Search

Magnetar-like activity has been observed in a large variety of neutron stars. PSR J1846-0258 is a young 327 ms radio-quiet pulsar with a large rotational power ($\sim 8 \times 10^{36}$ erg s$^{-1}$), and resides at the center of the supernova remnant Kes 75. It is one of the rare examples of a high magnetic field pulsar showing characteristics both of magnetars and radio pulsars, and can thus provide important clues on the differences in the emission mechanisms between these two classes. In 2006, PSR J1846-0258 was detected to undergo an outburst for the first time, accompanied by a large flux increase, millisecond X-ray bursts, significant spectral changes and a large timing glitch. In the period between May-June 2020, after fourteen years of quiescent stable emission, the source underwent a second magnetar-like outburst, which was followed up with several observations by NICER, XMM-Newton, NuSTAR and Swift. In this work, we report on the long-term timing and X-ray spectral properties of the source following the 2020 outburst, and place upper limits on any source activity at radio wavelengths. We demonstrate that the pulsed flux increased by a factor $> 6$ during the outburst, followed by non-trivial variability in the spin-down rate. Our timing analysis shows that the spin frequency and its derivative are clearly affected by magnetospheric activity due to the outburst. We find hints for an oscillation in the frequency derivative with a timescale of 50-60 days, recovering later on to stable quiescence., Comment: 22 pages, 10 figures; accepted for publication by ApJ; comments are welcome

We present the results from a monitoring campaign made with the Neil Gehrels Swift Observatory of the M51 galaxies, which contain several variable ultraluminous X-ray sources (ULXs). The ongoing campaign started in May 2018, and we report here on $\sim1.5$ years of observations. The campaign, which consists of 105 observations, has a typical cadence of 3--6 days, and has the goal of determining the long-term X-ray variability of the ULXs. Two of the most variable sources were ULX7 and ULX8, both of which are known to be powered by neutron stars that are exceeding their isotropic Eddington luminosities by factors of up to 100. This is further evidence that neutron star powered ULXs are the most variable. Our two main results are, first, that ULX7 exhibits a periodic flux modulation with a period of 38 days varying over a magnitude and a half in flux from peak to trough. Since the orbital period of the system is known to be 2 days, the modulation is super-orbital, which is a near-ubiquitous property of ULX pulsars. Secondly we identify a new transient ULX, M51 XT-1, the onset of which occurred during our campaign, reaching a peak luminosity of $\sim10^{40}$ erg s$^{-1}$, before gradually fading over the next $\sim200$ days until it slipped below the detection limit of our observations. Combined with the high-quality Swift/XRT lightcurve of the transient, serendipitous observations made with Chandra and XMM-Newton provide insights into the onset and evolution of a likely super-Eddington event., Comment: Submitted to ApJ

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies of strongly magnetized objects. We will focus on the physics and astrophysics of strongly magnetized objects, namely magnetars, accreting X-ray pulsars, and rotation powered pulsars. We also discuss the science potential of eXTP for QED studies. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s., Comment: Accepted for publication on Sci. China Phys. Mech. Astron. (2019)

We present the first X-ray and UV/optical observations of a very bright and fast nova in the disc of M31, M31N 2013-01b. The nova reached a peak magnitude $R\sim$15 mag and decayed by 2 magnitudes in only 3 days, making it one of the brightest and fastest novae ever detected in Andromeda. From archival multi-band data we have been able to trace its fast evolution down to $U>21$ mag in less than two weeks and to uncover for the first time the Super-Soft X-ray phase, whose onset occurred 10-30 days from the optical maximum. The X-ray spectrum is consistent with a blackbody with a temperature of $\sim$50 eV and emitting radius of $\sim$4$\times 10^{9}$ cm, larger than a white dwarf radius, indicating an expanded region. Its peak X-ray luminosity, 3.5$\times 10^{37}$ erg s$^{-1}$, locates M31N 2013-01b among the most luminous novae in M31. We also unambiguously detect a short 1.28$\pm$0.02 h X-ray periodicity that we ascribe to the binary orbital period, possibly due to partial eclipses. This makes M31N 2013-01b the first nova in M31 with an orbital period determined. The short period also makes this nova one of the few known below the 2-3 h orbital period gap. All the observed characteristics strongly indicate that M31N 2013-01b harbours a massive white dwarf and a very low-mass companion, consistent with being a nova belonging to the disc population of the Andromeda Galaxy., Comment: 9 pages, 3 figures, 2 tables; accepted by the Astrophysical Journal

