117 research outputs found
Magnetar-like Emission from the Young Pulsar in Kes 75
We report detection of magnetar-like X-ray bursts from the young pulsar PSR
J1846-0258, at the center of the supernova remnant Kes 75. This pulsar, long
thought to be rotation-powered, has an inferred surface dipolar magnetic field
of 4.9x10^13 G, higher than those of the vast majority of rotation-powered
pulsars, but lower than those of the ~12 previously identified magnetars. The
bursts were accompanied by a sudden flux increase and an unprecedented change
in timing behavior. These phenomena lower the magnetic and rotational
thresholds associated with magnetar-like behavior, and suggest that in neutron
stars there exists a continuum of magnetic activity that increases with
inferred magnetic field strength.Comment: 17 pages, 2 figures, accepted for publication in Science. Note: The
content of this paper is embargoed until February 21, 200
Long-term X-ray changes in the emission from the anomalous X-ray pulsar 4U 0142+61
We present results obtained from X-ray observations of the anomalous X-ray
pulsar (AXP) 4U 0142+61 taken between 2000-2007 using XMM-Newton, Chandra and
Swift. In observations taken before 2006, the pulse profile is observed to
become more sinusoidal and the pulsed fraction increased with time. These
results confirm those derived using the Rossi X-ray Timing Explorer and expand
the observed evolution to energies below 2 keV. The XMM-Newton total flux in
the 0.5-10 keV band is observed to be nearly constant in observations taken
before 2006, while an increase of ~10% is seen afterwards and coincides with
the burst activity detected from the source in 2006-2007. After these bursts,
the evolution towards more sinusoidal pulse profiles ceased while the pulsed
fraction showed a further increase. No evidence for large-scale, long-term
changes in the emission as a result of the bursts is seen. The data also
suggest a correlation between the flux and hardness of the spectrum, with
brighter observations on average having a harder spectrum. As pointed out by
other authors, we find that the standard blackbody plus power-law model does
not provide the best spectral fit to the emission from 4U 0142+61. We also
report on observations taken with the Gemini telescope after two bursts. These
observations show source magnitudes consistent with previous measurements. Our
results demonstrate the wide range of X-ray variability characteristics seen in
AXPs and we discuss them in light of current emission models for these sources.Comment: 10 pages, 9 figures, in emulateapj style. Submitted to Ap
High-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61 with ULTRACAM
We present high-speed, multi-colour optical photometry of the anomalous X-ray
pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel
Telescope. We detect 4U 0142+61 at magnitudes of i'=23.7+-0.1, g'=27.2+-0.2 and
u'>25.8, consistent with the magnitudes found by Hulleman et al.(2004) and
hence confirming their discovery of both a spectral break in the optical and a
lack of long-term optical variability. We also confirm the discovery of Kern &
Martin (2002) that 4U 0142+61 shows optical pulsations with an identical period
(~8.7 s) to the X-ray pulsations. The rms pulsed fraction in our data is
29+-8%, 5-7 times greater than the 0.2-8 keV X-ray rms pulsed fraction. The
optical and X-ray pulse profiles show similar morphologies and appear to be
approximately in phase with each other, the former lagging the latter by only
0.04+-0.02 cycles. In conjunction with the constraints imposed by X-ray
observations, the results presented here favour a magnetar interpretation for
the anomalous X-ray pulsars.Comment: 6 pages, 4 figures, accepted for publication in MNRA
Chandra and RXTE Observations of 1E 1547.0-5408: Comparing the 2008 and 2009 Outbursts
We present results from observations of the magnetar 1E 1547.0-5408 (SGR
J1550-5418) taken with the Chandra X-ray Observatory and the Rossi X-ray Timing
Explorer (RXTE) following the source's outbursts in 2008 October and 2009
January. During the time span of the Chandra observations, which covers days 4
through 23 and days 2 through 16 after the 2008 and 2009 events, respectively,
the source spectral shape remained stable, while the pulsar's spin-down rate in
the same span in 2008 increased by a factor of 2.2 as measured by RXTE. The
lack of spectral variation suggests decoupling between magnetar spin-down and
radiative changes, hence between the spin-down-inferred magnetic field strength
and that inferred spectrally. We also found a strong anti-correlation between
the phase-averaged flux and the pulsed fraction in the 2008 and 2009 Chandra
data, but not in the pre-2008 measurements. We discuss these results in the
context of the magnetar model.Comment: 4 figures, accepted for publication in Ap
RXTE Monitoring of the Anomalous X-ray Pulsar 1E 1048.1-5937
We report on long-term monitoring of the anomalous X-ray pulsar 1E
1048.1-5937 using the Rossi X-ray Timing Explorer. This pulsar's timing
behavior is different from that of other AXPs. In particular, the pulsar shows
significant deviations from simple spin-down such that phase-coherent timing
has not been possible over time spans longer than a few months. We show that in
spite of the rotational irregularities, the pulsar exhibits neither pulse
profile changes nor large pulsed flux variations. We discuss the implications
of our results for AXP models. We suggest that 1E 1048.1-5937 may be a
transition object between the soft gamma-ray repeater and AXP populations, and
the AXP most likely to one day undergo an outburst.Comment: 6 pages, to appear in Proceedings of the 20th Texas Symposium on
Relativistic Astrophysics, AIP pres
Search for Mid-IR Flux Variations from The Anomalous X-ray Pulsar 4U 0142+61
We report on our Spitzer observations of the anomalous X-ray pulsar 4U
0142+61, made following a large X-ray burst that occurred on 2007 February 7.
To search for mid-infrared flux variations, four imaging observations were
carried out at 4.5 and 8.0 m with the Infrared Array Camera from February
14 to 21. No significant flux variations were detected, and the average fluxes
were 32.12.0 Jy at 4.5 m and 59.8 Jy at 8.0 m,
consistent with those obtained in 2005. The non-detection of variability is
interesting in light of reported rapid variability from this source in the
near-infrared, but consistent with the fact that the source already went back
to its quiescent state before our observations began, as indicated by
contemporaneous X-ray observations. In order to understand the origin of the
near-infrared variability, frequent, simultaneous multi-wavelength observations
are needed.Comment: 5 pages, 1 figure, ApJ, accepte
A Second Glitch from the "Anomalous" X-ray Pulsar 1RXS J170849.0-4000910
We report on 5.4 yr of phase-coherent timing, using the Rossi X-ray Timing
Explorer, of the X-ray pulsar 1RXS 1708-4009, a member of the class known as
``anomalous X-ray pulsars.'' This object exhibited a rotational glitch in 1999.
Here we report a second much larger rotational glitch which occured ~1.5 yr
after the first. We show that the recoveries from the two glitches are
different, with the first showing only a possible slow, approximately linear
recovery, while the second showed a nearly complete recovery on a time scale of
\~50 days. The approximately exponential recovery time scale of the second
glitch is similar to that seen recently in 1E 2259+586 at the time of a major
outburst. This suggests 1RXS 1708-4009 undergoes similar bursting behavior,
although with our sparse observations we have detected no other evidence for
bursts from this source.Comment: 13 pages, 2 figures. Revised manuscript and Fig 1 following
refereeing. Accepted for publication in ApJL Aug 1
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