A search for radio emission from double-neutron star merger GW190425 using Apertif

ContextDetection of the electromagnetic emission from coalescing binary neutron stars (BNS) is important for understanding the merger and afterglow. Aims. We present a search for a radio counterpart to the gravitational-wave (GW) source GW190425, a BNS merger, using Apertif on the Westerbork Synthesis Radio Telescope (WSRT). MethodsWe observed a field of high probability in the associated localisation region for three epochs at ΔT\ue2€., =\ue2€., 68, 90, 109 d post merger. We identified all sources that exhibit flux variations consistent with the expected afterglow emission of GW190425. We also looked for possible transients. These are sources that are only present in one epoch. In addition, we quantified our ability to search for radio afterglows in the fourth and future observing runs of the GW detector network using Monte Carlo simulations. ResultsWe found 25 afterglow candidates based on their variability. None of these could be associated with a possible host galaxy at the luminosity distance of GW190425. We also found 55 transient afterglow candidates that were only detected in one epoch. All of these candidates turned out to be image artefacts. In the fourth observing run, we predict that up to three afterglows will be detectable by Apertif. ConclusionsWhile we did not find a source related to the afterglow emission of GW190425, the search validates our methods for future searches of radio afterglows

Apercal-The Apertif calibration pipeline

Apertif (APERture Tile In Focus) is one of the Square Kilometre Array (SKA) pathfinder facilities. The Apertif project is an upgrade to the 50-year-old Westerbork Synthesis Radio Telescope (WSRT) using phased-array feed technology. The new receivers create 40 individual beams on the sky, achieving an instantaneous sky coverage of 6.5 square degrees. The primary goal of the Apertif Imaging Survey is to perform a wide survey of 3500 square degrees (AWES) and a medium deep survey of 350 square degrees (AMES) of neutral atomic hydrogen (up to a redshift of 0.26), radio continuum emission and polarisation. Each survey pointing yields 4.6 TB of correlated data. The goal of Apercal is to process this data and fully automatically generate science ready data products for the astronomical community while keeping up with the survey observations. We make use of common astronomical software packages in combination with Python based routines and parallelisation. We use an object oriented module-based approach to ensure easy adaptation of the pipeline. A Jupyter notebook based framework allows user interaction and execution of individual modules as well as a full automatic processing of a complete survey observation. If nothing interrupts processing, we are able to reduce a single pointing survey observation on our five node cluster with 24 physical cores and 256 GB of memory each within 24 h keeping up with the speed of the surveys. The quality of the generated images is sufficient for scientific usage for 44% of the recorded data products with single images reaching dynamic ranges of several thousands. Future improvements will increase this percentage to over 80%. Our design allowed development of the pipeline in parallel to the commissioning of the Apertif system

A bright, high rotation-measure FRB that skewers the M33 halo

We report the detection of a bright fast radio burst, FRB\,191108, with Apertif on the Westerbork Synthesis Radio Telescope (WSRT). The interferometer allows us to localise the FRB to a narrow 5\arcsec\times7\arcmin ellipse by employing both multibeam information within the Apertif phased-array feed (PAF) beam pattern, and across different tied-array beams. The resulting sight line passes close to Local Group galaxy M33, with an impact parameter of only 18\,kpc with respect to the core. It also traverses the much larger circumgalactic medium of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute $\sim$10\% of its dispersion measure of 588\,pc\,cm$^{-3}$. FRB\,191108 has a Faraday rotation measure of +474\,$\pm\,3$\,rad\,m$^{-2}$, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetised plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with $\Delta\nu\approx40$\,MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data

Dexamethasone intravitreal implant in previously treated patients with diabetic macular edema : Subgroup analysis of the MEAD study

