IRIS and SDO Observations of Recurrent Explosive Events

Observations of recurrent explosive events (EEs) with timescales of 3-5 minutes are reported. These EEs have been observed with the Interface Region Imaging Spectrograph (IRIS) and have a spatial dimension of ∼ 1\buildrel{\prime\prime}\over{.} 5 along the slit. The spectral line profiles of C ii 1335/1336 Å and Si iv 1394/1403 Å become highly broadened both in red as well as blue wings. Several absorption lines on top of the broadened profiles were identified. In addition, emission lines corresponding to neutral lines such as Cl i 1351.66 Å, C i 1354.29 Å, and C i 1355.84 Å were identified. The C i 1354.29 Å and C i 1355.84 Å lines were found only during the EEs, whereas Cl i 1351.66 Å broadens during the EEs. The estimated lower limit on electron number density obtained using the line ratios of Si iv and O iv is about {10}^13.5 cm^-3, suggesting that the observed events are most likely occurring at heights corresponding to a lower chromosphere. To the best of our knowledge, for the first time we have detected short-period variability (30 s and 60-90 s) within the EE bursts. Observations of the photospheric magnetic fields underneath EEs indicate that a negative polarity field emerges in the neighborhood of oppositely directed positive fields that undergo repetitive reconnection (magnetic flux cancellation) events. The dynamic changes observed in AIA 1700 Å, 1600 Å, C ii 1330 Å, and Si iv 1400 Å intensity images corresponded very well with the emergence and cancellation of photospheric magnetic field (negative polarity) on a timescale of 3-5 minutes. The observations reported here suggest that these EEs are formed due to magnetic reconnection and are occurring in the lower chromosphere.