arXiv subjects

P. Esposito

Publications and source records attributed to P. Esposito.

At least 19 recordsLinked to original sources

arXiv2026

Understanding Pulsar Magnetospheres with the SKAO

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar magnetosphere. This chapter describes the advances that have been made in pulsar magnetosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar magnetosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.

astro-ph.HE↗

arXiv2026

Accurate distances of the Galactic spiral arms from dust-scattered X-ray emission of gamma-ray bursts

The details of the spiral structure of the Milky Way are still debated due to large uncertainties in the distance estimates obtained through the most common tracers. X-ray dust scattering rings produced by short extragalactic X-ray transients provide instead a direct method to measure the 3D distribution of interstellar clouds up to the edges of our Galaxy with a few percent precision. We report on the analysis of all the available XMM-Newton and Chandra follow-up observations of three low-latitude gamma-ray bursts: GRB 031203 ($l \sim 255{\deg}$, $b \sim -5{\deg}$), GRB 160623A ($l \sim 84{\deg}$, $b \sim -3{\deg}$), and GRB 221009A ($l \sim 53{\deg}$, $b \sim 4{\deg}$). The previous detection of X-ray rings in these observations, produced by dust clouds located beyond 5 kpc, can be associated with dust in the Perseus, Outer, and Outer Scutum-Centaurus arms, thus providing direct distance measurements to these structures along three distinct lines of sight. We have identified two additional rings in the direction of GRB 160623A, produced by dusty clouds at $6.91\, \pm\,0.06$ kpc and $9.9\,\pm\,0.6$ kpc, and confirmed -- through a second XMM-Newton observation -- the presence of one cloud at $9.7\,\pm\,0.4$ kpc toward GRB 031203. We also accurately measured the distance of dusty clouds up to $19.0\,\pm\,0.2$ kpc owing to the analysis of one Chandra and four XMM-Newton observations of GRB 221009A. The small statistical and systematic uncertainties of these measurements place tight constraints on the geometry of the outer Milky Way and reveal significant deviations from current models, which critically depend on spectroscopy-based Galactic rotation curves at large distances.

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arXiv2026

The spectrum of the persistent radio source associated with FRB 20190417A

Persistent radio sources (PRSs) are (sub-)parsec-scale compact non-thermal continuum sources associated with some repeating fast radio bursts (FRBs). Their nature is debated, but their properties provide insights into the FRB environment and progenitors. We measure the spectrum of the recently confirmed PRS associated with FRB 20190417A. Spectral features such as the self-absorption and cooling break can be used to constrain the age and size of PRSs and test theoretical models. We present observations made with the 1.26 GHz upgraded Giant Metrewave Radio Telescope (uGMRT) and observations from the 6 GHz Karl Jansky Very Large Array (VLA). With complementary archival data and the LOw Frequency ARray Two Meter Sky Survey (LoTSS), we characterise the spectrum of the PRS between 144 MHz and 6 GHz. The spectrum follows a power-law behaviour at gigahertz frequencies. The source is not detected at 144 MHz down to a $2\sigma=170 \; {\rm \mu Jy}$ sensitivity. We modelled the spectrum with a broken power law, obtaining a spectral index $\alpha = 0.20 \pm 0.05$ between 1-6 GHz. We placed a lower limit on the turn-over frequency of $> 370$ MHz ($95\%$ confidence). The flat spectrum and low-frequency turn-over of the target are consistent with the spectral properties predicted for magneto-ionic nebulae, inflated behind the supernova ejecta by a flaring young magnetar. Considering the multi-zone magnetar wind nebula scenario, we estimate an age of $t< 250$ yr and a radius of $R< 0.4$ pc for the target, which would thus be slightly older than the PRSs associated with FRB 20121102A and FRB 20190520B.

