arXiv subjects

D. John

Publications and source records attributed to D. John.

5 recordsLinked to original sources

arXiv2025

Shared-optical-path VLBI frequency phase transfer from 86 to 258 GHz on an 8600 km baseline: Demonstrated with the APEX and IRAM 30 m telescopes

The receiver N3AR operating at a frequency range between 67 and 116 GHz has been commissioned at the APEX telescope in October 2024. This adds a new low-frequency band for APEX, with the capability of simultaneous dual-frequency observations using a dichroic beamsplitter. The 3 mm receiver also allows APEX to join the existing 3 mm global VLBI network. One of our commissioning goals was to perform simultaneous dual-band VLBI observations at 86 and 258 GHz using receivers with shared-optical-paths (SOP) to correct the atmospheric phase fluctuations using the frequency phase transfer (FPT) technique. This was possible together with the IRAM 30 m telescope, which has already developed such a capability. We aimed to verify the expected phase coherence and sensitivity improvement at the higher frequency achievable by applying FPT. With the dual-band, single baseline data, we applied the FPT method, which uses the lower frequency data to correct the simultaneously observed higher-frequency data. We evaluate the improvement compared to the conventional single-band observing mode by analyzing the coherence factor in the higher frequency data. Our results show that the phase fluctuations at the two bands are well correlated. After applying FPT, the interferometric phases at the higher frequency vary much slower and the coherence factor is significantly improved. Our analysis confirms the feasibility of applying FPT to frequencies above 250 GHz with SOP receivers. Future observations in this mode could dramatically improve the sensitivity and imaging fidelity of high-frequency VLBI.

astro-ph.IM↗

arXiv2024

The LHCb VELO Upgrade Module Construction

The LHCb detector has undergone a major upgrade for LHC Run 3. This Upgrade I detector facilitates operation at higher luminosity and utilises full-detector information at the LHC collision rate, critically including the use of vertex information. A new vertex locator system, the VELO Upgrade, has been constructed. The core element of the new VELO are the double-sided pixelated hybrid silicon detector modules which operate in vacuum close to the LHC beam in a high radiation environment. The construction and quality assurance tests of these modules are described in this paper. The modules incorporate 200 \mum thick, n-on-p silicon sensors bump-bonded to 130 \nm technology ASICs. These are attached with high precision to a silicon microchannel substrate that uses evaporative CO$_2$ cooling. The ASICs are controlled and read out with flexible printed circuits that are glued to the substrate and wire-bonded to the chips. The mechanical support of the module is given by a carbon fibre plate, two carbon fibre rods and an aluminium plate. The sensor attachment was achieved with an average precision of 21 $\mathrm{\mu m}$, more than 99.5\% of all pixels are fully functional, and a thermal figure of merit of 3 \mathrm{Kcm^{2}W^{-1}}$ was achieved. The production of the modules was successfully completed in 2021, with the final assembly and installation completed in time for data taking in 2022.

physics.ins-det↗

arXiv2020

Detection of the magnetar XTE J1810-197 at 150 and 260 GHz with the NIKA2 Kinetic Inductance Detector camera

The investigation of pulsars between millimetre and optical wavelengths is challenging due to the faintness of the pulsar signals and the relative low sensitivity of the available facilities compared to 100-m class telescopes operating in the centimetre band. The Kinetic Inductance Detector (KID) technology offers large instantaneous bandwidths and a high sensitivity that can help to substantially increase the ability of existing observatories at short wavelengths to detect pulsars and transient emission. To investigate the feasibility of detecting pulsars with KIDs, we observed the anomalous X-ray pulsar XTE J1810-197 with the New IRAM KIDs Array-2 (NIKA2) camera installed at the IRAM 30-m Telescope in Spain. We detected the pulsations from the pulsar with NIKA2 at its two operating frequency bands, 150 and 260 GHz ($\lambda$=2.0 and 1.15 mm, respectively). This is the first time that a pulsar is detected with a receiver based on KID technology in the millimetre band. In addition, this is the first report of short millimetre emission from XTE J1810-197 after its reactivation in December 2018, and it is the first time that the source is detected at 260 GHz, which gives us new insights into the radio emission process of the star.

astro-ph.IM↗

arXiv2019

Calibration and Performance of the NIKA2 camera at the IRAM 30-meter Telescope

NIKA2 is a dual-band millimetric continuum camera of 2900 Kinetic Inductance Detectors (KID), operating at $150$ and $260\,\rm{GHz}$, installed at the IRAM 30-meter telescope. We present the performance assessment of NIKA2 after one year of observation using a dedicated point-source calibration method, referred to as the \emph{baseline} method. Using a large data set acquired between January 2017 and February 2018 that span the whole range of observing elevations and atmospheric conditions encountered at the IRAM 30-m telescope, we test the stability of the performance parameters. We report an instantaneous field of view (FOV) of 6.5' in diameter, filled with an average fraction of $84\%$ and $90\%$ of valid detectors at $150$ and $260\,\rm{GHz}$, respectively. The beam pattern is characterized by a FWHM of $17.6'' \pm 0.1''$ and $11.1''\pm 0.2''$, and a beam efficiency of $77\% \pm 2\%$ and $55\% \pm 3\%$ at $150$ and $260\,\rm{GHz}$, respectively. The rms calibration uncertainties are about $3\%$ at $150\,\rm{GHz}$ and $6\%$ at $260\,\rm{GHz}$. The absolute calibration uncertainties are of $5\%$ and the systematic calibration uncertainties evaluated at the IRAM 30-m reference Winter observing conditions are below $1\%$ in both channels. The noise equivalent flux density (NEFD) at $150$ and $260\,\rm{GHz}$ are of $9 \pm 1\, \rm{mJy}\cdot s^{1/2}$ and $30 \pm 3\, \rm{mJy}\cdot s^{1/2}$. This state-of-the-art performance confers NIKA2 with mapping speeds of $1388 \pm 174$ and $111 \pm 11 \,\rm{arcmin}^2\cdot \rm{mJy}^{-2}\cdot \rm{h}^{-1}$ at $150$ and $260\,\rm{GHz}$. With these unique capabilities of fast dual-band mapping at high (better that 18'') angular resolution, NIKA2 is providing an unprecedented view of the millimetre Universe.

astro-ph.IM↗

arXiv2017

The NIKA2 instrument at 30-m IRAM telescope: performance and results

The New IRAM KID Arrays 2 (NIKA2) consortium has just finished installing and commissioning a millimetre camera on the IRAM 30 m telescope. It is a dual-band camera operating with three frequency multiplexed kilo-pixels arrays of Lumped Element Kinetic Inductance Detectors (LEKID) cooled at 150 mK, designed to observe the intensity and polarisation of the sky at 260 and 150 GHz (1.15 and 2 mm). NIKA2 is today an IRAM resident instrument for millimetre astronomy, such as Intra Cluster Medium from intermediate to distant clusters and so for the follow-up of Planck satellite detected clusters, high redshift sources and quasars, early stages of star formation and nearby galaxies emission. We present an overview of the instrument performance as it has been evaluated at the end of the commissioning phase.

astro-ph.IM↗