The BL-Lac blazar PKS 0447-439 was detected at very high energy gamma-rays by HESS following the discovery by Fermi-LAT. The lack of both emission and absorption lines in BL-Lacs make the estimation of their redshifts very difficult. Modeling the drop in gamma-ray spectra it was possible to have an estimation of redshift for PKS 0447-439 of z∼0.2, which is compatible with the value z=0.205 reported by the identification of Ca II absorption lines in optical spectra. By the identification of a weak line of Mg II using spectra with average signal-to-noise S/N∼80, it has been recently reported a lower limit for the redshift of this blazar of z≤1.246. Triggered by this controversy, we have proposed new optical observations with the Gemini South telescope to perform further spectroscopic analysis with very high S/N ratio (∼200-500). In this work we present a new optical spectrum of PKS 0447-439, and report on the analysis and results of such observations. Even with this significantly high quality signal we were not able to identify any spectral features to allow an estimation of the redshift. In agreement with other recent studies, we identify the Mg II line reported previously as originated in the Earth’s atmosphere, and conclude the lower limit of the redshift is incorrect. More interestingly, we could not identify the Ca II absorption lines used to report a redshift of 0.205. © 2013 Sociedade Brasileira de Fisica. All Rights Reserved.
| Documento: | Conferencia |
| Título: | On the redshift of the gamma-ray blazar PKS 0447-439: Optical spectroscopy using Gemini observations with high S/N ratio |
| Autor: | Rovero, A.C.; Donzelli, C.; Muriel, H.; Cillis, A.; Pichel, A. |
| Filiación: | Instituto de Astronomía y Física del Espacio (CONICET-UBA), Buenos Aires, Argentina Instituto de Investigaciones en Astronomía Teórica y Experimental (CONICET), Córdoba, Argentina Observatorio Astronómico de Córdoba, Córdoba, Argentina |
| Palabras clave: | BL-Lac objects; Gamma-ray blazars; Optical spectroscopy; Redshift; Cosmic rays; Cosmology; Earth atmosphere; Magnesium compounds; Signal to noise ratio; Spectroscopic analysis; Spectrum analysis; Ultraviolet spectroscopy; BL-Lac objects; Blazars; Gamma ray spectra; Optical observations; Optical spectroscopy; Red shift; Spectral feature; Very high energies; Gamma rays |
| Año: | 2013 |
| Volumen: | 2013-October |
| Título revista: | 33rd International Cosmic Rays Conference, ICRC 2013 |
| Título revista abreviado: | Proc. Int. Cosmic Rays Conf., ICRC |
| Registro: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_97885890_v2013-October_n_p_Rovero |
