arXiv subjects

Frank Haberl

Publications and source records attributed to Frank Haberl.

At least 19 recordsLinked to original sources

arXiv2026

eRASSU J043115.8-711730 :the first pulsating symbiotic super-soft X-ray source in the Magellanic Bridge

The Magellanic Bridge stellar population is a relic of the tidal interaction between the Large and Small Magellanic Clouds. A comprehensive view of the evolution of the Bridge stellar population requires probing the compact remnants of stellar evolution, otherwise hidden at optical wavelengths. The all-sky survey conducted by the eROSITA instrument on-board the Spectrum Roentgen Gamma observatory has discovered a significant population of compact-object-powered systems in the Bridge using X-ray. The candidate super-soft source eRASSU J043115.8-711730 (hereafter J0431-71) was discovered as a part of this campaign, and we present here a deeper study of this source using XMM-Newton and SALT spectroscopy, long-term optical-infrared photometry using OGLE, ATLAS, ASAS-SN, WISE, and GAIA data. J0431-71 is a highly variable super-soft X-ray source, classified as a red giant with the GAIA color-magnitude diagram. The source exhibits: (a) a thermal X-ray spectrum with a temperature of kT$\sim$30 eV and a bright state luminosity of $3.2\times10^{37}$~erg~s$^{-1}$ in the 0.15-1 keV band, (b) Balmer emission lines, [Fe X] coronal line, HeII emission, and the Bowen fluorescence blend, (c) an optical and infrared periodicity of $\sim$500-560 days in phase with the X-ray-UV emission, (d) a 'redder-when-brighter' trend in the stellar emission with a $\sim$520 day period indicating a pulsating donor star. We argue that the observed spectral and temporal properties in J0431-71 are consistent with a high-accretion rate onto a white-dwarf via Roche-lobe overflow, making J0431-71 the first symbiotic source discovered in the Bridge.

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arXiv2026

Rapid Orbital Decay in the Ultracompact Double-degenerate Binary eRASSU J060839.5$-$704014

We present timing and spectral analysis of the recently identified ultracompact double-degenerate (DD) white dwarf binary eRASSU J060839.5$-$704014 using observations from NICER and Einstein Probe (EP), together with archival XMM-Newton data. By phase-connecting the long-term XMM-Newton, NICER, and EP observations, we obtain a coherent quadratic timing solution, yielding an orbital period of 374.15013 (2) s and an orbital decay rate of $\dot{P}= -4.7\,(1) \times 10^{-11} \mathrm{~s~s^{-1}}$. This orbital decay exceeds that measured in the prototypical DD binaries HM Cnc and V407 Vul. Assuming that the observed orbital evolution is primarily driven by gravitational-wave (GW) angular momentum loss, the inferred chirp mass is $\sim0.43\, M_{\odot}$, placing the source among the most massive known systems of this class. The phase-averaged spectra of NICER and EP-Follow-up X-ray Telescope (FXT) are described by a soft thermal component with temperatures of ~126 and ~144 eV, respectively, confirming the supersoft nature of the source. Phase-resolved spectroscopy reveals a clear decrease in temperature across the bright phase in both instruments, indicating a structured emission region with significant temperature gradients. These results establish eRASSU J060839.5$-$704014 as one of the most rapidly evolving ultracompact DD binaries presently known, belonging to the rare class of direct-impact ultracompact binaries, and a promising verification source for future low-frequency GW studies.

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arXiv2026

The SRG/eROSITA diffuse soft X-ray background II. spectra and morphology of the eROSITA bubbles in the western Galactic hemisphere