One of the primary science goals of the next generation of hard X-ray timing instruments is to determine the equation of state of the matter at supranuclear densities inside neutron stars, by measuring the radius of neutron stars with different masses to accuracies of a few percent. Three main techniques can be used to achieve this goal. The first involves waveform modelling. The flux we observe from a hotspot on the neutron star surface offset from the rotational pole will be modulated by the star's rotation, giving rise to a pulsation. Information about mass and radius is encoded into the pulse profile via relativistic effects, and tight constraints on mass and radius can be obtained. The second technique involves characterising the spin distribution of accreting neutron stars. The most rapidly rotating stars provide a very clean constraint, since the mass-shedding limit is a function of mass and radius. However the overall spin distribution also provides a guide to the torque mechanisms in operation and the moment of inertia, both of which can depend sensitively on dense matter physics. The third technique is to search for quasi-periodic oscillations in X-ray flux associated with global seismic vibrations of magnetars (the most highly magnetized neutron stars), triggered by magnetic explosions. The vibrational frequencies depend on stellar parameters including the dense matter equation of state. We illustrate how these complementary X-ray timing techniques can be used to constrain the dense matter equation of state, and discuss the results that might be expected from a 10m$^2$ instrument. We also discuss how the results from such a facility would compare to other astronomical investigations of neutron star properties. [Modified for arXiv], Comment: To appear in Reviews of Modern Physics as a Colloquium, 23 pages, 9 figures

X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil)., Comment: 49 pages, 14 figures, 6 tables. Paper published in Experimental Astronomy http://link.springer.com/journal/10686

Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slowly rotating, isolated neutron stars that sporadically undergo episodes of long-term flux enhancement (outbursts) generally accompanied by the emission of short bursts of hard X-rays. This behaviour can be understood in the magnetar model, according to which these sources are mainly powered by their own magnetic energy. This is supported by the fact that the magnetic fields inferred from several observed properties of AXPs and SGRs are greater than - or at the high end of the range of - those of radio pulsars. In the peculiar case of SGR 0418+5729, a weak dipole magnetic moment is derived from its timing parameters, whereas a strong field has been proposed to reside in the stellar interior and in multipole components on the surface. Here we show that the X-ray spectrum of SGR 0418+5729 has an absorption line, the properties of which depend strongly on the star's rotational phase. This line is interpreted as a proton cyclotron feature and its energy implies a magnetic field ranging from 2E14 gauss to more than 1E15 gauss., Comment: Nature, 500, 312 (including Supplementary Information)

On May 27th 2010, the Italian astronomical community learned with concern that the National Institute for Astrophysics (INAF) was going to be suppressed, and that its employees were going to be transferred to the National Research Council (CNR). It was not clear if this applied to all employees (i.e. also to researchers hired on short-term contracts), and how this was going to happen in practice. In this letter, we give a brief historical overview of INAF and present a short chronicle of the few eventful days that followed. Starting from this example, we then comment on the current situation and prospects of astronomical research in Italy., Comment: Also available at http://adoptitaastronom.altervista.org/index.html

