1,557 research outputs found
A computer operated mass spectrometer system
Digital computer system for processing mass spectrometer output dat
Computer control of mass analyzers
Digital computer control of mass spectrometer
Testing Lorentz Invariance with GRB021206
Since the discovery of the cosmological origin of GRBs there has been growing
interest in using these transient events to probe the quantum gravity energy
scale in the range 10^16--10^19 GeV, up to the Planck mass scale. This energy
scale can manifest itself through a measurable modification in the
electromagnetic radiation dispersion relation for high energy photons
originating from cosmological distances. We have used data from the gamma-ray
burst (GRB) of 6 December 2002 (GRB021206) to place an upper bound on the
energy dispersion of the speed of light. The limit on the first-order quantum
gravity effects derived from this single GRB indicate that the energy scale is
in excess of 1.8x10^17 GeV. We discuss a program to further constrain the
energy scale by systematically studying such GRBs.Comment: 10 pages, 3 figures, accepted for publication in ApJ
Discovery of a Transition to Global Spin-up in EXO 2030+375
EXO 2030+375, a 42-second transient X-ray pulsar with a Be star companion,
has been observed to undergo an outburst at nearly every periastron passage for
the last 13.5 years. From 1994 through 2002, the global trend in the pulsar
spin frequency was spin-down. Using RXTE data from 2003 September, we have
observed a transition to global spin-up in EXO 2030+375. Although the spin
frequency observations are sparse, the relative spin-up between 2002 June and
2003 September observations, along with an overall brightening of the outbursts
since mid 2002 observed with the RXTE ASM, accompanied by an increase in
density of the Be disk, indicated by infrared magnitudes, suggest that the
pattern observed with BATSE of a roughly constant spin frequency, followed by
spin-up, followed by spin-down is repeating. If so this pattern has
approximately an 11 year period, similar to the 15 +/- 3 year period derived by
Wilson et al. (2002) for the precession period of a one-armed oscillation in
the Be disk. If this pattern is indeed repeating, we predict a transition from
spin-up to spin-down in 2005.Comment: Accepted for publication in ApJ Letters, 4 pages, 5 figures, using
emulateapj.cl
Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer
Using a consistent set of models, we parameterized the X-ray spectra of all
accreting pulsars in the Rossi X-ray Timing Explorer database which exhibit
Cyclotron Resonance Scattering Features (CRSFs, or cyclotron lines). These
sources in our sample are Her X-1, 4U 0115+63, Cen X-3, 4U 1626-67, XTE
J1946-274, Vela X-1, 4U 1907+09, 4U 1538-52, GX 301-2, and 4U 0352+309 (X Per).
We searched for correlations among the spectral parameters, concentrating on
how the cyclotron line energy relates to the continuum and therefore how the
neutron star B-field influences the X-Ray emission. As expected, we found a
correlation between the CRSF energy and the spectral cutoff energy. However,
with our consistent set of fits we found that the relationship is more complex
than what has been reported previously. Also, we found that not only does the
width of the cyclotron line correlate with the energy (as suggested by theory),
but that the width scaled by the energy correlates with the depth of the
feature. We discuss the implications of these results, including the
possibility that accretion directly affects the relative alignment of the
neutron star spin and dipole axes. Lastly, we comment on the current state of
fitting phenomenological models to spectra in the RXTE/BeppoSAX era and the
need for better theoretical models of the X-Ray continua of accreting pulsars.Comment: 36 Pages, 9 Figures, 9 Tables, ApJ in pres
Integral results on GRB030320: a long gamma-ray burst detected at the edge of the field of view
GRB030320 is the 5th Gamma-ray burst (GRB) detected by INTEGRAL in the field
of view (FoV). It is so far the GRB with the largest off-axis angle with
respect to the INTEGRAL pointing direction, near to the edge of the FoV of both
main instruments, IBIS and SPI. Nevertheless, it was possible to determine its
