TABLE OF CONTENTS:
The GCN system has been modified to incorporate the distribution of GRB locations detected by the PCA instrument on the RXTE spacecraft.
The RXTE-PCA team has recently started a program of rapid follow-up observations of selected GRBs using the GCN/HUNTSVILLE LOCBURST locations. These ToO observations will occur within a short period of time after the GRB.
The sequence of activities follows. Since the procedures are still
being refined, the indicated nominal durations may change.
a) GCN sends the BATSE-LOCBURST GRB location to the RXTE SOC
if the LOCBURST total uncertaintly (stat+sys) is less than 2 degrees (<0.3 hrs),
b) Mission operations plan an observation (1 hr),
c) If it is not observable, an xte_can_not_observe notice will be issued OR
If it fits within the observing constraints, then an xte_will_observe
notice will be issued (1 min),
d) The commands are uploaded to the spacecraft (1 hr),
e) The GRB error box is raster scanned (1 hr),
f) The analysis of the scans is done in near real-time (1 hr), and
g) If a signal is detected the coordinates are sent back to GCN
for automated distribution OR
If no source is detected, then a non-detection notice will be
distributed (1 min).
The total time delay is ~5 hours.
Criteria to Make an Observation
The criteria that must be passed for RXTE-PCA to make a follow-up observation are:
a) The LOCBURST location uncertainty must be less than 2.0 degrees (statistical
plus systematic). While the uncertainty is a complicated function of the
intensity and fluence of the burst, it roughly corresponds to a peak intensity
of greater than 2500 counts/sec in the 50-300 keV band.
b) The GRB-to-Sun angle must be greater than 35 degrees.
c) The current observation being made by RXTE can be interrupted. That is
to say: (1) that the current observation is not a "correlated observation"
with some other spacecraft or ground-based instrument(s) or (2) that the
observation does not require a continous sequence of data.
d) The orbital observing efficiency is greater than 50%. The efficiency
is a result of (1) the Ra,Dec location of the burst on the sky and the
Earth occultation region, (2) orbital passages through the SAA, and (3)
the spacecraft slewing speed and slew distances.
e) Other miscellaneous "operations constraints" as determined by the
Duty Scientist.
The actual observing plan executed by the spacecraft is a double zig-zag scanning pattern over the LOCBURST location for the first part of the observation (item "e" above), and then for the second half, the spacecraft just stares at the LOCBURST location. During the stare-mode phase the scanning-mode data is analyzed. If a previously unknown source is detected, then the commands are immediately uploaded to make the small slew to the source location. The motivation for the pre-planned stare phase is that it builds into the spacecraft's schedule a period of time that is also located near the ultimate source location. If the slew to the source location is less than 2 degrees, then the SOC can send the commands to make that minor pointing adjustement without going through the POCC and the planners -- this saves time.
There are a total of four sub-type Notices for the RXTE-PCA program. There are two sub-types for the Alert Notices and two sub-types for the Position Notices. The two Alert sub-types handle the two cases of (1) RXTE-PCA will observe the GRB error box or (2) RXTE-PCA can not observe the error box. The two Position sub-types are (1) RXTE-PCA detected a counter-part and the coordinates are listed or (2) RXTE-PCA did not detect any source. Samples of the E-mail, Pager and Short-form Pager distribution methods (with simulated values) of the four GCN/RXTE-PCA Notice sub-types are attached below. The format is the standard for the GCN system; many of the fields are the same except the intensity is now in mCrab units.
The Internet socket formats are similarly modified from those in the GCN system and are described in detail in the socket definition document.
Unlike the four sub-types for the original BATSE Notices (Original, Final, MAXBC, and LOCBURST), there is no individual filtering for the four RXTE-PCA sub-types. If a site elects to receive RXTE-PCA Notices, it will receive all four sub-type (the two ALERT and the two POSITION Notices).
The uncertainty in the location will depend on the source intensity and its position relative to the pattern of raster scans. Systematic uncertainties are about 1 arcmin, but for weak (1 mCrab) sources the statistical uncertainty may be a few tenths of a degree. For some cases of the true source location with respect to the PCA angular response pattern, RXTE-PCA may produce two error circles or one long, narrow error box.
Sites should include Toshi Takeshima, Robin Corbet, & Frank Marshall (GSFC for RXTE-PCA); Craig Robinson, Chryssa Kouveliotou, Valerie Connaughton, Jerry Fishman, Marc Kippen, Chip Meegan, & Geoff Pendleton (MSFC); and Scott Barthelmy & Paul Butterworth (GSFC for GCN) in the author list of IAU Circulars, journal papers and conference presentations based on follow-up observations using these GCN/RXTE-PCA locations.
For further information on this, please contact
Toshi Takeshima (for RXTE-PCA issues),
Marc Kippen (for MSFC issues), or
Scott Barthelmy (for GCN issues),
or see the RXTE-PCA and these GCN web pages:
http://heasarc.gsfc.nasa.gov/docs/xte/XTE.html
http://gcn.gsfc.nasa.gov/gcn_main.html.
Examples of the four sub-types of the e-mail formats are shown below.
Note that for the two ALERT Notices, the RA,Dec position listed is that
carried over from the previous LOCBURST Notice, and the RA,Dec listed for the
POSITION Notice is the RXTE-PCA RA,Dec position.
