helium burning near the surface of the accreting white dwarf. The properties of our system provides evidence for extended pathways towards Chandrasekhar mass explosions based on helium accretion, in particular for stable burning in white dwarfs at lower accretion rates than expected so far. This may allow to recover the population of the sub-energetic so-called Type Iax supernovae, up to 30% of all Type Ia supernovae, within this scenario.

astro-ph.HE↗

arXiv2023

SRG/eROSITA-triggered XMM-Newton observations of three Be/X-ray binaries in the LMC: Discovery of X-ray pulsations

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. 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. 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. 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 Halpha emission lines with equivalent widths of -10.4 A (eRASSU J050810.4-660653) and -43.9 A (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. 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.

astro-ph.HE↗

arXiv2023

Study of the excess Fe XXV line emission in the central degrees of the Galactic centre using XMM-Newton data

The diffuse Fe XXV (6.7 keV) line emission observed in the Galactic ridge is widely accepted to be produced by a superposition of a large number of unresolved X-ray point sources. In the very central degrees of our Galaxy, however, the existence of an extremely hot ($\sim$7 keV) diffuse plasma is still under debate. In this work we measure the Fe XXV line emission using all available XMM-Newton observations of the Galactic centre (GC) and inner disc ($-10^{\circ}$$<\ell<10^{\circ}$, $-2^{\circ}<b<2^{\circ}$). We use recent stellar mass distribution models to estimate the amount of X-ray emission originating from unresolved point sources, and find that within a region of $\ell=\pm1^{\circ}$ and $b=\pm0.25^\circ$ the 6.7 keV emission is 1.3 to 1.5 times in excess of what is expected from unresolved point sources. The excess emission is enhanced towards regions where known supernova remnants are located, suggesting that at least a part of this emission is due to genuine diffuse very hot plasma. If the entire excess is due to very hot plasma, an energy injection rate of at least $\sim6\times10^{40}$ erg s$^{-1}$ is required, which cannot be provided by the measured supernova explosion rate or past Sgr A$^{*}$ activity alone. However, we find that almost the entire excess we observe can be explained by assuming GC stellar populations with iron abundances $\sim$1.9 times higher than those in the bar/bulge, a value that can be reproduced by fitting diffuse X-ray spectra from the corresponding regions. Even in this case, a leftover X-ray excess is concentrated within $\ell=\pm0.3^{\circ}$ and $b=\pm0.15^\circ$, corresponding to a thermal energy of $\sim2\times10^{52}$ erg, which can be reproduced by the estimated supernova explosion rate in the GC. Finally we discuss a possible connection to the observed GC Fermi-LAT excess.

astro-ph.HE↗

arXiv2022

eRASSt J040515.6-745202, an X-ray burster in the Magellanic Bridge

During the third all-sky survey (eRASS3), eROSITA, the soft X-ray instrument aboard Spectrum-Roentgen-Gamma, detected a new hard X-ray transient, eRASSt J040515.6-745202, in the direction of the Magellanic Bridge. We arranged follow-up observations and searched for archival data to reveal the nature of the transient. Using X-ray observations with XMM-Newton, NICER, and Swift, we investigated the temporal and spectral behaviour of the source for over about 10 days. The X-ray light curve obtained from the XMM-Newton observation with an 28 ks exposure revealed a type-I X-ray burst with a peak bolometric luminosity of at least 1.4e37 erg/s. The burst energetics are consistent with a location of the burster at the distance of the Magellanic Bridge. The relatively long exponential decay time of the burst of 70 s indicates that it ignited in a H-rich environment. The non-detection of the source during the other eROSITA surveys, twelve and six months before and six months after eRASS3, suggests that the burst was discovered during a moderate outburst which reached 2.6e36 erg/s in persistent emission. During the NICER observations, the source showed alternating flux states with the high level at a similar brightness as during the XMM-Newton observation. This behaviour is likely caused by dips as also seen during the last hour of the XMM-Newton observation. Evidence for a recurrence of the dips with a period of 21.8 hr suggests eRASSt J040515.6-745202 is a low-mass X-ray binary (LMXB) system with an accretion disk seen nearly edge on. We identify a multi-wavelength counterpart to the X-ray source in UVW1 and g, r, i, and z images obtained by the optical/UV monitor on XMM-Newton and the Dark Energy Camera at the Cerro Tololo Inter-American Observatory. (abbreviated)

astro-ph.HE↗

arXiv2022

New ASKAP Radio Supernova Remnants and Candidates in the Large Magellanic Cloud

We present a new Australian Square Kilometre Array Pathfinder (ASKAP) sample of 14 radio Supernova Remnant (SNR) candidates in the Large Magellanic Cloud (LMC). This new sample is a significant increase to the known number of older, larger and low surface brightness LMC SNRs. We employ a multi-frequency search for each object and found possible traces of optical and occasionally X-ray emission in several of these 14 SNR candidates. One of these 14 SNR candidates (MCSNR J0522-6543) has multi-frequency properties that strongly indicate a bona fide SNR. We also investigate a sample of 20 previously suggested LMC SNR candidates and confirm the SNR nature of MCSNR J0506-6815. We detect lower surface brightness SNR candidates which were likely formed by a combination of shock waves and strong stellar winds from massive progenitors (and possibly surrounding OB stars). Some of our new SNR candidates are also found in a lower density environments in which SNe type Ia explode inside a previously excavated interstellar medium (ISM).