This contribution summarizes, as of early 2008, the observational and theoretical understanding of the physics, and emission properties of two Double Degenerate Binaries with the shortest orbital period known to date. In particular, the Unipolar Inductor Model and its coupling to GW emission have been introduced to explain a number of puzzling features that these two sources have in common and that are thought difficult to reconcile with models of mass transfer in such systems. Emphasis was put on the relevant new physical features that characterize the model. The role of spin-orbit coupling through the Lorentz torque and the role of GW emission in keeping the electric interaction active at all times has been thoroughly discussed in all their implications. Application of the model to both HM Cnc and V407 Vul accounts in a natural way for their main observational properties. Constraints on physical parameters are derived in order for the model to work, and can be verified by future observations., Comment: 24 pages, appeared in the book "Physics of Relativistic Objects in Compact Binaries: From Birth to Coalescence", Astrophysics and Space Science Library, edited by M. Colpi, P. Casella, V. Gorini, U. Moschella, and A. Possenti 2009

We report here on the outburst onset and evolution of the new Soft Gamma Repeater SGR 0501+4516. We monitored the new SGR with XMM-Newton starting on 2008 August 23, one day after the source became burst-active, and continuing with 4 more observations, with the last one on 2008 September 30. Combining the data with the Swift-XRT and Suzaku data, we modelled the outburst decay over 160 days, and we found that the source flux decreased exponentially with a timescale of t_c=23.8 days. In the first XMM-Newton observation a large number of short X-ray bursts were observed, the rate of which decayed drastically in the following observations. We found large changes in the spectral and timing behavior of the source during the outburst, with softening emission as the flux decayed, and the non-thermal soft X-ray spectral component fading faster than the thermal one. Almost simultaneously to our XMM-Newton observations (on 2008 August 29 and September 2), we observed the source in the hard X-ray range with INTEGRAL, which clearly detected the source up to ~100keV in the first pointing, while giving only upper limits during the second pointing, discovering a variable hard X-ray component fading in less than 10 days after the bursting activation. We performed a phase-coherent X-ray timing analysis over about 160 days starting with the burst activation and found evidence of a strong second derivative period component (\ddot{P} = -1.6(4)x10^{-19} s/s^{-2}). Thanks to the phase-connection, we were able to study the the phase-resolved spectral evolution of SGR 0501+4516 in great detail. We also report on the ROSAT quiescent source data, taken back in 1992 when the source exhibits a flux ~80 times lower than that measured during the outburst, and a rather soft, thermal spectrum., Comment: 16 pages; accepted for publication in MNRAS

We present X-ray observations of the transient accretion-powered millisecond pulsar IGR J00291+5934 during quiescence. IGR J00291+5934 is the first source among accretion powered millisecond pulsars to show signs of a thermal component in its quiescent spectrum. Fitting this component with a neutron star atmosphere or a black body model we obtain soft temperatures (~64 eV and ~110 eV, respectively). As in other sources of this class a hard spectral component is also present, comprising more than 60% of the unabsorbed 0.5-10 keV flux. Interpreting the soft component as cooling emission from the neutron star, we can conclude that the compact object can be spun up to milliscond periods by accreting only <0.2 solar masses., Comment: 5 pages - 2 figures. Accepted for publication on ApJL

We present results from our Chandra and XMM-Newton observations of two low-luminosity X-ray pulsators SAX J1324.4-6200 and SAX J1452.8-5949 which have spin-periods of 172 s and 437 s respectively. The XMM-Newton spectra for both sources can be fitted well with a simple power-law model of photon index ~ 1.0. A black-body model can equally well fit the spectra with a temperature of ~ 2 keV for both sources. During our XMM-Newton observations, SAX J1324.4-6200 is detected with coherent X-ray pulsations at a period of $172.86 \pm 0.02$ s while no pulsations with a pulse fraction greater than 15% (at 98% confidence level) are detected in SAX J1452.8--5949. The spin period of SAX J1324.4-6200 is found to be increasing on a time-scale of $\dot{P}$ = $(6.34 \pm 0.08) \times 10^{-9}$ s s$^{-1}$ which would suggest that the accretor is a neutron star and not a white dwarf. Using sub-arcsec spatial resolution of the Chandra telescope, possible counterparts are seen for both sources in the near-infrared images obtained with the SOFI instrument on the New Technology Telescope. The X-ray and near-infrared properties of SAX J1324.4-6200 suggest it to be either a persistent high mass accreting X-ray pulsar or a symbiotic X-ray binary pulsar at a distance $\le$ 9 kpc. We identify the infrared counterpart of SAX J1452.8--5949 to be a late-type main sequence star at a distance $\le$ 10 kpc, thus ruling out SAX J1452.8--5949 to be a high mass X-ray binary. However with the present X-ray and near-infrared observations, we cannot make any further conclusive conclusion about the nature of SAX J1452.8-5949., Comment: 9 pages, 6 figures, 5 tables (Submitted to MNRAS)