For those sites/people that use daemons and/or incoming e-mail filters,
the "Subject" lines for the four notices are fixed, and the strings are:
1) GCN/RXTE_PCA_ALERT
2) GCN/RXTE_PCA_ALERT
3) GCN/RXTE_PCA_POSITION
4) GCN/RXTE_PCA_POSITION
TITLE: GCN/RXTE_PCA BURST ALERT NOTICE NOTICE_DATE: Mon 16 Jun 97 20:58:50 UT NOTICE_TYPE: RXTE-PCA TRIGGER_NUM: 6274 GRB_DATE: 10615 TJD; 167 DOY; 97/06/16 GRB_TIME: 65390.28 SOD {18:09:50.28} UT GRB_LOCBURST_RA: 152.40d {+10h 09m 37s} (J2000) GRB_LOCBURST_DEC: +3.26d {+03d 15' 26"} (J2000) COMMENTS: RXTE-PCA WILL observe this LOCBURST GRB location. COMMENTS: The RXTE-PCA observation will start at 97/06/16 22:09:12.00 UT.
TITLE: GCN/RXTE_PCA BURST ALERT NOTICE NOTICE_DATE: Sun 04 May 97 08:58:26 UT NOTICE_TYPE: RXTE-PCA TRIGGER_NUM: 6122 GRB_DATE: 10615 TJD; 167 DOY; 97/06/16 GRB_TIME: 65390.28 SOD {18:09:50.28} UT GRB_LOCBURST_RA: 152.40d {+10h 09m 37s} (J2000) GRB_LOCBURST_DEC: +3.26d {+03d 15' 26"} (J2000) COMMENTS: RXTE-PCA can NOT observe this LOCBURST GRB location.
TITLE: GCN/RXTE_PCA BURST POSITION NOTICE NOTICE_DATE: Sun 04 May 97 08:58:26 UT NOTICE_TYPE: RXTE-PCA TRIGGER_NUM: 6122 GRB_DATE: 10603 TJD; 155 DOY; 97/05/04 GRB_TIME: 12345.00 SOD {03:25:45.00} UT GRB_RXTE_RA: 152.40d {+10h 09m 37s} (J2000), 152.37d {+10h 09m 29s} (current), 151.76d {+10h 07m 01s} (1950) GRB_RXTE_DEC: +3.26d {+03d 15' 26"} (J2000), +3.27d {+03d 16' 12"} (current), +3.50d {+03d 30' 12"} (1950) GRB_RXTE_ERROR: 0.095 [deg radius, 1-sigma] GRB_RXTE_INTEN: 9.41 [mCrab] SUN_POSTN: 72.03d {+04h 48m 07s} +22.41d {+22d 24' 40"} SUN_DIST: 79.83 [deg] MOON_POSTN: 55.90d {+03h 43m 36s} +15.17d {+15d 10' 15"} MOON_DIST: 95.38 [deg] PROG_LEVEL: 3 COMMENTS: RXTE-PCA Coordinates for a BATSE LOCBURST GRB.
TITLE: GCN/RXTE_PCA BURST POSITION NOTICE NOTICE_DATE: Mon 16 Jun 97 22:45:55 UT NOTICE_TYPE: RXTE-PCA TRIGGER_NUM: 6274 GRB_DATE: 10615 TJD; 167 DOY; 97/06/16 GRB_TIME: 65390.28 SOD {18:09:50.28} UT COMMENTS: RXTE-PCA did not detect anything obvious. COMMENTS: A box of +/-2deg in Dec and +/-3deg in RA was scanned. COMMENTS: The intensity upper limit is 2 mCrab.
Examples of the four sub-types of the (regular) pager formats are shown below. There are no "Subject" lines for these e-mails sent to the pager companies because the Subject line would use up valuable character counts from the maximum displayable for the body of the message. Note that for the two ALERT Notices, the RA,Dec position listed is that carried over from the previous LOCBURST Notice, and the RA,Dec listed for the POSITION Notice is the RXTE-PCA RA,Dec position.
GCN/RXTE_PCA ALERT LOC_RA=152.40d DEC=+3.26d TIME: 03:25:45.00 UT RXTE-PCA WILL observe this GRB.
GCN/RXTE_PCA ALERT LOC_RA=152.4d DEC=+3.3d TIME: 03:25:45.00 UT RXTE-PCA can NOT observe this GRB.
GCN/RXTE_PCA GRB RA=152.40d DEC=+3.26d TIME: 03:25:45.00 UT I=9.41 mCrab RXTE-PCA GRB Coordinates.
GCN/RXTE_PCA GRB TIME: 03:25:45.00 UT RXTE-PCA was NOT able to localise this GRB.
Examples of the four sub-types of the short-form pager format are shown below. There are no "Subject" lines for these e-mails sent to the pager companies because the Subject line would use up valuable character counts from the maximum displayable for the body of the message. And it was the very limited display character count of some companies that motivated the short-form pager method in the first place.
RXTE-PCA WILL observe this GRB.
RXTE-PCA can NOT observe this GRB.
RXTE-PCA GRB RA=152.40 DEC=+3.26d
RXTE-PCA could NOT localise this GRB.
An example of the Subject-only pager/cell_phone format is shown below. Only the "Subject" line for these e-mails sent to the pager companies because that's the only part of the e-mail they display on the pager/cellphone.
RXTE-PCA WILL observe this GRB (RA=152.40,DEC=3.26).
RXTE-PCA can NOT observe this GRB (Trig=6122).
RXTE-PCA RA=152.40 DEC=+3.26d
RXTE-PCA could NOT localise this GRB (Trig=6122).