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We present a comprehensive study of the flaring mode of the transitional millisecond pulsar (tMSP) PSR J1023+0038 during its X-ray sub-luminous state, using strictly simultaneous X-ray, UV, optical, and radio observations. The X-ray flares exhibit UV and optical counterparts and coincide with the brightest radio flare observed in the past decade, reaching 1.2 mJy at 6 GHz and lasting ~1 hour. During the flare, the optical polarization drops from ~1.4% to ~0.5%, indicating the emergence of an unpolarized component. We propose that the thickening of the disc, which enlarges the shock region between the pulsar wind and the accretion flow and may drive the X-ray flaring observed in tMSPs, enhances the ionization level of the disc, thereby generating an increased number of free electrons. These electrons could then be channelled by magnetic field lines into the jet. This increased jet mass-loading could drive the associated radio and optical variability. The radio spectral evolution during flares is consistent with synchrotron self-absorption in jet ejecta or internal shocks within the compact jet. We infer radio polarization upper limits (<8.7%, <2.3%, and <8.2%, before, during, and after the radio flare) that further support a compact jet origin but do not rule out discrete ejections. Our findings suggest that tMSPs could serve as essential laboratories for investigating jet-launching mechanisms, mainly because they operate under very low mass accretion rates. This accretion regime has not been explored before in the context of the accretion-ejection coupling., Comment: Accepted for publication in A&AL

Stellar-mass and supermassive black holes abound in the Universe, whereas intermediate-mass black holes (IMBHs) of ~10^2-10^5 solar masses in between are largely missing observationally, with few cases found only. Here we report the real-time discovery of a long-duration X-ray transient, EP240222a, accompanied by an optical flare with prominent H and He emission lines revealed by prompt follow-up observations. Its observed properties evidence an IMBH located unambiguously in the halo of a nearby galaxy and flaring by tidally disrupting a star -- the only confirmed off-nucleus IMBH-tidal disruption event so far. This work demonstrates the potential of sensitive time-domain X-ray surveys, complemented by timely multi-wavelength follow-ups, in probing IMBHs, their environments, demographics, origins and connections to stellar-mass and supermassive black holes., Comment: 64 pages, 15 figures, submitted

Transitional millisecond pulsars (tMSPs) bridge the evolutionary gap between accreting neutron stars in low-mass X-ray binaries and millisecond radio pulsars. These systems exhibit a unique subluminous X-ray state characterized by the presence of an accretion disk and rapid switches between high and low X-ray emission modes. The high mode features coherent millisecond pulsations spanning from the X-ray to the optical band. We present multiwavelength polarimetric observations of the tMSP PSR J1023+0038 aimed at conclusively identifying the physical mechanism powering its emission in the subluminous X-ray state. During the high mode, we detect polarized emission in the 2-6 keV energy range, with a polarization degree of 12% +/- 3% and a polarization angle of -2deg +/- 9deg (1sigma) measured counterclockwise from the North celestial pole towards East. At optical wavelengths, we find a polarization degree of 1.41% +/- 0.04% and a polarization angle aligned with that in the soft X-rays, suggesting a common physical mechanism operating across these bands. Remarkably, the polarized flux spectrum matches the pulsed emission spectrum from optical to X-rays. The polarization properties differ markedly from those observed in other accreting neutron stars and isolated rotation-powered pulsars and are also inconsistent with an origin in a compact jet. Our results provide direct evidence that the polarized and pulsed emissions both originate from synchrotron radiation at the shock formed where the pulsar wind interacts with the inner regions of the accretion disk., Comment: Submitted

Massive stars end their life as core-collapse supernovae, amongst which some extremes are Type Ic broad-lined supernovae associated with long-duration gamma-ray bursts (LGRBs) having powerful relativistic jets. Their less-extreme brethren make unsuccessful jets that are choked inside the stars, appearing as X-ray flashes or low-luminosity GRBs. On the other hand, there exists a population of extragalactic fast X-ray transients (EFXTs) with timescales ranging from seconds to thousands of seconds, whose origins remain obscure. Known sources that contribute to the observed EFXT population include the softer analogs of LGRBs, shock breakouts of supernovae, or unsuccessful jets. Here, we report the discovery of the bright X-ray transient EP240414a detected by the Einstein Probe (EP), which is associated with the Type Ic supernova SN 2024gsa at a redshift of 0.401. The X-ray emission evolution is characterised by a very soft energy spectrum peaking at < 1.3 keV, which makes it distinct from known LGRBs, X-ray flashes, or low-luminosity GRBs. Follow-up observations at optical and radio bands revealed the existence of a weak relativistic jet that interacts with an extended shell surrounding the progenitor star. Located on the outskirts of a massive galaxy, this event reveals a new population of explosions of Wolf-Rayet stars characterised by a less powerful engine that drives a successful but weak jet, possibly owing to a progenitor star with a smaller core angular momentum than in traditional LGRB progenitors., Comment: 43 pages, 9 figures, 4 tables, submitted. Comments are welcome

CXOU J110926.4-650224 is a candidate transitional millisecond pulsar (tMSP) with X-ray and radio emission properties reminiscent of those observed in confirmed tMSPs in their X-ray 'subluminous' disc state. We present the results of observing campaigns that, for the first time, characterise the optical and near-infrared variability of this source and establish a connection with the mode-switching phenomenon observed in X-rays. The optical emission exhibited flickering activity, frequent dipping episodes where it appeared redder, and a multi-peaked flare where it was bluer. The variability pattern was strongly correlated with that of the X-ray emission. Each dip matched an X-ray low-mode episode, indicating that a significant portion of the optical emission originates from nearly the same region as the X-ray emission. The near-infrared emission also displayed remarkable variability, including a dip of 20 min in length during which it nearly vanished. Time-resolved optical spectroscopic observations reveal significant changes in the properties of emission lines from the disc and help infer the spectral type of the companion star to be between K0 and K5. We compare the properties of CXOU J110926.4-650224 with those of other tMSPs in the X-ray subluminous disc state and discuss our findings within the context of a recently proposed scenario that explains the phenomenology exhibited by the prototypical tMSP PSR J1023+0038., Comment: 12 pages, 7 figures, 2 tables. Accepted for publication on Astronomy & Astrophysics