The eROSITA bubbles (eRObub) were discovered in 2020 in the first SRG/eROSITA All-Sky Survey, and are among the most extended structures in the X-ray sky. Using eROSITA all-sky maps and spatially resolved spectra, we aim to infer the three-dimensional structure and measure the hot gas properties of the eRObub. We fit spectra binned to a constant S/N and high-S/N spectra from custom regions to examine gas properties in more detail. We fit the morphology of eRObub with a parametrised geometrical model that describes a blast wave propagating into an idealised Galactic halo from the centre. We found the interior of the western eRObub is best characterised by two emission components with relatively uniform temperatures: a hotter component at $kT=0.60\pm0.02$ keV, and a colder one at $kT=0.21^{+0.03}_{-0.01}$ keV, where the latter's emission measure is about five times higher on average. Our spectra suggest sub-solar abundances ($Z=0.2\pm0.1 Z_\odot$), consistent with expectations for the Galactic halo, while we find no conclusive evidence for $α$-element enhancement. In contrast, the North Polar Spur exhibits higher abundances ($Z>0.5 Z_\odot$), which, at face value, disfavours a common origin. We spectrally confirm an apparent cool shell at $kT\sim0.18$-$0.2$ keV surrounding the northern eRObub, assuming collisional ionisation equilibrium. We found no noticeable difference in X-ray emission in regions overlapping with the Fermi Bubbles. Our geometrical model suggests that the horizontal size of both eRObub is well-constrained (semi-minor axis $\sim 6$ kpc), but their vertical extent is uncertain, as the observed X-ray emission is almost insensitive to the existence and location of a bubble cap. Additionally, a tilt ($\sim 30^{\circ}$) towards $l\sim 220^{\circ}$ is needed to reproduce the projected image of the northern eRObub, whereas the southern bubble requires little tilt.

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arXiv2026

Broadband study of the Be/X-ray binary pulsar eRASSU J012422.9-724248 in the Magellanic Bridge, near the Eastern Wing of the Small Magellanic Cloud

The first four all-sky surveys with eROSITA the soft X-ray instrument on board the Spektrum-Roentgen-Gamma (SRG) satellite revealed a new X-ray source, eRASSU J012422.9-724248, in the Magellanic Bridge, near the Eastern Wing of the Small Magellanic Cloud (SMC). We performed a broadband timing and spectral analysis using the optical and X-ray data of eRASSU J012422.9-724248. Using the X-ray observations with eROSITA, Swift, NuSTAR and optical data from the optical Gravitational Lensing Experiment (OGLE) and the Las Cumbres Observatory (LCO), we confirm the nature of eRASSU J012422.9-724248 as a Be/X-ray binary (BeXRB) pulsar in the Magellanic bridge. The position is coincident with that of an early-type star (OGLE ID SMC732.10.7). We detect the spin period at 341.71 s in NuSTAR data and infer a period of 63.65 days from the 15 year monitoring with OGLE, that we interpret as the orbital period of the system. A tentative CRSF at ~12.3 keV is identified in NuSTAR spectra with ~1.8-sigma. The source appears to show a persistent X-ray luminosity and an optical magnitude transition on the long timescale. We propose eRASSU J012422.9-724248 is a new member of the class of persistent BeXRBs.

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arXiv2025

Unveiling the soft X-ray source population towards the inner Galactic disk with XMM-Newton

Across the Galactic disk lies a diverse population of X-ray sources, with the fainter end remaining poorly understood due to past survey sensitivity limits. We aim to classify and characterize faint X-ray sources detected in the eROSITA All-Sky Survey (eRASS1) towards the inner Galactic disk ($350^\circ < l < 360^\circ$, $-1^\circ < b < 1^\circ$) using deeper XMM-Newton observations (typical exposure of $\sim 20\,\text{ks}$). We analyzed 189 eRASS1 sources, combining X-ray spectral fitting ($0.2$--$10\,\text{keV}$) with Gaia astrometric and photometric data for robust classification. Our results show that the eRASS1 catalog towards the Galactic disk is overwhelmingly dominated by coronal sources ($\sim 74\%$), primarily active stars and binaries, with $\sim 8\%$ being wind-powered massive stars and $\sim 18\%$ being accreting compact objects. We propose an empirical hardness-ratio cut ($\text{HR} > -0.2$) to efficiently isolate these non-coronal sources. By stacking the classified population and comparing with the Galactic Ridge X-ray Emission (GRXE), we estimate that $\sim 6\%$ of the GRXE flux in the $0.5$--$2.0\,\text{keV}$ band is resolved into point sources above the eRASS1 flux limit ($\sim 5\times 10^{-14}\,\text{erg}\,\text{cm}^{-2}\,\text{s}^{-1}$). This resolved soft-band emission is dominated by active stars, while hard-band flux originates primarily from X-ray binaries. We conclude that the eRASS1 catalog retains a non-negligible population of compact objects that can be effectively distinguished using X-ray color selection.

