Observations of the Galactic Center have recently discovered a dense, dusty gas cloud, known as G2, infalling towards the dormant Super-Massive Black Hole (SMBH) Sgr A* at the center of our galaxy. This cloud is on a highly eccentric orbit, which should reach pericenter around September 2013. It has already started to show signs of tidal disruption by the black hole. The fragmentation of the cloud should lead to it becoming the dominant source of accretion activity over the next year or so. It is expected that high-energy emission from Sgr A* resulting from this encounter will increase significantly during and after this time. The circularization of some fraction of the cloud mass should dissipate a considerable fraction of its kinetic energy, resulting in large increases in emission at all wavelengths from the accretion disk. Multiwavelength observations are being planned to monitor the resulting flaring of Sgr A* in radio, X-rays, and gamma-rays. Near-IR observations will be crucial to this once in a lifetime opportunity, because accretion events always manifest themselves first and most often in the near-IR. We propose WFC3 IR monitoring observations of Sgr A* to be conducted simultaneously with already awarded X-ray observations from XMM-Newton. These multiwavelength observations will allow us study the radiation properties of Sgr A* as the cloud breaks up and its fragments feed gas into the central accretion flow, and will give us the ability to test features of many existing accretion models. HST/WFC3 is the only facility that can provide the long-duration and photometrically-stable near-IR measurements that are necessary. Our XMM observations will occur in 3 blocks of 53 ksec each, on Feb 27, Mar 15, and Apr 4, 2014, with the observation starts matching the VLT visibility windows of Sgr A* in Chile. Our plan is to use the 5-6 consecutive SAA-free orbits that are available each day to obtain WFC3/IR observations over a time span of ~8 hours, interrupted only by Earth occultation. We will obtain WFC3/IR observations with the F153M filter and the SPARS-25 readout sequence. This readout sequence not only gives us equally-spaced readout intervals of 25 secs to keep the detector stable, but also results in exposures of 5-6 min duration, which is long enough to perform WFC3 buffer dumps in parallel with the exposures, thus maximizing our on-source time. We will embed the exposures within 4-point dither pattern, in order to mitigate the effects of bad pixels, flat-field uncertainties, and persistence from bright stars. A total of 8 such exposures can be obtained within each orbit, giving us nearly constant coverage of Sgr A* over a span of about 50 mins per orbit. The 22 orbits of this proposal need to be scheduled in coordination with the 6 HST orbits from the companion joint XMM/HST program 13403 (PI: N. Grosso), such that as many of the 28 total orbits as possible are scheduled within the 3 XMM observing windows, in order to obtain simultaneous observations. The BETWEEN times listed for each visit are the current windows in which XMM observations will be taking place. We will be working with the XMM schedulers to see if any of those times could be shifted by a few hours or so, in order to more closely synchronize the XMM observing times with the HST SAA-free orbits, so that the HST target visibilities are not restricted or interrupted by SAA passages. AGN/QUASARS Default false false false false false SUPPORTED STAR ACCRETION DISK J2000 J2000 0.15 mJy in H-band WFC3/IR Imaging No No F153M WFC3/IR Imaging No No F153M WFC3/IR Imaging No No F153M POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false The scheduling data was generated by CASM 21.2. 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