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Detection of an X-ray Pulsation for the Gamma-ray Pulsar Centered in CTA 1

We report the detection of X-ray pulsations with a period of ~315.87 ms from the 2009 XMM-Newton observation for the radio-quiet gamma-ray pulsar, LAT PSR J0007+7303, centered in the supernova remnant CTA 1. The detected pulsed period is consistent with the gamma-ray periodicity at the same epoch found with the Fermi Gamma-ray Space Telescope. The broader sinusoidal structure in the folded light curve of the X-ray emission is dissimilar to that of the gamma-ray emission, and the phase of the peak is about 0.5 shifting from the peak in the gamma-ray bands, indicating that the main component of the X-rays originates from different sites of the pulsar. We conclude that the main component of the X-ray pulsation is contributed by the thermal emission from the neutron star. Although with a significantly different characteristic age, PSR~J0007+7303 is similar to Geminga in emission properties of X-rays and gamma-rays; this makes PSR J0007+7303 the second radio-quiet gamma-ray pulsar with detected X-ray pulsations after Geminga.Comment: 7 pages, 4 figures and 1 table; accepted by ApJ

Comparative study of the two large flares from SGR1900+14 with the BeppoSAX Gamma-Ray Burst Monitor

We report on spectral and temporal results of the 40-700 keV observations, obtained with the Gamma-Ray Burst Monitor (GRBM) on board BeppoSAX, of the two large flares from the Soft Gamma-ray Repeater SGR1900+14 occurred on August 27, 1998 and April 18, 2001. From their intensity, fluence and duration, the first one was classified as "giant" and the second as "intermediate". The spectral results have been obtained with an improved response function of the GRBM. We find that the two events have similar spectral properties, but different temporal properties. The major difference concerns the time profiles of the light curves, whereas the lack of evidence in the 2001 flare for the erratic time variability found at high frequencies (10-1000 Hz) in the 1998 flare could be ascribed to lower counting statistics. We discuss these results in the light of the magnetar model proposed for SGR sources.Comment: 15 pages, 20 figures, accepted for publication in A&

A search for VHE counterparts of Galactic Fermi bright sources and MeV to TeV spectral characterization

Very high-energy (VHE; E>100 GeV) gamma-rays have been detected from a wide range of astronomical objects, such as pulsar wind nebulae (PWNe), supernova remnants (SNRs), giant molecular clouds, gamma-ray binaries, the Galactic Center, active galactic nuclei (AGN), radio galaxies, starburst galaxies, and possibly star-forming regions as well. At lower energies, observations using the Large Area Telescope (LAT) onboard Fermi provide a rich set of data which can be used to study the behavior of cosmic accelerators in the MeV to TeV energy bands. In particular, the improved angular resolution of current telescopes in both bands compared to previous instruments significantly reduces source confusion and facilitates the identification of associated counterparts at lower energies. In this paper, a comprehensive search for VHE gamma-ray sources which are spatially coincident with Galactic Fermi/LAT bright sources is performed, and the available MeV to TeV spectra of coincident sources are compared. It is found that bright LAT GeV sources are correlated with TeV sources, in contrast to previous studies using EGRET data. Moreover, a single spectral component seems unable to describe the MeV to TeV spectra of many coincident GeV/TeV sources. It has been suggested that gamma-ray pulsars may be accompanied by VHE gamma-ray emitting nebulae, a hypothesis that can be tested with VHE observations of these pulsars.Comment: Astronomy and Astrophysics, in press, 17 pages, 12 figures, 5 table

X-ray observations of the Large Magellanic Cloud pulsar PSR B0540-69 and its PWN

PSR B0540-69 is a young pulsar in the Large Magellanic Cloud that has similar properties with respect to the Crab Pulsar, and is embedded in a Pulsar Wind Nebula. We have analyzed the complete archival RXTE dataset of observations of this source, together with new Swift-XRT and INTEGRAL-IBIS data. Accurate lightcurves are produced in various energy bands between 2 and 60 keV, showing no significant energy variations of the pulse shape. The spectral analysis shows that the pulsed spectrum is curved, and is best fitted up to 100 keV by a log-parabolic model: this strengthens the similarities with the Crab pulsar, and is discussed in the light of a phenomenologic multicomponent model. The total emission from this source is studied, the relative contributions of the pulsar and the PWN emission are derived, and discussed in the context of other INTEGRAL detected pulsar/PWN systems.Comment: 11 pages, 11 figures. Accepted for publication in MNRA