We present the first X-ray observation of the energetic millisecond pulsar binary PSR J1431-4715, performed with XMM-Newton and complemented with fast optical multi-band photometry acquired with the ULTRACAM instrument at ESO-NTT. It is found as a faint X-ray source without a significant orbital modulation. This contrasts with the majority of systems that instead display substantial X- ray orbital variability. The X-ray spectrum is dominated by non-thermal emission and, due to the lack of orbital modulation, does not favour an origin in an intrabinary shock between the pulsar and companion star wind. While thermal emission from the neutron star polar cap cannot be excluded in the soft X-rays, the dominance of synchrotron emission favours an origin in the pulsar magnetosphere that we describe at both X-ray and gamma-ray energies with a synchro-curvature model. The optical multi-colour light curve folded at the 10.8h orbital period is double-humped, dominated by ellipsoidal effects, but also affected by irradiation. The ULTRACAM light curves are fit with several models encompassing direct heating and a cold spot, or heat redistribution after irradiation either through convection or convection plus diffusion. Despite the inability to constrain the best irradiation models, the fits provide consistent system parameters, giving an orbital inclination of 59$\pm$6deg and a distance of 3.1$\pm$0.3 kpc. The companion is found to be an F-type star, underfilling its Roche lobe ( f_RL = 73$\pm$4%), with a mass of 0.20$\pm$0.04 M_sun, confirming the redback status, although hotter than the majority of redbacks. The stellar dayside and nightside temperatures of 7500K and 7400K, respectively, indicate a weak irradiation effect on the companion, likely due to its high intrinsic luminosity. Although the pulsar mass cannot be precisely derived, a heavy (1.8-2.2 M_sun) neutron star is favoured, Comment: 16 pages, 11 figures, Accepted for publication in A&A

We present a long-period radio transient (GLEAM-X J0704-37) discovered to have an optical counterpart, consistent with a cool main sequence star of spectral type M3. The radio pulsations occur at the longest period yet found, 2.9 hours, and were discovered in archival low-frequency data from the Murchison Widefield Array (MWA). High time resolution observations from MeerKAT show that pulsations from the source display complex microstructure and high linear polarisation, suggesting a pulsar-like emission mechanism occurring due to strong, ordered magnetic fields. The timing residuals, measured over more than a decade, show tentative evidence of a ~6-yr modulation. The high Galactic latitude of the system and the M-dwarf star excludes a magnetar interpretation, suggesting a more likely M-dwarf / white dwarf binary scenario for this system., Comment: 11 pages, 4 figures, accepted by ApJL 19th October 2024

On May 27 2024, the Wide-field X-ray Telescope onboard the Einstein Probe (EP) mission detected enhanced X-ray emission from a new transient source in the Small Magellanic Cloud (SMC) during its commissioning phase. Prompt follow-up with the EP Follow-up X-ray Telescope, the Swift X-ray Telescope and NICER have revealed a very soft, thermally emitting source (kT$\sim$0.1 keV at the outburst peak) with an X-ray luminosity of $L\sim4\times10^{38}$ erg s$^{-1}$, labelled EP J005245.1-722843. This super-soft outburst faded very quickly in a week time. Several emission lines and absorption edges were present in the X-ray spectrum, including deep Nitrogen (0.67 keV) and Oxygen (0.87 keV) absorption edges. The X-ray emission resembles the SSS phase of typical nova outbursts from an accreting white dwarf (WD) in a binary system, despite the X-ray source being historically associated with an O9-B0e massive star exhibiting a 17.55 days periodicity in the optical band. The discovery of this super-soft outburst suggests that EP J005245.1-722843 is a BeWD X-ray binary: an elusive evolutionary stage where two main-sequence massive stars have undergone a common envelope phase and experienced at least two episodes of mass transfer. In addition, the very short duration of the outburst and the presence of Ne features hint at a rather massive, i.e., close to the Chandrasekhar limit, Ne-O WD in the system., Comment: 9 pages, 5 figures; accepted for publication in ApJL

Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5--4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of $z=4.859$, EP240315a showed a much longer and more complicated light curve in the soft X-ray band than in gamma-rays. Benefiting from a large field-of-view ($\sim$3600 deg$^2$) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-$z$ GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs., Comment: 41 pages, 8 figures, 7 tables

Recent observations have led to the discovery of numerous optically selected binaries containing an undetected component with mass consistent with a compact object (neutron star or white dwarf). Using the the Neil Gehrels Swift Observatory we have carried out X-ray and UV observations of a small sample of these binaries. Four systems are wide (with orbital period P>300 d), and they were chosen because of their small distance (d<250 pc) and the mass of the collapsed component favoring a neutron star. Two other are compact systems (P<0.9 d), with convincing evidence of containing a neutron star. The source 2MASS J15274848$+$3536572 was detected in the X-ray band, with a flux of 5E-13 erg/cm2/s and a spectrum well fitted by a power law or a thermal plasma emission model. This source also showed an UV (2200 Angstrom) excess, which might indicate the presence of mass accretion. For the other targets we derived X-ray flux upper limits of the order of 1E-13}$ erg/cm2/s . These results are consistent with the hypothesis that the collapsed component in these six systems are neutron stars., Comment: 7 pages, 7 figures. Accepted for publication by A&A

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., Comment: 16 pages, 6 figures, accepted for publication on ApJ

The accretion flow / jet correlation in neutron star (NS) low-mass X-ray binaries (LMXBs) is far less understood when compared to black hole (BH) LMXBs. In this paper we will present the results of a dense multi-wavelength observational campaign on the NS LMXB 4U 1820-30, including X-ray (Nicer, NuSTAR and AstroSAT) and quasi-simultaneous radio (ATCA) observations in 2022. 4U 1820-30 shows a peculiar 170 day super-orbital accretion modulation, during which the system evolves between "modes" of high and low X-ray flux. During our monitoring, the source did not show any transition to a full hard state. X-ray spectra were well described using a disc blackbody, a Comptonisation spectrum along with a Fe K emission line at 6.6 keV. Our results show that the observed X-ray flux modulation is almost entirely produced by changes in the size of the region providing seed photons for the Comptonisation spectrum. This region is large (about 15 km) in the high mode and likely coincides with the whole boundary layer, while it shrinks significantly (<10 km) in low mode. The electron temperature of the corona and the observed RMS variability in the hard X-rays also exhibit a slight increase in low mode. As the source moves from high to low mode, the radio emission due to the jet becomes about 5 fainter. These radio changes appear not to be strongly connected to the hard-to-soft transitions as in BH systems, while they seem to be connected mostly to variations observed in the boundary layer., Comment: 12 pages, 6 figures. Accepted for publication by MNRAS

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 $\Gamma\simeq 1.9$, 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., Comment: 9 pages, 6 figures, 1 table. Accepted for publication in MNRAS

