305 research outputs found
Infrared observations of the candidate double neutron star system PSR J1811-1736
PSR J1811-1736 (P=104 ms) is an old (~1.89 Gyrs) binary pulsar (P_orb=18.8 d)
in a highly eccentric orbit (e=0.828) with an unidentified companion.
Interestingly enough, the pulsar timing solution yields an estimated companion
mass 0.93 M_{\odot}<M_C<1.5 M_{\odot}, compatible with that of a neutron star.
As such, it is possible that PSR J1811-1736 is a double neutron star (DNS)
system, one of the very few discovered so far. This scenario can be
investigated through deep optical/infrared (IR) observations. We used J, H,
K-band images, obtained as part of the UK Infrared Telescope (UKIRT) Infrared
Deep Sky Survey (UKIDSS), and available in the recent Data Release 9 Plus, to
search for its undetected companion of the PSR J1811-1736 binary pulsar. We
detected a possible companion star to PSR J1811-1736 within the 3 sigma radio
position uncertainty (1.32 arcsec), with magnitudes J=18.61+/-0.07,
H=16.65+/-0.03, and K=15.46+/-0.02. The star colours are consistent with either
a main sequence (MS) star close to the turn-off or a lower red giant branch
(RGB) star, at a pulsar distance of ~5.5 kpc and with a reddening of
E(B-V)~4.9. The star mass and radius would be compatible with the constraints
on the masses and orbital inclination of the binary system inferred from the
mass function and the lack of radio eclipses near superior conjunction. Thus,
it is possible that it is the companion to PSR J1811-1736. However, based on
the star density in the field, we estimated a quite large chance coincidence
probability of ~0.27 between the pulsar and the star, which makes the
association unlikely. No other star is detected within the 3 sigma pulsar radio
position down to J~20.5, H~19.4$ and K~18.6, which would allow us to rule out a
MS companion star earlier than a mid-to-late M spectral type.Comment: 10 pages, 6 figures, accepted for publication on Monthly Notices of
the Royal Astronomical Societ
Gemini optical observations of binary millisecond-pulsars
Milli-second pulsars (MSPs) are rapidly spinning neutron stars, with spin
periods P_s <= 10 ms, which have been most likely spun up after a phase of
matter accretion from a companion star. In this work we present the results of
the search for the companion stars of four binary milli-second pulsars, carried
out with archival data from the Gemini South telescope. Based upon a very good
positional coincidence with the pulsar radio coordinates, we likely identified
the companion stars to three MSPs, namely PSRJ0614-3329 (g=21.95 +- 0.05),
J1231-1411 (g=25.40 +-0.23), and J2017+0603 (g=24.72 +- 0.28). For the last
pulsar (PSRJ0613-0200) the identification was hampered by the presence of a
bright star (g=16 +- 0.03) at \sim 2" from the pulsar radio coordinates and we
could only set 3-sigma upper limits of g=25.0, r= 24.3, and i= 24.2 on the
magnitudes of its companion star. The candidate companion stars to
PSRJ0614-3329, J1231-1411, and J2017+0603 can be tentatively identified as He
white dwarfs (WDs) on the basis of their optical colours and brightness and the
comparison with stellar model tracks. From the comparison of our multi-band
photometry with stellar model tracks we also obtained possible ranges on the
mass, temperature, and gravity of the candidate WD companions to these three
MSPs. Optical spectroscopy observations are needed to confirm their possible
classification as He WDs and accurately measure their stellar parameters.Comment: 17 pages, 7 figures, 6 tables, accepted for publication in MNRA
Constraining population synthesis models via the binary neutron star population
The observed sample of double neutron-star (NS-NS) binaries presents a
challenge to population-synthesis models of compact object formation: the
parameters entering into these models must be carefully chosen so as to match
(i) the observed star formation rate and (ii) the formation rate of NS-NS
binaries, which can be estimated from the observed sample and the selection
effects related to the discoveries with radio-pulsar surveys. In this paper, we
select from an extremely broad family of possible population synthesis models
those few (2%) which are consistent with the observed sample of NS-NS binaries.
To further sharpen the constraints the observed NS-NS population places upon
our understanding of compact-object formation processes, we separate the
observed NS-NS population into two channels: (i) merging NS-NS binaries, which
will inspiral and merge through the action of gravitational waves within
Gyr, and (ii) wide NS-NS binaries, consisting of all the rest. With the subset
of astrophysically consistent models, we explore the implications for the rates
at which double black hole (BH-BH), black hole-neutron star (BH-NS), and NS-NS
binaries will merge through the emission of gravitational waves.Comment: (v1) Submitted to ApJ. Uses emulateapj.cls. 8 pages, 7 figures. (v2)
Minor textual changes in response to referee queries. Substantial additions
in appendicies, including a detailed discussion of sample multidimensional
population synthesis fit
A Shapiro delay detection in the binary system hosting the millisecond pulsar PSR J1910-5959A
PSR J1910-5959A is a binary pulsar with a helium white dwarf companion
located about 6 arcmin from the center of the globular cluster NGC6752. Based
on 12 years of observations at the Parkes radio telescope, the relativistic
Shapiro delay has been detected in this system. We obtain a companion mass Mc =
0.180+/-0.018Msun (1sigma) implying that the pulsar mass lies in the range
1.1Msun <= Mp <= 1.5Msun. We compare our results with previous optical
determinations of the companion mass, and examine prospects for using this new
measurement for calibrating the mass-radius relation for helium white dwarfs
and for investigating their evolution in a pulsar binary system. Finally we
examine the set of binary systems hosting a millisecond pulsar and a low mass
helium white dwarf for which the mass of both stars has been measured. We
confirm that the correlation between the companion mass and the orbital period
predicted by Tauris & Savonije reproduces the observed values but find that the
predicted Mp - Pb correlation over-estimates the neutron star mass by about
0.5Msun in the orbital period range covered by the observations. Moreover, a
few systems do not obey the observed Mp - Pb correlation. We discuss these
results in the framework of the mechanisms that inhibit the accretion of matter
by a neutron star during its evolution in a low-mass X-ray binary.Comment: 4 figures, 2 tables, accepted for publication in the Astrophysical
Journa
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
Radio pulsations from the -ray millisecond pulsar PSR J2039-5617
The predicted nature of the candidate redback pulsar 3FGL\,J2039.65618 was
recently confirmed by the discovery of -ray millisecond pulsations
(Clark et al. 2020, hereafter Paper\,I), which identify this -ray
source as \msp. We observed this object with the Parkes radio telescope in 2016
and 2019. We detect radio pulsations at 1.4\,GHz and 3.1\,GHz, at the 2.6ms
period discovered in -rays, and also at 0.7\,GHz in one 2015 archival
observation. In all bands, the radio pulse profile is characterised by a single
relatively broad peak which leads the main -ray peak. At 1.4\,GHz we
found clear evidence of eclipses of the radio signal for about half of the
orbit, a characteristic phenomenon in redback systems, which we associate with
the presence of intra-binary gas. From the dispersion measure of
\,pc\,cm we derive a pulsar distance of \,kpc
or \,kpc, depending on the assumed Galactic electron density model.
The modelling of the radio and -ray light curves leads to an
independent determination of the orbital inclination, and to a determination of
the pulsar mass, qualitatively consistent to the results in Paper\,I.Comment: 18 pages, accepted for publication on 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
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