XVP of Sgr A*


Welcome to the planning pages for the Chandra X-ray Visionary Project to observe Sgr A*, and the surrounding inner few arcminutes, with the Chandra High Energy Transmission Gratings.  We will obtain 3 Msec of observations over the course of Chandra Cycle 13, roughly between February 2012 and October 2012.  Here’s a brief rundown of what we plan to achieve with these observations.

  1. 1. We will obtain the first high-resolution spectrum of Sgr A*.  There is a known Fe line in the quiescent spectrum from the inner 1.5”, from the inflowing material (Advection Dominated Accretion Flow? Or emission from a cusp of stars in the inner region?).  There are other hypothesized lines from an ADAF-type flow, e.g., Sulfur, Silicon, Magnesium, Calcium, Argon.  We will resolve the energy and width of the Fe line, detect S & Si lines if they are at the minimum levels suggested by ADAF models, and have a shot at Mg, Ca, and Ar lines. (See this HETG observation of M81* for a possible, brighter analogy.)  This will be used to test ADAF models of the accretion flow.  Alternatively, we could resolve the Fe line into a 6.4 keV fluorescent line and a 6.7 keV Fe XXV line, lending support to the stellar cusp model.

  2. 2. Given that Sgr A* is a hard source, these observations will have about 1/3 the count rate as the current Chandra CCD observations.  About half of the counts go into the gratings arms, and half go into the 0th order image.  (Soft sources lose a bit more in the 0th order spectrum.)  Thus the combined spectrum will about double the total, quiescent counts collected from Sgr A*, with half of those new counts being at gratings resolution.

  3. 3. We also will double the counts obtained from the flare states of Sgr A*. Thanks to the presence of the gratings, far fewer of these flares will be piled up.  The very brightest flares (~factors of 100) have yet to be detected by Chandra, and are piled up beyond use without insertion of the gratings.  The flare spectra will be compared to ADAF and jet models of Sgr A*.

  4. 4.We will obtain 3 Msec in a single year of observations, which means a greatly increased sampling density of the Sgr A* lightcurve. These lightcurves can be compared to relativistic MHD models of the Sgr A* accretion flow (e.g., such as Chris Fragile and Charles Gammie have been performing).

  5. 5. The increased lightcurve sampling also means that there will be increased opportunities for multi-wavelength monitoring.  Multi-wavelength monitoring has been crucial in Sgr A* studies, and we plan to continue along those lines.  NuSTAR will be flying for most of the time period of these observations.

  6. 6.At the same time as we are obtaining spectra and lightcurves of Sgr A*, we will be obtaining spectra of Sgr A East, and spectra and lightcurves (with 3.2 sec resolution) of any point sources within the inner ~1 arcminute.  For the brightest of these we might have some interesting spectra at gratings resolution.





On the next page, we’ve included a list of names and e-mail addresses of investigators participating in this project.


On this page we give links to the long-term and short-term Chandra observation schedules.  These schedule pages should be considered the definitive resource for when these observations will occur.  Long term schedules give an approximately week long window during which the observations are currently scheduled.  The specific observing time within this window is not settled until the short term schedule is made.  Both long and short term schedules are subject to changes throughout the cycle.

As schedules for other spacecraft and ground-based facilities become available, we will also place links to their schedules on this page.


Here is a link to the excellent Galactic Center News list of papersHere is a page of references to Sgr A* papers (likely contains repeats of the GCNews list of abstracts).