61 research outputs found
Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900
We present results from observations of the Galactic Center magnetar, PSR
J1745-2900, at 2.3 and 8.4 GHz with the NASA Deep Space Network 70 m antenna,
DSS-43. We study the magnetar's radio profile shape, flux density, radio
spectrum, and single pulse behavior over a ~1 year period between MJDs 57233
and 57621. In particular, the magnetar exhibits a significantly negative
average spectral index of = -1.86 0.02 when the
8.4 GHz profile is single-peaked, which flattens considerably when the profile
is double-peaked. We have carried out an analysis of single pulses at 8.4 GHz
on MJD 57479 and find that giant pulses and pulses with multiple emission
components are emitted during a significant number of rotations. The resulting
single pulse flux density distribution is incompatible with a log-normal
distribution. The typical pulse width of the components is ~1.8 ms, and the
prevailing delay time between successive components is ~7.7 ms. Many of the
single pulse emission components show significant frequency structure over
bandwidths of ~100 MHz, which we believe is the first observation of such
behavior from a radio magnetar. We report a characteristic single pulse
broadening timescale of = 6.9 0.2 ms at 8.4 GHz.
We find that the pulse broadening is highly variable between emission
components and cannot be explained by a thin scattering screen at distances
1 kpc. We discuss possible intrinsic and extrinsic mechanisms for the
magnetar's emission and compare our results to other magnetars, high magnetic
field pulsars, and fast radio bursts.Comment: 18 pages, 12 figures, Accepted for publication in ApJ on 2018 August
30. v2: Updated to match published versio
Observations of Radio Magnetars with the Deep Space Network
The Deep Space Network (DSN) is a worldwide array of radio telescopes that
supports NASA's interplanetary spacecraft missions. When the DSN antennas are
not communicating with spacecraft, they provide a valuable resource for
performing observations of radio magnetars, searches for new pulsars at the
Galactic Center, and additional pulsar-related studies. We describe the DSN's
capabilities for carrying out these types of observations. We also present
results from observations of three radio magnetars, PSR J1745-2900, PSR
J1622-4950, and XTE J1810-197, and the transitional magnetar candidate, PSR
J1119-6127, using the DSN radio telescopes near Canberra, Australia.Comment: 14 pages, 8 figures, Accepted for publication in Advances in
Astronomy on 2019 January 27 (Invited paper for a special issue on magnetars
A Study of the 20 Day Superorbital Modulation in the High-Mass X-ray Binary IGR J16493-4348
We report on Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels
Swift Observatory (Swift) X-ray Telescope (XRT) and Swift Burst Alert Telescope
(BAT) observations of IGR J16493-4348, a wind-fed Supergiant X-ray Binary
(SGXB) showing significant superorbital variability. From a discrete Fourier
transform of the BAT light curve, we refine its superorbital period to be
20.058 0.007 days. The BAT dynamic power spectrum and a fractional root
mean square analysis both show strong variations in the amplitude of the
superorbital modulation, but no observed changes in the period were found. The
superorbital modulation is significantly weaker between MJD 55,700 and MJD
56,300. The joint NuSTAR and XRT observations, which were performed near the
minimum and maximum of one cycle of the 20 day superorbital modulation, show
that the flux increases by more than a factor of two between superorbital
minimum and maximum. We find no significant changes in the 3-50 keV pulse
profiles between superorbital minimum and maximum, which suggests a similar
accretion regime. Modeling the pulse-phase averaged spectra we find a possible
Fe K emission line at 6.4 keV at superorbital maximum. The feature is
not significant at superorbital minimum. While we do not observe any
significant differences between the pulse-phase averaged spectral continua
apart from the overall flux change, we find that the hardness ratio near the
broad main peak of the pulse profile increases from superorbital minimum to
maximum. This suggests the spectral shape hardens with increasing luminosity.
We discuss different mechanisms that might drive the observed superorbital
modulation.Comment: 17 pages, 14 figures, 3 tables, accepted for publication in The
Astrophysical Journal on 2019 May 1
Instrumental vetoes for transient gravitational-wave triggers using noise-coupling models: The bilinear-coupling veto
LIGO and Virgo recently completed searches for gravitational waves at their
initial target sensitivities, and soon Advanced LIGO and Advanced Virgo will
commence observations with even better capabilities. In the search for short
duration signals, such as coalescing compact binary inspirals or "burst"
events, noise transients can be problematic. Interferometric gravitational-wave
detectors are highly complex instruments, and, based on the experience from the
past, the data often contain a large number of noise transients that are not
easily distinguishable from possible gravitational-wave signals. In order to
perform a sensitive search for short-duration gravitational-wave signals it is
important to identify these noise artifacts, and to "veto" them. Here we
describe such a veto, the bilinear-coupling veto, that makes use of an
empirical model of the coupling of instrumental noise to the output strain
channel of the interferometric gravitational-wave detector. In this method, we
check whether the data from the output strain channel at the time of an
apparent signal is consistent with the data from a bilinear combination of
auxiliary channels. We discuss the results of the application of this veto on
recent LIGO data, and its possible utility when used with data from Advanced
LIGO and Advanced Virgo.Comment: Minor changes; To appear in Phys. Rev.
PROPERTIES OF THE 24 DAY MODULATION IN GX 13+1 FROM NEAR-INFRARED AND X-RAY OBSERVATIONS
A 24 day period for the low-mass X-ray binary (LMXB) GX 13+1 was previously proposed on the basis of seven years of RXTE All-Sky Monitor (ASM) observations and it was suggested that this was the orbital period of the system. This would make it one of the longest known orbital periods for a Galactic LMXB powered by Roche lobe overflow. We present here the results of (1) K-band photometry obtained with the SMARTS Consortium CTIO 1.3 m telescope on 68 nights over a 10 month interval; (2) continued monitoring with the RXTE ASM, analyzed using a semi-weighted power spectrum instead of the data filtering technique previously used; and (3) Swift Burst Alert Telescope (BAT) hard X-ray observations. Modulation near 24 days is seen in both the K band and additional statistically independent ASM X-ray observations. However, the modulation in the ASM is not strictly periodic. The periodicity is also not detected in the Swift BAT observations, but modulation at the same relative level as seen with the ASM cannot be ruled out. If the 24 day period is the orbital period of system, this implies that the X-ray modulation is caused by structure that is not fixed in location. A possible mechanism for the X-ray modulation is the dipping behavior recently reported from XMM-Newton observations
Observations of Radio Magnetars with the Deep Space Network
The Deep Space Network (DSN) is a worldwide array of radio telescopes which supports NASA’s interplanetary spacecraft missions. When the DSN antennas are not communicating with spacecraft, they provide a valuable resource for performing observations of radio magnetars, searches for new pulsars at the Galactic Center, and additional pulsar-related studies. We describe the DSN’s capabilities for carrying out these types of observations. We also present results from observations of three radio magnetars, PSR J1745–2900, PSR J1622–4950, and XTE J1810–197, and the transitional magnetar candidate, PSR J1119–6127, using the DSN radio telescopes near Canberra, Australia
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