Search

A bright transient x-ray source, V0332+53, was observed by Vela 5B for 3 months in 1973. It was first clearly detected in the 10 day period centered on 1973 June 1, rose to an intensity of approx.1.4 Crab in July, and was last definitely observed around 1973 August 30. The slow rise and symmetric fall of intensity are unusual for a transient X-ray source. Rapid fluctuations took the source to peak intensities above 2 Crab. The spectrum of this source (..cap alpha.. = 1.0 +- 0.2) was among the hardest ever observed by Vela 5B. The location of V0332+53, in Camelopardalis, was l = 146/sup 0/.11, b = -2/sup 0/.16, with an uncertainty of approx.0/sup 0/.1. No other X-ray spacecraft appear to have been in position to observe this event, and no recurrence was detected by Vela 5B. The transient source which was detected at the same location by Temma and EXOSAT, in 1983 November, 10 years after the Vela observation, with a 4.4 s pulsation period, is almost certainly identical to V0332+53.

Nine X-ray outbursts from the LMC have been observed with the HEAO 1 Large-Area Sky Survey Instrument. Some are shown to originate in the recurrent transient A0538-66, confirming the proposed 16 day periodicity and showing that the duration of the events can be as long as 14 days or as short as a few hours. Deviations from precise periodicity can be attributed to phase jitter or to a change in period occurring around the time of an exceptionally long outburst. Other outbursts which are irregular and consistently shorter originate in LMC X-4. A long-term light curve indicates that the LMC X-4 outbursts occur only when the source is in a high state, but are not strongly correlated with the binary phase.

Attosecond transient absorption is an ultrafast technique that has opened the possibility to study electron dynamics in condensed matter systems at its natural timescale. The extension to the x-ray regime permits one to use this powerful technique in combination with the characteristic element specificity of x-ray spectroscopy. At these timescales, the coherent effects of the electron transport are essential and have a relevant signature on the absorption spectrum. Typically, the complex light-driven dynamics requires a theoretical modeling for shedding light on the time-dependent changes in the spectrum. Here we construct a semiconductor Bloch equation model for resolving the light-induced and core-electron dynamics simultaneously, which enables to easily disentangle the interband and intraband contributions. By using the Bloch model, we demonstrate a universal feature on attosecond x-ray transient absorption spectra that emerges from the light-induced coherent intraband dynamics. This feature is linked to previous studies of light-induced Fano resonances in atomic systems, This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 702565 as well as from Comunidad de Madrid through the TALENTO program with ref. 2017-T1/IND-5432. LP acknowledges support from Junta de Castilla y León (Project SA046U16) and MINECO (FIS2016-75652-P). JB acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO), through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV- 2015-0522) Fundació Cellex Barcelona and the CERCA Programme / Generalitat de Catalunya, the European Research Council for ERC Advanced Grant TRANSFORMER (788218), MINECO for Plan Nacional FIS2017-89536-P; AGAUR for 2017 SGR 1639 and Laserlab-Europe (EU-H2020 654148)