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arXiv2025

Understanding pulsar magnetospheres with the SKAO

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar magnetosphere. This paper describes the advances that have been made in pulsar magnetosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar magnetosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.

astro-ph.HE↗

arXiv2025

A magnetar outburst with atypical evolution: the case of Swift J1555.2-5402

The magnetar Swift J1555.2-5402 was discovered in outburst on 2021 June 3 by the Burst Alert Telescope on board the Swift satellite. Early X-ray follow-up revealed a spin period P~3.86 s, a period derivative Pdot~3e-11 s/s, dozens of short bursts, and an unusually flux decline. We report here on the X-ray monitoring of Swift J1555.2-5402 over the first ~29 months of its outburst with Swift, NICER, NuSTAR, INTEGRAL and Insight-HXMT, as well as radio observations with Parkes soon after the outburst onset. The observed 0.3-10 keV flux remained at levels >~1e-11 erg/cm^2/s for nearly 500 days before dropping by a factor of ~10 from its June 2021 peak towards the end of the monitoring campaign. During this time span, the spectrum was dominated by a single blackbody, with temperature attaining approximately a constant value (~1.2 keV) while the inferred radius shrank from ~1.7 km to ~0.3 km (assuming a source distance of 10 kpc). The long-term spin-down rate (Pdot~3.6e-11 s/s) is only ~15 % higher than that measured in the first 30 days. No periodic or burst-like radio emission was detected, in line with what has been previously reported using different radio facilities. The persistently high temperature, shrinking hotspot, and a prolonged bright flux plateau followed by a fast dimming observed during the outburst evolution pose a challenge for the outburst mechanisms proposed so far.

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arXiv2025

The Northern Cross Fast Radio Burst project: V. Search for transient radio emission from Galactic magnetars

Context. The radio emission from magnetars is poorly understood and poorly characterized observationally, in particular for what concerns single pulses and sporadic events. The interest in it was boosted by the detection in 2020 of an extremely bright ms radio signal from the Galactic magnetar designated Soft Gamma Repeater (SGR) SGR J1935+2154, which occurred almost simultaneously with a typical magnetar short burst of X-rays. As of now, this event remains the Galactic radio pulse that is the most reminiscent of fast radio bursts (FRBs) and the only one with a sound association with a known progenitor. Aims. We aim to constrain the rate of impulsive radio events from magnetars, by means of an intensive monitoring using a high-sensitivity radio telescope. Methods. We performed a long-term campaign on seven Galactic magnetars (plus one candidate) using the Northern Cross transit radio telescope (in Medicina, Italy) searching for short timescales and dispersed radio pulses. Results. We obtained no detections in more than 560 hours of observation, setting an upper limit at 95% confidence level of <52 yr$^{-1}$ on the rate of events with energy >10$^{28}$ erg, which is consistent with limits in literature. Furthermore, under some assumptions on the magnetars properties and energetic behavior, we found that our upper limits point towards the fact that the entire population of FRBs observed cannot be explained by radio bursts emitted by magnetars.

astro-ph.HE↗

arXiv2025

The infrared counterpart and proper motion of magnetar SGR0501+4516

Soft gamma repeaters (SGRs) are highly magnetised neutron stars (magnetars) notable for their gamma-ray and X-ray outbursts. In this paper, we use near-infrared (NIR) imaging of SGR 0501+4516 in the days, weeks, and years after its 2008 outburst to characterise the multi-wavelength emission, and to obtain a proper motion from our long temporal baseline observations. Unlike most magnetars, the source has only moderate foreground extinction with minimal crowding. Our observations began only 2 hours after the first activation of SGR 0501+4516 in August 2008, and continued for 4 years, including two epochs of Hubble Space Telescope (HST) imaging. The proper motion constraint is improved by a third HST epoch 10 years later. The near-infrared and X-rays faded slowly during the first week, thereafter following a steeper power-law decay. The behaviour is satisfactorily fit by a broken power-law. Three epochs of HST imaging with a 10-year baseline allow us to determine a quiescent level, and to measure a proper motion of 5.4+/-0.6 mas/yr. This corresponds to a low transverse peculiar velocity of 51+/-14 km/s (at 2 kpc). The magnitude and direction of the proper motion rules out supernova remnant HB9 as the birth-site. We can find no other supernova remnants or groups of massive stars within the region traversed by SGR 0501+4516 during its characteristic lifetime (20 kyr). Our observations of SGR 0501+4516 suggest that some magnetars may be either significantly older than expected, that their progenitors produce low supernova ejecta masses, or alternatively that they can be formed through accretion-induced collapse (AIC) or low-mass neutron star mergers. Although the progenitor of SGR 0501+4516 remains unclear, we propose that SGR 0501+4516 is the best Galactic candidate for a magnetar formed through a mechanism other than massive star core-collapse.

