Tarana, A.A.TaranaCAPITANIO, FIAMMAFIAMMACAPITANIOCOCCHI, MASSIMOMASSIMOCOCCHI2020-10-142020-10-1420180035-8711http://hdl.handle.net/20.500.12386/27796The 2004-2012 X-ray time history of the NS LMXB GRS 1724-308 shows, along with the episodic brightenings associated with the low-high state transitions typical of the ATOLL sources, a peculiar, long lasting (∼300 d) flaring event, observed in 2008. This rare episode, characterized by a high-flux hard state, has never been observed before for GRS 1724-308, and in any case is not common among ATOLL sources. We discuss here different hypotheses on the origin of this peculiar event that displayed the spectral signatures of a failed transition, similar in shape and duration to those rarely observed in black hole binaries. We also suggest the possibility that the atypical flare occurred in coincidence with a new rising phase of the 12-yr superorbital modulation that has been previously reported by other authors. The analysed data also confirm for GRS 1724-308 the already reported orbital period of ∼90 d.STAMPAenArticle10.1093/mnras/sty8162-s2.0-85047123918000433893700035https://arxiv.org/pdf/1803.11350.pdfhttps://academic.oup.com/mnras/article/477/3/3353/49565392018MNRAS.477.3353TFIS/05 - ASTRONOMIA E ASTROFISICA