1,504 research outputs found
The emission of Cygnus X-1: observations with INTEGRAL SPI from 20 keV to 2 MeV
We report on Cyg X-1 observations performed by the SPI telescope onboard the
INTEGRAL mission and distributed over more than 6 years. We investigate the
variability of the intensity and spectral shape of this peculiar source in the
hard X-rays domain, and more particularly up to the MeV region. We first study
the total averaged spectrum which presents the best signal to noise ratio (4 Ms
of data). Then, we refine our results by building mean spectra by periods and
gathering those of similar hardness.
Several spectral shapes are observed with important changes in the curvature
between 20 and 200 keV, even at the same luminosity level. In all cases, the
emission decreases sharply above 700 keV, with flux values above 1 MeV (or
upper limits) well below the recently reported polarised flux (Laurent et al.
2011), while compatible with the MeV emission detected some years ago by
CGRO/COMPTEL (McConnell et al., 2002).
Finally, we take advantage of the spectroscopic capability of the instrument
to seek for spectral features in the 500 keV region with negative results for
any significant annihilation emission on 2 ks and days timescales, as well as
in the total dataset.Comment: 14 pages, 10 figures, accepted for publication in Ap
The High Energy Emission of the Crab Nebula from 20 keV to 6 MeV with INTEGRAL
The SPI spectrometer aboard the INTEGRAL mission observes regularly the Crab
Nebula since 2003. We report on observations distributed over 5.5 years and
investigate the variability of the intensity and spectral shape of this
remarkable source in the hard X-rays domain up to a few MeV. While single power
law models give a good description in the X-ray domain (mean photon index ~
2.05) and MeV domain (photon index ~ 2.23), crucial information are contained
in the evolution of the slope with energy between these two values. This study
has been carried out trough individual observations and long duration (~ 400
ks) averaged spectra. The stability of the emission is remarkable and excludes
a single power law model. The slopes measured below and above 100 keV agree
perfectly with the last values reported in the X-ray and MeV regions
respectively, but without indication of a localized break point. This suggests
a gradual softening in the emission around 100 keV and thus a continuous
evolution rather than an actual change in the mechanism parameters. In the MeV
region, no significant deviation from the proposed power law model is visible
up to 5-6 MeV. Finally, we take advantage of the spectroscopic capability of
the instrument to seek for previously reported spectral features in the covered
energy range with negative results for any significant cyclotron or
annihilation emission on 400 ks timescales. Beyond the scientific results, the
performance and reliability of the SPI instrument is explicitly demonstrated,
with some details about the most appropriate analysis method.Comment: accepted for publication in ApJ; 4 figures, 2 table
Absolute timing of the Crab pulsar with the INTEGRAL/SPI telescope
We have investigated the pulse shape evolution of the Crab pulsar emission in
the hard X-ray domain of the electromagnetic spectrum. In particular, we have
studied the alignment of the Crab pulsar phase profiles measured in the hard
X-rays and in other wavebands. To obtain the hard X-ray pulse profiles, we have
used six year (2003-2009, with a total exposure of about 4 Ms) of publicly
available data of the SPI telescope on-board of the INTEGRAL observatory,
folded with the pulsar time solution derived from the Jodrell Bank Crab Pulsar
Monthly Ephemeris. We found that the main pulse in the hard X-ray 20-100 keV
energy band is leading the radio one by milliperiods in phase, or
in time. Quoted errors represent only statistical
uncertainties.Our systematic error is estimated to be and is
mainly caused by the radio measurement uncertainties. In hard X-rays, the
average distance between the main pulse and interpulse on the phase plane is
. To compare our findings in hard X-rays with the soft 2-20
keV X-ray band, we have used data of quasi-simultaneous Crab observations with
the PCA monitor on-board the Rossi X-Ray Timing Explorer (RXTE) mission. The
time lag and the pulses separation values measured in the 3-20 keV band are
(corresponding to ) and
parts of the cycle, respectively. While the pulse separation values measured in
soft X-rays and hard X-rays agree, the time lags are statistically different.
Additional analysis show that the delay between the radio and X-ray signals
varies with energy in the 2 - 300 keV energy range. We explain such a behaviour
as due to the superposition of two independent components responsible for the
Crab pulsed emission in this energy band
Wood Property Variation Among Forty-Eight Families of American Sycamore
American sycamore (Platanus occidentalis L.) progeny from forty-eight half-sib families representing five geographic seed sources were analyzed at the end of the fifth growing season for variation in wood properties and growth rate. Stem analysis revealed that specific gravity increased towards the top of the tree while fiber length first increased and then decreased as a function of height within the stem. Diameter, height, volume, specific gravity, fiber length, and moisture content showed significant differences between families. Height and moisture content were the only traits that did not exhibit significant variation due to seed source. Wood properties exhibited considerably less variation than did the growth parameters. However, wood properties did exhibit a larger component of variance due to family effects than did the growth parameters. Diameter, height, and volume were positively correlated with specific gravity and fiber length
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