218 research outputs found
Multi-telescope timing of PSR J1518+4904
PSR J1518+4904 is one of only 9 known double neutron star systems. These
systems are highly valuable for measuring the masses of neutron stars,
measuring the effects of gravity, and testing gravitational theories. We
determine an improved timing solution for a mildly relativistic double neutron
star system, combining data from multiple telescopes. We set better constraints
on relativistic parameters and the separate masses of the system, and discuss
the evolution of PSR J1518+4904 in the context of other double neutron star
systems. PSR J1518+4904 has been regularly observed for more than 10 years by
the European Pulsar Timing Array (EPTA) network using the Westerbork, Jodrell
Bank, Effelsberg and Nancay radio telescopes. The data were analysed using the
updated timing software Tempo2. We have improved the timing solution for this
double neutron star system. The periastron advance has been refined and a
significant detection of proper motion is presented. It is not likely that more
post-Keplerian parameters, with which the individual neutron star masses and
the inclination angle of the system can be determined separately, can be
measured in the near future. Using a combination of the high-quality data sets
present in the EPTA collaboration, extended with the original GBT data, we have
constrained the masses in the system to m_p1.55 msun (95.4%
confidence), and the inclination angle of the orbit to be less than 47 degrees
(99%). From this we derive that the pulsar in this system possibly has one of
the lowest neutron star masses measured to date. From evolutionary
considerations it seems likely that the companion star, despite its high mass,
was formed in an electron-capture supernova.Comment: 11 pages, 8 figures, accepted by A&
Sardinia Radio Telescope wide-band spectral-polarimetric observations of the galaxy cluster 3C 129
We present new observations of the galaxy cluster 3C 129 obtained with the
Sardinia Radio Telescope in the frequency range 6000-7200 MHz, with the aim to
image the large-angular-scale emission at high-frequency of the radio sources
located in this cluster of galaxies. The data were acquired using the
recently-commissioned ROACH2-based backend to produce full-Stokes image cubes
of an area of 1 deg x 1 deg centered on the radio source 3C 129. We modeled and
deconvolved the telescope beam pattern from the data. We also measured the
instrumental polarization beam patterns to correct the polarization images for
off-axis instrumental polarization. Total intensity images at an angular
resolution of 2.9 arcmin were obtained for the tailed radio galaxy 3C 129 and
for 13 more sources in the field, including 3C 129.1 at the galaxy cluster
center. These data were used, in combination with literature data at lower
frequencies, to derive the variation of the synchrotron spectrum of 3C 129
along the tail of the radio source. If the magnetic field is at the
equipartition value, we showed that the lifetimes of radiating electrons result
in a radiative age for 3C 129 of t_syn = 267 +/- 26 Myrs. Assuming a linear
projected length of 488 kpc for the tail, we deduced that 3C 129 is moving
supersonically with a Mach number of M=v_gal/c_s=1.47. Linearly polarized
emission was clearly detected for both 3C 129 and 3C 129.1. The linear
polarization measured for 3C 129 reaches levels as high as 70% in the faintest
region of the source where the magnetic field is aligned with the direction of
the tail.Comment: 19 pages, 17 figures, accepted for publication in MNRA
Placing limits on the stochastic gravitational-wave background using European Pulsar Timing Array data
Direct detection of low-frequency gravitational waves (
Hz) is the main goal of pulsar timing array (PTA) projects. One of the main
targets for the PTAs is to measure the stochastic background of gravitational
waves (GWB) whose characteristic strain is expected to approximately follow a
power-law of the form , where is the
gravitational-wave frequency. In this paper we use the current data from the
European PTA to determine an upper limit on the GWB amplitude as a function
of the unknown spectral slope with a Bayesian algorithm, by modelling
the GWB as a random Gaussian process. For the case , which is
expected if the GWB is produced by supermassive black-hole binaries, we obtain
a 95% confidence upper limit on of , which is 1.8 times
lower than the 95% confidence GWB limit obtained by the Parkes PTA in 2006. Our
approach to the data analysis incorporates the multi-telescope nature of the
European PTA and thus can serve as a useful template for future
intercontinental PTA collaborations.Comment: 14 pages, 8 figures, 3 tables, mnras accepte
The new magnetar SGR J1830-0645 in outburst
The detection of a short hard X-ray burst and an associated bright soft X-ray
source by the Swift satellite in 2020 October heralded a new magnetar in
outburst, SGR J1830-0645. Pulsations at a period of ~10.4 s were detected in
prompt follow-up X-ray observations. We present here the analysis of the
Swift/BAT burst, of XMM-Newton and the Nuclear Spectroscopic Telescope Array
observations performed at the outburst peak, and of a Swift/XRT monitoring
campaign over the subsequent month. The burst was single-peaked, lasted ~6 ms,
and released a fluence of ~5e-9 erg cm^-2 (15-50 keV). The spectrum of the
X-ray source at the outburst peak was well described by an absorbed
double-blackbody model plus a power-law component detectable up to ~25 keV. The
unabsorbed X-ray flux decreased from ~5e-11 to ~2.5e-11 erg cm^-2 s^-1 one
month later (0.3-10 keV). Based on our timing analysis, we estimate a dipolar
magnetic field ~5.5e14 G at pole, a spin-down luminosity ~2.4e32 erg s^-1, and
a characteristic age ~24 kyr. The spin modulation pattern appears highly pulsed
in the soft X-ray band, and becomes smoother at higher energies. Several short
X-ray bursts were detected during our campaign. No evidence for periodic or
single-pulse emission was found at radio frequencies in observations performed
with the Sardinia Radio Telescope and Parkes. According to magneto-thermal
evolutionary models, the real age of SGR J1830-0645 is close to the
characteristic age, and the dipolar magnetic field at birth was slightly
larger, ~1e15 G.Comment: 10 pages, 4 figures, 2 tables. Accepted for publication in The
Astrophysical Journal Letter
The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis
[ABRIDGED] We present the discovery and follow-up observations of 142 pulsars
found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These
new discoveries bring the total number of pulsars found by the survey to 742.
