4 research outputs found
Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 during its Low-luminosity Accretion-disk State
3FGL J1544.6-1125 is a candidate transitional millisecond pulsar (tMSP). Similar to the well-established tMSPs - PSR J1023+0038, IGR J18245-2452, and XSS J12270-4859 - 3FGL J1544.6-1125 shows γ-ray emission and discrete X-ray "low"and "high"modes during its low-luminosity accretion-disk state. Coordinated radio/X-ray observations of PSR J1023+0038 in its current low-luminosity accretion-disk state showed rapidly variable radio continuum emission - possibly originating from a compact, self-absorbed jet, the "propellering"of accretion material, and/or pulsar moding. 3FGL J1544.6-1125 is currently the only other (candidate) tMSP system in this state, and can be studied to see whether tMSPs are typically radio-loud compared to other neutron star binaries. In this work, we present a quasi-simultaneous Very Large Array and Swift radio/X-ray campaign on 3FGL J1544.6-1125. We detect 10 GHz radio emission varying in flux density from 47.7 ± 6.0 μJy down to ≲15 μJy (3σ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is L 5 GHz = (2.17 ± 0.17) × 1027 erg s-1 for a quasi-simultaneous X-ray luminosity L 2-10 keV = (4.32 ± 0.23) × 1033 erg s-1 (for an assumed distance of 3.8 kpc). These luminosities are close to those of PSR J1023+0038, and the results strengthen the case that 3FGL J1544.6-1125 is a tMSP showing similar phenomenology to PSR J1023+0038.A.J. and J.W.T.H. acknowledge funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement nr. 337062 (DRAGNET). A.J. also acknowledges support from the NuSTAR mission. A.P. acknowledges support from an NWO Vidi Fellowship. J.C.A.M.-J. is the recipient of an Australian Research Council Future Fellowship (FT 140101082). S.B. was supported in part by NASA Swift Guest Investigator Cycle 12 program grant NNX16AN79G awarded through Columbia University
Probing the gravitational wave background from cosmic strings with LISA
International audienc
European Pulsar Timing Array Limits On An Isotropic Stochastic Gravitational-Wave Background
24 pages, 5 tables, 17 figuresInternational audienceWe present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar dataset spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar System ephemeris errors, obtaining a robust 95 upper limit on the dimensionless strain amplitude of the background of at a reference frequency of and a spectral index of , corresponding to a background from inspiralling super-massive black hole binaries, constraining the GW energy density to at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of ~Hz. Finally we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95 upper limits on the string tension, , characterising a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu-Goto field theory cosmic string network, we set a limit , identical to that set by the {\it Planck} Collaboration, when combining {\it Planck} and high- Cosmic Microwave Background data from other experiments. For a stochastic relic background we set a limit of , a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array
European Pulsar Timing Array Limits on Continuous Gravitational Waves from Individual Supermassive Black Hole Binaries
We have searched for continuous gravitational wave (CGW) signals produced by
individually resolvable, circular supermassive black hole binaries (SMBHBs) in
the latest EPTA dataset, which consists of ultra-precise timing data on 41
millisecond pulsars. We develop frequentist and Bayesian detection algorithms
to search both for monochromatic and frequency-evolving systems. None of the
adopted algorithms show evidence for the presence of such a CGW signal,
indicating that the data are best described by pulsar and radiometer noise
only. Depending on the adopted detection algorithm, the 95\% upper limit on the
sky-averaged strain amplitude lies in the range at . This limit varies
by a factor of five, depending on the assumed source position, and the most
constraining limit is achieved towards the positions of the most sensitive
pulsars in the timing array. The most robust upper limit -- obtained via a full
Bayesian analysis searching simultaneously over the signal and pulsar noise on
the subset of ours six best pulsars -- is . These limits, the
most stringent to date at , exclude the presence of
sub-centiparsec binaries with chirp mass M out to a
distance of about 25Mpc, and with M out to a
distance of about 1Gpc (). We show that state-of-the-art SMBHB
population models predict probability of detecting a CGW with the
current EPTA dataset, consistent with the reported non-detection. We stress,
however, that PTA limits on individual CGW have improved by almost an order of
magnitude in the last five years. The continuing advances in pulsar timing data
acquisition and analysis techniques will allow for strong astrophysical
constraints on the population of nearby SMBHBs in the coming years.Comment: 16 pages, 11 figures, accepted for publication in MNRA