We report on International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the soft γ-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with fluence of erg cm−2 were detected by the Imager on-board INTEGRAL (IBIS) instrument in the 20–200 keV range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and Survey for Transient Astronomical Radio Emission 2 (STARE2) radio telescopes at 400–800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by ∼29 ms time intervals, superimposed on a broad pulse lasting ∼0.6 s. The brightest peak had a delay of 6.5 ± 1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cutoff power law with photon index and peak energy , is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust-scattering ring seen in X-rays with the Neil Gehrels Swift Observatory X-ray Telescope (XRT) instrument, we derived a distance of kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20–200 keV fluence of erg cm−2 corresponds to an isotropic emitted energy of erg. This is the first burst with a radio counterpart observed from a soft γ-ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.

Calvera (1RXS J141256.0+792204) is an isolated neutron star detected only through its thermal X-ray emission. Its location at high Galactic latitude (b = +37°) is unusual if Calvera is a relatively young pulsar, as suggested by its spin period (59 ms) and period derivative (3.2 × 10−15 s s−1). Using the Neutron Star Interior Composition Explorer, we obtained a phase-connected timing solution spanning four years, which allowed us to measure the second derivative of the frequency ν ̈ = − 2.5 × 10 − 23 Hz s−2 and to reveal timing noise consistent with that of normal radio pulsars. A magnetized hydrogen atmosphere model, covering the entire star surface, provides a good description of the phase-resolved spectra and energy-dependent pulsed fraction. However, we found that a temperature map more anisotropic than that produced by a dipole field is required, with a hotter zone concentrated toward the poles. By adding two small polar caps, we found that the surface effective temperature and that of the caps are ∼0.1 and ∼0.36 keV, respectively. The inferred distance is ∼3.3 kpc. We confirmed the presence of an absorption line at 0.7 keV associated with the emission from the whole star surface, difficult to interpret as a cyclotron feature and more likely originating from atomic transitions. We searched for pulsed γ-ray emission by folding seven years of Fermi-LAT data using the X-ray ephemeris, but no evidence for pulsations was found. Our results favor the hypothesis that Calvera is a normal rotation-powered pulsar, with the only peculiarity of being born at a large height above the Galactic disk.

We report on the serendipitous discovery of a new transient in NGC 5907, at a peak luminosity of 6.4×10 39 erg s −1 . The source was undetected in previous 2012 Chandra observations with a 3σ upper limit on the luminosity of 1.5 × 10 38 erg s −1 , implying a flux increase of a factor of > 35. We analyzed three recent 60ks/50ks Chandra and 50ks XMM-Newton observations, as well as all the available Swift/XRT observations performed between August 2017/March 2018. Until the first half of October 2017, Swift/XRT observations do not show any emission from the source. The transient entered the ULX regime in less than two weeks and its outburst was still on-going at the end of February 2018. The 0.3-10 keV spectrum is consistent with a single multicolour blackbody disc (kT∼ 1.5 keV). The source might be a ∼30 M black hole accreting at the Eddington limit. However, although we did not find evidence of pulsations, we cannot rule-out the possibility that this ULX hosts an accreting neutron star.

We report on the X-ray properties of four rotation-powered pulsars with characteristic ages in the range 0.3 − 5 Myr, derived from the analysis of XMM-Newton archival observations. We found convincing evidence of thermal emission only in the phase-averaged spectrum of PSR B0114+58, that is well fitted by a blackbody with temperature kT = 0.17 ± 0.02 keV and emitting radius R = 405 +110 −90 m, consistent with the size of its polar cap. The other three considered pulsars, PSR B0628−28, PSR B0919+06 and PSR B1133+16, have phase-averaged spectra well described by single power-laws with photon index Γ ∼ 3. The 3σ upper limits on the bolometric luminosity of a possible thermal component with temperature in the range ∼ 0.05 − 2 keV are L bol 3.2 × 10 28 erg s −1 and L bol 2.4 × 10 29 erg s −1 , for PSR B0628−28 and PSR B0919+06, respectively. On the other hand, we found possible evidence that the pulsed emission of PSR B0628−28 is thermal. Two absorption lines at ∼ 0.22 keV and ∼ 0.44 keV are detected in the spectrum of PSR B1133+16. They are best interpreted as proton cyclotron features, implying the presence of multipolar components with a field of a few 10 13 G at the neutron star polar caps. We discuss our results in the context of high-energy emission models of old rotation-powered pulsars.

