NuSTAR images (3–79 keV) of the J17407 field. Top panels: images for the modules A (left) and B (right) obtained using the entire observation. Bottom panels: images obtained during the first part of the observation (t < 59836.372534 MJD), where J17407 is faint and its flux constant (see Fig. 2). The red circle shows the extraction regions centred on the target. Magenta ellipses and circles show the extraction regions used for the background. Colorbars in the bottom show the count rate for each pixel.