195 research outputs found
A Giant Sample of Giant Pulses from the Crab Pulsar
We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a
timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and
seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses
(GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken
with the same telescope and backend and analyzed as one data set. We calculated
power-law fits to amplitude distributions for main pulse (MP) and interpulse
(IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz
and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also
correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank
Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9
GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2
GHz and 39900 GPs from the GBT were recorded during these contemporaneous
observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at
8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP
GPs were detected within one spin period of high-frequency IP GPs, with a
chance probability of 9%. This indicates that the emission processes at high
and low radio frequencies are related, despite significant pulse profile shape
differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to
see if increased pair production in the magnetosphere is the mechanism
responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons
were used in this correlation analysis. No significant correlations were found
between GPs and gamma-ray photons. This indicates that increased pair
production in the magnetosphere is likely not the dominant cause of GPs.
Possible methods of GP production may be increased coherence of synchrotron
emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap
Discovery of a New Transient Magnetar Candidate: XTE J1810-197
We report the discovery of a new X-ray pulsar, XTE J1810-197. The source was
serendipitously discovered on 2003 July 15 by the Rossi X-ray Timing Explorer
(RXTE) while observing the soft gamma repeater SGR 1806-20. The pulsar has a
5.54 s spin-period and a soft spectrum (photon index ~ 4). We detect the source
in earlier RXTE observations back to 2003 January. These show that a transient
outburst began between 2002 November 17 and 2003 January 23 and that the pulsar
has been spinning down since then, with a high rate Pdot ~ 10^-11 s/s showing
significant timing noise, but no evidence for Doppler shifts due to a binary
companion. The rapid spin-down rate and slow spin-period imply a super-critical
magnetic field B=3x10^14 G and a young characteristic age < 7600 yr. These
properties are strikingly similar to those of anomalous X-ray pulsars and soft
gamma repeaters, making the source a likely new magnetar. A follow-up Chandra
observation provided a 2".5 radius error circle within which the 1.5 m
Russian-Turkish Optical Telescope RTT150 found a limiting magnitude of
R_c=21.5, in accord with other recently reported limits. The source is present
in archival ASCA and ROSAT data as well, at a level 100 times fainter than the
\~ 3 mCrab seen in 2003. This suggests that other X-ray sources that are
currently in a state similar to the inactive phase of XTE J1810-197 may also be
unidentified magnetars awaiting detection via a similar activity.Comment: Submitted to ApJL; 4 pages; 4 figure
GBT Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30
We report the discovery of two binary millisecond pulsars in the
core-collapsed globular cluster M30 using the Green Bank Telescope (GBT) at 20
cm. PSR J2140-2310A (M30A) is an eclipsing 11-ms pulsar in a 4-hr circular
orbit and PSR J2140-23B (M30B) is a 13-ms pulsar in an as yet undetermined but
most likely highly eccentric (e>0.5) and relativistic orbit. Timing
observations of M30A with a 20-month baseline have provided precise
determinations of the pulsar's position (within 4" of the optical centroid of
the cluster), and spin and orbital parameters, which constrain the mass of the
companion star to be m_2 >~ 0.1Msun. The position of M30A is coincident with a
possible thermal X-ray point source found in archival Chandra data which is
most likely due to emission from hot polar caps on the neutron star. In
addition, there is a faint (V_555 ~ 23.8) star visible in archival HST F555W
data that may be the companion to the pulsar. Eclipses of the pulsed radio
emission from M30A by the ionized wind from the compact companion star show a
frequency dependent duration (\propto\nu^{-\alpha} with \alpha ~ 0.4-0.5) and
delay the pulse arrival times near eclipse ingress and egress by up to 2-3 ms.
Future observations of M30 may allow both the measurement of post-Keplerian
orbital parameters from M30B and the detection of new pulsars due to the
effects of strong diffractive scintillation.Comment: 10 pages, 6 figures, Submitted to ApJ. This version includes many
recommended modifications, an improved structure, a new author, and a
completely redone optical analysi
Your: Your Unified Reader
The advancement in signal processing and GPU based systems has enabled new
transient detectors at various telescopes to perform much more sensitive
searches than their predecessors. Typically the data output from the telescopes
is in one of the two commonly used formats: psrfits and Sigproc filterbank.