In 2003 a previously unpulsed Einstein and ROSAT source cataloged as soft and dim (Lx of few 10^33 ergs) thermal emitting object, namely XTE J1810-197, was identified as the first unambiguous transient Anomalous X-ray Pulsar. Two years later this source was also found to be a bright highly polarized transient radio pulsar, a unique property among both AXPs and radio pulsars. In September 2006 the Swift Burst Alert Telescope (BAT) detected an intense burst from the candidate AXP CXOU J164710.2-455216, which entered in an outburst state reaching a peak emission of at least a factor of 300 higher than quiescence. Here, we briefly outline the recent results concerning the outburst phenomena observed in these two AXPs. In particular, XTE J1810-197 has probed to be a unique laboratory to monitor the timing and spectral properties of a cooling/fading AXP, while new important information have been inferred from X-ray and radio band simultaneous observations. CXOU J164710.2-455216 has been monitored in X-rays and radio bands since the very beginning of its outbursting state allowing us to cover the first phases of the outburst and to study the timing and spectral behavior during the first months., Comment: 5 pages, 3 figures, proceedings of the conference "40 Years of Pulsars, Millisecond Pulsars, Magnetars and More", Montreal, August 12-17 2007. To be published by AIPC

(Abridged) The open cluster NGC 1893, illuminating the HII region IC410, contains a moderately large population of O-type stars and is one of the youngest clusters observable in the optical range. We have probed the stellar population of NGC 1893 in an attempt to determine its size and extent. We classify a large sample of cluster members with new intermediate resolution spectroscopy. We use H-alpha slitless spectroscopy of the field to search for emission line objects, identifying 18 emission-line PMS stars. We then combine existing optical photometry with 2MASS JHKs photometry to detect stars with infrared excesses, finding close to 20 more PMS candidates. While almost all stars earlier than B2 indicate standard reddening, all later cluster members show strong deviations from a standard reddening law, which we interpret in terms of infrared excess emission. Emission-line stars and IR-excess objects show the same spatial distribution, concentrating around two localised areas, the immediate vicinity of the pennant nebulae Sim 129 and Sim 130 and the area close to the cluster core where the rim of the molecular cloud associated with IC 410 is illuminated by the nearby O-type stars. In and around the emission nebula Sim 130 we find three Herbig Be stars with spectral types in the B1-4 range and several other fainter emission-line stars. We obtain a complete census of B-type stars by combining Stroemgren, Johnson and 2MASS photometry and find a deficit of intermediate mass stars compared to massive stars. We observe a relatively extended halo of massive stars surrounding the cluster without an accompanying population of intermediate-mass stars. The overall picture of star formation in NGC 1893 suggests a very complex process., Comment: Acepted for publication in Astronomy & Astrophysics, 11 figures, uses new aa macro. For a version with full resolution figures (Fig. 7 and 8 in colour) use http://www.dfists.ua.es/~ignacio/download/aa6654.pdf

