3,095 research outputs found
X-Ray Grating Observations of Recurrent Nova T Pyxidis During The 2011 Outburst
The recurrent nova T Pyx was observed with the X-ray gratings of Chandra and
XMM-Newton, 210 and 235 days, respectively, after the discovery of the 2011
April 14 outburst. The X-ray spectra show prominent emission lines of C, N, and
O, with broadening corresponding to a full width at half maximum of ~2000-3000
km/s, and line ratios consistent with high-density plasma in collisional
ionization equilibrium. On day 210 we also measured soft X-ray continuum
emission that appears to be consistent with a white dwarf (WD) atmosphere at a
temperature ~420,000 K, partially obscured by anisotropic, optically thick
ejecta. The X-ray continuum emission is modulated with the photometric and
spectroscopic period observed in quiescence. The continuum at day 235 indicated
a WD atmosphere at a consistent effective temperature of 25 days earlier, but
with a lower flux. The effective temperature indicates a mass of ~1 solar mass.
The conclusion of partial WD obscuration is supported by the complex geometry
of non-spherically-symmetric ejecta confirmed in recent optical spectra
obtained with the Southern African Large Telescope (SALT) in November and
December of 2012. These spectra exhibited prominent [O III] nebular lines with
velocity structures typical of bipolar ejecta.Comment: Accepted to ApJ 2013 October 23, 14 pages, 9 figures, 3 table
The 2011 Outburst of Recurrent Nova T Pyx: X-ray Observations Expose the White Dwarf Mass and Ejection Dynamics
The recurrent nova T Pyx underwent its sixth historical outburst in 2011, and
became the subject of an intensive multi-wavelength observational campaign. We
analyze data from the Swift and Suzaku satellites to produce a detailed X-ray
light curve augmented by epochs of spectral information. X-ray observations
yield mostly non-detections in the first four months of outburst, but both a
super-soft and hard X-ray component rise rapidly after Day 115. The super-soft
X-ray component, attributable to the photosphere of the nuclear-burning white
dwarf, is relatively cool (~45 eV) and implies that the white dwarf in T Pyx is
significantly below the Chandrasekhar mass (~1 M_sun). The late turn-on time of
the super-soft component yields a large nova ejecta mass (>~10^-5 M_sun),
consistent with estimates at other wavelengths. The hard X-ray component is
well fit by a ~1 keV thermal plasma, and is attributed to shocks internal to
the 2011 nova ejecta. The presence of a strong oxygen line in this thermal
plasma on Day 194 requires a significantly super-solar abundance of oxygen and
implies that the ejecta are polluted by white dwarf material. The X-ray light
curve can be explained by a dual-phase ejection, with a significant delay
between the first and second ejection phases, and the second ejection finally
released two months after outburst. A delayed ejection is consistent with
optical and radio observations of T Pyx, but the physical mechanism producing
such a delay remains a mystery.Comment: Re-submitted to ApJ after revision
Collimation and asymmetry of the hot blast wave from the recurrent nova V745 Scorpii
The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was
observed on February 22 and 23 by the Chandra X-ray Observatory Transmission
Grating Spectrometers. By that time the supersoft source phase had already
ended and Chandra spectra are consistent with emission from a hot, shock-heated
circumstellar medium with temperatures exceeding 10^7K. X-ray line profiles are
more sharply peaked than expected for a spherically-symmetric blast wave, with
a full width at zero intensity of approximately 2400 km/s, a full width at half
maximum of 1200 +/- 30 km/s and an average net blueshift of 165 +/- 10 km/s.
