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We report on the analysis of 100 ks INTEGRAL observations of the Galacticmicroquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when thesource was found to exhibit a new type of variability as preliminarily reportedin Hannikainen et al. (2003). The variability pattern, which we name $\xi$, ischaracterized by a pulsing behaviour, consisting of a main pulse and a shorter,softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes inthe JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From astudy of the individual RXTE/PCA pulse profiles we find that the rising phaseis shorter and harder than the declining phase, which is opposite to what hasbeen observed in other otherwise similar variability classes in this source.The position in the colour-colour diagram throughout the revolution correspondsto State A (Belloni et al. 2000) but not to any previously known variabilityclass. We separated the INTEGRAL data into two subsets covering the maxima andminima of the pulses and fitted the resulting two broadband spectra with ahybrid thermal--non-thermal Comptonization model. The fits show the source tobe in a soft state characterized by a strong disc component below ~6 keV andComptonization by both thermal and non-thermal electrons at higher energies.

Characterizing a new class of variability in GRS 1915+105 with simultaneousINTEGRAL/RXTEobservations