We present an empirical spectral modelling of the high energy emission of the anomalous X-ray pulsar 4U 0142+614, based on simultaneous Swift and INTEGRAL observations from X to gamma-ray energies. We adopted models contained in the XSPEC analysis package, as well as models based on recent theoretical studies, and restricted ourselves to those combinations of up to three components which produce a good fit while requiring the lowest number of free parameters. Only three models were found to fit satisfactorily the 0.5-250keV spectrum of 4U 0142+614: i) a ~0.4keV blackbody and two power-laws, ii) a resonant cyclotron scattering model plus a power-law and iii) two log-parabolic functions. We found that only the latter two models do not over-predict the infrared/optical emission observed simultaneously from this AXP, and only the log-parabolic functions can naturally account for the upper limits set by COMPTEL in the gamma-ray range. A possible interpretation of the two log-parabolae in terms of inverse Compton scattering of soft X-ray photons by very energetic particles is discussed., Comment: 5 pages, 2 figures; accepted for publication in ApJ Letter

We had reported in Chaty, Mignani, Israel (2002) on the near-infrared (NIR) identification of a possible counterpart to the black hole candidate XTE J1908+094 obtained with the ESO/NTT. Here, we present new, follow-up, CFHT adaptive optics observations of the XTE J1908+094 field, which resolved the previously proposed counterpart in two objects separated by about 0.8". Assuming that both objects are potential candidate counterparts, we derive that the binary system is a low-mass system with a companion star which could be either an intermediate/late type (A-K) main sequence star at a distance of 3-10 kpc, or a late-type ($>$K) main sequence star at a distance of 1-3 kpc. However, we show that the brighter of the two objects (J ~ 20.1, H ~ 18.7, K' ~ 17.8) is more likely to be the real counterpart of the X-ray source. Its position is more compatible with our astrometric solution, and colours and magnitudes of the other object are not consistent with the lower limit of 3 kpc derived independently from the peak bolometric flux of XTE J1908+094. Further multi-wavelength observations of both candidate counterparts are crucial in order to solve the pending identification., Comment: accepted for publication in MNRAS, 5 pages, 3 figures

There is growing evidence that two classes of high-energy sources, the Soft Gamma Repeaters and the Anomalous X-ray Pulsars contain slowly spinning ``magnetars'', i.e. neutron stars whose emission is powered by the release of energy from their extremely strong magnetic fields (>10^15 G. We show here that the enormous energy liberated in the 2004 December 27 giant flare from SGR1806-20 (~5 10^46 erg), together with the likely recurrence time of such events, requires an internal field strength of > 10^16 G. Toroidal magnetic fields of this strength are within an order of magnitude of the maximum fields that can be generated in the core of differentially-rotating neutron stars immediately after their formation, if their initial spin period is of a few milliseconds. A substantial deformation of the neutron star is induced by these magnetic fields and, provided the deformation axis is offset from the spin axis, a newborn fast-spinning magnetar would radiate for a few weeks a strong gravitational wave signal the frequency of which (0.5-2 kHz range) decreases in time. The signal from a newborn magnetar with internal field > 10^16.5 G could be detected with Advanced LIGO-class detectors up to the distance of the Virgo cluster (characteristic amplitude h_c about 10^-21). Magnetars are expected to form in Virgo at a rate approx. 1/yr. If a fraction of these have sufficiently high internal magnetic field, then newborn magnetars constitute a promising new class of gravitational wave emitters., Comment: Accepted for publication on ApJ Letters

The sky region including the Chandra position of SGR 1806-20 was monitored in the IR band during 2004, following its increased high energy bursting activity. Observations were performed using NAOS-CONICA, the adaptive optics IR camera mounted on Yepun VLT, which provided images of unprecedented quality (FWHM better than 0.1"). After the 2004 December 27th giant flare, the source position has been nailed by VLA observations of its radio counterpart, reducing the positional uncertainty to 0.04". Using IR data from our monitoring campaign, we discovered the likely IR counterpart to SGR 1806-20 based on positional coincidence with the Chandra and VLA uncertainty regions and flux variability of a factor of about 2 correlated with that at higher energies. We compare our findings with other isolated neutron star classes thought to be related, at some level, with SGRs., Comment: 4 pages, 2 figures. Accepted for publication on A&A Letters

