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Neutron stars are thought to be born rapidly rotating and then exhibit a phase of a rotation-powered pulsations as they slow down to 1-10 s periods. The significant population of millisecond pulsars observed in our Galaxy is explained by the recycling concept: during an epoch of accretion from a donor star in a binary system, the neutron star is spun up to millisecond periods. However, only a few pulsars are observed during this recycling process, with relatively high rotational frequencies. Here we report the detection of an X-ray pulsar with $P_{\rm spin} = 1.20$ s in the globular cluster B091D in the Andromeda galaxy, the slowest pulsar ever found in a globular cluster. This bright (up-to 30% of the Eddington luminosity) spinning-up pulsar, persistent over the 12 years of observations, must have started accreting less than 1 Myr ago and has not yet had time to accelerate to hundreds of Hz. The neutron star in this unique wide binary with an orbital period $P_{\rm orb} = 30.5$ h in a 12 Gyr old, metal rich star cluster, accretes from a low mass, slightly evolved post-main sequence companion. We argue that we are witnessing a binary formed at relatively recent epoch by getting a $\sim 0.8M_\odot$ star in a dynamical interaction -- a viable scenario in a massive dense globular cluster like B091D with high global and specific stellar encounter rates. This intensively accreting non-recycled X-ray pulsar provides therefore a long-sought missing piece in the standard pulsar recycling picture., Comment: 16 pages, 8 figures, accepted to ApJ

A0535+26 is a slowly rotating pulsar accreting from the wind of a massive Be star, and that exhibits two cyclotron absorption lines in its X-ray spectrum, at about 45 and 100 keV, respectively. Unlike similar sources, no significant variations of the energy of its cyclotron lines with flux were observed to date. The bright outburst of February 2011 thus offers a unique occasion to probe this peculiar behavior at flux levels not yet observed with present-day instruments. Here we report on the spectral and timing analysis of the data from the spectrometer SPI on-board INTEGRAL collected during the outburst. At the peak of the outburst the estimated luminosity is ~4.9x10^37 erg/s. The fundamental cyclotron feature is detected at all flux levels, and its centroid energy is positively-correlated with the flux of the source, confirming that A0535+26 is accreting at a sub-critical regime. The correlation seems to fall off at ~10^37 erg/s, suggesting the transition from a Coulomb-stopping regime to a gas-mediated shock regime. From the timing analysis we found that the pulsar was spinning up during most of the outburst, and that the spin-up rate correlates with the flux of the source, albeit the correlation is steeper than the one expected from the standard disk accretion theory. Finally, we show that the pulse profile of the source changes dramatically as the flux increases. At high luminosity the profile is highly asymmetric, implying an asymmetry in the geometry of the accretion flow., Comment: 16 pages, 12 figures, 3 tables. Accepted for publication in ApJ

Using a new XMM-Newton observation, we have characterized the X-ray properties of the middle-aged radio-quiet gamma-ray pulsar J0357+3205 (named Morla) and its tail. The X-ray emission from the pulsar is consistent with a magnetospheric non-thermal origin plus a thermal emission from a hot spot (or hot spots). The lack of a thermal component from the whole surface makes Morla the coldest neutron star in its age range. We found marginal evidence for a double-peaked modulation of the X-ray emission. The study of the 9'-long tail confirmed the lack of extended emission near the pulsar itself. The tail shows a very asymmetric brightness profile and its spectrum lacks any spatial variation. We found the nebular emission to be inconsistent with a classical bow-shock, ram-pressure dominated pulsar wind nebula. We propose thermal bremsstrahlung as an alternative mechanism for Morla's tail emission. In this scenario, the tail emission comes from the shocked interstellar medium (ISM) material heated up to X-ray temperatures. This can fully explain the peculiar features of the tail, assuming a hot, moderately dense interstellar medium around the pulsar. For a bremsstrahlung-emitting tail, we can estimate the pulsar distance to be between 300 and 900 pc. A pulsar velocity of about 1900 km/s is required - which would make Morla the pulsar with the largest velocity - and high inclination angles (>70 degrees) are preferred. We propose Morla's nebula as the first example of a new "turtle's tail" class of thermally-emitting nebulae associated to high velocity pulsars., Comment: 39 pages, 2 tables and 6 figures. Accepted by the Astrophysical Journal

Intermediate mass black holes (IMBHs) are among the most elusive objects in contemporary astrophysics. Both theoretical and observational evidence of their existence is subject of debate. Conversely, both theory and observations confirm the presence of a large population of millisecond pulsars (MSPs) with low mass companions residing in globular cluster (GC) centers. If IMBHs are common in GC centers as well, then dynamical interactions will inevitably break up many of these binaries, causing the ejection of several fast MSPs in the Galactic halo. Such population of fast halo MSPs, hard to produce with 'standard' MSP generation mechanisms, would provide a strong, albeit indirect, evidence of the presence of a substantial population of IMBHs in GCs. In this paper we study in detail the dynamical formation and evolution of such fast MSPs population, highlighting the relevant observational properties and assessing detection prospects with forthcoming radio surveys., Comment: 13 pages, 7 figures, 2 tables, accepted for publication in MNRAS