151 research outputs found
Is the Compact Source at the Center of Cas A Pulsed?
A 50 ksec observation of the Supernova Remnant Cas A was taken using the
Chandra X-Ray Observatory High Resolution Camera (HRC) to search for periodic
signals from the compact source located near the center. Using the HRC-S in
imaging mode, problems with correctly assigning times to events were overcome,
allowing the period search to be extended to higher frequencies than possible
with previous observations. In an extensive analysis of the HRC data, several
possible candidate signals are found using various algorithms, including
advanced techniques developed by Ransom to search for low significance periodic
signals. Of the candidate periods, none is at a high enough confidence level to
be particularly favored over the rest. When combined with other information,
however (e.g., spectra, total energetics, and the historical age of the
remnant), a 12 ms candidate period seems to be more physically plausible than
the others, and we use it for illustrative purposes in discussing the possible
properties of a putative neutron star in the remnant. We emphasize that this is
not necessarily the true period, and that a follow-up observation, scheduled
for the fall of 2001, is required.
A 50 ksec Advanced CCD Imaging Spectrometer (ACIS) observation was taken, and
analysis of these data for the central object shows that the spectrum is
consistent with several forms, and that the emitted X-ray luminosity in the 0.1
-10 keV band is 10^{33}-10^{35}erg cm^{-2}sec^{-1} depending on the spectral
model and the interstellar absorption along the line of sight to the source.Comment: 14 pages, 3 figures Submitted to ApJ 2001 June 2
A New Search Technique for Short Orbital Period Binary Pulsars
We describe a new and efficient technique which we call sideband or
phase-modulation searching that allows one to detect short period binary
pulsars in observations longer than the orbital period. The orbital motion of
the pulsar during long observations effectively modulates the phase of the
pulsar signal causing sidebands to appear around the pulsar spin frequency and
its harmonics in the Fourier transform. For the majority of binary radio
pulsars or Low-Mass X-ray Binaries (LMXBs), large numbers of sidebands are
present, allowing efficient searches using Fourier transforms of short portions
of the original power spectrum. Analysis of the complex amplitudes and phases
of the sidebands can provide enough information to solve for the Keplerian
orbital parameters. This technique is particularly applicable to radio pulsar
searches in globular clusters and searches for coherent X-ray pulsations from
LMXBs and is complementary to more standard ``acceleration'' searches.Comment: 22 pages. 8 figures. Submitted to Ap
X-Ray Timing of the Young Pulsar in 3C 58
PSR J0205+6449 is a young pulsar in the Crab-like pulsar wind nebula 3C 58
which is thought to be a result of the historical supernova SN1181 CE. The
65.7-ms pulsar is the second most energetic of the known Galactic pulsars and
has been shown to be remarkably cool for its age, implying non-standard cooling
processes in the neutron star core. We report on RXTE timing observations taken
during AO7 and supplemented by monthly radio observations of the pulsar made
with the Green Bank Telescope (GBT). The total duration covered with the timing
solutions is 450 days. We measure very high levels of timing noise from the
source and find evidence for a ``giant'' glitch of magnitude Delta nu/nu ~
1x10^-6 that occurred in 2002 October. We have also measured the phase-resolved
spectra of the pulsations and find them to be surprisingly hard, with photon
indices Gamma = 0.84 +0.06/-0.15 for the main pulse and Gamma = 1.0 +0.4/-0.3
for the interpulse assuming an absorbed power-law model.Comment: 4 pages, 6 figures. To appear in the proceedings of X-ray Timing
2003: Rossi and Beyond, ed. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville, NY:
American Institute of Physics
QPO Frequency - Color Radius Connection in GRS 1915+105: a Possible Turnover supporting AEI predictions
It is widely believed that the low frequency quasi-periodic X-ray
oscillations observed in microquasars are correlated to, but do not originate
at, the physical radius of the inner edge of the accretion disk. Models
relating the QPO frequency and color radius are hindered by observations
showing contradicting trend correlations between the microquasars GRO 1655-40,
XTE J1550-564 and GRS 1915+105. The first shows a negative correlation and the
latter two a positive one. By taking into account relativistic rotation in the
accretion disk, the Accretion-Ejection Instability (AEI) model predicts a
turnover in the frequency-radius relationship, and has been successfully
compared with observations of GRO J1655-40 and GRS 1915+105. We present further
evidence supporting the AEI model prediction by using observations of the
microquasar GRS 1915+105. By combining a data set including -, -
and -class X-ray light curves, we observe positive, negative and null
correlations in the frequency-radius relationship. This is the first time a
single source has shown a possible inversion in the QPO frequency-color radius
curve predicted by the AEI model
Ensemble Concerts: Wind Symphony, April 25, 2010
Center for the Performing ArtsSunday AfternoonApril 25, 20103:00 p.m
A Binary Millisecond Pulsar in Globular Cluster NGC6544
We report the detection of a new 3.06 ms binary pulsar in the globular
cluster NGC6544 using a Fourier-domain ``acceleration'' search. With an implied
companion mass of ~0.01 solar masses and an orbital period of only P_b~1.7
hours, it displays very similar orbital properties to many pulsars which are
eclipsed by their companion winds. The orbital period is the second shortest of
known binary pulsars after 47 Tuc R. The measured flux density of 1.3 +/- 0.4
mJy at 1332 MHz indicates that the pulsar is almost certainly the known
steep-spectrum point source near the core of NGC6544.Comment: Accepted by ApJ Letters on 11 October 2000, 5 page
Habitat Appraisal Guide for Rio Grande Wild Turkey
24 pp., 13 figures, 5 tablesThe Rio Grande wild turkey habitat appraisal guide gives landowners and managers a standardized, systematic way to evaluate current habitat conditions. It can be used to identify limiting factors. It also contains suggestions for improving the habitat of the wild turkey throughout its range
Discovery of X-ray Pulsations from the Compact Central Source in the Supernova Remnant 3C 58
We report on high time resolution observations of the SNR 3C 58 using the
High Resolution Camera on the Chandra X-ray Observatory. These data show a
point-like central source, from which we detect 65.68 ms pulsations at 6.7
sigma significance. We interpret these pulsations as corresponding to a young
rotation-powered pulsar (PSR J-205+6449) which is associated with, and powers,
3C 58. Analysis of archival RXTE data from three years earlier confirms these
pulsations, and allows us to determine a spin-down rate of P-dot=1.93x10^-13
s/s. Assuming a magnetic dipole model for PSR J0205+6449, we infer a surface
magnetic field of 3.6x10^12 G. The characteristic age for this pulsar is 5400
yr, indicating either that 3C 58 was not the supernova of 1181 CE, or that the
pulsar's initial spin period was ~60 ms.Comment: 11 pages, 4 figures, 1 tabl
- …