We have discovered rapid Quasi Periodic Oscillations (QPOs) in RXTE/PCA measurements of the pulsating tail of the 27th December 2004 giant flare of SGR 1806-20. QPOs at about 92.5Hz are detected in a 50s interval starting 170s after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed component and are seen only over phases of the 7.56s spin period pulsations away from the main peak. QPOs at about 18 and 30Hz are also detected, 200-300s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected in the flux of a Soft Gamma-ray Repeater, or any other magnetar candidate. We interpret the highest QPOs in terms of the coupling of toroidal seismic modes with Alfven waves propagating along magnetospheric field lines. The lowest frequency QPO might instead provide indirect evidence on the strength of the internal magnetic field of the neutron star., Comment: Accepted for publication on ApJ Letters. 4 Pages, 3 figures. emulateapj5 style used

During 2002-2003 the number of IR-identified counterparts to the Anomalous X-ray Pulsars (AXPs) has grown to four (4U0142+614, 2E2259+584, 1E 1048-59 and 1RXS J170849-400910) out of the six assessed objects of this class, plus two candidates. More importantly, some new common observational characteristics have been identified, such as the IR variability, the IR flattening in the broad band energy spectrum, the X-ray spectral variability as a function of pulse phase (which are not predicted by the magnetar model), and the SGR-like bursts (which can not be explained in terms of standard accretion models). We present the results obtained from an extensive multi-wavelength observational campaign carried out collecting data from the NTT, CFHT for the optical/IR bands, and XMM, Chandra (plus BeppoSAX archival data) in the X-rays. Based on these results and those reported in the literature, the IR-to-X-ray band emission of AXPs has been compared and studied., Comment: 6 pages. To appear in "Young Neutron Stars and Their Environments" (IAU Symposium 218, ASP Conference Proceedings), eds F. Camilo and B. M. Gaensler

A nearly simultaneous X-ray/optical (Chandra and VLT) observational campaign of RX J0806.3+1527 has been carried out during November 2001. These observations allowed us to phase the X-ray and optical light curves for the first time. We measured a phase-shift of about 0.5, in good agreement with the presence of two distinct emission regions and with the X-ray irradiation process predictions. The Chandra data allowed us also to study in details the X-ray spectrum of RX J0806.3+1527, which is consistent with a soft (kT<70 eV) and small (R_BB<20 km) blackbody component. We discuss the present findings on the light of the models proposed so far to account for the X-ray emission detected from RX J0806.3+1527, and its twin source RX J1914.4+2456., Comment: 7 pages. To be published in Proc. Cape Town Workshop on magnetic CVs. Dec 2002

We present optical spectroscopy and optical and infrared photometry of the counterpart to the transient X-ray source KS 1947+300. The counterpart is shown to be a moderately reddened V=14.2 early-type Be star located in an area of low interstellar absorption slightly above the Galactic plane. Changes in brightness are accompanied by correlated reddening of the source, as is expected in this kind of object. From intermediate resolution spectroscopy, we derive a spectral type B0Ve. If the intrinsic luminosity of the star is normal for its spectral type, KS 1947+300 is situated at a distance of ~10 kpc, implying that its X-ray luminosity at the peak of the spring 2000 X-ray outburst was typical of Type II outbursts in Be/X-ray transients. KS 1947+300 is thus the first Be/X-ray recurrent transient showing Type II outbursts which has an almost circular orbit., Comment: 7 pages, 5 figures, uses new A&A format (included). Accepted for publication in A&A

