69 research outputs found
The infrared counterpart to the magnetar 1RXS J170849.0-400910
We have analyzed both archival and new infrared imaging observations of the
field of the Anomalous X-ray Pulsar 1RXS J170849.0-400910, in search of the
infrared counterpart. This field has been previously investigated, and one of
the sources consistent with the position of the AXP suggested as the
counterpart. We, however, find that this object is more likely a background
star, while another object within the positional error circle has non-stellar
colors and shows evidence for variability. These two pieces of evidence, along
with a consistency argument for the X-ray-to-infrared flux ratio, point to the
second source being the more likely infrared counterpart to the AXP.Comment: 19 pages AASTEX, 4 figure. Accepted for publication in ApJ. Full
resolution figures at: http://www.astro.utoronto.ca/~durant/1708.ps.g
Intrinsic Emission of PSR B1937+21 at 327 MHz
At 327 MHz, the observed emission of PSR B1937+21 is greatly affected by
scattering in the interstellar medium, on a timescale of order the pulse
period. We use the bright impulsive giant pulses emitted by the pulsar to
measure the impulse response of the interstellar medium and then recover the
intrinsic emission of the pulsar by deconvolution -- revealing fine structure
on timescales not normally observable. We find that the intrinsic widths of the
main pulse and interpulse in the pulse profile are similar to those measured at
higher frequencies. We detect 60,270 giant pulses which typically appear as
narrow, ~100 ns bursts consisting of one to few nanoshots with widths ns. However, about 10% of the giant pulses exhibit multiple bursts which
seem to be causally related to each other. We also report the first detection
of giant micropulses in PSR B1937+21, primarily associated with the regular
main pulse emission. These are distinct from giant pulses not only in the
phases at which they occur, but also in their larger widths, of order a
microsecond, and steeper energy distribution. These measurements place useful
observational constraints on emission mechanisms for giant pulses as well as
the regular radio emission of millisecond pulsars.Comment: 55 pages, 48 figures, submitted to Ap
Using Giant Pulses to Measure the Impulse Response of the Interstellar Medium
Giant pulses emitted by PSR B1937+21 are bright, intrinsically impulsive
bursts. Thus, the observed signal from a giant pulse is a noisy but direct
measurement of the impulse response from the ionized interstellar medium. We
use this fact to detect 13,025 giant pulses directly in the baseband data of
two observations of PSR B1937+21. Using the giant pulse signals, we model the
time-varying impulse response with a sparse approximation method, in which the
time dependence at each delay is decomposed in Fourier components, thus
constructing a wavefield as a function of delay and differential Doppler shift.
We find that the resulting wavefield has the expected parabolic shape, with
several diffuse structures within it, suggesting the presence of multiple
scattering locations along the line of sight. We also detect an echo at a delay
of about 2.4 ms, over 1.5 times the rotation period of the pulsar, which
between the two observations moves along the trajectory expected from geometry.
The structures in the wavefield are insufficiently sparse to produce a complete
model of the system, and hence the model is not predictive across gaps larger
than about the scintillation time. Nevertheless, within its range, it
reproduces about 75% of the power of the impulse response, a fraction limited
mostly by the signal-to-noise ratio of the observations. Furthermore, we show
that by deconvolution, using the model impulse response, we can successfully
recover the intrinsic pulsar emission from the observed signal.Comment: 14 pages, 8 figures, Accepted for publication in Ap
The Broad-Band Spectrum and Infrared Variability of the Magnetar AXP 1E1048.1-5937
We present photometry of the Anomalous X-ray pulsar 1E1048.1-5937 in the
infrared and optical, taken at Magellan and the VLT. The object is detected in
the I, J and Ks bands under excellent conditions. We find that the source has
varied greatly in its infrared brightness and present these new magnitudes. No
correlation is found between the infrared flux and spin-down rate, but the
infrared flux and X-ray flux may be anti-correlated. Assuming nominal reddening
values, the resultant spectral energy distribution is found to be inconsistent
with the only other AXP SED available (for 4U0142+61). We consider the effect
of the uncertainty in the reddening to the source on its SED. We find that
although both the X-ray and infrared fluxes have varied greatly for this
source, the most recent flux ratio is remarkably consistent with what is is
found for other AXPs. Finally, we discuss the implications of our findings in
the context of the magnetar model.Comment: 21 pages, 5 eps figures. Submitted to Ap
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