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arXiv2025

Old Galactic novae in the eROSITA All Sky Survey

Nova explosions occur on accreting white dwarfs. A thermonuclear runaway in the H-rich accreted envelope causes its ejection without destroying the white dwarf, and an increase in the luminosity by several magnitudes. Accretion is re-established some time after the explosion. The explosion of the nova itself is expected to affect the mass-transfer rate from the secondary and the accretion rate, but these effects have been little explored observationally. Most novae are observed only in outburst and the properties of the host systems are unknown. X-ray observations of novae happen mostly during outburst; only a few have been the target of dedicated X-ray observations years or decades after outburst. However, the X-ray emission long after the outburst provides a powerful diagnostics of the accretion rate and the possible magnetic nature of the white dwarf. We have explored the first two years of the SRG/eROSITA All Sky Survey (eRASS) for X-ray sources correlated with Galactic historical novae. We present the first population study of nova hosting systems in X-rays, focus on the evolution of accretion rate as a function of the time since last outburst, and look for new candidates for magnetic systems. In total, 32 X-ray counterparts of novae are found in the western Galactic hemisphere. Combined with 53 nova detections published for the eastern hemisphere, the fraction of X-ray detected novae in quiescence is 18% of the Galactic novae. We have, for the first time, enough statistics to observationally determine the evolution of accretion rate as a function of time since the last nova outburst for a time span of 120 years. The results confirm that magnetic systems remain systematically at higher fluxes and that accretion is enhanced during the first years after the outburst, as predicted theoretically. We also identify new IP candidates in AT Cnc and RR Cha.

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arXiv2025

Stingrays in the radio sky: Two unusual diffuse radio relic sources in the direction of the Magellanic Stream

We present the discovery of two extended, low surface brightness radio continuum sources, each consisting of a near-circular body and an extended tail of emission, nicknamed Stingray 1 (ASKAP J0129-5350) and Stingray 2 (ASKAP J0245-5642). Both are found in the direction of the Magellanic Stream (MS) and were discovered in the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey at 944 MHz. We combine the ASKAP data with low-frequency radio observations from the GaLactic and Extragalactic All-sky MWA Survey (GLEAM) to conduct a radio continuum analysis. We explore both Galactic/near Galactic scenarios, including runaway or circumgalactic supernova remnants (SNRs) and parentless pulsar-wind nebulae (PWNe), and extragalactic scenarios including radio active galactic nuclei (AGNs), dying radio galaxies, galaxy clusters, galaxy pairs or groups, head-tail radio galaxies, and Odd Radio Circles (ORCs), as well as the possibility that the morphology is due to a chance alignment. The Stingrays exhibit non-thermal emission with spectral indices of $α$ = -0.89 $\pm$ 0.09 for Stingray 1 and $α$ = -1.77 $\pm$ 0.06 for Stingray 2. We find that none of the proposed scenarios can explain all of the observed properties, however we determine it most likely that their shape is caused by some kind of complex environmental interaction. The most likely scenario from the available data is that of a head-tail radio galaxy, but more data is required for a definitive classification.

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arXiv2025

Studying the multi-phase interstellar medium in the Large Magellanic Cloud with SRG/eROSITA -- I. Analysis of diffuse X-ray emission

The Large Magellanic Cloud (LMC), being a nearby and actively star-forming satellite galaxy of the Milky Way, is an ideal site to observe the multi-phase interstellar medium (ISM) of a galaxy across the electromagnetic spectrum. We aim to exploit the available SRG/eROSITA all-sky survey data to study the distribution, composition and properties of the diffuse X-ray emitting hot gas in the LMC. We construct multi-band X-ray images of the LMC, reflecting the morphology and temperatures of the diffuse hot gas. By performing spatially resolved X-ray spectroscopy of 175 regions, we constrain the distribution, physical state, and composition of the hot ISM phase throughout the LMC. We combine our constraints with multiwavelength data to obtain a comprehensive view of the different ISM phases. We measure a total X-ray luminosity of the hot ISM phase of $1.9\times10^{38}\,\mathrm{erg\,s^{-1}}$ ($0.2-5.0\,\mathrm{keV}$ band), and constrain its thermal energy to around $5\times10^{54}\,\mathrm{erg}$. The typical density and temperature of the X-ray emitting plasma are around $5\times10^{-3}\,\mathrm{cm^{-3}}$ and $0.25\,\mathrm{keV}$, respectively, with both exhibiting broad peaks in the southeast of the LMC. The observed degree of X-ray absorption correlates strongly with the distribution of foreground HI gas, whereas a spatial anticorrelation between the hot and cold ISM phases is visible on sub-kpc scales within the disk. The abundances of light metals show a strong gradient throughout the LMC, with the north and east exhibiting a strong $α$-enhancement, as expected from observed massive stellar populations there. In contrast, the enigmatic ``X-ray spur'' exhibits a local deficit in $α$-elements, and a peak in hot-gas pressure at $P/k\sim10^5\,\mathrm{K\,cm^{-3}}$, consistent with a dominant energy input through tidally driven gas collisions.

