Title:    SN 1987A in a Lull or a New Phase ? 

Object:    SN 1987A
Exposure:  150 ks (min),  300 -- 600 ks preferred. 
Lead scientist:  Dan Dewey
[X] Primary or [X] Backup  <-- as desired
Constraints (none/easy/average) NONE.
    (Based on the past, observation in Spring 2013.)
[  ] TOO?

Brief description:

  The X-ray flux from SN 1987A grew dramatically from 2003 to ~ 2009
and now appears to be leveling-off and/or declining in the 0.5-2 keV range,
see figure.
  This can be interpreted as indicating that the forward shock has interacted
with most of the "inner ring" material and has overtaken the ring even in the plane
of the ring.  Though another interpretation is that the "main ring" has not yet
been shocked and the emission will re-grow in (near) future.
  Deep HETG observations (our GTOs) were done in Springs of 2007 and 2011 and provide
spectra during the flux increase and near maximum (if that is what it is, it may
be a lull), and suggest and measure a "very-broad" component to the emission
that comes from lower-density material out of the ring plane - Dewey+ 2012 [*].
  We would nominally observe '87A again in the _next_ cycle at the
time labeled "HETG-14" on the figure.  At HETG-14 the difference between the
"past the ring" ("thin" on the plot) and the "still interacting" ("thick" on
the plot) is estimated to be a factor of 3 and the HETG spectrum will provide
good continued monitoring of the emssion including the very-broad component.
  However, one could observe SN 1987A one year earlier in _this_ cycle,
at the epoch "hetg-13" on the plot: at this time a factor of 2 in flux difference
is predicted between the two scenarios.
  As for the exposure time, a ~25% increase is expected in the very-broad component
(interesting because it includes shocked ejecta emission) irrespective of the overall
flux change, and so a new observation of  ~ 150 ks
would have comparable very-broad counts to the HETG-11 observation (180 ks).
However, it is desired to have better statistics than in the 2011 data, so
useful-improvement exposures could be in the range:  300 ks to  600 ks.

Pointers to any additional material:

-  [*] Dewey+ (2012) '87A paper as submitted (revisions in progress):
      http://arxiv.org/abs/1111.5314

-  Fig.8 of the paper is attached and shows the next cycle "hetg-13"
   and the following cycle, "HETG-14", epochs on the X-ray light curves.