position and to extract spectra and fluxes. The GRB nature of the event was
confirmed by an IPN triangulation. It is a ~ 60 s long GRB with two prominent
peaks separated by ~ 35 s. The spectral shape of the GRB is best represented by
a single power law with a photon index Gamma ~ 1.7. The peak flux in the 20 -
200 keV band is determined to ~ 5.7 photons cm-2 s-1 and the GRB fluence to 1.1
x 10-5 erg cm-2. Analysing the spectral evolution of the GRB, a
``hard-to-soft'' behaviour emerges. A search for an optical counterpart has
been carried out, but none was found.Comment: 5 pages, 3 figures. Accepted for publication in A&AL (INTEGRAL issue
The 1999 Hercules X-1 Anomalous Low State
A failed main-on in the 35d cycle of Her X-1 was observed with the Rossi
X-Ray Timing Explorer (RXTE) on 1999 April 26. Exceptions to the normal 35d
cycle have been seen only twice before; in 1983 and again 1993. We present
timing and spectral results of this latest Anomalous Low State (ALS) along with
comparisons to the main-on and normal low states. Pulsations were observed in
the 3-18 keV band with a fractional RMS variation of (0.037+-0.003). Spectral
analysis indicates that the ALS spectrum has the same shape as the main-on but
is modified by heavy absorption and scattering. We find that 70% of the
observed emission has passed through a cold absorber (N_H=5.0x10^{23}cm^{-2}).
This partially absorbing spectral fit can be applied to the normal low state
with similar results. We find that the ALS observations may be interpreted as a
decrease in inclination of the accretion disk causing the central X-Ray source
to be obscured over the entire 35d cycle.Comment: revised text, 6 revised figures, accepted for publication in Ap
IGRJ17361-4441: a possible new accreting X-ray binary in NGC6388
IGRJ17361-4441 is a newly discovered INTEGRAL hard X-ray transient, located
in the globular cluster NGC6388. We report here the results of the X-ray and
radio observations performed with Swift, INTEGRAL, RXTE, and the Australia
Telescope Compact Array (ATCA) after the discovery of the source on 2011 August
11. In the X-ray domain, IGRJ17361-4441 showed virtually constant flux and
spectral parameters up to 18 days from the onset of the outburst. The
broad-band (0.5-100 keV) spectrum of the source could be reasonably well
described by using an absorbed power-law component with a high energy cut-off
(N_H\simeq0.8x10^(22) cm^(-2), {\Gamma}\simeq0.7-1.0, and E_cut\simeq25 keV)
and displayed some evidence of a soft component below \sim2 keV. No coherent
timing features were found in the RXTE data. The ATCA observation did not
detect significant radio emission from IGRJ17361-4441, and provided the most
stringent upper limit (rms 14.1 {\mu}Jy at 5.5 GHz) to date on the presence of
any radio source close to the NGC6388 center of gravity. The improved position
of IGRJ17361-4441 in outburst determined from a recent target of opportunity
observation with Chandra, together with the X-ray flux and radio upper limits
measured in the direction of the source, argue against its association with the
putative intermediate-mass black hole residing in the globular cluster and with
the general hypothesis that the INTEGRAL source is a black hole candidate.
IGRJ17361-4441 might be more likely a new X-ray binary hosting an accreting
neutron star. The ATCA radio non-detection also permits us to derive an upper
limit to the mass of the suspected intermediate massive black hole in NGC6388
of <600 M\odot. This is a factor of 2.5 lower than the limit reported
previously.Comment: Accepted for publication on A&A lette
Learning physics in context: a study of student learning about electricity and magnetism
This paper re-centres the discussion of student learning in physics to focus
on context. In order to do so, a theoretically-motivated understanding of
context is developed. Given a well-defined notion of context, data from a novel
university class in electricity and magnetism are analyzed to demonstrate the
central and inextricable role of context in student learning. This work sits
within a broader effort to create and analyze environments which support
student learning in the sciencesComment: 36 pages, 4 Figure
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