4,699 research outputs found
Combining visible and infrared radiometry and lidar data to test simulations in clear and ice cloud conditions
Measurements taken during the 2003 Pacific THORPEX Observing System Test (P-TOST) by the MODIS Airborne Simulator (MAS), the Scanning High-resolution Interferometer Sounder (S-HIS) and the Cloud Physics Lidar (CPL) are compared to simulations performed with a line-by-line and multiple scattering modeling methodology (LBLMS). Formerly used for infrared hyper-spectral data analysis, LBLMS has been extended to the visible and near infrared with the inclusion of surface bi-directional reflectance properties. A number of scenes are evaluated: two clear scenes, one with nadir geometry and one cross-track encompassing sun glint, and three cloudy scenes, all with nadir geometry. <br><br> CPL data is used to estimate the particulate optical depth at 532 nm for the clear and cloudy scenes and cloud upper and lower boundaries. Cloud optical depth is retrieved from S-HIS infrared window radiances, and it agrees with CPL values, to within natural variability. MAS data are simulated convolving high resolution radiances. The paper discusses the results of the comparisons for the clear and cloudy cases. LBLMS clear simulations agree with MAS data to within 20% in the shortwave (SW) and near infrared (NIR) spectrum and within 2 K in the infrared (IR) range. It is shown that cloudy sky simulations using cloud parameters retrieved from IR radiances systematically underestimate the measured radiance in the SW and NIR by nearly 50%, although the IR retrieved optical thickness agree with same measured by CPL. <br><br> MODIS radiances measured from Terra are also compared to LBLMS simulations in cloudy conditions, using retrieved cloud optical depth and effective radius from MODIS, to understand the origin for the observed discrepancies. It is shown that the simulations agree, to within natural variability, with measurements in selected MODIS SW bands. <br><br> The impact of the assumed particles size distribution and vertical profile of ice content on results is evaluated. Sensitivity is much smaller than differences between measured and simulated radiances in the SW and NIR. <br><br> The paper dwells on a possible explanation of these contradictory results, involving the phase function of ice particles in the shortwave
A new model for the X-ray continuum of the magnetized accreting pulsars
Accreting highly magnetized pulsars in binary systems are among the brightest
X-ray emitters in our Galaxy. Although a number of high statistical quality
broad-band (0.1-100 keV) X-ray observations are available, the spectral energy
distribution of these sources is usually investigated by adopting pure
phenomenological models, rather than models linked to the physics of accretion.
In this paper, a detailed spectral study of the X-ray emission recorded from
the high-mass X-ray binary pulsars Cen X-3, 4U 0115+63, and Her X-1 is carried
out by using BeppoSAX and joined Suzaku+NuStar data, together with an advanced
version of the compmag model. The latter provides a physical description of the
high energy emission from accreting pulsars, including the thermal and bulk
Comptonization of cyclotron and bremsstrahlung seed photons along the neutron
star accretion column. The compmag model is based on an iterative method for
solving second-order partial differential equations, whose convergence
algorithm has been improved and consolidated during the preparation of this
paper. Our analysis shows that the broad-band X-ray continuum of all considered
sources can be self-consistently described by the compmag model. The cyclotron
absorption features, not included in the model, can be accounted for by using
Gaussian components. From the fits of the compmag model to the data we inferred
the physical properties of the accretion columns in all sources, finding values
reasonably close to those theoretically expected according to our current
understanding of accretion in highly magnetized neutron stars. The updated
version of the compmag model has been tailored to the physical processes that
are known to occur in the columns of highly magnetized accreting neutron stars
and it can thus provide a better understanding of the high energy radiation
from these sources.Comment: 19 pages, 10 figures, accepted for publication in A&
An Environmental Scan of Weight-Inclusive Resources
This summer, alongside another USRI student, I began to further explore weight-inclusive physical activity. This approach to movement emphasizes that health and well-being can be achieved by anyone, regardless of their size, if provided with accessible, non-stigmatizing environments and support. Though this approach has increased in prevalence over the years, little is known about the application of weight-inclusive approaches in real-world contexts. Using an environmental scan protocol, this study will aim to examine the breadth of online weight-inclusive resources and services within grey literature (internet, social media, experts); synthesize and evaluate the content within identified materials; and discover gaps in the environment. To our knowledge, this will be the first environmental scan of physical activity resources and services that have adopted, or been informed by, the weight-inclusive approach
Swift J1734.5-3027: a new long type-I X-ray bursting source
Swift J1734.5-3027 is a hard X-ray transient discovered by Swift while
undergoing an outburst in September 2013. Archival observations showed that
this source underwent a previous episode of enhanced X-ray activity in May-June
2013. In this paper we report on the analysis of all X-ray data collected
during the outburst in September 2013, the first that could be intensively
followed-up by several X-ray facilities. Our data-set includes INTEGRAL, Swift,
and XMM-Newton observations. From the timing and spectral analysis of these
observations, we show that a long type-I X-ray burst took place during the
source outburst, making Swift J1734.5-3027 a new member of the class of
bursting neutron star low-mass X-ray binaries. The burst lasted for about 1.9
ks and reached a peak flux of (6.01.8)10 erg cm
