Notice: For the foreseeable future, the daily reports may contain

apparent discrepancies between some proposal descriptions and the listed

instrument usage. This is due to the conversion of previously approved

ACS WFC or HRC observations into WFPC2, or NICMOS observations

subsequent to the loss of ACS CCD science capability in late January.

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT        # 4333

PERIOD COVERED: UT April 04, 2007 (DOY 093)

OBSERVATIONS SCHEDULED

NIC1 10859

Precise Measurements of Sgr A* Flare Activity

Correlated X-ray and near-IR flare emission from Sgr A*, the closest

supermassive black hole, contains information about the hydrodynamics,

energetics, and accretion behavior of matter within the innermost ten

Schwarzschild radii of the hole. We propose HST/NICMOS observations of

near-IR flares, in conjunction with already approved obsrevations using

XMM-Newton {214 ksec} and CSO {3 nights}, which can make the precise,

new measurements necessary to understand the radiation mechanism and low

luminosity of Sgr A*. HST/NICMOS is required due to its very low and

stable background, and its stable, tightly focused PSF, which allow

accurate measurement of fainter flares than can be observed using

groundbased adaptive optics systems. We will measure the spectral index

distribution, the time-averaged flux and duration of flares, and the

statistics of flare activity, and will confirm previously reported

quasi-periodic variability. These measurements will have far-reaching

implications for testing the inverse Compton scattering {ICS} and

synchrotron models of low-luminosity flares, for understanding the

process of accretion onto and outflow from supermassive black holes, and

for constraining the acceleration mechanism of flares and the inferred

black hole spin. This knowledge, in turn, will help us understand more

generally low-luminosity AGN and X-ray binaries in a very low/quiescent

accretion state.

NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration - CR Persistence Part 6

A new proceedure proposed to alleviate the CR-persistence problem of

NICMOS. Dark frames will be obtained immediately upon exiting the SAA

contour 23, and everytime a NICMOS exposure is scheduled within 50

minutes of coming out of the SAA. The darks will be obtained in parallel

in all three NICMOS Cameras. The POST-SAA darks will be non- standard

reference files available to users with a USEAFTER date/time mark. The

keyword 'USEAFTER=date/time' will also be added to the header of each

POST-SAA DARK frame. The keyword must be populated with the time, in

addition to the date, because HST crosses the SAA ~8 times per day so

each POST-SAA DARK will need to have the appropriate time specified, for

users to identify the ones they need. Both the raw and processed images

will be archived as POST-SAA DARKSs. Generally we expect that all NICMOS

science/calibration observations started within 50 minutes of leaving an

SAA will need such maps to remove the CR persistence from the science i

mages. Each observation will need its own CRMAP, as different SAA

passages leave different imprints on the NICMOS detectors.

WFPC2 11022

WFPC2 Cycle 15 Decontaminations and Associated Observations

This proposal is for the WFPC2 decons. Also included are instrument

monitors tied to decons: photometric stability check, focus monitor,

pre- and post-decon internals {bias, intflats, kspots, & darks}, UV

throughput check, VISFLAT sweep, and internal UV flat check.

WFPC2 11083

The Structure, Formation and Evolution of Galactic Cores and Nuclei

A surprising result has emerged from the ACS Virgo Cluster Survey

{ACSVCS}, a program to obtain ACS/WFC gz imaging for a large, unbiased

sample of 100 early-type galaxies in the Virgo Cluster. On subarcsecond

scales {i.e., <0.1"-1"}, the HST brightness profiles vary systematically

from the brightest giants {which have nearly constant surface brightness

cores} to the faintest dwarfs {which have compact stellar nuclei}.

Remarkably, the fraction of galaxy mass contributed by the nuclei in the

faint galaxies is identical to that contributed by supermassive black

holes in the bright galaxies {0.2%}. These findings strongly suggest

that a single mechanism is responsible for both types of Central Massive

Object: most likely internally or externally modulated gas inflows that

feed central black holes or lead to the formation of "nuclear star

clusters". Understanding the history of gas accretion, star formation

and chemical enrichment on subarcsecond scales has thus emerged as the

single most pressing question in the study of nearby galactic nuclei,

either active or quiescent. We propose an ambitious HST program {199

orbits} that constitutes the next, obvious step forward:

high-resolution, ultraviolet {WFPC2/F255W} and infrared {NIC1/F160W}

imaging for the complete ACSVCS sample. By capitalizing on HST's unique

ability to provide high-resolution images with a sharp and stable PSF at

UV and IR wavelengths, we will leverage the existing optical HST data to

obtain the most complete picture currently possible for the history of

star formation and chemical enrichment on these small scales. Equally

important, this program will lead to a significant improvement in the

measured structural parameters and density distributions for the stellar

nuclei and the underlying galaxies, and provide a sensitive measure of

"frosting" by young stars in the galaxy cores. By virtue of its superb

image quality and stable PSF, NICMOS is the sole instrument capable of

the IR observations proposed here. In the case of the WFPC2

observations, high-resolution UV imaging {< 0.1"} is a capability unique

to HST, yet one that could be lost at any any time.

FLIGHT OPERATIONS SUMMARY:

Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)

HSTARS: (None)

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

                         SCHEDULED      SUCCESSFUL  

FGS GSacq                10                       10                 

FGS REacq                04                       04                 

OBAD with Maneuver 26                      26                

SIGNIFICANT EVENTS:

Flash Report: Update on WFPC2 performance at lowered temperature.

We continue to received additional test data from WFPC2 at the new

reduced operating temperature. All results so far look excellent.

Observations of the Omega Cen star cluster were taken on Sunday to

evaluate the image quality. No significant change was seen. The stellar

FWHM on the PC1 CCD was 1.75 ± 0.03 pixels prior to the temperature

change, and 1.76 ± 0.02 pixels afterwards. Similar results are seen in

all 4 CCDs.

Bias levels in the WF4 CCD continue to be relatively stable (283 to 303

DN range) , and are close to the normal value ~311 DN.

Small changes in the relative positions of the CCDs in the HST focal

plane continue to be confirmed, typically around ~0.1 pixel. These are

very similar to the changes seen across the January and February 2006

temperature adjustments, and should be of no consequence.

This is the third temperature reduction we have performed, and we have

yet to see any negative effects from them. This suggests we should be

able to keep the WF4 CCD operational until SM4 via additional

temperature reductions.