In addition to tabulating spin and astrometric parameters, along with pulse
width and flux density information, we present orbital characteristics for 13
binary pulsars which form part of the new sample. Combining these results from
another recent Parkes multibeam survey at high Galactic latitudes, we have a
sample of 1008 normal pulsars which we use to carry out a determination of
their Galactic distribution and birth rate. We infer a total Galactic
population of 30000 +/- 1100 potentially detectable pulsars (i.e. those beaming
towards us) having 1.4-GHz luminosities above 0.1 mJy kpc squared. Using a
pulsar current analysis, we derive the birth rate of this population to be 1.4
+/- 0.2 pulsars per century. An important conclusion from our work is that the
inferred radial density function of pulsars depends strongly on the assumed
distribution of free electrons in the Galaxy. As a result, any analyses using
the most recent electron model of Cordes & Lazio predict a dearth of pulsars in
the inner Galaxy. We show that this model can also bias the inferred pulsar
scale height with respect to the Galactic plane. Combining our results with
other Parkes multibeam surveys we find that the population is best described by
an exponential distribution with a scale height of 330 pc.Comment: 30 pages, 8 figures, 9 tables, accepted for publication in MNRA
Broad-band X-ray spectra of the persistent black hole candidates LMC X-1 and LMC X-3
We report on observations of the two persistent black hole candidates LMC X-3
and LMCX-1 performed with \BS in October 1997. The flux of LMC X-1 was possibly
measured up to 60 keV, but there is a possible confusion with PSR 0540-69. Fits
with an absorbed multicolor disk black body are not satisfactory, while the
superposition of this model with a power law is acceptable. The sources showed
little variations during the observations. However in LMC X-1 some X-ray color
dependence on intensity is apparent, indicating a hardening of the spectrum in
the second half of the observation. The inner disk radius and temperature
change, featuring the same (anti)correlation found in {\it RXTE} data (Wilms et
al. 2000). QPOs were searched for. In LMC X-3 none was detected; in LMCX-1 a 3
sigma upper (9% rms) limit is given at 0.07 Hz, the frequency of the QPO
discovered with Ginga.Comment: 10 pages, 5 figures. To be published in the ApJ Supplement
LOFT - a Large Observatory For x-ray Timing
The high time resolution observations of the X-ray sky hold the key to a
number of diagnostics of fundamental physics, some of which are unaccessible to
other types of investigations, such as those based on imaging and spectroscopy.
Revealing strong gravitational field effects, measuring the mass and spin of
black holes and the equation of state of ultradense matter are among the goals
of such observations. At present prospects for future, non-focused X-ray timing
experiments following the exciting age of RXTE/PCA are uncertain. Technological
limitations are unavoidably faced in the conception and development of
experiments with effective area of several square meters, as needed in order to
meet the scientific requirements. We are developing large-area monolithic
Silicon Drift Detectors offering high time and energy resolution at room
temperature, which require modest resources and operation complexity (e.g.,
read-out) per unit area. Based on the properties of the detector and read-out
electronics that we measured in the lab, we developed a realistic concept for a
very large effective area mission devoted to X-ray timing in the 2-30 keV
energy range. We show that effective areas in the range of 10-15 square meters
are within reach, by using a conventional spacecraft platform and launcher of
the small-medium class.Comment: 13 pages, 8 figures, 1 table, Proceedings of SPIE Vol. 7732, Paper
No. 7732-66, 201
Vitamin D responsive elements within the HLA-DRB1 promoter region in Sardinian multiple sclerosis associated alleles
Vitamin D response elements (VDREs) have been found in the promoter region of the MS-associated allele HLA-DRB1*15:01, suggesting that with low vitamin D availability VDREs are incapable of inducing *15:01 expression allowing in early life autoreactive T-cells to escape central thymic deletion. The Italian island of Sardinia exhibits a very high frequency of MS and high solar radiation exposure. We test the contribution of VDREs analysing the promoter region of the MS-associated DRB1 *04:05, *03:01, *13:01 and *15:01 and non-MS-associated *16:01, *01, *11, *07:01 alleles in a cohort of Sardinians (44 MS patients and 112 healthy subjects). Sequencing of the DRB1 promoter region revealed a homozygous canonical VDRE in all *15:01, *16:01, *11 and in 45/73 *03:01 and in heterozygous state in 28/73 *03:01 and all *01 alleles. A new mutated homozygous VDRE was found in all *13:03, *04:05 and *07:01 alleles. Functionality of mutated and canonical VDREs was assessed for its potential to modulate levels of DRB1 gene expression using an in vitro transactivation assay after stimulation with active vitamin D metabolite. Vitamin D failed to increase promoter activity of the *04:05 and *03:01 alleles carrying the new mutated VDRE, while the *16:01 and *03:01 alleles carrying the canonical VDRE sequence showed significantly increased transcriptional activity. The ability of VDR to bind the mutant VDRE in the DRB1 promoter was evaluated by EMSA. Efficient binding of VDR to the VDRE sequence found in the *16:01 and in the *15:01 allele reduced electrophoretic mobility when either an anti-VDR or an anti-RXR monoclonal antibody was added. Conversely, the Sardinian mutated VDRE sample showed very low affinity for the RXR/VDR heterodimer. These data seem to exclude a role of VDREs in the promoter region of the DRB1 gene in susceptibility to MS carried by DRB1* alleles in Sardinian patients
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