121 research outputs found
Her X-1: the positive cyclotron line energy / luminosity correlation
Studies of some bright, super-Eddington transient pulsars show a negative
correlation between the energy of the cyclotron resonance scattering feature
(CRSF) and the bolometric luminosity. For Her X-1, using repeated RXTE
observations during 1996-2005, the inverse dependence was found: the energy of
the cyclotron line increases as the luminosity increases. The X-ray flux
measured by the RXTE/ASM (2-10 keV) has been assumed to represent the
luminosity - more precisely: the maximum X-ray flux reached during the
respective 35 d Main-On. Here, we question whether the ASM flux is really an
accurate measure of the bolometric luminosity of the source. We redetermined
the energy of the cyclotron line and performed spectral fits using the combined
data from the PCA (3.5-60 keV) and HEXTE (20-75 keV) instruments on RXTE of the
same 35 d cycles as used in the original work to determine the bolometric flux
from those spectra. We confirm the result of the original analysis that the
cyclotron line energy changes by ~7% for a change in flux by a factor of two.Comment: 5 pages, 5 figures, accepted by A&A on 23.06.201
Updating the orbital ephemeris of Her X-1; rate of decay and eccentricity of the orbit
We present an update of the orbital ephemeris of the binary X-ray pulsar Her
X-1 and determine an improved value for the rate of orbital decay. In addition,
we report the first measurement of the orbital eccentricity. We have analyzed
pulse timing data of Her X-1 from X-ray observations by RXTE (Rossi X-Ray
Timing Explorer) and INTEGRAL over the period 1996-2007. Accurate pulse arrival
times were determined from solar system bary-centered photon arrival times by
generating pulse profiles averaged over appropriately short integration times.
Applying pulse phase connection techniques, it was possible to determine
sufficiently accurate local ephemeris data for seven observation periods
distributed over 12 years. Combining the new local T90 values with historical
values from the literature we update the orbital ephemeris of Her X-1 to T90 =
MJD 46359.871940(6) and Porb = 1.700167590(2) d and measure a continuous change
of the orbital period of dPorb/dt = -(4.85 +/- 0.13) x 10-11 s/s. For the first
time, a value for the eccentricity of the orbit of Her X-1 is measured to be e
= (4.2 +/- 0.8) x 10-4.Comment: 7 pages, 4 figures, accepted by A&A on 30.03.200
Continuous monitoring of pulse period variations in Her X-1 using Swift/BAT
Context: Monitoring of pulse period variations in accreting binary pulsars is
an important tool to study the interaction between the magnetosphere of the
neutron star and the accretion disk. While the X-ray flux of the brightest
X-ray pulsars have been successfully monitored over many years (e.g. with
RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their pulse timing
properties continuously has so far been very limited. Aims: In our work we show
that the Swift/BAT observations can be used to monitor coherent pulsations of
bright X-ray sources and use the Swift archival data to study one of the most
enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the
pulse period and the pulse period derivative of an X-ray pulsar, here Her X-1,
is achieved over a long time (<~ 4 yrs). We compare our observational results
with predictions of accretion theory and use them to test different aspects of
the physical model of the system. Methods: In our analysis we use the data
accumulated with Swift/BAT starting from the beginning of 2005 (shortly after
launch) until the present time. To search for pulsations and for their
subsequent analysis we used the count rate measured by the BAT detector in the
entire field of view. Results: The slope of the correlation between the locally
determined spin-up rate and the X-ray luminosity is measured for Her X-1 and
found to be in agreement with predictions of basic accretion torque theory. The
observed behaviour of the pulse period together with the previously measured
secular decrease of the system's orbital period is discussed in the frame of a
model assuming ejection of matter close to the inner boundary of the accretion
disk.Comment: 7 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Two ~35 day clocks in Her X-1: evidence for neutron star free precession
We present evidence for the existence of two ~35 day clocks in the Her X-1/HZ
Her binary system. ~35 day modulations are observed 1) in the Turn-On cycles
with two on- and two off-states, and 2) in the changing shape of the pulse
profiles which re-appears regularly. The two ways of counting the 35 day cycles
are generally in synchronization. This synchronization did apparently break
down temporarily during the long Anomalous Low (AL3) which Her X-1 experienced
in 1999/2000, in the sense that there must have been one extra Turn-On cycle.
