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Astrophysical jet power A small fraction of active galaxies are extreme phenomena, powered by the release of gravitational energy near the supermassive black hole at the galaxy's centre. Just what goes on in the emitting zone, where inflowing gases interact with the outflowing jets, is not clear. One such extreme object is the blazar 3C 279. Multi-band observations of 3C 279 using the Fermi space telescope have revealed a spectacular γ-ray flare coincident with a dramatic change of optical polarization angle. This points to co-spatiality of the optical and γ-ray emission regions and indicates a highly ordered jet magnetic field. Future observation of cosmic accelerators of this type should throw light on how the immense power required to accelerate matter to close to the speed of light is generated. It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. However, the size of the emitting zone and the location of this region relative to the central supermassive black hole are poorly understood. Here, the coincidence of a γ-ray flare with a dramatic change of optical polarization angle is reported, providing evidence for co-spatiality of optical and γ-ray emission regions and indicating a highly ordered jet magnetic field. It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight 1 . The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma (γ)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and γ-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10 5 gravitational radii.

Millisecond pulsars, old neutron stars spun up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such \"recycled\" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311—3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.

We report on the Fermi Large Area Telescope's detection of γ-ray (> 100 mega-electron volts) pulsations from pulsar J1823-3021A in the globular cluster NGC 6624 with high significance (-~7σ). Its γ-ray luminosity, Lγ = (8.4 ± 1.6) ÷ 10³₄ ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The nondetection of the cluster in the off-pulse phase implies that it contains < 32 γ-ray MSPs, not -100 as previously estimated. The γ-ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823-3021A has the largest magnetic field and is the youngest MSP ever detected and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs.

It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight1. Furthermore, the size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. We report the coincidence of a gamma (γ)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and γ-ray emission regions and indicates a highly ordered jet magnetic field. Our results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 105 gravitational radii.

Geminga is the second brightest persistent source in the GeV gamma-ray sky. Discovered in 1975 by SAS-2 mission, it was identified as a pulsar only in the 90s, when ROSAT detected the 237 ms X-ray periodicity, that was later also found by EGRET in gamma rays. Even though Geminga has been one of the most intensively studied isolated neutron star during the last 30 years, its interest remains intact especially at gamma-ray energies, where instruments like the Large Area Telescope (LAT) aboard the Fermi mission will provide an unprecedented view of this pulsars. We will report on the preliminary results obtained on the analysis of the first year of observations. We have been able to do precise timing of Geminga using solely gamma rays, producing a timing solution and allowing a deep study of the evolution of the light curve with energy. We have also measured and studied the high-energy cutoff in the phase-averaged spectrum and produced a detailed study of the spectral evolution with phase.

Forty six gamma-ray pulsars were reported in the First Fermi Large Area Telescope (LAT) Catalog of Gamma-ray Pulsars. Over forty more have been seen since then. A simple but effective figure-of-merit for gamma-detectability is sqrt(Edot)/d^2, where Edot is the pulsar spindown power and d the distance. We are tracking down the best gamma-ray candidates not yet seen. We present the timing and spectral analysis results of some new high spindown power, nearby gamma-ray pulsars. We also update some population distribution plots in preparation for the 2nd Fermi LAT gamma-ray Pulsar Catalog.

We report the discovery of two millisecond pulsars in a search for radio pulsations at the positions of \\emph{Fermi Large Area Telescope} sources with no previously known counterparts, using the Nançay radio telescope. The two millisecond pulsars, PSRs J2017+0603 and J2302+4442, have rotational periods of 2.896 and 5.192 ms and are both in binary systems with low-eccentricity orbits and orbital periods of 2.2 and 125.9 days respectively, suggesting long recycling processes. Gamma-ray pulsations were subsequently detected for both objects, indicating that they power the associated \\emph{Fermi} sources in which they were found. The gamma-ray light curves and spectral properties are similar to those of previously-detected gamma-ray millisecond pulsars. Detailed modeling of the observed radio and gamma-ray light curves shows that the gamma-ray emission seems to originate at high altitudes in their magnetospheres. Additionally, X-ray observations revealed the presence of an X-ray source at the position of PSR J2302+4442, consistent with thermal emission from a neutron star. These discoveries along with the numerous detections of radio-loud millisecond pulsars in gamma rays suggest that many \\emph{Fermi} sources with no known counterpart could be unknown millisecond pulsars.

Dark matter (DM) particle annihilation or decay can produce monochromatic \\(\\gamma\\)-rays readily distinguishable from astrophysical sources. \\(\\gamma\\)-ray line limits from 30 GeV to 200 GeV obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a \\(\\gamma\\)-ray line analysis, and integrated over most of the sky. We obtain \\(\\gamma\\)-ray line flux upper limits in the range \\(0.6-4.5\\times 10^{-9}\\mathrm{cm}^{-2}\\mathrm{s}^{-1}\\), and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.

(Abridged) We have conducted a detailed investigation of the broad-band spectral properties of the \\gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical and other hard X-ray/gamma-ray data, collected within three months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous Spectral Energy Distributions (SED) for 48 LBAS blazars.The SED of these gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual Log \\(\\nu \\) - Log \\(\\nu\\) F\\(_\\nu\\) representation, the typical broad-band spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SEDs to characterize the peak intensity of both the low and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broad-band colors (i.e. the radio to optical and optical to X-ray spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency \\(\\nu_p^S\\) is positioned between 10\\(^{12.5}\\) and 10\\(^{14.5}\\) Hz in broad-lined FSRQs and between \\(10^{13}\\) and \\(10^{17}\\) Hz in featureless BL Lacertae objects.We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron - inverse Compton scenarios. However, simple homogeneous, one-zone, Synchrotron Self Compton (SSC) models cannot explain most of our SEDs, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. (...)