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arXiv2025

A sample of ionised Fe line-emitting X-ray sources in the inner Galactic disc

Previous studies suggest that the Galactic diffuse X-ray emission is composed of unresolved point sources, primarily mCVs. However, nearby mCVs have a much lower 6.7 keV line equivalent width ($\rm EW_{6.7}$) compared to the diffuse X-ray emission. Therefore, the primary contributors to the unresolved X-ray emission remain unclear. We detected a total of 859 sources in the 6.5-7 keV band using XMM-Newton observations of the inner Galactic disc, of which 72 sources show significant iron line emission at 6.7 keV. The distribution of spectral index $Γ$ for these 72 sources is bimodal, with peaks at $Γ=0.5\pm0.4$ and $1.8\pm0.3$, suggesting two populations of sources. The soft X-ray sources have significantly larger $\rm EW_{6.7}$ than the hard X-ray sources. Furthermore, 18 of the 32 hard sources are associated with previously known CVs. We identify CV candidates in our sample as those with spectral index $Γ<1.25$. The line ratio, 2-10 keV luminosity, and previous detection of spin period suggest that most of these hard sources are mCVs. The distribution of the $\rm EW_{6.7}$ line for the combined sample of previously identified and candidate CVs has a mean value of <$\rm EW_{6.7}$>$=415\pm39$ eV. Furthermore, we computed the stacked spectra of all sources detected in the 6.5-7 keV band for different flux groups, and we find evidence in the stacked spectra of hard sources that the $\rm EW_{6.7}$ increases with decreasing flux. The soft X-ray sources have <$\rm EW_{6.7}$>$=1.1\pm0.1$ keV. We identified 13 of the 30 soft sources associated with active stars, young stellar objects, and active binaries of RS CVn type. The <$\rm EW_{6.7}$> of our CV candidate sample is more than twice as large as the typical $\rm EW_{6.7}$ found in mCVs within 500 pc, and the <$\rm EW_{6.7}$> of our CV candidate sample is close to the $\rm EW_{6.7}$ value of Galactic diffuse X-ray emission.

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arXiv2025

A New Radio Continuum Study of the Large Magellanic Cloud Supernova Remnant MC SNR J0519-6902

We present a new radio continuum study of the Large Magellanic Cloud supernova remnant (SNR) MC SNR J0519-6902. With a diameter of ~8 pc, this SNR shows a radio ring-like morphology with three bright regions toward the north, east, and south. Its linear polarisation is prominent with average values of 5 +- 1% and 6 +- 1% at 5500 and 9000 MHz, and we find a spectral index of -0.62 +- 0.02 , typical of a young SNR. The average rotation measure is estimated at -124 +- 83 rad m-2 and the magnetic field strength at ~11 muG. We also estimate an equipartition magnetic field of 72 +- 5 muG and minimum explosion energy of Emin = 2.6x1048 erg. Finally, we identified an H I cloud that may be associated with MC SNR J0519-6902, located in the southeastern part of the remnant, along with a potential wind-bubble cavity.

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arXiv2025

Two decades of optical variability of Small Magellanic Cloud high-mass X-ray binaries

We present an analysis of the long-term optical/IR behavior of 111 high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud based on data from the OGLE collaboration. Most systems exhibit variability on a range of time scales. This variability regulates the mass transfer to the compact object, while the compact object can, in turn, affect the donor star's behavior. To better understand this complex interaction and the resulting X-ray properties in these systems, we define a new taxonomy for the observed super-orbital variability. This taxonomy connects to the color changes, orbital periods, and X-ray behavior of the sources. In most cases, these properties can be explained by differences between the flux of the disk around the Be star and the flux from the star itself. We also refine and present new potential orbital periods and sub-orbital variability in the sources.

