We present results based on the first INTEGRAL AGN catalogue. The catalogue includes 42 AGN, of which 10 are Seyfert 1, 17 are Seyfert 2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rather small with 5 detected objects, and only one galaxy cluster and no star-burst galaxies have been detected so far. The sample consists of bright (fx > 5e-12 erg/cm**2/s), low luminosity (L = 2e43 erg/s), local (z = 0.020) AGN. Although the sample is not flux limited, we find a ratio of obscured to unobscured AGN of 1.5 - 2.0, consistent with luminosity dependent unified models for AGN. Only four Compton-thick AGN are found in the sample. This implies that the missing Compton-thick AGN needed to explain the cosmic hard X-ray background would have to have lower fluxes than discovered by INTEGRAL so far.
Microquasar Spotted Microquasars are binary star systems where a normal star sheds matter onto a neutron star or a black hole, generating x-ray radiation and jets of material moving at relativistic speeds. Microquasars have proved difficult to detect in high-energy gamma rays (> 100 megaelectron volts). Using the Fermi Large Area Telescope, Abdo et al. (p. 1512 , published online 26 November; see the Perspective by Bignami ) now report the detection of variable gamma-ray emission from the microquasar Cygnus X-3. The gamma-ray flux is modulated at the orbital period of Cygnus X-3, and its variation is correlated with the radio emission originating from the microquasar's relativistic jets.
We report on the search for 0.1-10 GeV emission from magnetars in 17 months of Fermi Large Area Telescope (LAT) observations. No significant evidence for gamma-ray emission from any of the currently-known magnetars is found. The most stringent upper limits to date on their persistent emission in the Fermi-LAT energy range are estimated between ~10^{-12}-10^{-10} erg/s/cm2, depending on the source. We also searched for gamma-ray pulsations and possible outbursts, also with no significant detection. The upper limits derived support the presence of a cut-off at an energy below a few MeV in the persistent emission of magnetars. They also show the likely need for a revision of current models of outer gap emission from strongly magnetized pulsars, which, in some realizations, predict detectable GeV emission from magnetars at flux levels exceeding the upper limits identified here using the Fermi-LAT observations.
We present all OSSE observations to date of the Cas A supernova remnant. The objectives are to detect the 44Ti lines, one of which has been reportedly detected by COMPTEL, and the hard X-ray continuum above 40 keY, as indicated by HEAO-A2 measurements. Our best fit flux in each of three 44Ti lines is (+1.76 ± i:~~) x 10-5 , cm-2 with X~ = 1.01, d.o.f.=1780. The implied 44Ti mass of '10-4 M8 is compatible with explosive nucleosynthesis calculations. OSSE detected also a continuum below 200 keV at better than 4(7 confidence level with a flux of ,9 x 10-4 , cm-2 MeV1 at 100 keY. This continuum can be fitted equally well with a power law, an exponential, or a thermal bremsstrahlung model. The implied temperature of kT ~35 keV can be interpreted as the emission from the shocked circumstellar matter (CSM) by the primary blastwave of the supernova. Alternatively, the continuum can also be interpreted as bremsstrahlung from accelerated electrons that are also producing the observed radio emission.
The heavy ion counter (HIC) on the Galileo spacecraft consists of two low‐energy telescopes that were proof‐test models of the telescopes used for the cosmic ray subsystem (CRS) on Voyager. The telescopes on HIC were improved to better withstand the intense radiation environment of the Jovian system and to measure higher‐energy particles with greater sensitivity. The similarity of these two instruments makes it natural to compare the data in an effort to glean insight on the behavior of heavy ion fluxes at higher energies and how the inner Jovian magnetosphere has changed in the last 18 years. Inside L = 6, the oxygen spectrum suggests a spectral break at ∼ 7500 MeV/Gauss, corresponding to ions with gyroradii of ∼ 1.5 R Io at L = 6. A comparison of the phase space densities show remarkable agreement between the two time periods outside of the Io orbit, with differential spectra consistent with γ ∼ −8 above ∼ 6 MeV/nucleon. Near Io Galileo observed a large density gradient not apparent in the Voyager data that may be due to local time asymmetries or a decrease in the radial diffusion rate.
We searched for X-ray serendipitous sources in over 370 Swift-XRT fields centered on gamma ray bursts detected between 2004 and 2008 and observed with total exposures ranging from 10 ks to over 1 Ms. This defines the Swift Serendipitous Survey in deep XRT GRB fields, which is quite broad compared to existing surveys (~33 square degrees) and medium depth, with a faintest flux limit of 7.2e-16 erg cm^-2 s^-1 in the 0.5 to 2 keV energy range. The survey has a high degree of uniformity thanks to the stable point spread function and small vignetting correction factors of the XRT, moreover is completely random on the sky as GRBs explode in totally unrelated parts of the sky. In this paper we present the sample and the X-ray number counts of the high Galactic-latitude sample, estimated with high statistics over a wide flux range (i.e., 7.2e-16 to ~5e-13 erg cm^-2 s^-1 in the 0.5-2 keV band and 3.4e-15 to ~6e-13 erg cm^-2 s^-1 in the 2-10 keV band). We detect 9387 point-like sources, while 7071 point-like sources are found at high Galactic-latitudes (i.e. >=20 deg). The large number of detected sources resulting from the combination of large area and deep flux limits make this survey a new important tool for investigating the evolution of AGN. In particular, the large area permits finding rare high-luminosity objects like QSO2, which are poorly sampled by other surveys, adding precious information for the luminosity function bright end. The high Galactic-latitude logN-logS relation is well determined over all the flux coverage, and it is nicely consistent with previous results at 1 sigma confidence level. By the hard X-ray color analysis, we find that the Swift Serendipitous Survey in deep XRT GRB fields samples relatively unobscured and mildly obscured AGN, with a fraction of obscured sources of ~37% (~15%) in the 2-10 (0.3-3 keV) band.
Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signal-to-noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, {\it narrow-band} analyses methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of eleven pulsars using data from Advanced LIGO's first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched: in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far.
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