Swift J1818.0-1607 is a radio-loud magnetar with a spin period of 1.36 s and a dipolar magnetic field strength of B~3E14 G, which is very young compared to the Galactic pulsar population. We report here on the long-term X-ray monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift from the activation of its first outburst in March 2020 until October 2021, as well as INTEGRAL upper limits on its hard X-ray emission. The 1-10 keV magnetar spectrum is well modeled by an absorbed blackbody with a temperature of kT_BB~1.1 keV, and apparent reduction in the radius of the emitting region from ~0.6 to ~0.2 km. We also confirm the bright diffuse X-ray emission around the source extending between ~50'' and ~110''. A timing analysis revealed large torque variability, with an average spin-down rate nudot~-2.3E-11 Hz^2 that appears to decrease in magnitude over time. We also observed Swift J1818.0-1607 with the Karl G. Jansky Very Large Array (VLA) on 2021 March 22. We detected the radio counterpart to Swift J1818.0-1607 measuring a flux density of S_v = 4.38+/-0.05 mJy at 3 GHz, and a half ring-like structure of bright diffuse radio emission located at ~90'' to the west of the magnetar. We tentatively suggest that the diffuse X-ray emission is due to a dust scattering halo and that the radio structure may be associated with the supernova remnant of this young pulsar, based on its morphology., Comment: 19 pages, 8 figures, accepted for publication on ApJ

We observed the periodic radio transient GLEAM-X J162759.5-523504.3 (GLEAM-X J1627) using the Chandra X-ray Observatory for about 30-ks on January 22-23, 2022, simultaneously with radio observations from MWA, MeerKAT and ATCA. Its radio emission and 18-min periodicity led the source to be tentatively interpreted as an extreme magnetar or a peculiar highly magnetic white dwarf. The source was not detected in the 0.3-8 keV energy range with a 3-sigma upper-limit on the count rate of 3x10^{-4} counts/s. No radio emission was detected during our X-ray observations either. Furthermore, we studied the field around GLEAM-X J1627 using archival ESO and DECam data, as well as recent SALT observations. Many sources are present close to the position of GLEAM-X J1627, but only two within the 2" radio position uncertainty. Depending on the assumed spectral distribution, the upper limits converted to an X-ray luminosity of L_{X}<6.5x10^{29} erg/s for a blackbody with temperature kT=0.3 keV, or L_{X}<9x10^{29} erg/s for a power-law with photon index Gamma = 2 (assuming a 1.3 kpc distance). Furthermore, we performed magneto-thermal simulations for neutron stars considering crust- and core-dominated field configurations. Based on our multi-band limits, we conclude that: i) in the magnetar scenario, the X-ray upper limits suggest that GLEAM-X J1627 should be older than ~1 Myr, unless it has a core-dominated magnetic field or has experienced fast-cooling; ii) in the white dwarf scenario, we can rule out most binary systems, a hot sub-dwarf and a hot magnetic isolated white dwarf (T>10.000 K), while a cold isolated white dwarf is still compatible with our limits., Comment: 17 pages, 9 figures; ApJ accepted

We present the results of simultaneous observations of the transitional millisecond pulsar (tMSP) candidate CXOU J110926.4-650224 with the XMM-Newton satellite and the MeerKAT telescope. The source was found at an average X-ray luminosity of $L_{\rm X}\simeq7\times10^{33}$ erg s$^{-1}$ over the 0.3-10 keV band (assuming a distance of 4 kpc) and displayed a peculiar variability pattern in the X-ray emission, switching between high, low and flaring modes on timescales of tens of seconds. A radio counterpart was detected at a significance of 7.9$\sigma$ with an average flux density of $\simeq$33$\mu$Jy at 1.28 GHz. It showed variability over the course of hours and emitted a $\simeq$10-min long flare just a few minutes after a brief sequence of multiple X-ray flares. No clear evidence for a significant correlated or anticorrelated variability pattern was found between the X-ray and radio emissions over timescales of tens of minutes and longer. CXOU J110926.4-650224 was undetected at higher radio frequencies in subsequent observations performed with the Australia Telescope Compact Array, when the source was still in the same X-ray sub-luminous state observed before, down to a flux density upper limit of 15$\mu$Jy at 7.25 GHz (at 3$\sigma$). We compare the radio emission properties of CXOU J110926.4-650224 with those observed in known and candidate tMSPs and discuss physical scenarios that may account for its persistent and flaring radio emissions., Comment: 10 pages, 4 figures. Accepted for publication on A&A

After 15 years, in late 2018, the magnetar XTE J1810-197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM-Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of two change in its spin-down rate from $\sim7.2\times10^{-12}$ s s$^{-1}$ to $\sim1.5\times10^{-11}$ s s$^{-1}$ after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810-197 is well-modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810-197 has likely evolved relative to that found for the 2003 event., Comment: 14 pages, 12 figures, 4 tables. Accepted for publications in MNRAS

We report on multi-band observations of the transient source Swift J0840.7-3516, which was detected in outburst in 2020 February by the Neil Gehrels Swift Observatory. The outburst episode lasted just ~5 days, during which the X-ray luminosity quickly decreased from ~3E37 erg/s at peak down to ~5E33 erg/s in quiescence (0.3-10 keV; at 10 kpc). Such a marked and rapid decrease in the flux was also registered at UV and optical wavelengths. In outburst, the source showed considerable aperiodic variability in the X-rays on timescales as short as a few seconds. The spectrum of the source in the energy range 0.3-20 keV was well described by a thermal, blackbody-like, component plus a non-thermal, power law-like, component and it softened considerably as the source returned to quiescence. The spectrum of the optical counterpart in quiescence showed broad emission features associated mainly with ionised carbon and oxygen, superposed on a blue continuum. No evidence for bright continuum radio emission was found in quiescence. We discuss possible scenarios for the nature of this source, and show that the observed phenomenology points to a transient ultra-compact X-ray binary system., Comment: 13 pages, 7 figures, accepted for publication on A&A

In the last 25 years, a new generation of X-ray satellites imparted a significant leap forward in our knowledge of X-ray pulsars. The discovery of accreting and transitional millisecond pulsars proved that disk accretion can spin up a neutron star to a very high rotation speed. The detection of MeV-GeV pulsed emission from a few hundreds of rotation-powered pulsars probed particle acceleration in the outer magnetosphere, or even beyond. Also, a population of two dozens of magnetars has emerged. INTEGRAL played a central role to achieve these results by providing instruments with high temporal resolution up to the hard X-ray/soft gamma-ray band and a large field of view imager with good angular resolution to spot hard X-ray transients. In this article, we review the main contributions by INTEGRAL to our understanding of the pulsating hard X-ray sky, such as the discovery and characterization of several accreting and transitional millisecond pulsars, the generation of the first catalog of hard X-ray/soft gamma-ray rotation-powered pulsars, the detection of polarization in the hard X-ray emission from the Crab pulsar, and the discovery of persistent hard X-ray emission from several magnetars., Comment: Accepted for publication on New Astronomy Reviews as invited contribution

