3,310 research outputs found
Red Noise in Anomalous X-ray Pulsar Timing Residuals
Anomalous X-ray Pulsars (AXPs), thought to be magnetars, exhibit poorly
understood deviations from a simple spin-down called "timing noise". AXP timing
noise has strong low-frequency components which pose significant challenges for
quantification. We describe a procedure for extracting two quantities of
interest, the intensity and power spectral index of timing noise. We apply this
procedure to timing data from three sources: a monitoring campaign of five
AXPs, observations of five young pulsars, and the stable rotator PSR B1937+21.Comment: submitted to the proceedings of the "40 Years of Pulsars" conferenc
A spliceosomal intron of mitochondrial DNA origin
SummaryThe origin of spliceosomal introns is one of the most enduring mysteries in molecular biology. In nuclear genomes such as our own, the protein-coding regions of genes (exons) can be separated from one another by hundreds of thousands of base pairs (bp) of intronic (non-coding) DNA, and while they are often considered ‘junk’, introns are increasingly ascribed important regulatory functions [1]. Here we present evidence that an intron in a GTPase superfamily gene in the unicellular alga Bigelowiella natans is derived from — and was created by — the insertion of a fragment of mitochondrial DNA. Organelle-to-nucleus DNA transfer is an increasingly well-understood phenomenon, one that has the potential to greatly influence genome structure [2,3]. Our data suggest that such transfers could represent a hitherto underappreciated source of new spliceosomal introns
No detectable radio emission from the magnetar-like pulsar in Kes 75
The rotation-powered pulsar PSR J1846-0258 in the supernova remnant Kes 75
was recently shown to have exhibited magnetar-like X-ray bursts in mid-2006.
Radio emission has not yet been observed from this source, but other
magnetar-like sources have exhibited transient radio emission following X-ray
bursts. We report on a deep 1.9 GHz radio observation of PSR J1846-0258 with
the 100-m Green Bank Telescope in late 2007 designed to search for radio
pulsations or bursts from this target. We have also analyzed three shorter
serendipitous 1.4 GHz radio observations of the source taken with the 64-m
Parkes telescope during the 2006 bursting period. We detected no radio emission
from PSR J1846-0258 in either the Green Bank or Parkes datasets. We place an
upper limit of 4.9 \mu Jy on coherent pulsed emission from PSR J1846-0258 based
on the 2007 November 2 observation, and an upper limit of 27 \mu Jy around the
time of the X-ray bursts. Serendipitously, we observed radio pulses from the
nearby RRAT J1846-02, and place a 3\sigma confidence level upper limit on its
period derivative of 1.7 * 10^{-13}, implying its surface dipole magnetic field
is less than 2.6 * 10^{13} G.Comment: 15 pages, 2 figures, submitted to Ap
On the X-ray variability of magnetar 1RXS J170849.0-400910
We present a long-term X-ray flux and spectral analysis for 1RXS
J170849.0-400910 using Swift/XRT spanning over 8 years from 2005-2013. We also
analyze two observations from Chandra and XMM in the period from 2003-2004. In
this 10-yr period, 1RXS J170849.0-400910 displayed several rotational glitches.
