## 1 Introduction  
Since its discovery by [PERSON] and coworkers in 1996 [1], the phenomenon of laser-induced ultrafast demagnetization has attracted worldwide attention and initiated an entirely new research field [2]. However, despite more than 20 years of ongoing experimental and theoretical work, the mechanisms underlying the femtosecond magnetization dynamics in ferromagnetic films following ultrafast optical excitation remain intensively debated [3; 4; 5; 6; 7]. The problem is interesting from a fundamental perspective--to date, it is not clear how angular momentum is transferred between the spin and electron systems and the crystalline lattice on sub-picosecond time scales--but it is also technologically relevant, as using light to steer magnetization on sub-ps timescales might pave the way for ultrafast all-optical spintronics and data storage [8; 9; 10]. Recent developments illustrating the application potential of ultrafast optical excitations include, for example, the creation of artificial neural networks [11], or the demonstration that focusing grating couplers can be used for photonic-electronic integration with magnetoresistive random access memory technology [12].  
X-ray experiments are an ideal tool to study the dynamics of the spin, electron, and phonon sub-systems, since they combine high spatial resolution and element selectivity. In general, time-resolved scattering and absorption experiments mainly focus on spin and lattice dynamics, yielding information about superdiffusive spin currents [13; 14; 15; 16], the role of spin-orbit coupling [17], the interaction of different magnetic sublattices [18], and the link between lattice and spin dynamics [19; 20; 21]. So far, only few studies have simultaneously looked at electron and spin dynamics [17; 22; 23; 24]. Indeed, performing pure absorption measurements at X-ray free electron lasers (FELs) has been challenging, due to intrinsic fluctuations of the photon parameters and the lack of a reliable and linear incident intensity monitor [25]. However, motivated by time-resolved absorption experiments performed at femtoslicing facilities [17; 22], as well as time- and spin-resolved photoelectron spectroscopy at high harmonic generation (HHG) sources [26; 27], new technical advances were recently made to probe X-ray absorption dynamics using FEL [25; 28; 29; 30; 31] and HHG [32; 33], thereby laying the ground for a systematic analysis of charge and spin dynamics [30; 34].  
Within this context, the investigation of the impact of the probing energy on the measured absorption and magnetic circular dichroism (MCD) dynamics has attracted increasing interest [35; 36; 37]. In a recent study, [PERSON] et al. [34] provided experimental and theoretical evidence for an electronic and magnetic elemental absorption resonance redshift on ultrafast timescales. Unfortunately, the use of an HHG setup in this study [34] results in photon energies separated by approximately 3 eV, which impedes a detailed investigation of the absorption edge itself. To circumvent this shortcoming, we employed X-ray streaking at the extreme ultraviolet (XUV)-FEL at FERMI in Italy, to probe five energies at the Ni \(M_{2,3}\)-edges (spanning from 64 to 68 eV). Our results confirm that absorption and MCD spectra are shifting but also hint at a more complicated scenario involving changes in spectra shapes after optical excitation. This calls for additional systematic experimental studies and in-depth theoretical calculations.