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arXiv2024

First Study of the Supernova Remnant Population in the Large Magellanic Cloud with eROSITA

The study of the entire population of SNRs in a galaxy helps us to understand the underlying stellar populations, the environments, in which the SNRs are evolving, and the stellar feedback on the ISM. The all-sky survey carried out by the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on board Spektrum-Roentgen-Gamma (Spektr-RG, SRG) has provided us with spatially and spectrally resolved X-ray data of the entire Large Magellanic Cloud (LMC) and its immediate surroundings in the soft X-ray band down to 0.2 keV. We performed a multiwavelength analysis of previously known SNR candidates and newly detected SNRs and SNR candidates. We applied the Gaussian gradient magnitude (GGM) filter to the eROSITA images of the LMC to highlight the edges of the shocked gas in order to find new SNRs. We compared the X-ray images with those of their optical and radio counterparts to investigate the true nature of the extended emission. We used the Magellanic Cloud Emission Line Survey (MCELS) for the optical data. For the radio comparison, we used data from the Australian Square Kilometre Array Pathfinder (ASKAP) survey of the LMC. Using the VISTA survey of the Magellanic Clouds (VMC) we have investigated the possible progenitors of the new SNRs and SNR candidates in our sample. We present the most updated catalogue of SNRs in the LMC. The eROSITA data have allowed us to confirm 1 of the previous SNR candidates and discover 16 new extended sources. We confirm 3 of them as new SNRs, while we propose the remaining 13 as new X-ray SNR candidates. We also present the first analysis of the follow-up XMM-Newton observation of MCSNR J0456-6533 discovered with eROSITA. Among the new candidates, we propose J0614-7251 (4eRASSU J061438.1-725112) as the first X-ray SNR candidate in the outskirts of the LMC.

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arXiv2024

The hot circumgalactic medium in the eROSITA All-Sky Survey III. Star-forming and quiescent galaxies

The circumgalactic medium (CGM), as the gas repository for star formation, might contain the answer to the mysterious galaxy quenching and bimodal galaxy population origin. We measured the X-ray emission of the hot CGM around star-forming and quiescent galaxies. We detect extended X-ray emission from the hot CGM around star-forming galaxies with $\log(M_*/M_\odot)>11.0$ and quiescent galaxies with $\log(M_*/M_\odot)>10.5$, extending out to $R_{\rm 500c}$. $L_{\rm X, CGM}$ of star-forming galaxies with median stellar masses $\log(M_{\rm *,med}/M_\odot) = 10.7, 11.1, 11.3$ are approximately $0.8\,, 2.3\,, 4.0 \times 10^{40}\,\rm erg/s$, while for quiescent galaxies with $\log(M_{\rm *,med}/M_\odot) = 10.8, 11.1, 11.4$, they are $1.1\,, 6.2\,, 30 \times 10^{40}\,\rm erg/s$. Notably, quiescent galaxies with $\log(M_{\rm *,med}/M_\odot) > 11.0$ exhibit brighter hot CGM than their star-forming counterparts. In halo mass bins, we detect similar X-ray emission around star-forming and quiescent galaxies with $\log(M_{\rm 200m}/M_\odot) > 12.5$, suggesting that galaxies in the same mass dark matter halos host equally bright hot CGM. We emphasize the observed $L_{\rm X, CGM} - M_{\rm 500c}$ relations of star-forming and quiescent galaxies are sensitive to the stellar-to-halo mass relation (SHMR). A comparison with cosmological hydrodynamical simulations (EAGLE, TNG100, and SIMBA) reveals varying degrees of agreement, contingent on the simulation and the specific stellar or halo mass ranges considered. Either selected in stellar mass or halo mass, the star-forming galaxies do not host brighter stacked X-ray emission from the hot CGM than their quiescent counterparts at the same mass range. The result provides useful constraints on the extent of feedback's impacts as a mechanism for quenching star formation as implemented in current cosmological simulations.

