Calibration and performance of the NIKA2 camera at the IRAM 30-m Telescope

Abstract

Context. NIKA2 is a dual-band millimetre continuum camera of 2 900 kinetic inductance detectors, operating at 150 and 260 GHz, installed at the IRAM 30-m telescope in Spain. Open to the scientific community since October 2017, NIKA2 will provide key observations for the next decade to address a wide range of open questions in astrophysics and cosmology. Aims. Our aim is to present the calibration method and the performance assessment of NIKA2 after one year of observation. Methods. We used a large data set acquired between January 2017 and February 2018 including observations of primary and secondary calibrators and faint sources that span the whole range of observing elevations and atmospheric conditions encountered by the IRAM 30-m telescope. This allowed us to test the stability of the performance parameters against time evolution and observing conditions. We describe a standard calibration method, referred to as the “Baseline” method, to translate raw data into flux density measurements. This includes the determination of the detector positions in the sky, the selection of the detectors, the measurement of the beam pattern, the estimation of the atmospheric opacity, the calibration of absolute flux density scale, the flat fielding, and the photometry. We assessed the robustness of the performance results using the Baseline method against systematic effects by comparing results using alternative methods. Results. We report an instantaneous field of view of 6.5′ in diameter, filled with an average fraction of 84%, and 90% of valid detectors at 150 and 260 GHz, respectively. The beam pattern is characterised by a FWHM of 17.6″ ± 0.1″ and 11.1″ ± 0.2″, and a main-beam efficiency of 47%±3%, and 64%±3% at 150 and 260 GHz, respectively. The point-source rms calibration uncertainties are about 3% at 150 GHz and 6% at 260 GHz. This demonstrates the accuracy of the methods that we deployed to correct for atmospheric attenuation. 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 at 150 and 260 GHz are of 9 ± 1 mJy s1/2 and 30 ± 3 mJy s1/2. This state-of-the-art performance confers NIKA2 with mapping speeds of 1388 ± 174 and 111 ± 11 arcmin2 mJy−2 h−1 at 150 and 260 GHz. Conclusions. 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.

Detection of the magnetar XTE J1810−197 at 150 and 260 GHz with the NIKA2 kinetic inductance detector camera

“…In recent years, a new technology based on kinetic inductance detectors (KIDs) has been used to fabricate sensitive large-array detectors (for a review, see Mauskopf 2018). KID arrays of thousands of pixels can be built and operated with the most advanced sensitivity (Monfardini et al 2011;Mazin et al 2013;Catalano et al 2014;Calvo et al 2016;Perotto et al 2020).…”

“…The KID-based NIKA2 camera installed at the IRAM 30 m telescope (Adam et al 2018) is a dual wide-band camera operating simultaneously at 150 and 260 GHz (λ = 2.0 and 1.15 mm) with 45 GHz of bandwidth and a total of 2896 KIDs cooled down to about 150 mK (Calvo et al 2016). NIKA2 offers an excellent performance with typical sensitivities per detector of 9 and 30 mJy s 1/2 at 150 and 260 GHz, respectively (Perotto et al 2020). In the future, NIKA2 will also offer polarisation measurements in the 260 GHz band (Ritacco et al 2020).…”

The Cluster HEritage project with XMM-Newton: Mass Assembly and Thermodynamics at the Endpoint of structure formation

“…Joint X-ray and SZE analyses would allow detailed reconstructions of the internal structure of the physical properties of the hot gas (e.g., Adam et al 2017;Ruppin et al 2018). In particular, NIKA2 (Perotto et al 2020) and MUSTANG-2 (Dicker et al 2014), currently operating on the Institut de Radioastronomie Millimétrique (IRAM) 30 m and Green Bank Telescope (GBT) 100 m telescopes, obtain 18 and 9 arcsec FWHM resolutions at 150 and 90 GHz, respectively. Even higher resolution SZE observations are possible with current large interferometric observatories such as the Atacama Large Millimetre Array (ALMA) and the Northern Extended Millimeter Array (NOEMA; see, e.g., Kitayama et al 2016).…”

Sensitivity of LEKID for space applications between 80 GHz and 600 GHz

“…The kilo-pixel, dual-band New IRAM Kids Arrays (NIKA2) camera was the first KID-based instrument operating at millimetre wavelengths. This camera showed that lumped element kinetic inductance detectors (LEKID) are limited by photon noise when they operate under an optical load typical of ground-based observations (Adam et al 2018;Perotto et al 2020). The last space-borne instrument devoted to cosmic microwave background (CMB) observations, Planck, has used 52 high-impedance spider-web bolometers in the high-frequency instrument (HFI) and has already shown their sensitivities were limited by CMB photon noise (Planck Collaboration I 2011; Planck Collaboration XVI 2014; Planck Collaboration I 2016; Planck Collaboration XIII 2016; Planck Collaboration X 2020).…”