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arXiv2025

The persistent nature of the Be X-ray binary pulsar 4U 0728-25

We report the results obtained with a XMM-Newton observation, performed in April 2023, of the poorly known Galactic Be X-ray binary pulsar 4U 0728-25. It was revealed at a flux level (not corrected for the absorption) $f_{\rm X}$(0.2-12 keV) = 1.7$\times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$, which implies an unabsorbed source luminosity $L_{\rm X} \simeq 1.3 \times 10^{35}$ erg s$^{-1}$: this is the minimum luminosity ever observed for this source. We measured a pulse period $P_{\rm spin}$ = 103.301(5) s, a value $\simeq $ 0.15 % longer than that estimated in 2016 with AstroSat. The pulse profile shows a broad single peak at all energies, with a limited energy dependence and a small increase in the pulsed fraction with energy. The time-averaged EPIC spectrum can be described equally well by four different emission models, either with a single non-thermal component (a partially covered power law or a cut-off power law), or with a thermal component in addition to the non-thermal one (a black body plus a power law, or a collisionally ionised gas plus a cut-off power law). All of them provided an equally good fit and, in the case of the power-law plus black-body model, the thermal component is characterized by a high temperature ($kT_{\rm BB} \simeq$ 1.5 keV) and a small size ($R_{\rm BB} \simeq$ 240 m), comparable with that of the neutron-star polar caps. A spectral variability along the pulse phase is present, which suggests a flux variation of the black-body component. These results show that, for its luminosity level, flux variabilty over long time scales, and spectral properties, 4U 0728-25 is very similar to most of the persistent Be X-ray binaries. Therefore, it can be considered a member of this class of sources.

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arXiv2025

Probing the interstellar medium toward GRB 221009A through X-ray dust scattering

The observation of 21 X-ray dust-scattering rings around the extraordinarily bright gamma-ray burst (GRB) 221009A provides a unique opportunity to study the interstellar medium (ISM) through which the X-ray radiation traveled in our Galaxy and, by difference, in the host galaxy as well. In particular, since the ring intensity and radius at a given time depend on the amount of dust and on its distance, respectively XMM-Newton and Swift images allowed us to map the ISM around the direction of the GRB with better resolution than in the existing optical and infrared-based 3D dust maps, both in the plane of the sky (few arcminutes) and along the line of sight (from $\simeq 1$ pc for dust clouds within 1 kpc to $\simeq 100$ pc for structures at distances larger than 10 kpc). As a consequence, we can revise prior estimates of the GRB soft X-ray fluence, obtaining a $\sim$35\% lower value, which, however, still indicates a substantial excess with respect to the extrapolation of the spectral models constrained by hard X-ray observations. Additionally, we detect significant spectral variability in two azimuthal sectors of the X-ray rings, which can be fully attributed to different Galactic absorption in these two directions. The comparison of the total hydrogen column density inferred from spectral fitting, with the Galactic contribution derived from the intensity of the X-ray rings, in the same sectors, allowed us to more robustly constrain the absorption in the host galaxy to $N_{\rm{H,z=0.151}}= (3.7\pm0.3)\,\times\,10^{21}\,\rm{cm^{-2}}$. This result is relevant not only to characterize the ISM of the host galaxy and to understand how the GRB radiation might have affected it, but also to model the broad-band spectrum of the GRB afterglow and to constrain the properties of a possible underlying supernova.

