Context :

Aims : Here we report evidence of a large solar filament eruption on 2013 , September 29 .
This smooth eruption , which passed without any previous flare , formed after a two-ribbon flare and a coronal mass ejection towards Earth .
The coronal mass ejection generated a moderate geomagnetic storm on 2013 , October 2 with very serious localized effects .
The whole event passed unnoticed to flare-warning systems .

Methods : We have conducted multi-wavelength analyses of the Solar Dynamics Observatory through Atmospheric Imaging Assembly ( AIA ) and Helioseismic and Magnetic Imager ( HMI ) data .
The AIA data on 304 , 193 , 211 , and 94 Å sample the transition region and the corona , respectively , while HMI provides photospheric magnetograms , continuum , and linear polarization data , in addition to the fully inverted data provided by HMI .

Results : This flux emergence happened very close to a filament barb that was very active in mass motion , as seen in 304 Å images .
The observed flux emergence exhibited hectogauss values .
The flux emergence extent appeared just beneath the filament , and the filament rose during the following hours .
The emergence acquired a size of 33 ^ { \prime \prime } in \sim 12 h , about \sim 0.16 { km } \ > { s } ^ { -1 } \ > .
The rate of signed magnetic flux is around 2 \times 10 ^ { 17 } Mx min ^ { -1 } for each polarity .
We have also studied the eruption speed , size , and dynamics .
The mean velocity of the rising filament during the \sim 40 min previous to the flare is 115 \pm 5 { km } \ > { s } ^ { -1 } \ > , and the subsequent acceleration in this period is 0.049 \pm 0.001 { km } \ > { s } ^ { -2 } \ > .

Conclusions : We have observed a supergranular-sized emergence close to a large filament in the boundary of the active region NOAA11850 .
Filament dynamics and magnetogram results suggest that the magnetic flux emergence takes place in the photospheric level below the filament .
Reconnection occurs underneath the filament between the dipped lines that support the filament and the supergranular emergence .
The very smooth ascent is probably caused by this emergence and torus instability may play a fundamental role , which is helped by the emergence .