Software developed for transient searches often only works with one of these
two formats, limiting their general applicability. Therefore, researchers have
to write custom scripts to read/write the data in their format of choice before
they can begin any data analysis relevant for their research. \textsc{Your}
(Your Unified Reader) is a python-based library that unifies the data
processing across multiple commonly used formats. \textsc{Your} implements a
user-friendly interface to read and write in the data format of choice. It also
generates unified metadata corresponding to the input data file for a quick
understanding of observation parameters and provides utilities to perform
common data analysis operations. \textsc{Your} also provides several
state-of-the-art radio frequency interference mitigation (RFI) algorithms,
which can now be used during any stage of data processing (reading, writing,
etc.) to filter out artificial signals.Comment: 3 pages, Published in JOSS, Github:
https://github.com/thepetabyteproject/you
An XTE Archival Search for Coherent X-ray Pulsations in LMXB 4U 1820-30
As part of a large-scale search for coherent pulsations from LMXBs in the
RXTE archive, we have completed a detailed series of searches for coherent
pulsations of 4U 1820-30 -- an ultracompact LMXB with a binary period of 11.4
min, located in the globular cluster NGC6624. The short binary period implies
any coherent signal would be highly accelerated, so we used phase modulation
searches, orbital-parameter-fitting coherent searches, and standard
acceleration searches to give significant sensitivity to millisecond
pulsations. We searched, in four energy bands and at a range of luminosities, a
total of 34 archival RXTE observations, 32 of which had on-source integration
times longer than 10 ks, and some of which were made consecutively which
allowed us to combine them. We found no pulsations. Using our phase modulation
search technique, which we ran on all 34 observations, we have been able to
place the first stringent (95% confidence) pulsed fraction limits of <~0.8% for
all realistic spin frequencies (i.e. <~2kHz) and likely companion masses
(0.02Msun <= M_c <= 0.3Msun). Using our orbital-parameter-fitting coherent
search, which we ran on only 11 selected observations, we have placed a pulsed
fraction limit of <~0.3% for spin frequencies <~1.25kHz and companion masses M_
<= 0.106Msun. By contrast, all five LMXBs known to emit coherent pulsations
have intrinsic pulsed fractions in the range 3% to 7% when pulsations are
observed. Hence, our searches rule out pulsations with significantly lower
pulsed fractions than those already observed.Comment: 10 pages, 5 figures, published in ApJ, the text of this astro-ph
version is now identical to the text of the published versio
A Multi-telescope Campaign on FRB 121102: Implications for the FRB Population
We present results of the coordinated observing campaign that made the first
subarcsecond localization of a Fast Radio Burst, FRB 121102. During this
campaign, we made the first simultaneous detection of an FRB burst by multiple
telescopes: the VLA at 3 GHz and the Arecibo Observatory at 1.4 GHz. Of the
nine bursts detected by the Very Large Array at 3 GHz, four had simultaneous
observing coverage at other observatories. We use multi-observatory constraints
and modeling of bursts seen only at 3 GHz to confirm earlier results showing
that burst spectra are not well modeled by a power law. We find that burst
spectra are characterized by a ~500 MHz envelope and apparent radio energy as
high as erg. We measure significant changes in the apparent
dispersion between bursts that can be attributed to frequency-dependent
profiles or some other intrinsic burst structure that adds a systematic error
to the estimate of DM by up to 1%. We use FRB 121102 as a prototype of the FRB
class to estimate a volumetric birth rate of FRB sources Mpc yr, where is the number of bursts per
source over its lifetime. This rate is broadly consistent with models of FRBs
from young pulsars or magnetars born in superluminous supernovae or long
gamma-ray bursts, if the typical FRB repeats on the order of thousands of times
during its lifetime.Comment: 17 pages, 7 figures. Submitted to AAS Journal
Properties and Evolution of the Redback Millisecond Pulsar Binary PSR J2129-0429
PSR J2129−0429 is a "redback" eclipsing millisecond pulsar binary with an unusually long 15.2 hr orbit. It was discovered by the Green Bank Telescope in a targeted search of unidentified Fermi gamma-ray sources. The pulsar companion is optically bright (mean m_R = 16.6 mag), allowing us to construct the longest baseline photometric data set available for such a system. We present 10 years of archival and new photometry of the companion from the Lincoln Near-Earth Asteroid Research Survey, the Catalina Real-time Transient Survey, the Palomar Transient Factory, the Palomar 60 inch, and the Las Cumbres Observatory Global Telescope. Radial velocity spectroscopy using the Double-Beam Spectrograph on the Palomar 200 inch indicates that the pulsar is massive: 1.74 ± 0.18 M_☉. The G-type pulsar companion has mass 0.44 ± 0.04 M_☉, one of the heaviest known redback companions. It is currently 95 ± 1% Roche-lobe filling and only mildly irradiated by the pulsar. We identify a clear 13.1 mmag yr^(−1) secular decline in the mean magnitude of the companion as well as smaller-scale variations in the optical light curve shape. This behavior may indicate that the companion is cooling. Binary evolution calculations indicate that PSR J2129−0429 has an orbital period almost exactly at the bifurcation period between systems that converge into tighter orbits as black widows and redbacks and those that diverge into wider pulsar–white dwarf binaries. Its eventual fate may depend on whether it undergoes future episodes of mass transfer and increased irradiation
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
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