The red wings of lines are increasingly absorbed toward longer wavelengths by
material within the remnant. We conclude that the blast wave was sculpted by an
aspherical circumstellar medium in which an equatorial density enhancement
plays a role, as in earlier symbiotic nova explosions. Expansion of the
dominant X-ray emitting material is aligned close to the plane of the sky and
most consistent with an orbit seen close to face-on. Comparison of an
analytical blast wave model with the X-ray spectra, Swift observations and
near-infrared line widths indicates the explosion energy was approximately
10^43 erg, and confirms an ejected mass of approximately 10^-7 Msun. The total
mass lost is an order of magnitude lower than the accreted mass required to
have initiated the explosion, indicating the white dwarf is gaining mass and is
a supernova Type 1a progenitor candidate.Comment: To appear in the Astrophysical Journa
Spectroscopy of high mass X-ray binaries with Swift/XRT
We present the X-ray spectroscopy study of three high mass X-ray binary systems, Vela X-1, Cen X-3 and V0332+53 using data obtained with Swift/XRT. The continuum emission of Vela X-1 is consistent with two absorbed power laws, each of them modified by different absorbing columns and with the same power law index. Moreover, the high energy part of the spectrum is modified by absorption components, like Gaussian profile, smedge} or edge} functions. We also detect emission lines and fit as Gaussians at 6.406^+0.004_-0.021 keV (Fe Kalpha) and 2.44^+0.04_-0.03 keV (S XV He_alpha). The continuum emission of Cen X-3 is consistent with two absorbed power laws, each of them modified by different absorbing columns and with the same power law index. We also detect emission lines and fit as Gaussians at 6.432^+0.020_-0.023 keV (Fe Kalpha), 6.84^+0.12_-0.10 keV (Fe XXVI), 2.90 +/- 0.18 keV Ar Kalpha and 1.12^+0.07_-0.06 keV (Ne X Ly_alpha). The presence of iron emission lines at 6.4 keV and 6.8 keV simultaneously indicates that there are at least two distinct emission sites. Fluorescence in a localized region of relatively low ionization may be responsible for the 6.4 keV emission. We could interpret the emission line at 6.8 keV as a blend of several narrow lines due to scattering of radiation from the neutron star in an extended highly ionized stellar wind. Finally, the continuum emission of V0332+53 is consistent with an absorbed power law and a Gaussian emission line to describe the soft excess at low energies. No emission lines are present in this system.Part of this work was supported by the Spanish Ministry of Education and Science Primera ciencia con el GTC: La astronomía española en vanguardia de la astronomía europea CSD200670 and Multiplicidad y evolución de estrellas masivas project number AYA200806166C0303. KLP and JPO acknowledge support from STFC. JMT & JJRR acknowledge support by the Spanish Ministerio de Educación y Ciencia (MEC) under grants PR2007-0176 & PR2009-0455. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester
Friendship groups and physical activity: qualitative findings on how physical activity is initiated and maintained among 10–11 year old children
<p>Abstract</p> <p>Background</p> <p>Many youth physical activity interventions have minimal effect. To design better interventions we need to understand more about the factors that influence youth activity. Application of self-determination theory to youth physical activity, particularly the relatedness and competence, might suggest that friends and friendship groups influence the initiation and maintenance of youth physical activity. In this study we examined this issue.</p> <p>Methods</p> <p>Seventeen focus groups were conducted with 113, 10–11 year old children, from 11 primary schools in Bristol, UK. Focus groups examined: 1) the nature of children's friendship groups; 2) associations between physical activity and social group status; and 3) how friendship groups affect the initiation and maintenance of physical activity. All focus groups were audio-taped and transcribed verbatim. Data were analyzed using content analysis.</p> <p>Results</p> <p>Participants reported that there were three different types of friendship groups; School friends; Neighborhood friends; and Other Friends who were friends from organized activities or children of their parents' friends. Participants had multiple groups of friends and engaged in different activities with the different groups. Possessing several groups of friends was desirable as it kept the friendships fresh and interesting. Physical activity was perceived as a positive attribute and linked to social status among boys. Among girls the association between physical activity ability and social status was more complex, appearing to differ by the norms of the group to which participants belonged. Some participants reported that low activity ability could be perceived as desirable in some social groups. Participants reported that friends provide support to initiate physical activity via co-participation (i.e. engaging in activity together); modeling of being active; and providing verbal support to engage in activity. Enjoyment was the most important factor in maintaining activity participation with participating in activity with friends a key factor influencing enjoyment.</p> <p>Conclusion</p> <p>Friendship groups affect both the initiation and maintenance of youth physical activity. Children belong to several groups and engage in different activities with different groups. Simple strategies that aim to promote physical activity via the different friendship groups could be an effective means of promoting increased physical activity in young people.</p
Period-doubling bifurcation in strongly anisotropic Bianchi I quantum cosmology
We solve the Wheeler-DeWitt equation for the minisuperspace of a cosmological
model of Bianchi type I with a minimally coupled massive scalar field as
source by generalizing the calculation of Lukash and Schmidt [1]. Contrarily to