We report on the discovery and confirmation of the optical counterparts of the two transient X-ray pulsars, RXJ0052.1-7319 and XTEJ0111.2-7317. In the narrow (~3" radius) X-ray error circle of RXJ0052.1-7319 we found a V=14.6 (B-V=0.1) 09.5IIIe (a classification as a B0Ve star is also possible, since the luminosity class depends on the uncertainty on the adopted reddening). Medium resolution spectra for this object show Balmer lines in emission with an equivalent width of Halpha=-12/-16A. In the X-ray error box of XTEJ0111.2-7317 we found a relatively bright object (V=15.4, B-V=0.06) which has been classified as a B0.5-B1Ve star and that was later confirmed by Coe et al. (2000) as the most plausible counterpart for XTEJ0111.2-7317. Also in this case we easily detect Balmer emission lines with an Halpha equivalent width of about -21A. There is also evidence for the presence of a surrounding nebula, possibly a supernova remnant. A further bright B0Ve star was found just outside the X-ray error circle of XTEJ0111.2-7317. We discuss the implication of these results in the light of the current knowledge of Be/X-ray binary systems in the Magellanic Clouds and within our Galaxy., Comment: Accepted by A&A. 8 pages, 8 figures

We report on the identification of the optical/IR counterpart of the 29.5-s transient X-ray pulsar GS 1843+009. We re-analysed an archival ROSAT HRI observation of GS 1843+009, obtaining a new refined position. The optical and IR follow-up observations carried out for the new error circle allowed us to find a relatively faint (V=20.9) and variable early type reddened star (V-R=2.1). The optical spectra show the Balmer and Paschen series in emission, while the IR observations confirm the presence of a flux excess (H=13.2, J-H=0.54), suggesting that the star is surrounded by a circumstellar envelope. Spectroscopic and photometric data together indicate a B0-B2 IV-Ve spectral-type star located at a distance of > 10kpc confirming the Be-star/X-ray binary nature of GS 1843+009., Comment: 6 pages (3 figures included). Accepted for publication in A&A

We report evidence for an ~ 80 d periodicity in the X-ray flux of the hard transient pulsar XTE J1946+274. The 1.3-12 keV light curve obtained with the RossiXTE All Sky Monitor shows five regularly spaced flares over a ~ 1 year baseline starting from the outburst onset in Sept. 1998. The first and strongest flare is somewhat longer than the subsequent four flares, which recur in a fairly periodic fashion. This suggests that the profile of the first flare is dominated by the time variability of the Be star ejection episode, while the following four flares are primarily caused by the neutron star motion along an eccentric orbit., Comment: A&A Letter in press (4 pages + 2 figures; requires A&A and psfig macros)

We report the results of two ROSAT HRI observations of the recently discovered 11s X-ray pulsar 1RXS J170849.0-400910. A refined position with a smaller error radius (10" uncertainty) and a new spin period measurement were obtained. These results allowed to derive a period derivative of about 7 times 10^-4 s yr^-1 and to perform a photometric and spectroscopic study of the possible optical counterparts of the source. The limits derived from the optical to X-ray flux ratio exclude the presence of a massive OB companion. These findings, together with the nearly constant X-ray flux, the stability of the pulse shape and pulsed fraction across observations spanning three years, strongly support the inclusion of this 11s pulsar in the class of Anomalous X-ray Pulsars (AXPs)., Comment: 4 pages plus 4 postscript figures. emulateapj style. Accepted for publication in Astrophysical Journal Letters

We report the results of BeppoSAX and ASCA observations of the X-ray source 1E1743.1-2843, located in the region of the galactic center, performed between 1993 and 1998. Observations spanning almost twenty years show that 1E1743.1-2843 is a persistent X-ray source, most likely powered by accretion onto a compact galactic object. The absence of periodic pulsations and the relatively soft X-ray spectrum favour a Low Mass X-ray Binary containing a neutron star. However, no Type I X-ray bursts have been observed in more than 650 ks of observations, leaving other interpretations possible., Comment: A&A in press