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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

Nighttime sensitivity of ionospheric VLF measurements to X-ray bursts from a remote cosmic source

Texto completo
Autor(es):
Raulin, Jean-Pierre [1] ; Trottet, Gerard [2] ; Guillermo Gimenez de Castro, C. [1] ; Correia, Emilia [1, 3] ; Liliana Macotela, E. [1]
Número total de Autores: 5
Afiliação do(s) autor(es):
[1] Univ Presbiteriana Mackenzie, CRAAM, Sao Paulo - Brazil
[2] Observ Paris, Meudon - France
[3] INPE, Sao Jose Dos Campos - Brazil
Número total de Afiliações: 3
Tipo de documento: Artigo Científico
Fonte: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS; v. 119, n. 6, p. 4758-4766, JUN 2014.
Citações Web of Science: 8
Resumo

On 22 January 2009, a series of X-ray bursts were emitted by the soft gamma ray repeater SGR J1550-5418. Some of these bursts produced enhanced ionization in the nighttime lower ionosphere. These ionospheric disturbances were studied using X-ray measurements from the Anti-Coincidence Shield of the Spectrometer for Integral onboard the International Gamma-Ray Astrophysics Laboratory and simultaneous phase and amplitude records from two VLF propagation paths between the transmitter Naval Radio Station, Pearl Harbor (Hawaii) and the receivers Radio Observatorio do Itapetinga (Brazil) and Estacao Antarctica Commandante Ferraz (Antarctic Peninsula). The VLF measurements have been obtained with an unprecedented high time resolution of 20 ms. We find that the illumination factor I (illuminated path length times the cosine of the zenith angle), which characterizes the propagation paths underlying the flaring object, is a key parameter which determines the sensitivity threshold of the VLF detection of X-ray bursts from nonsolar transients. For the present VLF measurements of bursts from SGR J1550-5418, it is found that for I >= 1.8Mm, all X-ray bursts with fluence in the 25 keV to 2MeV range larger than F-25\_min similar to 1.0x10(-6) erg/cm(2) produce a measurable ionospheric disturbance. Such a lower limit of the X-ray fluence value indicates that moderate X-ray bursts, as opposed to giant X-ray bursts, do produce ionospheric disturbances larger than the sensitivity limit of the VLF technique. Therefore, the frequency of detection of such events could be improved, for example by increasing the coverage of existing VLF receiving networks. The VLF detection of high-energy astrophysical bursts then appears as an important observational diagnostic to complement their detection in space. This would be especially important when space observations suffer from adverse conditions, like saturation, occultation from the Earth, or the passage of the spacecraft through the South Atlantic anomaly. (AU)

Processo FAPESP: 11/24117-9 - Processos de alta energia no sol, meio interplanetário e seus efeitos na atmosfera terrestre
Beneficiário:Jean Pierre Raulin
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 06/02979-0 - Monitoramento da atividade solar e da Anomalia Magnética do Atlântico Sul (AMAS) utilizando uma rede de receptores de ondas de muito baixa frequência (VLF): SAVNET - South America VLF NETwork
Beneficiário:Jean Pierre Raulin
Linha de fomento: Auxílio à Pesquisa - Regular