Black Hole Formation in Failing Core-Collapse Supernovae

We present results of a systematic study of failing core-collapse supernovae and the formation of stellar-mass black holes (BHs). Using our open-source general-relativistic 1.5D code GR1D equipped with a three-species neutrino leakage/heating scheme and over 100 presupernova models, we study the effects of the choice of nuclear equation of state (EOS), zero-age main sequence (ZAMS) mass and metallicity, rotation, and mass-loss prescription on BH formation. We find that the outcome, for a given EOS, can be estimated, to first order, by a single parameter, the compactness of the stellar core at bounce. By comparing protoneutron star (PNS) structure at the onset of gravitational instability with solutions of the Tolman-Oppenheimer-Volkof equations, we find that thermal pressure support in the outer PNS core is responsible for raising the maximum PNS mass by up to 25% above the cold NS value. By artificially increasing neutrino heating, we find the critical neutrino heating efficiency required for exploding a given progenitor structure and connect these findings with ZAMS conditions, establishing, albeit approximately, for the first time based on actual collapse simulations, the mapping between ZAMS parameters and the outcome of core collapse. We also study the effect of progenitor rotation and find that the dimensionless spin of nascent BHs may be robustly limited below a^* = Jc/GM^2 = 1 by the appearance of nonaxisymmetric rotational instabilities.Comment: 20 emulateapj pages, 13 figures, published in the Astrophysical Journal, minor revision

Identifying Vessel Branching from Fluid Stresses on Microscopic Robots

Objects moving in fluids experience patterns of stress on their surfaces determined by the geometry of nearby boundaries. Flows at low Reynolds number, as occur in microscopic vessels such as capillaries in biological tissues, have relatively simple relations between stresses and nearby vessel geometry. Using these relations, this paper shows how a microscopic robot moving with such flows can use changes in stress on its surface to identify when it encounters vessel branches.Comment: Version 2 has minor clarification

Why is soluble intercellular adhesion molecule-1 related to cardiovascular mortality?

Background: Increased plasma levels of soluble adhesion molecules are associated with an increased risk of atherothrombosis. The pathophysiological mechanisms responsible for these associations are not known. The aim of the present study was to investigate the association of soluble intercellular adhesion molecule-1 (sICAM-1) concentration and risk of cardiovascular and all-cause mortality among individuals with and without type 2 diabetes. In addition, we assessed potential pathophysiological mechanisms by which sICAM-1 may promote mortality. Materials and methods: Six hundred and thirty-one subjects taken from a general population of the middle-aged and elderly participated in this prospective cohort study. Baseline data collection was performed from 1989 to 1992; subjects were followed until 1 January 2000. Results: Subjects who died had higher levels of sICAM-1 than those who survived (506(164) vs. 477(162) ng m

The Distribution of Redshifts in New Samples of Quasi-stellar Objects

Two new samples of QSOs have been constructed from recent surveys to test the hypothesis that the redshift distribution of bright QSOs is periodic in $\log(1+z)$. The first of these comprises 57 different redshifts among all known close pairs or multiple QSOs, with image separations $\leq$ 10\arcsec, and the second consists of 39 QSOs selected through their X-ray emission and their proximity to bright comparatively nearby active galaxies. The redshift distributions of the samples are found to exhibit distinct peaks with a periodic separation of $\sim 0.089$ in $\log(1+z)$ identical to that claimed in earlier samples but now extended out to higher redshift peaks $z = 2.63, 3.45$ and 4.47, predicted by the formula but never seen before. The periodicity is also seen in a third sample, the 78 QSOs of the 3C and 3CR catalogues. It is present in these three datasets at an overall significance level $10^{-5}$ - $10^{-6}$, and appears not to be explicable by spectroscopic or similar selection effects. Possible interpretations are briefly discussed.Comment: submitted for publication in the Astronomical Journal, 15 figure

X-ray and Radio Timing of the Pulsar in 3C 58

We present timing data spanning 6.4 yr for the young and energetic PSR J0205+6449, in the supernova remnant 3C 58. Data were obtained with the Rossi X-ray Timing Explorer, the Jodrell Bank Observatory and the Green Bank Telescope. We present phase-coherent timing analyses showing timing noise and two spin-up glitches with fractional frequency increases of ~3.4E-7 near MJD 52555, and ~3.8E-6 between MJDs 52777 and 53062. These glitches are unusually large if the pulsar was created in the historical supernova in 1181 as has been suggested. For the X-ray timing we developed a new unbinned maximum-likelihood method for determining pulse arrival times which performs significantly better than the traditional binned techniques. In addition, we present an X-ray pulse profile analysis of four years of RXTE data showing that the pulsar is detected up to ~40 keV. We also present the first measurement of the phase offset between the radio and X-ray pulse for this source, showing that the radio pulse leads the X-ray pulse by phi=0.10+/-0.01 in phase. We compile all known measurements of the phase offsets between radio and X-ray and radio and gamma-ray pulses for X-ray and gamma-ray pulsars. We show that there is no relationship between pulse period and phase offset, supported by our measurement of the phase offset for PSR J0205+6449.Comment: 19 pages, 12 figures. Published in the Astrophysical Journal. Includes additional data analysis and two new figure