The detection of a short hard X-ray burst and an associated bright soft X-ray source by the Swift satellite in 2020 October heralded a new magnetar in outburst, SGR J1830-0645. Pulsations at a period of ~10.4 s were detected in prompt follow-up X-ray observations. We present here the analysis of the Swift/BAT burst, of XMM-Newton and the Nuclear Spectroscopic Telescope Array observations performed at the outburst peak, and of a Swift/XRT monitoring campaign over the subsequent month. The burst was single-peaked, lasted ~6 ms, and released a fluence of ~5e-9 erg cm^-2 (15-50 keV). The spectrum of the X-ray source at the outburst peak was well described by an absorbed double-blackbody model plus a power-law component detectable up to ~25 keV. The unabsorbed X-ray flux decreased from ~5e-11 to ~2.5e-11 erg cm^-2 s^-1 one month later (0.3-10 keV). Based on our timing analysis, we estimate a dipolar magnetic field ~5.5e14 G at pole, a spin-down luminosity ~2.4e32 erg s^-1, and a characteristic age ~24 kyr. The spin modulation pattern appears highly pulsed in the soft X-ray band, and becomes smoother at higher energies. Several short X-ray bursts were detected during our campaign. No evidence for periodic or single-pulse emission was found at radio frequencies in observations performed with the Sardinia Radio Telescope and Parkes. According to magneto-thermal evolutionary models, the real age of SGR J1830-0645 is close to the characteristic age, and the dipolar magnetic field at birth was slightly larger, ~1e15 G., Comment: 10 pages, 4 figures, 2 tables. Accepted for publication in The Astrophysical Journal Letters

We report on simultaneous radio and X-ray observations of the radio-emitting magnetar 1E1547.0-5408 on 2009 January 25 and February 3, with the 64-m Parkes radio telescope and the Chandra and XMM-Newton X-ray observatories. The magnetar was observed in a period of intense X-ray bursting activity and enhanced X-ray emission. We report here on the detection of two radio bursts from 1E1547.0-5408, reminiscent of Fast Radio Bursts (FRBs). One of the radio bursts was anticipated by ~1s (about half a rotation period of the pulsar) by a bright SGR-like X-ray burst, resulting in a F_radio/F_X ~ 10^-9. Radio pulsations were not detected during the observation showing the FRB-like radio bursts, while they were detected in the previous radio observation. We also found that the two radio bursts are neither aligned with the latter radio pulsations nor with the peak of the X-ray pulse profile (phase shift of ~0.2). Comparing the luminosity of these FRB-like bursts and those reported from SGR1935+2154, we find that the wide range in radio efficiency and/or luminosity of magnetar bursts in the Galaxy may bridge the gap between "ordinary" pulsar radio bursts and the extragalactic FRB phenomenon., Comment: Accepted for publication in ApJ. 9 pages, 3 figures

A few years after its discovery as a magnetar, SGR J1935+2154 started a new burst-active phase on 2020 April 27, accompanied by a large enhancement of its X-ray persistent emission. Radio single bursts were detected during this activation, strengthening the connection between magnetars and fast radio bursts. We report on the X-ray monitoring of SGR J1935+2154 from ~3 days prior to ~3 weeks after its reactivation, using Swift, NuSTAR, and NICER. We detected X-ray pulsations in the NICER and NuSTAR observations, and constrained the spin period derivative to |Pdot| < 3e-11 s/s (3 sigma c.l.). The pulse profile showed a variable shape switching between single and double-peaked as a function of time and energy. The pulsed fraction decreased from ~34% to ~11% (5-10 keV) over ~10 days. The X-ray spectrum was well fit by an absorbed blackbody model with temperature decreasing from kT ~ 1.6 to 0.45-0.6 keV, plus a non-thermal component (Gamma ~ 1.2) observed up to ~25 keV with NuSTAR. The 0.3-10 keV X-ray luminosity (at 6.6 kpc) increased in less than four days from ~ 6e33 erg/s to about 3e35 erg/s and then decreased again to 2.5e34 erg/s over the following three weeks of the outburst. We also detected several X-ray bursts, with properties typical of short magnetar bursts., Comment: 10 pages, 3 figures, 2 tables. Accepted to ApJL

The magnetar Swift ,J1818.0-1607 was discovered in March 2020 when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was $L_{\rm burst} \sim2\times 10^{39}$ erg/s (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody ($N_{\rm H} = (1.13\pm0.03) \times 10^{23}$ cm$^{-2}$ and $kT = 1.16\pm0.03$ keV) plus a power-law ($\Gamma=0.0\pm1.3$) in the 1-20 keV band, with a luminosity of $\sim$$8\times10^{34}$ erg/s, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field $B \sim 7\times10^{14}$ G, spin-down luminosity $\dot{E}_{\rm rot} \sim 1.4\times10^{36}$ erg/s and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity $<$$5.5\times10^{33}$ erg/s, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 min$^{-1}$ and accounted for $\sim$50% of the total pulsed radio fluence. We conclude that Swift ,J1818.0-1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence., Comment: 10 pages, 4 figures, 1 table; revised version accepted for publication in The Astrophysical Journal Letters

We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic repeater FRB 180916 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ~ 30 hours. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multi-wavelength campaign we performed on FRB 180916, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of ~$10^{45}$ erg/s for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of $ 10^{-8}$ erg cm$^{-2}$.Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts., Comment: ApJL, 896 L40

The magnetar SGR J1745-2900 discovered at parsecs distance from the Milky Way central black hole, Sagittarius A*, represents the closest pulsar to a supermassive black hole ever detected. Furthermore, its intriguing radio emission has been used to study the environment of the black hole, as well as to derive a precise position and proper motion for this object. The discovery of SGR J1745-2900 has opened interesting debates about the number, age and nature of pulsars expected in the Galactic center region. In this work, we present extensive X-ray monitoring of the outburst of SGR J1745-2900 using the Chandra X-ray Observatory, the only instrument with the spatial resolution to distinguish the magnetar from the supermassive black hole (2.4" angular distance). It was monitored from its outburst onset in April 2013 until August 2019, collecting more than fifty Chandra observations for a total of more than 2.3 Ms of data. Soon after the outburst onset, the magnetar emission settled onto a purely thermal emission state that cooled from a temperature of about 0.9 to 0.6 keV over 6 years. The pulsar timing properties showed at least two changes in the period derivative, increasing by a factor of about 4 during the outburst decay. We find that the long-term properties of this outburst challenge current models for the magnetar outbursts., Comment: 11 pages, 6 figures. Accepted by ApJ