Our working hypothesis is that there are two clocks in the system, both with a
period of about ~35 days: precession of the accretion disk (the less stable
"Turn-On clock") and free precession of the neutron star (the more stable
"Pulse profile clock"). We suggest that free precession of the neutron star is
the master clock, and that the precession of the accretion disk is basically
synchronized to that of the neutron star through a feed-back mechanism in the
binary system. However, the Turn-On clock can slip against its master when the
accretion disk has a very low inclination, as is observed to be the case during
AL3. We take the apparent correlation between the histories of the Turn-Ons, of
the Anomalous Lows and of the pulse period evolution, with a 5 yr
quasi-periodicity, as evidence for strong physical interaction and feed-back
between the major components in the system. We speculate that the 5 yr (10 yr)
period is either due to a corresponding activity cycle of HZ Her or a natural
ringing period of the physical system of coupled components. The question
whether free precession really exists in neutron stars is of great importance
for the understanding of matter with supra-nuclear density.Comment: 6 pages, 5 figures, accepted for publication by A&
Association between Sexual Activity and Human Papillomavirus (HPV) Vaccine Initiation and Completion among College Students
HPV vaccination is most effective if received before initiation of sexual activity. Previous studies suggested that young adult women who were not sexually active were not interested in receiving the vaccine because they did not think it was necessary. Whether this misperception is still prevalent today-and also shared by men-is unknown. This study examined whether sexual activity was associated with HPV vaccine uptake (initiation and completion) among university students. A cross-sectional study was conducted between February and May 2021 among students (n = 951) at a public Midwestern University. Sexual activity was categorized as never or ever had oral and/or vaginal sex. Outcome variables were HPV vaccine initiation, defined as receipt of â„1 dose, and completion, defined as receipt of â„3 doses. Multivariable logistic regression models estimated the association between sexual activity and HPV vaccine uptake, adjusting for sociodemographic factors. Approximately 18% of students reported never engaging in sexual activity. Overall, 45.5% initiated the HPV vaccine, and 16.5% completed the vaccine series. After adjusting for covariates, compared to students that reported never engaging in sexual activity, those that had ever engaged in sexual activity were more likely to have initiated the vaccine series (aOR = 2.06, 95% CI: 1.34-3.17); however, no difference was observed for completion. HPV vaccination was low; sexually naĂŻve students were less likely to initiate the HPV vaccine. Since sexually naĂŻve students may benefit from receiving the HPV vaccination, targeted interventions should be implemented towards this population to help increase vaccination rates and prevent HPV-associated diseases
Observational Implications of Precessing Protostellar Discs and Jets
We consider the dynamics of a protostellar disc in a binary system where the
disc is misaligned with the orbital plane of the binary, with the aim of
determining the observational consequences for such systems. The disc wobbles
with a period approximately equal to half the binary's orbital period and
precesses on a longer timescale. We determine the characteristic timescale for
realignment of the disc with the orbital plane due to dissipation. If the
dissipation is determined by a simple isotropic viscosity then we find, in line
with previous studies, that the alignment timescale is of order the viscous
evolution timescale. However, for typical protostellar disc parameters, if the
disc tilt exceeds the opening angle of the disc, then tidally induced shearing
within the disc is transonic. In general, hydrodynamic instabilities associated
with the internally driven shear result in extra dissipation which is expected
to drastically reduce the alignment timescale. For large disc tilts the
alignment timescale is then comparable to the precession timescale, while for
smaller tilt angles , the alignment timescale varies as . We discuss the consequences of the wobbling, precession and
rapid realignment for observations of protostellar jets and the implications
for binary star formation mechanisms.Comment: MNRAS, in press. 10 pages. Also available at
http://www.ast.cam.ac.uk/~mbat
INTEGRAL observations of Her X-1
Aims: We investigate the X-ray spectral and timing properties of the
accreting X-ray pulsar Her X-1 observed with the INTEGRAL satellite in
July-August 2005. Methods: The data analyzed in this work cover a substantial
part of one main-on state of the source. The short-time scale pulse period
development is measured. X-ray pulse profiles for different energy ranges and
time intervals are constructed. Pulse-averaged and pulse-phase resolved broad