astro-ph.HE↗

arXiv2022

Abundance and temperature of the outer hot circum-Galactic medium: The SRG/eROSITA view of the soft X-ray background in the eFEDS field

Despite their vital importance to understand galaxy evolution and our own Galactic ecosystem, our knowledge of the physical properties of the hot phase of the Milky Way is still inadequate. However, sensitive SRG/eROSITA large area surveys are now providing us with the long sought-after data needed to mend this state of affairs. We present the properties of the soft X-ray emission as observed by eROSITA in the eFEDS field. We measure the temperature and metal abundance of the hot circum-Galactic medium (CGM) to be within $kT_{CGM}=0.153-0.178$ keV and $Z_{CGM}=0.052-0.072$ $Z_\odot$, depending on the contribution of solar wind charge exchange (SWCX). Slightly larger CGM abundances $Z_{CGM}=0.05-0.10$ $Z_\odot$ are possible, considering the uncertain extrapolation of the extragalactic Cosmic X-ray background (CXB) emission below $\sim1$ keV. To recover CGM abundances as large as $Z_{CGM}=0.3$ $Z_\odot$, it must be postulated the presence of an additional component, likely associated with the warm-hot intergalactic medium, providing $\sim15-20$% of the flux in the soft X-ray band. The emission in the soft band is dominated by the CGM, with contributions from the CXB and the local hot bubble. Moreover, the eROSITA data require the presence of an additional component associated with the elusive Galactic corona plus a possible contribution from unresolved M dwarf stars. This component has a temperature of $kT\sim0.4-0.7$ keV and it might be out of thermal equilibrium. It contributes $\sim9$% to the total emission in the 0.6--2 keV band, therefore it is a likely candidate to produce part of the unresolved CXB flux observed in X-ray ultra-deep fields. We also observe a significant contribution to the soft X-ray flux due to SWCX, during periods characterised by stronger solar wind activity, and causing the largest uncertainty on the determination of the CGM temperature.

astro-ph.HE↗

arXiv2022

Broadband study and the discovery of pulsations from the Be/X-ray binary eRASSU J052914.9-662446 in the Large Magellanic Cloud

Context. The Magellanic Clouds are our nearest star-forming galaxies. While the population of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud (SMC) is relatively well studied, our knowledge about the Large Magellanic Cloud (LMC) is far from complete given its large angular extent and insufficient coverage with X-ray observations. Aims. We conducted a search for new HMXBs in the LMC using data from eROSITA, the soft X-ray instrument on board the Spektrum-Roentgen-Gamma (SRG) satellite. Methods. After confirming the nature of eRASSU J052914.9-662446 as a hard X-ray source positionally coincident with an early type star, we followed it up with optical spectroscopic observations from South African Large Telescope (SALT) and a dedicated NuSTAR observation. Results. We study the broadband timing and spectral behaviour of the newly discovered HMXB eRASSU J052914.9-662446 through eROSITA, Swift and NuSTAR data in X-rays and the Optical Gravitational Lensing Experiment (OGLE) and SALT RSS data at optical wavelength. We report on detection of the spin period at 1412 s and suggest an orbital period of the system of ~151 days, and thereby establish eRASSU J052914.9-662446 as an accreting pulsar. Further, through optical spectroscopic observations and the existence of H alpha emission the source is identified as a Be X-ray binary pulsar in the LMC. We also investigate the variability of the source in the optical and X-ray regime over the last decades and provide estimates on the possible magnetic field strength of the neutron star.

astro-ph.HE↗

arXiv2022

An X-ray view of the 2021 outburst of SXP 15.6: constraints on the binary orbit and magnetic field of the Neutron Star

We conducted a spectral and temporal analysis of X-ray data from the Be X-ray binary pulsar SXP 15.6 located in the Small Magellanic Cloud based on NuSTAR, NICER and Swift observations during the 2021 outburst. We present for the first time the broadband X-ray spectra of the system based on simultaneous NuSTAR and NICER observations. Moreover we use monitoring data to study the spectral and temporal properties of the system during the outburst. Comparison of the evolution of the 2021 outburst with archival data reveals a consistent pattern of variability with multiple peaks occurring at time intervals similar to the orbital period of the system (~36 d). Our spectral analysis indicates that most of the energy is released at high energies above 10 keV while we found no cyclotron absorption line in the spectrum. Analysis of the spectral evolution during the outburst, we find that the spectrum is softer-when-brighter, which in turn reveals that the system is probably in the super-critical regime where the accretion column is formed. This places an upper limit to the magnetic field of the system of the order of 7$\times$10$^{11}$ G. The spin-evolution of the neutron star (NS) during the outburst is consistent with an NS with a low magnetic field ($\sim{5}\times$10$^{11}$ G), while there is evident orbital modulation which we modelled and derived the orbital parameters. We found the orbit to have a moderate eccentricity of ~0.3. Our estimates of the magnetic field are consistent with the lack of an electron cyclotron resonance scattering feature in the broadband X-ray spectrum.

astro-ph.HE↗