New Observing Modes for the DBBC3

The DBBC3 was further enhanced by introducing\ua0new modes. Three different firmwares have\ua0recently been implemented for observing: Direct Sampling\ua0Conversion (DSC), arbitrary selection of bands\ua0(OCT), and Digital Down Conversion (DDC). These\ua0modes cover all the requirements of astronomical,\ua0VGOS, and legacy geodetic VLBI for the time being\ua0and the immediate future. In addition, the DBBC3\ua0offers unsurpassed compatibility to the relatively large\ua0number of other existing VLBI backends. A number\ua0of test observations were performed in the last months\ua0to achieve the best performance of the VGOS modes,\ua0and similar tests are planned for the EVN network. At\ua0the same time the DBBC3 is an important platform\ua0for additional new modes to be implemented for\ua0the BRAND receiver. Several DBBC3 systems are\ua0deployed in the field and more are under construction,\ua0with the number of 4-GHz bands ranging from two up\ua0to eight with resulting output data rates from 32 Gbps\ua0to 128 Gbps

DBBC3 Towards the BRAND EVN Receiver

The DBBC3 is a flexible VLBI backend and\ua0environment that supports a wide range of observational\ua0needs via a suite of FPGA firmware types. The\ua0hardware can sample up to eight 4 GHz-wide baseband\ua0signals and convert to digital streams over multiple\ua010GE links on fibre. The development team has an ongoing\ua0development programme that has enhanced existing\ua0modes and introduced new desired modes as user\ua0requirements evolve. Three dierent firmware types for\ua0observing have been implemented which will be briefly\ua0summarised: Direct Sampling Conversion (DSC), arbitrary\ua0selection of bands (OCT), Digital Down Conversion\ua0(DDC). These modes cover all the requirements\ua0of astronomical, VGOS and legacy geodetic VLBI of\ua0the present, but also of the near future. At the same\ua0time the DBBC3 is an important platform for additional\ua0new modes to be implemented for the BRAND\ua0receiver. This paper describes the use of the DBBC3\ua0for the receiver development, pointing out which element\ua0in the current DBBC3 structure will be part of\ua0the BRAND receiver in order to simplify its introduction\ua0into the existing VLBI environment at telescopes\ua0with a DBBC3 backend

First results from BRASS-p broadband searches for hidden photon dark matter

We discuss first results from hidden photon dark matter searches made with a prototype of the Broadband Radiometric Axion/ALPs Search Setup (BRASS-p) in the range of particle mass of 49.63-74.44 $\mu$eV (frequency range of 12-18 GHz). The conceptual design of BRASS and a detailed description of its present prototype, BRASS-p, are given, with a view of the potential application of such setups to hidden photon, axion, and axion-like particle (ALP) dark matter searches using heterodyne detectors in the range of particle mass from 40$\mu$eV to 4000$\mu$eV (10 GHz to 1 THz). Pioneering measurements made with BRASS-p achieve the record sensitivity of (0.3--1.0)$\times$$10^{-13}$ to the kinetic mixing between the normal and hidden photons, assuming the dark matter is made entirely of unpolarized hidden photons. Based on these results, a discussion of further prospects for dark matter searches using the BRASS-p apparatus is presented.Comment: 17 pages, 13 figures. Prepared for submission to JCA

A ring-like accretion structure in M87 connecting its black hole and jet

The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation^{1,2}. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole^3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of 8.4_{-1.1}^{+0.5} Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow.Comment: 50 pages, 18 figures, 3 tables, author's version of the paper published in Natur

A ring-like accretion structure in M87 connecting its black hole and jet

The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation1,2. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of [Formula: see text] Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects, in addition\ua0to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow

First Sagittarius A* Event Horizon Telescope results. II. EHT and multiwavelength observations, data processing, and calibration

We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5–11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ∼50 μas, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.http://iopscience.iop.org/2041-8205Physic

First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration

We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5–11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ∼50 μas, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*’s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior

Shocks at large banks and banking sector distress: the banking granular residual

Size matters in banking. In this paper, we explore whether shocks originating at large banks affect the probability of distress of smaller banks and thus the stability of the banking system. Our analysis proceeds in two steps. In a first step, we follow Gabaix [Gabaix, X., 2008a. The Granular Origins of Aggregate Fluctuations. Available at SSRN: http://ssrn.com/abstract=1111765] and construct a measure of idiosyncratic shocks at large banks, the so-called Banking Granular Residual. This measure documents the importance of size effects for the German banking system. In a second step, we incorporate this measure of idiosyncratic shocks at large banks into an integrated stress-testing model for the German banking system following De Graeve et al. (2008). We find that positive shocks at large banks reduce the probability of distress of small banks