Background: Dexamethasone intravitreal implant 0.7 mg (DEX 0.7) was approved for treatment of diabetic macular edema (DME) after demonstration of its efficacy and safety in the MEAD registration trials. We performed subgroup analysis of MEAD study results to evaluate the efficacy and safety of DEX 0.7 treatment in patients with previously treated DME. Methods: Three-year, randomized, sham-controlled phase 3 study in patients with DME, best-corrected visual acuity (BCVA) of 34.68 Early Treatment Diabetic Retinopathy Study letters (20/200.20/50 Snellen equivalent), and central retinal thickness (CRT) 65300 \u3bcm measured by time-domain optical coherence tomography. Patients were randomized to 1 of 2 doses of DEX (0.7 mg or 0.35 mg), or to sham procedure, with retreatment no more than every 6 months. The primary endpoint was 6515-letter gain in BCVA at study end. Average change in BCVA and CRT from baseline during the study (area-under-the-curve approach) and adverse events were also evaluated. The present subgroup analysis evaluated outcomes in patients randomized to DEX 0.7 (marketed dose) or sham based on prior treatment for DME at study entry. Results: Baseline characteristics of previously treated DEX 0.7 (n = 247) and sham (n=261) patients were similar. In the previously treated subgroup, mean number of treatments over 3 years was 4.1 for DEX 0.7 and 3.2 for sham, 21.5 % of DEX 0.7 patients versus 11.1 % of sham had 6515-letter BCVA gain from baseline at study end (P = 0.002), mean average BCVA change from baseline was +3.2 letters with DEX 0.7 versus +1.5 letters with sham (P = 0.024), and mean average CRT change from baseline was -126.1 \u3bcm with DEX 0.7 versus -39.0 \u3bcm with sham(P < 0.001). Cataract-related adverse events were reported in 70.3 % of baseline phakic patients in the previously treated DEX 0.7 subgroup; vision gains were restored following cataract surgery. Conclusions: DEX 0.7 significantly improved visual and anatomic outcomes in patients with DME previously treated with laser, intravitreal anti-vascular endothelial growth factor, intravitreal triamcinolone acetonide, or a combination of these therapies. The safety profile of DEX 0.7 in previously treated patients was similar to its safety profile in the total study population

Continuum source catalog for the first APERTIF data release

The first data release from Apertif survey contains 3074 radio continuum images, covering a thousand square degrees of the sky. The observations were performed between August 2019 and July 2020. The continuum images were produced at a central frequency 1355 MHz, with a bandwidth of ~150 MHz and angular resolution of up to 10âà  ³. In this work, we introduce and apply a new method to obtain a primary beam model based on a machine-learning approach, namely, Gaussian process regression. The primary beam models obtained with this method have been published, along with the data products for the first Apertif data release. We applied the method to the continuum images, carried out a mosaicking process on their basis, and extracted the source catalog. The catalog contains 249672 radio sources, many of which have been detected for the first time at these frequencies. We cross-matched the coordinates with the NVSS, LOFAR/DR1/value-Added, and LOFAR/DR2 catalogs a resulting in 44523, 22825, and 152824 common sources, respectively. The first sample provides a unique opportunity for detecting long-Term transient sources, which have significantly changed their flux density over the past 25 yr. A combination of the second and the third samples provides valuable information on the spectral properties of the sources in addition to redshift estimates

Continuum source catalog for the first APERTIF data release

The first data release from Apertif survey contains 3074 radio continuum images, covering a thousand square degrees of the sky. The observations were performed between August 2019 and July 2020. The continuum images were produced at a central frequency 1355 MHz, with a bandwidth of ~150 MHz and angular resolution of up to 10âà  ³. In this work, we introduce and apply a new method to obtain a primary beam model based on a machine-learning approach, namely, Gaussian process regression. The primary beam models obtained with this method have been published, along with the data products for the first Apertif data release. We applied the method to the continuum images, carried out a mosaicking process on their basis, and extracted the source catalog. The catalog contains 249672 radio sources, many of which have been detected for the first time at these frequencies. We cross-matched the coordinates with the NVSS, LOFAR/DR1/value-Added, and LOFAR/DR2 catalogs a resulting in 44523, 22825, and 152824 common sources, respectively. The first sample provides a unique opportunity for detecting long-Term transient sources, which have significantly changed their flux density over the past 25 yr. A combination of the second and the third samples provides valuable information on the spectral properties of the sources in addition to redshift estimates