astro-ph.HE↗

arXiv2024

New interpretation of the two hard X-ray sources IGR J17503-2636 and IGR J17507-2647

We report on the results of X-ray observations (XMM-Newton, INTEGRAL and Swift) of two hard X-ray sources, IGR J17503-2636 and IGR J17507-2647, whose nature is not fully elucidated in the literature. Three XMM-Newton observations covered the field of IGR J17503-2636, in 2020 and twice in 2023. The analysis of the two XMM-Newton observations performed in September 2023, six days apart, did not detect IGR J17503-2636, allowing us to pose the most stringent 3sigma upper limit on the source flux to date (~9.5x10^-14 erg/cm2/s, 2-10 keV, flux corrected for absorption). This value implies that the amplitude of the X-ray flux variability exceeds a factor of ~2100, compared with the discovery outburst in 2018. A candidate X-ray periodicity at 0.335397(3) seconds has been barely detected (significance of about 3.8sigma) from IGR J17503-2636 with XMM-Newton (pulsed fraction of (10+/-1) per cent). The new data, put into the context of previous literature, allow us to propose a new classification of IGR J17503-2636 as a symbiotic X-ray binary, rather than a candidate supergiant fast X-ray transient. IGR J17507-2647 was formerly reported below 10 keV only during Chandra observations performed in 2009. We report here on two XMM-Newton observations that serendipitously covered the source field in 2020 and in 2023, finding a stable X-ray emission, both in X-ray flux and spectral shape. The long-term, persistent X-ray emission has also been probed by several Swift/XRT short observations and by INTEGRAL data spanning several years. We have detected an iron line in the emission (with centroid energy in the range of 6.3-6.6 keV), never reported before in the IGR J17507-2647 spectrum. The source properties favor the identification with a cataclysmic variable.

astro-ph.HE↗

arXiv2024

The role of XMM-Newton in the investigation of persistent BeXRBs

The persistent BeXRBs are a class of High-Mass X-ray Binaries (HMXRBs), which are characterized by persistent low X-ray luminosities ($L_{\rm X} \sim 10^{34}$ erg s$^{-1}$) and wide ($P_{\rm orb} >$ 30 d), almost circular orbits. In these sources the NS is slowly rotating (with $P_{\rm spin}$ well above 100 s) and accretes matter directly from the wind of the companion Be star, without the formation of an accretion disk. Since the '90s, when the first four members of this class were identified, several other sources of the same type have been discovered and investigated. Thanks to follow-up XMM-Newton observations, we have verified that most of them share common spectral and timing properties, such as a pulsed fraction that does not vary with the photon energy and a hot (kT = 1-2 keV) blackbody spectral component which contributes for 20-40 % to the total flux and has a size consistent with the NS polar cap. Here we provide an overview of how XMM-Newton contributed to constrain the observational properties and the current understanding of this type of sources. We also report about the first results obtained with a very recent XMM-Newton observation of the poorly known BeXRB 4U 0728-25.

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arXiv2024

On the nature of the 2.4 hr-period eclipsing cataclysmic variable W2 in 47 Tuc

W2 (CXOGlb J002415.8-720436) is a cataclysmic variable (CV) in the Galactic globular cluster 47 Tucanae. Its modulation was discovered within the CATS@BAR project. The source shows all the properties of magnetic CVs, but whether it is a polar or an intermediate polar is still a matter of debate. This paper investigates the spectral and temporal properties of the source, using all archival X-ray data from Chandra and eROSITA Early Data Release, to establish whether the source falls within the category of polars or intermediate polars. We fitted Chandra archival spectra with three different models: a power law, a bremsstrahlung and an optically thin thermal plasma. We also explored the temporal properties of the source with searches for pulsations with a power spectral density analysis and a Rayleigh test ($Z_n^2$). W2 displays a mean luminosity of $\sim 10^{32}$ erg s$^{-1}$ over a 20-year span, despite lower values in a few epochs. The source is not detected in the latest observation, taken with Chandra in 2022, and we infer an X-ray luminosity $\leq 7 \times 10^{31}$ erg s$^{-1}$. The source spectral shape does not change over time and can be equally well fitted with each of the three models, with a best-fit photon index of 1.6 for the power law and best-fit temperatures of 10 keV for both the bremsstrahlung and the thermal plasma models. We confirm the previously detected period of 8649 s, ascribed to the binary orbital period, and found a cycle-to-cycle variability associated with this periodicity. No other significant pulsation is detected. Considering the source orbital period, luminosity, spectral characteristics, long-term evolution and strong cycle-to-cycle variability, we suggest that W2 is a magnetic CV of the polar type.