band X-ray spectra are studied. Spectral changes during X-ray dips are
explored. Results: The X-ray pulse profiles are found to change significantly
during the period of observations. For the first time a strong spinup is
measured within one 35 d cycle. Spectral characteristics observed during the
X-ray dips are consistent with their interpretaion as due to partial covering
as has been reported by several authors. The fundamental cyclotron absorption
line is firmly observed in both pulse-averaged and pulse-phase resolved X-ray
spectra. The energy, width, and the depth of the line are found to vary
significantly with pulse phase.Comment: 9 pages, 10 figures, accepted for publication in A&A on 29/01/200
HPV vaccine decision making in pediatric primary care: a semi-structured interview study
<p>Abstract</p> <p>Background</p> <p>Despite national recommendations, as of 2009 human papillomavirus (HPV) vaccination rates were low with < 30% of adolescent girls fully vaccinated. Research on barriers to vaccination has focused separately on parents, adolescents, or clinicians and not on the decision making process among all participants at the point of care. By incorporating three distinct perspectives, we sought to generate hypotheses to inform interventions to increase vaccine receipt.</p> <p>Methods</p> <p>Between March and June, 2010, we conducted qualitative interviews with 20 adolescent-mother-clinician triads (60 individual interviews) directly after a preventive visit with the initial HPV vaccine due. Interviews followed a guide based on published HPV literature, involved 9 practices, and continued until saturation of the primary themes was achieved. Purposive sampling balanced adolescent ages and practice type (urban resident teaching versus non-teaching). Using a modified grounded theory approach, we analyzed data with NVivo8 software both within and across triads to generate primary themes.</p> <p>Results</p> <p>The study population was comprised of 20 mothers (12 Black, 9 < high school diploma), 20 adolescents (ten 11-12 years old), and 20 clinicians (16 female). Nine adolescents received the HPV vaccine at the visit, eight of whom were African American. Among the 11 not vaccinated, all either concurrently received or were already up-to-date on Tdap and MCV4. We did not observe systematic patterns of vaccine acceptance or refusal based on adolescent age or years of clinician experience. We identified 3 themes: (1) Parents delayed, rather than refused vaccination, and when they expressed reluctance, clinicians were hesitant to engage them in discussion. (2) Clinicians used one of two strategies to present the HPV vaccine, either presenting it as a routine vaccine with no additional information or presenting it as optional and highlighting risks and benefits. (3) Teens considered themselves passive participants in decision making, even when parents and clinicians reported including them in the process.</p> <p>Conclusions</p> <p>Programs to improve HPV vaccine delivery in primary care should focus on promoting effective parent-clinician communication. Research is needed to evaluate strategies to help clinicians engage reluctant parents and passive teens in discussion and measure the impact of distinct clinician decision making approaches on HPV vaccine delivery.</p
Developing cancer warning statements for alcoholic beverages
Background: There is growing evidence of the increased cancer risk associated with alcohol consumption, but this is not well understood by the general public. This study investigated the acceptability among drinkers of cancer warning statements for alcoholic beverages. Methods: Six focus groups were conducted with Australian drinkers to develop a series of cancer-related warning statements for alcohol products. Eleven cancer warning statements and one general health warning statement were subsequently tested on 2,168 drinkers via an online survey. The statements varied by message frame (positive vs negative), cancer reference (general vs specific), and the way causality was communicated (âincreases risk of cancerâ vs âcan cause cancerâ). Results: Overall, responses to the cancer statements were neutral to favorable, indicating that they are unlikely to encounter high levels of negative reaction from the community if introduced on alcoholic beverages. Females, younger respondents, and those with higher levels of education generally found the statements to be more believable, convincing, and personally relevant. Positively framed messages, those referring to specific forms of cancer, and those using âincreases risk of cancerâ performed better than negatively framed messages, those referring to cancer in general, and those using the term âcan cause cancerâ. Conclusion: Cancer warning statements on alcoholic beverages constitute a potential means of increasing awareness about the relationship between alcohol consumption and cancer risk
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