Abstract
ABSTRACT Recently the EDGES experiment has claimed the detection of an absorption feature centred at 78 MHz. When interpreted as a signature of cosmic dawn, this feature appears at the correct wavelength (corresponding to a redshift range of z ≈ 15–20) but is larger by at least a factor of two in amplitude compared to the standard 21-cm models. One way to explain the excess radio absorption is by the enhancement of the diffuse radio background at ν = 1.42 GHz (λ = 21 cm) in the rest frame of the absorbing neutral hydrogen. Astrophysical scenarios, based on the acceleration of relativistic electrons by accretion on to supermassive black holes (SMBHs) and by supernovae (SN) from first stars, have been proposed to produce the enhanced radio background via synchrotron emission. In this letter, we show that either the synchrotron or the inverse-Compton (IC) cooling time for such electrons is at least three orders of magnitude shorter than the duration of the EDGES signal centred at z ≈ 17, irrespective of the magnetic field strength. The synchrotron radio emission at 1.42 GHz due to rapidly cooling electrons is ∼103 times smaller than the non-cooling estimate. Thus astrophysical scenarios for excess radio background proposed to explain the EDGES signal appear very unlikely.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Monthly Notices of the Royal Astronomical Society: Letters
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