s in the 0.5-100 keV energy range. The estimated burst fluence in the
same energy range is (1.100.10)10 erg cm. By
assuming that a photospheric radius expansion took place during the first
200 s of the burst and that the accreted material was predominantly
composed by He, we derived a distance to the source of 7.21.5 kpc.Comment: Accepted for publication on A&
Swift monitoring of the new accreting millisecond X-ray pulsar IGRJ17511-3057 in outburst
A new accreting millisecond X-ray pulsar, IGR J17511-3057, was discovered in
outburst on 2009 September 12 during the INTEGRAL Galactic bulge monitoring
programme. To study the evolution of the source X-ray flux and spectral
properties during the outburst, we requested a Swift monitoring of
IGRJ17511-3057. In this paper we report on the results of the first two weeks
of monitoring the source. The persistent emission of IGR J17511-3057 during the
outburst is modeled well with an absorbed blackbody (kT~0.9 keV) and a
power-law component (photon index~1-2), similar to what has been observed from
other previously known millisecond pulsars. Swift also detected three type-I
Xray bursts from this source. By assuming that the peak luminosity of these
bursts is equal to the Eddington value for a pure helium type-I X-ray burst, we
derived an upper limit to the source distance of ~10 kpc. The theoretical,
expected recurrence time of the bursts according to the helium burst hypothesis
is 0.2-0.9 days, in agreement with the observations.Comment: Accepted for publication in A&A Letters. V2: corrected some typos and
added one referenc
Glancing through the accretion column of EXO 2030+375
We took advantage of the large collecting area and good timing capabilities
of the EPIC cameras on-board XMM-Newton to investigate the accretion geometry
onto the magnetized neutron star hosted in the high mass X-ray binary EXO
2030+375 during the rise of a source Type-I outburst in 2014. We carried out a
timing and spectral analysis of the XMM-Newton observation as function of the
neutron star spin phase. We used a phenomenological spectral continuum model
comprising the required fluorescence emission lines. Two neutral absorption
components are present: one covering fully the source and one only partially.
The same analysis was also carried out on two Suzaku observations of the source
performed during outbursts in 2007 and 2012, to search for possible spectral
variations at different luminosities. The XMM-Newton data caught the source at
an X-ray luminosity of erg s and revealed the presence
of a narrow dip-like feature in its pulse profile that was never reported
before. The width of this feature corresponds to about one hundredth of the
neutron star spin period. From the results of the phase-resolved spectral
analysis we suggest that this feature can be ascribed to the self-obscuration
of the accretion stream passing in front of the observer line of sight. We
inferred from the Suzaku observation carried out in 2007 that the
self-obscuration of the accretion stream might produce a significantly wider
feature in the neutron star pulsed profile at higher luminosities
( erg s).Comment: Accepted for publication on A&
The magnetospheric radius of an inclined rotator in the magnetically threaded disk model
The estimate of the magnetospheric radius in a disk-fed neutron star X-ray
binary is a long standing problem in high energy Astrophysics. We review the
magnetospheric radius calculations in the so-called magnetically threaded disk
model, comparing the simplified approach originally proposed by Ghosh & Lamb
(1979) with the revised version proposed by Wang (1987), Wang (1995), and Wang
(1997). We show that for a given set of fixed parameters (assuming also a
comparable screening factor of the neutron star magnetic field by the currents
induced on the disk surface) the revised magnetically threaded disk model
predicts a magnetospheric radius that is significantly smaller than that
derived from the Ghosh & Lamb (1979) treatment. For a fixed value of the
neutron star magnetic field and a wide range of mass accretion rates, the
inclusion of a large inclination angle between the neutron star rotation and
magnetic field axes (60 deg) leads to a further decrease of the
magnetospheric radius. To illustrate the relevance of these calculations, we
consider, as an example, the case of the transitional pulsars. During the
so-called "high mode" of their sub-luminous accretion disk state, these sources
have shown X-ray pulsations interpreted as due to accretion at an unprecedented
low luminosity level compared to other neutron stars in X-ray binaries. In the
context of the magnetic threaded disk model, we show that accretion at
luminosities of 10 erg s (and thus accretion-driven X-ray
pulsations) can be more easily explained when the prescription of the
magnetospheric radius provided by Wang (1997) is used. This avoids the need of
invoking very strong propeller outflows in the transitional pulsars, as
proposed in other literature works.Comment: Accepted for publication in A&
The supergiant fast X-ray transient IGRJ18483-0311 in quiescence: XMM-Newton, Swift, and Chandra observations
IGR J18483-0311 was discovered with INTEGRAL in 2003 and later classified as
a supergiant fast X-ray transient. It was observed in outburst many times, but
its quiescent state is still poorly known. Here we present the results of
XMM-Newton, Swift, and Chandra observations of IGRJ18483-0311. These data
improved the X-ray position of the source, and provided new information on the
timing and spectral properties of IGR J18483-0311 in quiescence. We report the
detection of pulsations in the quiescent X-ray emission of this source, and
give for the first time a measurement of the spin-period derivative of this
source. In IGRJ18483-0311 the measured spin-period derivative of
-(1.3+-0.3)x10^(-9) s/s likely results from light travel time effects in the
binary. We compare the most recent observational results of IGRJ18483-0311 and
SAXJ1818.6-1703, the two supergiant fast X-ray transients for which a similar
orbital period has been measured.Comment: Accepted for publication in MNRA
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