After 15 yr, 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 2 change in its spin-down rate from ∼7.2 × 10−12 to ∼1.5 × 10−11 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.

GRB 221009A is the brightest gamma-ray burst (GRB) ever detected that has occurred at low Galactic latitude. Owing to this exceptional combination, its prompt X-ray emission could be detected for weeks in the form of expanding X-ray rings produced by scattering in Galactic dust clouds. We report on the analysis of 20 rings, generated by dust at distances ranging from 0.3 to 18.6 kpc, detected during two X‐ray Multi Mirror (XMM)-Newton observations performed about 2 and 5 days after the GRB. By fitting the spectra of the rings with different models for the dust composition and grain size distribution, we reconstructed the spectrum of the GRB prompt emission in the 0.7–4 keV energy range as an absorbed power law with photon index Γ = 1–1.4 and absorption in the host galaxy N H,z = (4.1–5.3) × 1021 cm−2. Taking into account the systematic uncertainties regarding the column density of dust contained in the clouds producing the rings, the 0.5–5 keV fluence of GRB 221009A can be constrained between 10−3 and 7 × 10−3 erg cm−2. Both the fluence and the photon index indicate the presence of a possible soft excess with respect to the extrapolation of the main GRB peak observed at higher energies.

We present the results of an XMM-Newton observation of the slowly rotating (P = 3.4 s), highly magnetized (B ≈ 3×10 13 G) radio pulsar PSR J0726−2612. A previous X-ray observation with the Chandra satellite showed that some of the properties of PSR J0726−2612 are similar to those of the X-ray Dim Isolated Neutron Stars (XDINSs), a small class of nearby slow pulsars characterized by purely thermal X-ray spectra and undetected in the radio band. We confirm the thermal nature of the X-ray emission of PSR J0726−2612, which can be fit by the sum of two blackbodies with temperatures kT 1 = 0.074 +0.006 −0.011 keV and kT 2 = 0.14 +0.04 −0.02 keV and emitting radii R 1 = 10.4 +10.8 −2.8 km and R 2 = 0.5 +0.9 −0.3 km, respectively (assuming a distance of 1 kpc). A broad absorption line modeled with a Gaussian profile centred at 0.39 +0.02 −0.03 keV is required in the fit. The pulse profile of PSR J0726−2612 is characterized by two peaks with similar intensity separated by two unequal minima, a shape and pulsed fraction that cannot be reproduced without invoking magnetic beaming of the X-ray emission. The presence of a single radio pulse suggests that in PSR J0726−2612 the angles that the dipole axis and the line of sight make with the rotation axis, ξ and χ respectively, are similar. This geometry differs from that of the two radio-silent XDINSs with a double peaked pulse profile similar to that of PSR J0726−2612, for which ξ ∼ 90 • and χ ∼ 45 • have been recently estimated. These results strengthen the similarity between PSR J0726−2612 and the XDINSs and support the possibility that the lack of radio emission from the latter might simply be due to an unfavourable viewing geometry.

PSR B0943+10 is a mode-switching radio pulsar characterized by two emission modes with different radio and X-ray properties. Previous studies, based on simple combinations of blackbody and power law models, showed that its X-ray flux can be decomposed in a pulsed thermal plus an unpulsed non-thermal components. However, if PSR B0943+10 is a nearly aligned rotator seen pole-on, as suggested by the radio data, it is difficult to reproduce the high observed pulsed fraction unless magnetic beaming is included. In this work we reanalyze all the available X-ray observations of PSR B0943+10 with simultaneous radio coverage, modeling its thermal emission with polar caps covered by a magnetized hydrogen atmosphere or with a condensed iron surface. The condensed surface model provides good fits to the spectra of both pulsar modes, but, similarly to the blackbody, it can not reproduce the observed pulse profiles, unless an additional power law with an ad hoc modulation is added. Instead, the pulse profiles and phase-resolved spectra are well described using the hydrogen atmosphere model to describe the polar cap emission, plus an unpulsed power law. For the X-ray brighter state (Q-mode) we obtain a best fit with a temperature kT ∼ 0.09 keV, an emitting radius R ∼ 260 m, a magnetic field consistent with the value of the dipole field of 4 × 10 12 G inferred from the timing parameters, and a small angle between the magnetic and spin axis, ξ = 5 • . The corresponding parameters for the X-ray fainter state (B-mode) are kT ∼ 0.08 keV and R ∼ 170 m.