Context :

Aims : We present in this letter the first analysis of a z \sim 8 galaxy candidate found in the Hubble and Spitzer imaging data of Abell 2744 as part of the Hubble Frontier Fields legacy program .

Methods : We applied the most commonly used methods to select exceptionally high-redshift galaxies by combining non-detection and color criteria using seven HST bands .
We used GALFIT on IRAC images to fit and subtract contamination of bright nearby sources.The physical properties were inferred from Spectral Energy Distribution-fitting using templates with and without nebular emission .

Results : This letter is focused on the brightest candidate we found ( m _ { F 160 W } =26.2 ) over the 4.9 arcmin ^ { 2 } field of view covered by the WFC3 .
It is not detected in the ACS bands and at 3.6 \mu m , while it is clearly detected at 4.5 \mu m with rather similar depths .
This break in the IRAC data might be explained by strong [ OIII ] +H \beta lines at z \sim 8 that contribute to the 4.5 \mu m photometry .
The best photo- z is found at z \sim 8.0 ^ { +0.2 } _ { -0.5 } , although solutions at low-redshift ( z \sim 1.9 ) can not be completely excluded , but they are strongly disfavored by the SED-fitting .
The amplification factor is relatively small at \mu =1.49 \pm 0.02 .
The star formation rate in this object ranges from 8 to 60 M _ { \odot } .yr ^ { -1 } , the stellar mass is in the order of M ^ { \star } = ( 2.5-10 ) \times 10 ^ { 9 } M _ { \odot } , and the size is r \approx 0.35 \pm 0.15 kpc .

Conclusions : This object is one of the first z \sim 8 Lyman Break Galaxy candidates showing a clear break between 3.6 \mu m and 4.5 \mu m which is consistent with the IRAC properties of the first spectroscopically confirmed galaxy at a similar redshift .
Due to its brightness , the redshift of this object could potentially be confirmed by near infrared spectroscopy with current 8-10m telescopes .
The nature of this candidate will be revealed in the coming months with the arrival of new ACS and Spitzer data , increasing the depth at optical and near-IR wavelengths .