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arXiv2024

The hot circumgalactic medium in the eROSITA All-Sky Survey I. X-ray surface brightness profiles

The circumgalactic medium (CGM) provides the material needed for galaxy formation and influences galaxy evolution. The hot ($T>10^6K$) CGM is poorly detected around galaxies with stellar masses ($M_*$) lower than $3\times10^{11}M_\odot$ due to the low surface brightness. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of $z_{\rm spec}<0.2$ and stellar masses of $10.0<\log(M_*/M_\odot)<11.5$ (85,222 galaxies) -- or halo masses of $11.5<\log(M_{\rm 200m}/M_\odot)<14.0$ (125,512 galaxies). By stacking the X-ray emission around galaxies, masking the detected X-ray point sources and carefully modeling the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB), we obtain the X-ray emission from the hot CGM. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius ($R_{\rm vir}$). We used a $β$ model to describe the X-ray surface brightness profile and found $β=0.43^{+0.10}_{-0.06}\,(0.37^{+0.04}_{-0.02})$ for MW-mass (M31-mass) galaxies.We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of $Λ$CDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within $R_{\rm vir}$ to larger radii and found that within $\approx 3 R_{\rm vir}$, the baryon budget is close to the $Λ$CDM cosmology prediction. Our results set a firm footing for the presence of the hot CGM around such galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.

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arXiv2024

The hot circumgalactic medium in the eROSITA All-Sky Survey II. Scaling relations between X-ray luminosity and galaxies' mass

Understanding how the properties of galaxies relate to the properties of the hot circum-galactic medium (CGM) around them can constrain galaxy evolution models. We measured the X-ray luminosity of the hot CGM based on the surface brightness profiles of central galaxy samples measured from Spectrum Roentgen Gamma (SRG)/eROSITA all-sky survey data. We related the X-ray luminosity to the galaxies' stellar and halo mass, and we compared the observed relations to the self-similar model and intrinsic (i.e., not forward-modeled) output of the IllustrisTNG, EAGLE, and SIMBA simulations. The average hot CGM X-ray luminosity ($L_{\rm X,CGM}$) correlates with the galaxy's stellar mass ($M_*$). It increases from $(1.6 \pm 2.1)\times10^{39} \rm erg\,s^{-1}$ to $(3.4 \pm 0.3)\times10^{41} \rm erg\,s^{-1}$, when $\log(M_*)$ increases from 10.0 to 11.5. A power law describes the correlation as $\log(L_{\rm X,CGM})= (2.4\pm 0.1)\times \log(M_*)+(14.6\pm1.5)$. The hot CGM X-ray luminosity as a function of halo mass is measured within $\log(M_{\rm 500c})=11.3-13.7$, extending our knowledge of the scaling relation by more than two orders of magnitude. $L_{\rm X,CGM}$ increases with $M_{\rm 500c}$ from $(3.0 \pm 1.6)\times10^{39}\ \rm erg\,s^{-1}$ at $\log(M_{\rm 500c})=11.3$ to $(1.3 \pm 0.1)\times10^{42}\ \rm erg\,s^{-1}$ at $\log(M_{\rm 500c})=13.7$. The relation follows a power law of $\log(L_{\rm X,CGM})= (1.32\pm 0.05)\times \log(M_{\rm 500c})+(24.1\pm0.7)$. Our observations highlight the necessity of non-gravitational processes at the galaxy group scale while suggesting these processes are sub-dominant at the galaxy scale. We show that the outputs of current cosmological galaxy simulations generally align with the observational results uncovered here but with possibly important deviations in selected mass ranges.

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arXiv2024

XMM-Newton and NuSTAR discovery of a likely IP candidate XMMU J173029.8-330920 in the Galactic Disk

