RXTE Galactic Center Observation

Commentary

Craig Markwardt writes:

I've not been sending out galactic bulge summaries for some time.
Here is my attempt to catch up, giving a brief recap.  As such, some
of the items will not be of immediate interest, but rather a status
update.  This covers the period ~Jul-Sep 24 2000.

All fluxes are approximate, in the 2-10 keV band.

* EXO 1745-248 was discovered in outburst at the beginning of July.
  After a very choppy rise phase, ranging from < 2 to 200 mCrab, the
  source very quickly rose to a peak of ~450 mCrab around August 19.
  Since then it has been following a roughly linear decay and is now
  at about 130 mCrab.  Follow-up pointed PCA observations show a QPO
  and harmonic.  The bursts are rather peculiar, but type I is not
  ruled out, neither by the rapidity of the bursts, nor their energy
  spectrum.  A hint of cooling is suggested in the burst tails.

* GRS 1747-312 had another outburst starting on 03 August, reaching an
  immediate peak of ~47 mCrab.  As you recall we were expecting the
  next outburst of this source around July 1 based on its previous
  pattern.  It seems to have come late by about a month, and brighter
  by about 30%.  [ However we didn't resolve the rise; the previous
  observation was ~4 days earlier. ]  The source has since declined
  into non-detectability.

* XTE J1819-254 (V4641 Sgr) has a high point in the most recent bulge
  scan, around 1.7 +/- 0.5 mCrab.  However the observation to watch is
  the next bulge scan where we rest on the source at a scan endpoint,
  so the errors will be much smaller.

* KS 1731-260, after having it's "typical" outbursts, appears to be in
  a curiously steady mode.  It has remained at 55 +/- 2 mCrab over the
  past ~1.5 months.

* XTE J1743-363 seems to have turned off in the past week.  It had
  been variable in the 1-10 mCrab range, with a single 450 mCrab point
  which may have been a burst.  There was no exponential decay.

* You can't keep SAX J1747.0-2853 down!  After its initial outburst,
  it continued to have repeated minioutbursts.  The envelope of the
  combined profiles appears to be an exponential decay (ie, the mini
  outbursts are getting fainter over time), with an efolding time of
  about 100 days.

* The rapid burster had another "dwarf" outburst.  We saw bursts
  again, and I have not yet been able to model them.

* 4U 1820-30 has gone from trough to peak, from ~100 mCrab to 500
  mCrab most recently.

* GX 1+4 is of course extremely variable, and hard to measure since
  its pulse period is shorter than the scan timeframe.  Still, we can
  detect crude variability patterns.  After the winter hiatus
  (1999-2000) the source was consistently much fainter (<5 mCrab,
  compared to 20 before), but around June 2000 it became brighter
  again for a time.  It's not clear what is happening now...

* XTE J1710-281 is still going.  However in the most recent 2-3 months
  the peaks of its minioutbursts seem to be declining somewhat.  Where
  the peaks used to be ~8 mCrab, the most recent peaks have been more
  like 6 and 4 mCrabs.

* Strange trends department.  GRS 1758-258, GS 1826-238 and GX 3+1
  seem to be on a steady increase in flux.  Where will it end? [ GX
  3+1 has doubled over the past two years. ]

Craig

Known Sources: ASCII table

Scan Light Curve

	Legend -------------------------- 1 - XTE J1710-281 3 - OPH CLU 6 - IGR J17191-2821 7 - XTE J1719-291 8 - XTE J1719-356 9 - XTE J1720-318 10 - RXS J172006.1 11 - XTE J1723-376 12 - EXO 1722-363 13 - RXS J172525.5 14 - XTE J1726-283 15 - TERZAN 2 18 - 4U 1728-34 19 - GX 1+4 20 - RXS J173251.1
	Legend -------------------------- 19 - GX 1+4 24 - XTE J1734-234 25 - KS 1731-260 26 - KS 1732-273 27 - GRS 1734-292 28 - IGR J17375-3022 30 - SLX 1735-269 31 - XTE J1739-302 32 - XTE J1739-285 33 - SLX 1737-282 35 - XTE J1743-363 36 - 1E1740.7-2942 37 - XTE J1744-230 38 - KS 1741-293 39 - GCRT J1745-3009 40 - EXO 1742-326 41 - SGR A 42 - 2S1742-294 43 - GCRT J1746-2757 44 - 1E1743.1-2843 45 - H1743-322 46 - SAXJ1747.0-2853 48 - SLX 1744-300 51 - GX 3+1 54 - XTE J1748-288 59 - SLX 1746-331 60 - 2E1746.7-3225 62 - SAXJ1750.8-2900 63 - GRS 1747-312 65 - XTE J1751-305 71 - XTE J1755-312 72 - XTE J1756-342 191 - GX 1+4
	Legend -------------------------- 37 - XTE J1744-230 46 - SAXJ1747.0-2853 53 - EXO 1745-248 54 - XTE J1748-288 62 - SAXJ1750.8-2900 63 - GRS 1747-312 65 - XTE J1751-305 67 - XTE J1752-223 68 - XTE J1752-280 70 - RXS J175428.3 71 - XTE J1755-312 72 - XTE J1756-342 73 - SW J1756.9-2508 74 - XTE J1757-306 75 - IGR J17586-2129 77 - GX 5-1 78 - GRS 1758-258 81 - RXS J180326.2 83 - XTE J1805-295 86 - 2S1803-245 192 - GX 3+1 193 - EXO 1745-248 194 - GX 5-1
	Legend -------------------------- 85 - SAXJ1806.5-2215 86 - 2S1803-245 87 - RXS J180824.5 90 - SGR 1806-20 95 - XTE J1812-230 101 - XTE J1819-254 102 - XTE J1819-254P 103 - 4U 1820-30 104 - GS 1826-238 105 - R 1832-330 150 - G11.2-0.3 195 - 4U 1820-30 196 - 4U 1820-30

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