We report on the first NuSTAR observation of the transitional millisecond pulsar binary XSS J12270-4859 during its current rotation-powered state, complemented with a 2.5yr-long radio monitoring at Parkes telescope and archival XMM-Newton and Swift X-ray and optical data. The radio pulsar is mainly detected at 1.4GHz displaying eclipses over about 40% of the 6.91h orbital cycle. We derive a new updated radio ephemeris to study the 3-79keV light curve that displays a significant orbital modulation with fractional amplitude of 28+/-3%, a structured maximum centred at the inferior conjunction of the pulsar and no cycle-to-cycle or low-high-flaring mode variabilities. The average X-ray spectrum, extending up to about 70keV without a spectral break, is well described by a simple power-law with photon index Gamma = 1.17+/-0.08 giving a 3-79keV luminosity of 7.6(-0.8;+3.8)x10**32 erg/s, for a distance of 1.37(-0.15;+0.69)kpc. Energy resolved orbital light curves reveal that the modulation is not energy dependent from 3keV to 25keV and is undetected with an upper limit of about 10% above 25keV. Comparison with previous X-ray XMM-Newton observations in common energy ranges confirms that the modulation amplitudes vary on timescales of a few months, indicative of a non-stationary contribution of the intrabinary shock formed by the colliding winds of the pulsar and the companion. A more detailed inspection of energy resolved modulations than previously reported gives hints of a mild softening at superior conjunction of the pulsar below 3keV, likely due to the contribution of the thermal emission from the neutron star. The intrabinary shock emission, if extending into the MeV range, would be energetically capable alone to irradiate the donor star., Comment: 15 pages, 12 figures, 5 tables - Accepted for publication in MNRAS Main Journal

With the opening of the X and gamma--ray windows in the sixties, thanks to to sounding rockets and satellite-borne instruments, extremely energetic and violent phenomena were discovered and subsequently found to be ubiquitous in the Universe. Observations in the high energy domain are fundamental for understanding how matter is organized and behaves around black holes; unravelling how these extreme objects influence their environments on a very large scale; and finding the still elusive obscured massive objects in the centre of galaxies. Other major problems in contemporary astrophysics, such as the understanding of acceleration processes at shocks of all sizes (those of pulsar wind nebulae, supernova remnants, but also at larger scales those of Active Galactic Nuclei radio lobes) in relation to the origin of cosmic-rays, or the definitive characterization of the debated non-thermal X-ray energy content of clusters of galaxies, also requires observations at very high energies. An observatory type medium mission operating from around 1 keV to about 600 keV can provide direct insights into these major questions. The essential characteristics will be coverage of the full energy range by telescopes featuring a large throughput and arc-second resolution optics, coupled to a compact focal plane assembly, with excellent imaging resolution and spectroscopy. In addition, the mission will provide unique polarimetry measurements in the hard X-ray domain, an important new diagnostic tool at energies for which the non-thermal processes dominate. The Polarimetric High-Energy Modular Telescope Observatory (PHEMTO) is designed to have performance several orders of magnitude better than the present hard X-ray instruments. This gives to PHEMTO the improvements in scientific performance needed for a mission in the 2050 era., Comment: 20 pages, White Paper submitted for High Energy Astrophysics to the Voyage 2050 ESA Call

PSR J1023+0038 is the first millisecond pulsar discovered to pulsate in the visible band; such a detection took place when the pulsar was surrounded by an accretion disk and also showed X-ray pulsations. We report on the first high time resolution observational campaign of this transitional pulsar in the disk state, using simultaneous observations in the optical (TNG, NOT, TJO), X-ray (XMM-Newton, NuSTAR, NICER), infrared (GTC) and UV (Swift) bands. Optical and X-ray pulsations were detected simultaneously in the X-ray high intensity mode in which the source spends $\sim$ 70% of the time, and both disappeared in the low mode, indicating a common underlying physical mechanism. In addition, optical and X-ray pulses were emitted within a few km, had similar pulse shape and distribution of the pulsed flux density compatible with a power-law relation $F_{\nu} \propto \nu^{-0.7}$ connecting the optical and the 0.3-45 keV X-ray band. Optical pulses were detected also during flares with a pulsed flux reduced by one third with respect to the high mode; the lack of a simultaneous detection of X-ray pulses is compatible with the lower photon statistics. We show that magnetically channeled accretion of plasma onto the surface of the neutron star cannot account for the optical pulsed luminosity ($\sim 10^{31}$ erg/s). On the other hand, magnetospheric rotation-powered pulsar emission would require an extremely efficient conversion of spin-down power into pulsed optical and X-ray emission. We then propose that optical and X-ray pulses are instead produced by synchrotron emission from the intrabinary shock that forms where a striped pulsar wind meets the accretion disk, within a few light cylinder radii away, $\sim$ 100 km, from the pulsar., Comment: 26 pages, 14 figures, first submitted to ApJ on 2019, January 18

Magnetic field geometry is expected to play a fundamental role in magnetar activity. The discovery of a phase-variable absorption feature in the X-ray spectrum of SGR 0418+5729, interpreted as cyclotron resonant scattering, suggests the presence of very strong non-dipolar components in the magnetic fields of magnetars. We performed a deep XMM-Newton observation of pulsar 1E 2259+586, to search for spectral features due to intense local magnetic fields. In the phase-averaged X-ray spectrum, we found evidence for a broad absorption feature at very low energy (0.7 keV). If the feature is intrinsic to the source, it might be due to resonant scattering/absorption by protons close to star surface. The line energy implies a magnetic field of ~ 10^14 G, roughly similar to the spin-down measure, ~ 6x10^13 G. Examination of the X-ray phase-energy diagram shows evidence for a further absorption feature, the energy of which strongly depends on the rotational phase (E >~ 1 keV ). Unlike similar features detected in other magnetar sources, notably SGR 0418+5729, it is too shallow and limited to a small phase interval to be modeled with a narrow phase-variable cyclotron absorption line. A detailed phase-resolved spectral analysis reveals significant phase-dependent variability in the continuum, especially above 2 keV. We conclude that all the variability with phase in 1E 2259+586 can be attributed to changes in the continuum properties which appear consistent with the predictions of the Resonant Compton Scattering model.

