Dear colleagues,

We are pleased to announce the Version 1 0 release of Epoch 1 of Abell 370, after the completion of all the ACS and WFC3/IR imaging for this epoch on the main cluster and parallel field from our Frontier Fields program (14038, PI: J Lotz) These mosaics complete the full depth of Epoch 1 obtained with ACS F435W, F606W and F814W on the main cluster, along with WFC3/IR F105W, F125W, F140W and F160W on the parallel field, and also include public archival ACS and WFC3/IR imaging obtained in these filters from programs 11108 (PI : E Hu), 11507 (PI : K Noll), 11591 (PI : J -P Kneib), 13459 (PI : T Treu), 13790 (PI : S Rodney), and 14216 (PI : R Kirshner) All the mosaics in this v1 0 release have been fully recalibrated relative to the v0 5 mosaics that we released during this epoch For ACS, the v1 0 mosaics incorporate new bias and dark current reference files, along with CTE correction and bias destriping, and also include a set of mosaics that have been processed with the new selfcal approach to better account for the low-level dark current structure The WFC3/IR v1 0 mosaics have improved masking for persistence and bad pixels, and in addition include a set of mosaics that have been corrected for time-variable sky emission that can occur during the orbit and can otherwise impact the up-the-ramp count-rate fitting if not properly corrected Further details are provided in the readme file, which can be obtained along with all the mosaics at the following location:

• Latest mosaics: http://archive stsci edu/pub/hlsp/frontier/abell370/images/hst/v1 0-epoch1/
• All mosaics: http://archive stsci edu/prepds/frontier/abell370 html

More general information about the data for the Frontier Fields project can be obtained from our Frontier Fields MAST archive website: * http://archive stsci edu/prepds/frontier/ as well as our main Frontier Fields HST project website: * http://www stsci edu/hst/campaigns/frontier-fields/ and our Frontier Fields astronomer's blog and other social media: * https://blogs stsci edu/hstff/ * https://twitter com/MAST_News/ * https://facebook com/MASTArchive/

We hope that these high-level science products are useful for your research, and we welcome any suggestions or questions that you may have about them

Best regards, Anton Koekemoer and the STScI Frontier Fields Team http://archive stsci edu/prepds/frontier/ http://www stsci edu/hst/campaigns/frontier-fields/Contact

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