other approaches we allow strong anisotropy. Combining analytical and numerical
methods, we apply an adiabatic approximation for , and as new feature we
find a period-doubling bifurcation. This bifurcation takes place near the
cosmological quantum boundary, i.e., the boundary of the quasiclassical region
with oscillating -function where the WKB-approximation is good. The
numerical calculations suggest that such a notion of a ``cosmological quantum
boundary'' is well-defined, because sharply beyond that boundary, the
WKB-approximation is no more applicable at all. This result confirms the
adequateness of the introduction of a cosmological quantum boundary in quantum
cosmology.Comment: Latest update of the paper at
http://www.physik.fu-berlin.de/~mbach/publics.html#
X-Ray Flashes in Recurrent Novae: M31N 2008-12a and the Implications of the Swift Non-detection
Models of nova outbursts suggest that an X-ray flash should occur just after
hydrogen ignition. However, this X-ray flash has never been observationally
confirmed. We present four theoretical light curves of the X-ray flash for two
very massive white dwarfs (WDs) of 1.380 and 1.385 M_sun and for two recurrence
periods of 0.5 and 1 years. The duration of the X-ray flash is shorter for a
more massive WD and for a longer recurrence period. The shortest duration of 14
hours (0.6 days) among the four cases is obtained for the 1.385 M_sun WD with
one year recurrence period. In general, a nova explosion is relatively weak for
a very short recurrence period, which results in a rather slow evolution toward
the optical peak. This slow timescale and the predictability of very short
recurrence period novae give us a chance to observe X-ray flashes of recurrent
novae. In this context, we report the first attempt, using the Swift
observatory, to detect an X-ray flash of the recurrent nova M31N 2008-12a (0.5
or 1 year recurrence period), which resulted in the non-detection of X-ray
emission during the period of 8 days before the optical detection. We discuss
the impact of these observations on nova outburst theory. The X-ray flash is
one of the last frontiers of nova studies and its detection is essentially
important to understand the pre-optical-maximum phase. We encourage further
observations.Comment: 12 pages, including 9 figures and 3 tables. To appear in the
Astrophysical Journa
Pan-chromatic observations of the remarkable nova LMC 2012
We present the results of an intensive multiwavelength campaign on nova LMC
2012. This nova evolved very rapidly in all observed wavelengths. The time to
fall two magnitudes in the V band was only 2 days. In X-rays the super soft
phase began 135 days after discovery and ended around day 50 after
discovery. During the super soft phase, the \Swift/XRT and \Chandra\ spectra
were consistent with the underlying white dwarf being very hot, 1 MK,
and luminous, 10 erg s. The UV, optical, and near-IR
photometry showed a periodic variation after the initial and rapid fading had
ended. Timing analysis revealed a consistent 19.240.03 hr period in all
UV, optical, and near-IR bands with amplitudes of 0.3 magnitudes which
we associate with the orbital period of the central binary. No periods were
detected in the corresponding X-ray data sets. A moderately high inclination
system, = 6010^{\arcdeg}, was inferred from the early optical
emission lines. The {\it HST}/STIS UV spectra were highly unusual with only the
\ion{N}{5} (1240\AA) line present and superposed on a blue continuum. The lack
of emission lines and the observed UV and optical continua from four epochs can
be fit with a low mass ejection event, 10 M, from a hot
and massive white dwarf near the Chandrasekhar limit. The white dwarf, in turn,
significantly illuminated its subgiant companion which provided the bulk of the
observed UV/optical continuum emission at the later dates. The inferred extreme
white dwarf characteristics and low mass ejection event favor nova LMC 2012
being a recurrent nova of the U Sco subclass.Comment: 18 figures, 6 tables (one online only containing all the photometry
Resolving iron emission lines in 4U 1538-52 with XMM-Newton
The X-ray Universe 2011, Presentations of the Conference held in Berlin, Germany, 27-30 June 2011. Available online at: http://xmm.esac.esa.int/external/xmm_science/workshops/2011symposium/, article id.275We present the results of a XMM-Newton observation of the high-mass X-ray binary 4U 1538-52 at orbital phases between 0.75-1.00 (in the eclipse-ingress phase). Here we concentrate on the study of discrete features in the energy range from 5.9 keV to 7.8 keV, i.e. on the iron Kα line region, using the EPIC/PN instrument on board XMM-Newton observatory. We clearly see a Kα neutral iron line at around 6.4 keV and were able to distinguish two hot lines from highly photoionized Fe XXV and Fe XXVI. We discuss the implications of the simultaneous presence of iron with both low and high ionization levels.This work was supported by the Spanish Ministry of Education and Science De INTEGRAL a IXO: binarias de rayos X y estrellas activas AYA2010-15431 and partially supported by Primera ciencia con el GTC: La astronomía española en vanguardia de la astronomía europea CSD200670. KLP and JPO acknowledge support from the UK Space Agency. JJRR acknowledges support by the Spanish Ministerio de Educación y Ciencia (MEC) under grant PR2009-0455. This work made use of data obtained through the XMM-Newton Science Archive (XSA), rovided by European Space Agency (ESA)
Constraints on diffuse neutrino background from primordial black holes
We calculated the energy spectra and the fluxes of electron neutrino emitted
in the process of evaporation of primordial black holes (PBHs) in the early
universe. It was assumed that PBHs are formed by a blue power-law spectrum of
primordial density fluctuations. We obtained the bounds on the spectral index
of density fluctuations assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.Comment: 18 pages,(with 7 figures
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