RXTE Galactic Center Observation

Commentary

Craig Markwardt writes:
Here is a summary of the galactic bulge observations on 20 Sep 1999
(day 2088).  This observation is primarily east-west.  Unfortunately
we lost half of the ACS data -- the first orbit's worth.  I hope that
the production data delivery tomorrow will have it restored, otherwise
the first half of the observation is close to useless.  Still, I have
a lot to report!

  * We saw a burst from a source near the galactic center.  The peak
    occurred 20 Sep 1999 02:59:21 UT.  Jean (i. Z.), it would be
    interesting to know if the WFC saw it as well.  The pointing
    position of the satellite at burst onset was (266.816, -29.4413),
    but of course the position of the source could be within a degree
    of that.

    The galactic center is crowded, and we scan quickly over that
    area, so it is probably not possible to say with 100% certainty
    what it was.  There are three SAX bursters in that field

     1SAX J1744-2916  266.175 -29.2817  0.58 deg sep
     SAX J1747.0-2853 266.758 -28.8833  0.56 deg sep
     SAX J1750.8-2900 267.700 -29.0000  0.88 deg sep

    My money is on SAX J1747.0-2853.  This source would be consistent
    with when we see the drop in intensity due to the collimator.  I
    tried plugging in a template exponential model using that source,
    and got an excellent fit, the best-fit e-folding time being about
    4.7 sec (+/- 0.5).  Peak flux in that case would have been about
    7700 ct/s/5PCU (2-13 keV), or about 770 mCrab.

    No measurable quiescent emission was seen from the source.

  * XTE J1819-254 was remarkable in that I can only put an upper limit
    on its intensity of ~10 ct/s this time.

    That's kind of depressing... we missed the X-ray outburst in the
    last observation by a few hours (too early), and now the source
    has died.  Without the ASM/BATSE/Optical, we would have totally
    missed the outburst.

  * 4U 1711-34 may be on the upswing again.  It's reached 150 +/- 50
    ct/s.

  * KS 1731-260, after being "high" for two weeks, has dropped back
    into a low state, 450 ct/s.

  * I registered a very high rate for SLX 1744-300/299 in this
    observation, 880 +/- 60 ct/s.  However, SAX J1747 is very close to
    this source and I fear that confusion may have played a part.

  * XTE J1710-281, after being low for about a week, has popped back
    up to 55 ct/s.

Jean in 't Zand writes:

Regarding your burst, indeed it is a crowded field. In our most recent
observation we viewed the region up to Sep. 18.86 and found the following 
sources to be active in your error box:

A 1742-294:        0.26 deg
SLX J1744-299/300: 0.56 deg
1E 1740.7-2942:    0.79 deg

This fall we have not detected yet any activity from SAX J1747.0-2853. 

From A 1742-294 we detected 3 X-ray bursts in our observation which is 
more frequent than usual for this source. Apart from that, this source is
the most frequent burster in the error box, up to this summer we had 46 
bursts from it. SLX 1744-299/300 is also a regular burster but it did not 
burst during our last observation. This may be related to the increased 
persistent level that you note. So, my money would go to A 1742-294.

We also saw no (flaring) activity from SAX J1819-2525.

Our next observation starts tomorrow morning.

Craig Markwardt writes:
Thanks for your mail.  Alas, but this scanning technique isn't really
designed to figure out burst sources.  Oh well.

After having a go at fitting several of the sources you talked about,
I think the best fit is actually SLX J1744-300/299.  The formal fit is
better by a bit, and the inspection of the residuals shows a better
shape than for the others.  This trial also had the least impact on
the other sources in the region, and I didn't require the exponential
template to fit it.  And, if these things have memories, we saw a
burst (putatively) from SLX 1744-300/299 a few weeks ago, so that must
be it. :-)

Thus, I'll change my vote to SLX 1744-300/299.

Known Sources: ASCII table

Scan Light Curve

	Legend -------------------------- 8 - XTE J1719-356 11 - XTE J1723-376 12 - EXO 1722-363 18 - 4U 1728-34 20 - RXS J173251.1 35 - XTE J1743-363 55 - A1744-361 59 - SLX 1746-331 61 - 4U 1746-371 72 - XTE J1756-342 96 - XTE J1814-338 103 - 4U 1820-30 105 - R 1832-330
	Legend -------------------------- 4 - 4U 1711-34 10 - RXS J172006.1 13 - RXS J172525.5 15 - TERZAN 2 18 - 4U 1728-34 31 - XTE J1739-302 36 - 1E1740.7-2942 40 - EXO 1742-326 42 - 2S1742-294 45 - H1743-322 48 - SLX 1744-300 59 - SLX 1746-331 60 - 2E1746.7-3225 63 - GRS 1747-312 65 - XTE J1751-305 71 - XTE J1755-312 74 - XTE J1757-306 83 - XTE J1805-295 103 - 4U 1820-30 195 - 4U 1820-30
	Legend -------------------------- 0 - RXJ1709.5-263 1 - XTE J1710-281 5 - WGAJ1715.3-2635 7 - XTE J1719-291 10 - RXS J172006.1 15 - TERZAN 2 16 - XTE J1728-295 25 - KS 1731-260 26 - KS 1732-273 27 - GRS 1734-292 30 - SLX 1735-269 31 - XTE J1739-302 32 - XTE J1739-285 33 - SLX 1737-282 36 - 1E1740.7-2942 41 - SGR A 42 - 2S1742-294 43 - GCRT J1746-2757 46 - SAXJ1747.0-2853 48 - SLX 1744-300 49 - SLX 1744-300B 51 - GX 3+1 57 - AX J1749.1-2639 58 - IGR J17497-2821 62 - SAXJ1750.8-2900 68 - XTE J1752-280 73 - SW J1756.9-2508 77 - GX 5-1 78 - GRS 1758-258 81 - RXS J180326.2 86 - 2S1803-245 93 - SAXJ1810.8-2609 100 - XTE J1818-245 101 - XTE J1819-254 102 - XTE J1819-254P 104 - GS 1826-238 193 - GX 3+1 194 - GX 5-1
	Legend -------------------------- 0 - RXJ1709.5-263 3 - OPH CLU 5 - WGAJ1715.3-2635 19 - GX 1+4 24 - XTE J1734-234 25 - KS 1731-260 37 - XTE J1744-230 69 - SAXJ1753.5-2349 73 - SW J1756.9-2508 79 - GX 9+1 80 - SAXJ1802.7-2017 85 - SAXJ1806.5-2215 87 - RXS J180824.5 90 - SGR 1806-20 95 - XTE J1812-230 191 - GX 1+4 192 - GX 1+4 194 - GX 5-1

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