Previous studies have claimed variations in the X-ray emission associated with
some of the glitches. From our analysis we find no evidence for significant
X-ray flux variations and evidence for only low-level spectral variations. We
also present an updated timing solution for 1RXS J170849.0-400910, from RXTE
and Swift observations, which includes a previously unreported glitch at MJD
56019. We discuss the frequency and implications of radiatively quiet glitches
in magnetars.Comment: 9 pages, 2 figures, accepted for publication in Ap
Current mixed methods practices in qualitative research: a content analysis of leading journals
Mixed methods research (MMR) has become increasingly popular in recent years. Yet, methodological challenges of mixing qualitative and quantitative data remain. Understanding how MMR is approached in qualitative research journals provides insights into lingering mixing issues. In this article, we content analyzed five leading qualitative research journals from 2003 to 2014, which represents the reflective period of MMR. Of the 5,254 articles published, 94, or 1.79%, were mixed methods in nature, comprising 44 theoretically oriented articles and 50 empirical articles. In terms of theoretical articles, five content-based themes were identified: (a) MMR advocacy, (b) philosophy issues, (c) procedural suggestions, (d) practical issues and best practices, and (e) future directions. In terms of empirical articles, 36% used exploratory sequential designs, primarily to develop instruments, and 52% explicitly identified as MMR. None of the studies included MMR questions, and development (21%) and complementarity (14%) were the primary rationales for mixing. In virtually all studies (98%), mixing occurred at the data interpretation stage through some comparison of qualitative and quantitative research. Qualitative data were prioritized in 86% of the studies. Based on these findings, it appears that MMR affects qualitative research most directly by influencing study design and study purpose; however, there is a strong tendency to conduct and publish qualitative and quantitative studies separately. Recommendations for publishing future MMR are discussed.Mandy M. Archibald, Amanda I. Radil, Xiaozhou Zhang, William E. Hanso
X-ray Observations of XSS J12270-4859 in a New Low State: A Transformation to a Disk-Free Rotation-Powered Pulsar Binary
We present XMM-Newton and Chandra observations of the low-mass X-ray binary
XSS J12270--4859, which experienced a dramatic decline in optical/X-ray
brightness at the end of 2012, indicative of the disappearance of its accretion
disk. In this new state, the system exhibits previously absent
orbital-phase-dependent, large-amplitude X-ray modulations with a decline in
flux at superior conjunction. The X-ray emission remains predominantly
non-thermal but with an order of magnitude lower mean luminosity and
significantly harder spectrum relative to the previous high flux state. This
phenomenology is identical to the behavior of the radio millisecond pulsar
binary PSR J1023+0038 in the absence of an accretion disk, where the X-ray
emission is produced in an intra-binary shock driven by the pulsar wind. This
further demonstrates that XSS J12270-4859 no longer has an accretion disk and
has transformed to a full-fledged eclipsing "redback" system that hosts an
active rotation-powered millisecond pulsar. There is no evidence for diffuse
X-ray emission associated with the binary that may arise due to outflows or a
wind nebula. An extended source situated 1.5' from XSS J12270--4859 is unlikely
to be associated, and is probably a previously uncatalogued galaxy cluster.Comment: 8 pages, 6 figures; accepted for publication in the Astrophysical
Journa
Binary evolution with LOFT
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of very faint X-ray binaries,
orbital period distribution of black hole X-ray binaries and neutron star spin
up. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timing. (v2 few typos corrected
The SCUBA 8-mJy survey - I: Sub-millimetre maps, sources and number counts
We present maps, source lists, and number counts from the largest, unbiassed,
extragalactic sub-mm survey so far undertaken with the SCUBA camera on the
JCMT. Our maps cover 260 sq. arcmin, to a noise level S(850)=2.5 mJy/beam. We
have reduced the data using both SURF, and our own pipeline which produces
zero-footprint maps and noise images. The uncorrelated noise maps produced by
the latter approach have allowed application of a maximum-likelihood method to
measure the statistical significance of each peak, leading to properly
quantified flux-density errors for all potential sources. We detect 19 sources
with S/N > 4, 38 with S/N > 3.5, and 72 with S/N > 3. To assess completeness
and the impact of source confusion we have applied our source extraction
algorithm to a series of simulated images. The result is a new estimate of the
sub-mm source counts in the flux-density range S(850)=5-15mJy, which we compare
with other estimates, and with model predictions. Our estimate of the
cumulative source count at S(850) > 8 mJy is 320 (+80,-100) per square degree.
Assuming that the majority of sources have z > 1.5, the co-moving number
density of high-z galaxies forming stars at a rate >1000 solar masses per year
is 10^-5 per Mpc^3, with only a weak dependence on the precise redshift
distribution. This number density corresponds to that of massive ellipticals
with L > 3-4 L* at low redshift and is also the same as the co-moving number
density of comparably massive, passively-evolving objects in the redshift band
1<z<2 inferred from recent surveys of extremely red objects. Thus the bright
sub-mm sources can plausibly account for the formation of all present-day
massive ellipticals. Improved z constraints, and a proper measurement of sub-mm
clustering can refine or refute this picture.Comment: Minor revisions. 27 pages, 13 figures. Higher resolution versions of
Figs 5,6,7 and 8 are available from the autho
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