astro-ph.HE↗

arXiv2024

The restless population of bright X-ray sources of NCG 3621

We report on the multi-year evolution of the population of X-ray sources in the nuclear region of NGC 3621 based on Chandra, XMM-Newton and Swift observations. Among these, two sources, X1 and X5, after their first detection in 2008, seem to have faded below the detectability threshold, a most interesting fact as X1 is associated with the AGN of the galaxy. Two other sources, X3 and X6 are presented for the first time, the former showing a peculiar short-term variability in the latest available dataset, suggesting an egress from eclipse, hence belonging to the handful of known eclipsing ultra-luminous X-ray sources. One source, X4, previously known for its "heart-beat", i.e. a characteristic modulation in its signal with a period of $\approx1$ h, shows a steady behaviour in the latest observation. Finally, the brightest X-ray source in NGC 3621, here labelled X2, shows steady levels of flux across all the available datasets but a change in its spectral shape, reminiscent of the behaviours of Galactic disk-fed X-ray binaries.

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arXiv2024

The Northern Cross Fast Radio Burst project IV. Multi-wavelength study of the actively repeating FRB 20220912A

Fast radio bursts (FRBs) are energetic, millisecond-duration radio pulses observed at extragalactic distances and whose origins are still a subject of heated debate. A fraction of the FRB population have shown repeating bursts, however it's still unclear whether these represent a distinct class of sources. We investigated the bursting behaviour of FRB 20220912A, one of the most active repeating FRBs known thus far. In particular, we focused on its burst energy distribution, linked to the source energetics, and its emission spectrum, with the latter directly related to the underlying emission mechanism. We monitored FRB 20220912A at $408$ MHz with the Northern Cross radio telescope and at $1.4$ GHz using the $32$-m Medicina Grueff radio telescope. Additionally, we conducted $1.2$ GHz observations taken with the upgraded Giant Meter Wave Radio Telescope (uGMRT) searching for a persistent radio source coincident with FRB 20220912A, which included high energy observations in the $0.3-10$ keV, $0.4-100$ MeV and $0.03-30$ GeV energy range. We report $16$ new bursts from FRB 20220912A at $408$ MHz during the period between October 16$^{\rm th}$ 2022 and December 31$^{\rm st}$ 2023. Their cumulative spectral energy distribution follows a power law with slope $\alpha_E = -1.3 \pm 0.2$ and we measured a repetition rate of $0.19 \pm 0.03$ hr$^{-1}$ for bursts having a fluence of $\mathcal{F} \geq 17$ Jy ms. Furthermore, we report no detections at 1.4 GHz for $\mathcal{F} \geq 20$ Jy ms. These non-detections imply an upper limit of $\beta < -2.3$, with $\beta$ being the $408$ MHz $-$ $1.4$ GHz spectral index of FRB 20220912A. This is inconsistent with positive $\beta$ values found for the only two known cases in which an FRB has been detected in separate spectral bands. We find that FRB 20220912A shows a decline of four orders of magnitude in its bursting activity at $1.4$ GHz over a .. (abridged)

