English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The BL-Lac blazar PKS 0447-439 was detected at very high energy gamma-rays byHESS following the discovery by Fermi-LAT. The lack of both emission andabsorption lines in BL-Lacs make the estimation of their redshifts verydifficult. Modeling the drop in gamma-ray spectra it was possible to have anestimation of redshift for PKS 0447-439 of z approx 0.2, which is compatiblewith the value z=0.205 reported by the identification of Ca II absorption linesin optical spectra. By the identification of a weak line of Mg II using spectrawith average signal-to-noise S/N approx 80, it has been recently reported alower limit for the redshift of this blazar of z<=1.246. Triggered by thiscontroversy, we have proposed new optical observations with the Gemini Southtelescope to perform further spectroscopic analysis with very high S/N ratio(approx 200-500). In this work we present a new optical spectrum of PKS0447-439, and report on the analysis and results of such observations. Evenwith this significantly high quality signal we were not able to identify anyspectral features to allow an estimation of the redshift. In agreement withother recent studies, we identify the Mg II line reported previously asoriginated in the Earth's atmosphere, and conclude the lower limit of theredshift is incorrect. More interestingly, we could not identify the Ca IIabsorption lines used to report a redshift of 0.205.

On the redshift of the gamma-ray blazar PKS 0447-439: Optical spectroscopy using Gemini observations with high S/N ratio