We observed the slowly revolving pulsar 1E 161348-5055 (1E 1613, spin period of 6.67 h) in the supernova remnant RCW 103 twice with XMM-Newton and once with the Very Large Telescope (VLT). The VLT observation was performed on 2016 June 30, about a week after the detection of a large outburst from 1E 1613. At the position of 1E 1613, we found a near-infrared source with K_S = 20.68 +/- 0.12 mag that was not detected (K_S > 21.2 mag) in data collected with the same instruments in 2006, during X-ray quiescence. Its position and behavior are consistent with a counterpart in the literature that was discovered with the Hubble Space Telescope in the following weeks in adjacent near-IR bands. The XMM-Newton pointings were carried out on 2016 August 19 and on 2018 February 14. While the collected spectra are similar in shape between each other and to what is observed in quiescence (a blackbody with kT~0.5 keV plus a second, harder component, either another hotter blackbody with kT ~ 1.2 keV or a power law with photon index ~3), the two pointings caught 1E 1613 at different luminosity throughout its decay pattern: about 4.8E34 erg/s in 2016 and 1.2E34 erg/s in 2018 (0.5-10 keV, for the double-blackbody model and for 3.3 kpc), which is still almost about ten times brighter than the quiescent level. The pulse profile displayed dramatic changes, apparently evolving from the complex multi-peak morphology observed in high-luminosity states to the more sinusoidal form characteristic of latency. The inspection of the X-ray light curves revealed two flares with unusual properties in the 2016 observation: they are long (~1 ks to be compared with 0.1-1 s of typical magnetar bursts) and faint (~1E34 erg/s, with respect to 1E38 erg/s or more in magnetars). Their spectra are comparatively soft and resemble the hotter thermal component of the persistent emission., Comment: Accepted by A&A; 6 pages, 6 figures; this version includes minor changes to match the final version; abstract abridged

After two major outbursts in 2006 and 2011, on 2017 May 16 the magnetar CXOU J164710.2-455216, hosted within the massive star cluster Westerlund I, emitted a short (20 ms) burst, which marked the onset of a new active phase. We started a long-term monitoring campaign with Swift (45 observations), Chandra (5 observations) and NuSTAR (4 observations) from the activation until 2018 April. During the campaign, Swift BAT registered the occurrence of multiple bursts, accompanied by two other enhancements of the X-ray persistent flux. The long time span covered by our observations allowed us to study the spectral as well as the timing evolution of the source. After 11 months since the 2017 May outburst onset, the observed flux was about 15 times higher than its historical minimum level and a factor of 3 higher than the level reached after the 2006 outburst. This suggests that the crust has not fully relaxed to the quiescent level, or that the source quiescent level has changed following the multiple outburst activities in the past 10 years or so. This is another case of multiple outbursts from the same source on a yearly time scale, a somehow recently discovered behaviour in magnetars., Comment: Accepted for publication in MNRAS, 14 pages, 7 figures

We present the spin frequency and profile evolution of the radio pulsar J1119$-$6127 following magnetar-like X-ray bursts from the system in 2016 July. Using data from the Parkes radio telescope, we observe a smooth and fast spin-down process subsequent to the X-ray bursts resulting in a net change in the pulsar rotational frequency of $\Delta\nu\approx-4\times10^{-4}$\,Hz. During the transition, a net spin-down rate increase of $\Delta\dot\nu\approx-1\times10^{-10}$\,Hz\,s$^{-1}$ is observed, followed by a return of $\dot{\nu}$ to its original value. In addition, the radio pulsations disappeared after the X-ray bursts and reappeared about two weeks later with the flux density at 1.4\,GHz increased by a factor of five. The flux density then decreased and undershot the normal flux density followed by a slow recovery back to normal. The pulsar's integrated profile underwent dramatic and short-term changes in total intensity, polarization and position angle. Despite the complex evolution, we observe correlations between the spin-down rate, pulse profile shape and radio flux density. Strong single pulses have been detected after the X-ray bursts with their energy distributions evolving with time. The peculiar but smooth spin frequency evolution of PSR~J1119$-$6127 accompanied by systematic pulse profile and flux density changes are most likely to be a result of either reconfiguration of the surface magnetic fields or particle winds triggered by the X-ray bursts. The recovery of spin-down rate and pulse profile to normal provides us the best case to study the connection between high magnetic-field pulsars and magnetars., Comment: Accepted for publication in MNRAS on 2018 July 24

We report on a new NuSTAR observation and on the ongoing Swift XRT monitoring campaign of the peculiar source 1E 161348-5055, located at the centre of the supernova remnant RCW 103, which is recovering from its last outburst in June 2016. The X-ray spectrum at the epoch of the NuSTAR observation can be described by either two absorbed blackbodies ($kT_{BB_1}$ ~ 0.5 keV, $kT_{BB_2}$ ~ 1.2 keV) or an absorbed blackbody plus a power law ($kT_{BB_1}$ ~ 0.6 keV, $\Gamma$ ~ 3.9). The observed flux was ~ 9 $\times$ 10$^{-12}$ erg s$^{-1}$ cm$^{-2}$, ~ 3 times lower than what observed at the outburst onset, but about one order of magnitude higher than the historical quiescent level. A periodic modulation was detected at the known 6.67 hr periodicity. The spectral decomposition and evolution along the outburst decay are consistent with 1E 161348-5055 being a magnetar, the slowest ever detected., Comment: Accepted for publication in MNRAS

We used the 10.4m Gran Telescopio Canarias to search for the optical counterparts to four isolated $\gamma$-ray pulsars, all detected in the X-rays by either \xmm\ or \chan\ but not yet in the optical. Three of them are middle-aged pulsars -- PSR\, J1846+0919 (0.36 Myr), PSR\, J2055+2539 (1.2 Myr), PSR\, J2043+2740 (1.2 Myr) -- and one, PSR\, J1907+0602, is a young pulsar (19.5 kyr). For both PSR\, J1907+0602 and PSR\, J2055+2539 we found one object close to the pulsar position. However, in both cases such an object cannot be a viable candidate counterpart to the pulsar. For PSR\, J1907+0602, because it would imply an anomalously red spectrum for the pulsar and for PSR\, J2055+2539 because the pulsar would be unrealistically bright ($r'=20.34\pm0.04$) for the assumed distance and interstellar extinction. For PSR\, J1846+0919, we found no object sufficiently close to the expected position to claim a possible association, whereas for PSR\, J2043+2740 we confirm our previous findings that the object nearest to the pulsar position is an unrelated field star. We used our brightness limits ($g' \approx 27$), the first obtained with a large-aperture telescope for both PSR\, J1846+0919 and PSR\, J2055+2539, to constrain the optical emission properties of these pulsars and investigate the presence of spectral turnovers at low energies in their multi-wavelength spectra., Comment: 10 pages, 11 figures, accpted for publication in MNRAS

