ROSAT Status #132: New Hot Spot in the HRI

[REQUEST@rosat.gsfc.nasa.gov]

	             ROSAT Status Report # 132
			   Oct 31 1995



 			New Hot Spot in HRI
			===================

Sometime between June and August, 1995, a small "hot spot" appeared on
the HRI.  Its approximate location in "detector" coordinates is:

		rawx = 440    rawy = 484

which is very close to a corner of the usable region of the detector,
well away from the center of the field of view.  The spot is about 6
pixels in radius and has a count rate that varies between 0 and 25
c/s.  The high rate does not persist, and the typical average rate
during an observation is less than a few counts/sec.  Since it was
first noticed, the hot spot has remained fixed on the detector and, on
average, has neither brightened nor dimmed.  Events from the hot spot
peak in PH channel 1, and all occur in the lowest 3 channels.

The hot spot does NOT appear to pose any immediate threat to the health
of the HRI detector, and it should have little or no impact on the
science program.  MPE, GSFC, and SAO are gearing up to monitor in real
time the HRI behavior more closely, and to have contingency plans in
place should the situation change.

In its effort to understand the cause of this feature, the HRI team is
continuing to analyze data from July and August to determine exactly
when the hot spot appeared and to look for correlations of its
intensity with spacecraft orbital position, bright earth radiation,
particle background, etc.  One hypothesis is that a small pinhole has
formed in the UV/Ion shield.

It would be helpful if observers would check their recent observations
and notify the U.S. RSDC if they see anything in their data at the
location of this hot spot.  In the normal (wobbled) sky maps, the hot
spot appears as a streak in a corner (which one depends upon the roll
angle) or as a clump of apparent knots, with these features often
protruding beyond the apparent edge of the field.

Please email HRI hot spot information to: rsdc@cfa.harvard.edu
                                          ^^^^^^^^^^^^^^^^^^^^

Below we include recipes for creating a full resolution image of the 
hot spot in detector coordinates using PROS and ftools.

-----------------------------------------------------------------------

In ftools, use the routine f2dhisto as follows:

> f2dhisto <infile> <out.fits> 1 1 RAWX RAWY '43.0,843.0' '86.0,886.0'
 
where <infile> = Name + extension containing the accepted photon list.
 			For data in RDF format, the accepted photon list
 			is given in the 2nd extension of the BASIC
 			(*_bas.fits) file.  So if the dataset is
 			rh123456n00, the value of infile would be
 			rh123456n00_bas.fits[2].

In PROS, use the command:

> xdispl "rh123456n00.qp[key=(rawx,rawy)][186:697,230:741]"