We aim at characterizing the population of low-luminosity X-ray sources in the Galactic plane by studying their X-ray spectra and periodic signals in the light curves. We are performing an X-ray survey of the Galactic disk using XMM-Newton, and the source XMMU J173029.8-330920 was serendipitously discovered in our campaign. We performed a follow-up observation of the source using our pre-approved NuSTAR target of opportunity time. We used various phenomenological models in xspec for the X-ray spectral modeling. We also computed the Lomb-Scargle periodogram to search for X-ray periodicity. A Monte Carlo method was used to simulate 1000 artificial light curves to estimate the significance of the detected period. We also searched for X-ray, optical, and infrared counterparts of the source in various catalogs. The spectral modeling indicates the presence of an intervening cloud with $N_{\rm H}\sim(1.5-2.3)\times10^{23}\ \rm cm^{-2}$ that partially absorbs the incoming X-ray photons. The X-ray spectra are best fit by a model representing emission from a collisionally ionized diffuse gas with plasma temperature $kT=26^{+11}_{-5}$ keV. Furthermore, an Fe $K_α$ line at $6.47^{+0.13}_{-0.06}$ keV was detected with an equivalent width of the line of $312\pm104$ eV. We discovered a coherent pulsation with a period of $521.7\pm0.8$ s. The 3-10 keV pulsed fraction of the source is around $\sim$50-60\%. The hard X-ray emission with plasma temperature $kT=26^{+11}_{-5}$ keV, iron $K_α$ emission at 6.4 keV and a periodic behavior of $521.7\pm0.8$ s suggest XMMU J173029.8-33092 to be an intermediate polar. We estimated the mass of the central white dwarf to be $0.94-1.4\ M_{\odot}$ by assuming a distance to the source of $\sim1.4-5$ kpc.

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arXiv2024

New quasars behind the Magellanic Clouds. II. Spectroscopic confirmation of 136 near-infrared selected candidates

Quasi-stellar objects (QSOs) are a basis for an absolute reference system for astrometric studies. There is a need for creating such system behind nearby galaxies, to facilitate the measuring of the proper motions of these galaxies. However, the foreground contamination from the galaxies themselves is a problem for the QSO identification. We search for new QSOs behind both Magellanic Clouds, the Magellanic Bridge, and the Magellanic Stream. We identify QSO candidates with a combination of near-infrared colors and variability criteria from the public ESO Visual and Infrared Survey Telescope for Astronomy (VISTA) Magellanic Clouds (VMC) survey. We confirm their nature from broad emission lines with low-resolution optical spectroscopy. We confirmed the QSO nature of 136 objects. They are distributed as follows: 12 behind the LMC, 37 behind the SMC, 63 behind the Bridge, and 24 behind the Stream. The QSOs span a redshift range from z~0.1 to z~2.9. A comparison of our quasar selection with the Quaia quasar catalog, based on Gaia low-resolution spectra, yields a selection and confirmation success rate of 6-19%, depending on whether the quality of the photometry, the magnitude ranges and the colors are considered. Our candidate list is rather incomplete, but the objects in it are likely to be confirmed as quasars with ~90% probability. Finally, we report a list of 3609 objects across the entire VMC survey that match our color and variability selection criteria; only 1249 of them have Gaia counterparts. Our combined infrared color and variability criteria for QSO selection prove to be efficient - ~90% of the observed candidates are bona fide QSOs and allow to generate a list of new high-probability quasar candidates.

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arXiv2024

Fast as Potoroo: Radio Continuum Detection of a Bow-Shock Pulsar Wind Nebula Powered by Pulsar J1638-4713

We report the discovery of a bow-shock pulsar wind nebula (PWN), named Potoroo, and the detection of a young pulsar J1638-4713 that powers the nebula. We present a radio continuum study of the PWN based on 20-cm observations obtained from the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. PSR J1638-4713 was identified using Parkes radio telescope observations at frequencies above 3 GHz. The pulsar has the second-highest dispersion measure of all known radio pulsars (1553 pc/cm^3), a spin period of 65.74 ms and a spin-down luminosity of 6.1x10^36 erg/s. The PWN has a cometary morphology and one of the greatest projected lengths among all the observed pulsar radio tails, measuring over 21 pc for an assumed distance of 10 kpc. The remarkably long tail and atypically steep radio spectral index are attributed to the interplay of a supernova reverse shock and the PWN. The originating supernova remnant is not known so far. We estimated the pulsar kick velocity to be in the range of 1000-2000 km/s for ages between 23 and 10 kyr. The X-ray counterpart found in Chandra data, CXOU J163802.6-471358, shows the same tail morphology as the radio source but is shorter by a factor of 10. The peak of the X-ray emission is offset from the peak of the radio total intensity (Stokes I) emission by approximately 4.7", but coincides well with circularly polarised (Stokes V) emission. No infrared counterpart was found.

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