We currently know about 30 magnetars: seemingly isolated neutron stars whose properties can be (in part) comprehended only acknowledging that they are endowed with magnetic fields of complex morphology and exceptional intensity-at least in some components of the field structure. Although magnetars represent only a small percentage of the known isolated neutron stars, there are almost certainly many more of them, since most magnetars were discovered in transitory phases called outbursts, during which they are particularly noticeable. In outburst, in fact, a magnetar can be brighter in X-rays by orders of magnitude and usually emit powerful bursts of hard-X/soft-gamma-ray photons that can be detected almost everywhere in the Galaxy with all-sky monitors such as those on board the Fermi satellite or the Neil Gehrels Swift Observatory. Magnetars command great attention because the large progress that has been made in their understanding is proving fundamental to fathom the whole population of isolated neutron stars, and because, due to their extreme properties, they are relevant for a vast range of different astrophysical topics, from the study of gamma-ray bursts and superluminous supernovae, to ultraluminous X-ray sources, fast radio bursts, and even to sources of gravitational waves. Several excellent reviews with different focuses were published on magnetars in the last few years: among others, Israel and Dall'Osso (2011); Rea and Esposito (2011); Turolla and Esposito (2013); Mereghetti et al. (2015); Turolla et al. (2015); Kaspi and Beloborodov (2017). Here, we quickly recall the history of these sources and travel through the main observational facts, trying to touch some recent and sometimes little-discussed ramifications of magnetars., Comment: Review to appear in T. Belloni, M. Mendez, C. Zhang, editors, "Timing Neutron Stars: Pulsations, Oscillations and Explosions", ASSL, Springer. arXiv admin note: text overlap with arXiv:1409.2004 by other authors

The mass of the stellar precursor of supernova (SN) 1987A and the burst of neutrinos observed at the moment of the explosion are consistent with the core-collapse formation of a neutron star. However, no compelling evidence for the presence in SN 1987A of a compact object of any kind has been found yet in any band of the electromagnetic spectrum, prompting questions on whether the neutron star survived and, if it did, on its properties. Starting from the analysis of recent Chandra observations, here we appraise the current observational situation. We derived limits on the X-ray luminosity of a compact object with a nonthermal, Crab-pulsar-like spectrum of the order of $\approx$$(1$-$5)\times10^{35}$ erg s$^{-1}$, corresponding to limits on the rotational energy loss of a possible X-ray pulsar in SN 1987A of $\approx$$(0.5$-$1.5)\times10^{38}$ erg s$^{-1}$. However, a much brighter X-ray source cannot be excluded if, as is likely, it is enshrouded in a cloud of absorbing matter with metallicity similar to that expected in the outer layers of a massive star towards the end of its life. We found that other limits obtained from various arguments and observations in other energy ranges either are unbinding or allow a similar maximum luminosity of the order of $\approx$$10^{35}$ erg s$^{-1}$. We conclude that while a pulsar alike the one in the Crab Nebula in both luminosity and spectrum is hardly compatible with the observations, there is ample space for an `ordinary' X-ray-emitting young neutron star, born with normal initial spin period, temperature and magnetic field, to be hiding inside the evolving remnant of SN 1987A., Comment: Accepted for publication in the Astrophysical Journal; 10 pages, 3 color figures, 2 tables

We report on the first simultaneous XMM-Newton, NuSTAR and Swift observations of the transitional millisecond pulsar PSR J1023+0038 in the X-ray active state. Our multi-wavelength campaign allowed us to investigate with unprecedented detail possible spectral variability over a broad energy range in the X-rays, as well as correlations and lags among emissions in different bands. The soft and hard X-ray emissions are significantly correlated, with no lags between the two bands. On the other hand, the X-ray emission does not correlate with the UV emission. We refine our model for the observed mode switching in terms of rapid transitions between a weak propeller regime and a rotation-powered radio pulsar state, and report on a detailed high-resolution X-ray spectroscopy using all XMM-Newton Reflection Grating Spectrometer data acquired since 2013. We discuss our results in the context of the recent discoveries on the system and of the state of the art simulations on transitional millisecond pulsars, and show how the properties of the narrow emission lines in the soft X-ray spectrum are consistent with an origin within the accretion disc., Comment: 13 pages, 5 figures, accepted for publication in A&A

We report on the first continuous, 80 day optical monitoring of the transitional millisecond pulsar PSR J1023+0038 carried out in mid-2017 with Kepler in the K2 configuration, when an X-ray subluminous accretion disk was present in the binary. Flares lasting from minutes to 14 hr were observed for 15.6% of the time, which is a larger fraction than previously reported on the basis of X-ray and past optical observations, and more frequently when the companion was at the superior conjunction of the orbit. A sinusoidal modulation at the binary orbital period was also present with an amplitude of ~16%, which varied by a few percent over timescales of days, and with a maximum that took place 890 +/- 85 s earlier than the superior conjunction of the donor. We interpret these phenomena in terms of reprocessing of the X-ray emission by an asymmetrically heated companion star surface and/or a non-axisymmetric outflow possibly launched close to the inner Lagrangian point. Furthermore, the non-flaring average emission varied by up to ~ 40% over a time scale of days in the absence of correspondingly large variations of the irradiating X-ray flux. The latter suggests that the observed changes in the average optical luminosity might be due to variations of the geometry, size, and/or mass accretion rate in the outer regions of the accretion disk., Comment: 6 pages, 4 figures. Published in ApJ Letters

Rotation-powered pulsars and magnetars are two different observational manifestations of neutron stars: rotation powered pulsars are rapidly spinning objects that are mostly observed as pulsating radio sources, while magnetars, neutron stars with the highest known magnetic fields, often emit short-duration X-ray bursts. Here we report simultaneous observations of the high-magnetic-field radio pulsar PSR J1119-6127 at X-ray, with XMM-Newton & NuSTAR, and at radio energies with Parkes radio telescope, during a period of magnetar-like bursts. The rotationally powered radio emission shuts off coincident with the occurrence of multiple X-ray bursts, and recovers on a time scale of ~70 seconds. These observations of related radio and X-ray phenomena further solidify the connection between radio pulsars and magnetars, and suggest that the pair plasma produced in bursts can disrupt the acceleration mechanism of radio emitting particles., Comment: 8 pages, 4 figures. Submitted to ApJL

We present the results of deep optical imaging of the radio/$\gamma$-ray pulsar PSR J2043+2740, obtained with the Large Binocular Telescope (LBT). With a characteristic age of 1.2 Myr, PSR J2043+2740 is one of the oldest (non recycled) pulsars detected in $\gamma$-rays, although with still a quite high rotational energy reservoir ($\dot{E}_{\rm rot} = 5.6 \times 10^{34}$ erg s$^{-1}$). The presumably close distance (a few hundred pc), suggested by the hydrogen column density ($N_{\rm H} \lesssim 3.6 \times 10^{20}$ cm$^{-2}$), would make it a viable target for deep optical observations, never attempted until now. We observed the pulsar with the Large Binocular Camera of the LBT. The only object (V=25.44$\pm$0.05) detected within ~3" from the pulsar radio coordinates is unrelated to it. PSR J2043+2740 is, thus, undetected down to V~26.6 (3-$\sigma$), the deepest limit on its optical emission. We discuss the implications of this result on the pulsar emission properties., Comment: 4 pages, 3 figures, accepted for publication on MNRAS

