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 $\gamma$-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 $47.7 \pm 6.0$ $\mu$Jy down to $\sim$15 $\mu$Jy (3$\sigma$ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is $L_{5 GHz}$ $= (2.17 \pm 0.17) \times 10^{27}$ erg s$^{-1}$ for a quasi-simultaneous X-ray luminosity $L_{2-10 keV}$ $= (4.32 \pm 0.23) \times 10^{33}$ 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.Comment: Accepted for publication in the Astrophysical Journa

Constraining emission estimates of carbon monoxide using a perturbed emissions ensemble with observations: a focus on Beijing

Funder: Tsinghua University Initiative Scientific Research ProgramFunder: National Centre for Atmospheric Science; doi: http://dx.doi.org/10.13039/501100000662Funder: Met Office; doi: http://dx.doi.org/10.13039/501100000847Abstract: The reliability of air quality simulations has a strong dependence on the input emissions inventories, which are associated with various sources of uncertainties, particularly in regions undergoing rapid emission changes where inventories can be ‘out of date’ almost as soon as they are compiled. This work provides a new methodology for updating emissions inventories by source sector using air quality ensemble simulations and observations from a dense monitoring network. It is adopted to determine the short-term trends in carbon monoxide (CO) emissions, an important pollutant and precursor to tropospheric ozone, in a study area centred around Beijing following the implementation of clean air policies. We sample the uncertainties associated with using an a priori emissions inventory for the year 2013 in air quality simulations of 2016, using an atmospheric dispersion model combined with a perturbed emissions ensemble (PEE), which is constructed based on expert-elicited uncertainty ranges for individual source sectors in the inventory. By comparing the simulation outputs with observational constraints, we are able to constrain the emissions of key source sectors relative to those in the a priori emissions inventory. From 2013 to 2016, we find a 44–88% reduction in the transport sector emissions (0.92–4.4×105 Mg in 2016) and a minimum 61% decrease in residential sector emissions (<3.5×105 Mg in 2016) within the study area. We also provide evidence that the night-time fraction of traffic sources in 2016 was higher than that in the 2013 emissions inventory. This study shows the applicability of PEEs and high-resolution observations in providing timely updates of emission estimates by source sector