Flare-related Recurring Active Region Jets: Evidence for Very Hot Plasma

We present a study of two active region jets (AR jets) that are associated with two C-class X-ray flares. The recurrent, homologous jets originated from the northern periphery of a sunspot. We confirm flare-like temperatures at the footpoints of these jets using spectroscopic observations of Fe XXIII (263.76 Å) and Fe XXIV (255.11 Å) emission lines. The emission measure loci method was used to obtain an isothermal temperature, and the results show a decrease (17.7 to 13.6 MK) in the temperature during the decay phase of the C 3.0 flare. The electron number densities at the footpoints were found to range from 1.7 ×10¹⁰ to 2.0 ×10¹¹cm−³ using the Fe XIV line pair ratio. Nonthermal velocities were found to range from 34 - 100 km/s for Fe XXIV and 51 - 89 km/s for Fe XXIII. The plane-of-sky velocities were calculated to be 462 ±21 and 228 ±23 km/s for the two jets using the Atmospheric Imaging Assembly (AIA) 171 Å channel. The AIA light curves of the jet footpoint regions confirmed the temporal and spatial correlation between the two X-ray flares and the jet footpoint emission. The Gamma-ray Burst Monitor (GBM) also confirmed superhot plasma of 27 (25) MK with a nonthermal energy of 2.38 ×10²⁶ (2.87 ×10²⁷) ergs−¹ in the jet footpoint region during the rise (peak) phase of one of the flares. The temperatures of the jet footpoint regions obtained from EIS agree very well (within an uncertainty of 20%) with temperatures obtained from the Geostationary Environmental Operational Satellite (GOES) flux ratios. These results provide clear evidence for very hot plasma (>10 MK) at the footpoints of the flare-related jets, and they confirm the heating and cooling of the plasma during the flares.