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arXiv2024

An X-ray and radio view of the 2022 reactivation of the magnetar SGRJ1935+2154

Recently, the Galactic magnetar SGR J1935+2154 has garnered attention due to its emission of an extremely luminous radio burst, reminiscent of Fast Radio Bursts (FRBs). SGR J1935+2154 is one of the most active magnetars, displaying flaring events nearly every year, including outbursts as well as short and intermediate bursts. Here, we present our results on the properties of the persistent and bursting X-ray emission from SGR J1935+2154, during the initial weeks following its outburst on October 10, 2022. The source was observed with XMM-Newton and NuSTAR (quasi-)simultaneously during two epochs, separated by $\sim$5 days. The persistent emission spectrum is well described by an absorbed blackbody plus power-law model up to an energy of $\sim$25 keV. No significant changes were observed in the blackbody temperature ($kT_{\rm BB}\sim$ 0.4 keV) and emitting radius ($R_{\rm BB}\sim$ 1.9 km) between the two epochs. However, we observed a slight variation in the power-law parameters. Moreover, we detected X-ray pulsations in all the datasets and derived a spin period derivative of $\dot{P} = 5.52(5) \times 10^{-11}$ ss. This is 3.8 times larger than the value measured after the first recorded outburst in 2014. Additionally, we performed quasi-simultaneous radio observations using three 25--32-m class radio telescopes for a total of 92.5 hr to search for FRB-like radio bursts and pulsed emission. However, our analysis did not reveal any radio bursts or periodic emission.

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arXiv2023

A soft and transient ultraluminous X-ray source with 6-h modulation in the NGC 300 galaxy

We investigate the nature of CXOU J005440.5-374320 (J0054), a peculiar bright ($\sim$$4\times10^{39}$ erg/s) and soft X-ray transient in the spiral galaxy NGC 300 with a 6-hour periodic flux modulation that was detected in a 2014 Chandra observation. Subsequent observations with Chandra and XMM-Newton, as well as a large observational campaign of NGC 300 and its sources performed with the Swift Neil Gehrels Observatory, showed that this source exhibits recurrent flaring activity: four other outbursts were detected across $\sim$8 years of monitoring. Using data from the Swift/UVOT archive and from the XMM-Newton/OM and Gaia catalogues, we noted the source is likely associated with a bright blue optical/ultraviolet counterpart. This prompted us to perform follow-up observations with the Southern African Large Telescope in December 2019. With the multi-wavelength information at hand, we discuss several possibilities for the nature of J0054. Although none is able to account for the full range of the observed peculiar features, we found that the two most promising scenarios are a stellar-mass compact object in a binary system with a Wolf$-$Rayet star companion, or the recurrent tidal stripping of a stellar object trapped in a system with an intermediate-mass ($\sim1000$ $M_\odot$) black hole.

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arXiv2023

Probing the nature of the X-ray source IGR J16327-4940 with Chandra

We report on the results of a Chandra observation of the source IGRJ16327-4940, suggested to be a high mass X-ray binary hosting a luminous blue variable star (LBV). The source field was imaged by ACIS-I in 2023 to search for X-ray emission from the LBV star and eventually confirm this association. No X-ray emission is detected from the LBV star, with an upper limit on the X-ray luminosity of L$_{\rm 0.5-10 keV}<2.9(^{+1.6} _{-1.1})\times10^{32}$ erg/s (at the LBV distance d=12.7$^{+3.2} _{-2.7}$ kpc). We detected 21 faint X-ray sources, 8 of which inside the INTEGRAL error circle. The brightest one is the best candidate soft X-ray counterpart of IGRJ16327-4940, showing a hard power law spectrum and a flux corrected for the absorption UF$_{\rm 0.5-10 keV}$=$2.5\times10^{-13}$ erg/cm2/s, mplying a luminosity of $3.0\times10^{33}$ d$_{10~kpc}^2$ erg/s. No optical/near-infrared counterparts have been found. Previous X--ray observations of the source field with Swift/XRT and ART-XC did not detect any source consistent with the INTEGRAL position. These findings exclude the proposed LBV star as the optical association, and pinpoint the most likely soft X-ray counterpart. In this case, the source properties suggest a low mass X-ray binary, possibly a new member of the very faint X-ray transient class.

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.

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