Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

  title={Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR},
  author={F G Mertens and Maaijke Mevius and L{\'e}on V. E. Koopmans and Andr{\'e} R. Offringa and Garrelt Mellema and Saleem Zaroubi and Michiel Brentjens and H. Gan and B K Gehlot and Vishambhar N. Pandey and Ahmad Mouri Sardarabadi and Harish K. Vedantham and Sarod Yatawatta and K. M. B. Asad and Benedetta Ciardi and Emma Chapman and Simon Gazagnes and Raghunath Ghara and A. Ghosh and Sambit K. Giri and Ilian T Iliev and Vibor Jeli'c and Robin Kooistra and Rajesh Mondal and Joop Schaye and M. B. Silva},
  journal={Monthly Notices of the Royal Astronomical Society},
A new upper limit on the 21-cm signal power spectrum at a redshift of $z \approx 9.1$ is presented, based on 141 hours of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally-smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally-weighted power spectrum inference. Previously seen `excess power' due to spectral structure in the gain solutions has markedly reduced but some excess power still… Expand
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