Whilst astronomy as a science is historically founded on observations at optical wavelengths, studying the Universe in other bands has yielded remarkable discoveries, from pulsars in the radio, signatures of the Big Bang at submm wavelengths, through to high energy emission from accreting, gravitationally-compact objects and the discovery of gamma-ray bursts. Unsurprisingly, the result of combining multiple wavebands leads to an enormous increase in diagnostic power, but powerful insights can be lost when the sources studied vary on timescales shorter than the temporal separation between observations in different bands. In July 2015, the workshop "Paving the way to simultaneous multi-wavelength astronomy" was held as a concerted effort to address this at the Lorentz Center, Leiden. It was attended by 50 astronomers from diverse fields as well as the directors and staff of observatories and spaced-based missions. This community white paper has been written with the goal of disseminating the findings of that workshop by providing a concise review of the field of multi-wavelength astronomy covering a wide range of important source classes, the problems associated with their study and the solutions we believe need to be implemented for the future of observational astronomy. We hope that this paper will both stimulate further discussion and raise overall awareness within the community of the issues faced in a developing, important field., Comment: 52 pages, 15 figures, accepted, invited review (to appear in New Astronomy Reviews), v3: updated figure and text

We present deep observations of the field of the magnetar CXOJ164710.2-455216 in the star cluster Westerlund 1, obtained in the near-infrared with the adaptive optics camera NACO@VLT. We detected a possible candidate counterpart at the {\em Chandra} position of the magnetar, of magnitudes $\mathrm{J} = 23.5 \pm 0.2$, $\mathrm{H} = 21.0 \pm 0.1$, and $\mathrm{K}_\mathrm{S} = 20.4 \pm 0.1$. The K$_{\rm S}$-band measurements available for two epochs (2006 and 2013) do not show significant signs of variability but only a marginal indication that the flux varied (at the 2 $\sigma$ level), consistent with the fact that the observations were taken when CXOJ164710.2-455216 was in quiescence. At the same time, we also present colour--magnitude and colour--colour diagrams in the J, H, and K$_{\rm S}$ bands from the 2006 epoch only, the only one with observations in all three bands, showing that the candidate counterpart lies in the main bulk of objects describing a relatively well--defined sequence. Therefore, based on its colours and lack of variability, we cannot yet associate the candidate counterpart to CXOJ164710.2-455216. Future near-infrared observations of the field, following-up a source outburst, would be crucial to confirm the association from the detection of near-infrared variability and colour evolution., Comment: 5 pages, 3 figures, accepted for publication in MNRAS

We report on 3.5 years of Chandra monitoring of the Galactic Centre magnetar SGR J1745-2900 since its outburst onset in April 2013. The magnetar spin-down has shown at least two episodes of period derivative increases so far, and it has slowed down regularly in the past year or so. We observed a slightly increasing trend in the time evolution of the pulsed fraction, up to about 55 per cent in the most recent observations. SGR J1745-2900 has not reached the quiescent level yet, and so far the overall outburst evolution can be interpreted in terms of a cooling hot region on the star surface. We discuss possible scenarios, showing in particular how the presence of a shrinking hot spot in this source is hardly reconcilable with internal crustal cooling and favors the untwisting bundle model for this outburst. Moreover, we also show how the emission from a single uniform hot spot is incompatible with the observed pulsed fraction evolution for any pair of viewing angles, suggesting an anisotropic emission pattern., Comment: 11 pages, 6 figures, accepted for publication on MNRAS

CONTEXT - Transient low-mass X-ray binaries (LMXBs) often show outbursts lasting typically a few-weeks and characterized by a high X-ray luminosity ($L_{x} \approx 10^{36}-10^{38}$ erg/sec), while for most of the time they are found in X-ray quiescence ($L_X\approx10^{31} -10^{33}$ erg/sec). EXO 1745-248 is one of them. AIMS - The broad-band coverage, and the sensitivity of instrument on board of {\xmm} and {\igr}, offers the opportunity to characterize the hard X-ray spectrum during {\exo} outburst. METHODS - In this paper we report on quasi-simultaneous {\xmm} and {\igr} observations of the X-ray transient {\exo} located in the globular cluster Terzan 5, performed ten days after the beginning of the outburst (on 2015 March 16th) shown by the source between March and June 2015. The source was caught in a hard state, emitting a 0.8-100 keV luminosity of $\simeq10^{37}$~{\lumcgs}. RESULTS - The spectral continuum was dominated by thermal Comptonization of seed photons with temperature $kT_{in}\simeq1.3$ keV, by a cloud with moderate optical depth $\tau\simeq2$ and electron temperature $kT_e\simeq 40$ keV. A weaker soft thermal component at temperature $kT_{th}\simeq0.6$--0.7 keV and compatible with a fraction of the neutron star radius was also detected. A rich emission line spectrum was observed by the EPIC-pn on-board {\xmm}; features at energies compatible with K-$\alpha$ transitions of ionized sulfur, argon, calcium and iron were detected, with a broadness compatible with either thermal Compton broadening or Doppler broadening in the inner parts of an accretion disk truncated at $20\pm6$ gravitational radii from the neutron star. Strikingly, at least one narrow emission line ascribed to neutral or mildly ionized iron is needed to model the prominent emission complex detected between 5.5 and 7.5 keV. (Abridged), Comment: 14 pages, 6 figure, 2 tables. Accepted for publication on A&A (21/03/2017)

We report on the results of a detailed phase-resolved spectroscopy of archival XMM--Newton observations of X-ray Dim Isolated Neutron Stars (XDINSs). Our analysis revealed a narrow and phase-variable absorption feature in the X-ray spectrum of RX J1308.6+2127. The feature has an energy of $\sim$740 eV and an equivalent width of $\sim$15 eV. It is detected only in $\sim$ 1/5 of the phase cycle, and appears to be present for the entire timespan covered by the observations (2001 December - 2007 June). The strong dependence on the pulsar rotation and the narrow width suggest that the feature is likely due to resonant cyclotron absorption/scattering in a confined high-B structure close to the stellar surface. Assuming a proton cyclotron line, the magnetic field strength in the loop is B$_{loop} \sim 1.7 \times 10^{14}$ G, about a factor of $\sim$5 higher than the surface dipolar magnetic field (B$_{surf} \sim 3.4 \times 10^{13}$ G). This feature is similar to that recently detected in another XDINS, RX J0720.4-3125, showing (as expected by theoretical simulations) that small scale magnetic loops close to the surface might be common to many highly magnetic neutron stars (although difficult to detect with current X-ray instruments). Furthermore, we investigated the available XMM--Newton, data of all XDINSs in search for similar narrow phase-dependent features, but could derive only upper limits for all the other sources., Comment: 10 pages, 5 figures, 4 tables. Accepted for publication in MNRAS