TABLE OF CONTENTS:
The GCN system has been modified to incorporate the distribution of GRB locations detected by the All Sky Monitor (ASM) on the RXTE spacecraft.
About 8 times a year, there is a GRB in the instaneous FOV of the ASM instrument that is bright enough for the ASM to produce a location. The RXTE-ASM team has recently started a program of rapidly responding to alerts that there is a GRB in their FOV and to analyze their data to yield a location and error box within a short time after the burst.
Like all the other sources of GRB locations within the GCN system, users can elect to receive (or not) this RXTE-ASM source as well.
The sequence of activities follows. Since the procedures are still
being refined, the indicated nominal durations may change.
a) Continously running software at the ASM SOC monitors the telemetry stream (RXTE to TDRSS to White Sands to GSFC) and detects the presence of a GRB in the data stream. (a few sec)
b) The software then brackets the section containing the burst and calculates a location plus error box (usually the leading and trailing dwell intervals are required). (3*90 sec)
c) A human on the instrument team is notified (pager) that a burst has been detected. The human checks the location calculation and verifies that the s/c orientation information is correct (some recalculation using known sources in the FOV may be required). (2-4 hrs for almost all bursts)
d) The location is sent to the GCN where it is detected by a daemon looking for incoming GRB messages. (60 sec)
e) GCN reads the message in, parses it, reformats it into the standard GCN format, and
distributes it by all the methods/media to all those sites requesting the ASM source of GRB locations. (1-65 sec)
The total time delay is 2-4 hours.
There is an additional sequence of events that can generate an early warning
heads-up Alert Notice that the ASM team may soon be providing a location
for GRBs that are in their FOV and also detected by the BATSE instrument.
The sequence is:
a) The GCN program checks all GRBs detected by the BATSE instrument to see
if the BATSE location is within the FOV of the ASM instrument.
This is done by maintaining knowledge of the RXTE spacecraft orientation and
the ASM orientation.
b) If there is a match between the two, then an Alert Notice is issued. (~60 sec)
The total time delay is ~60 sec.
Notice Types, Content, and Purpose
There are two notice types for the RXTE-ASM program. There is the Alert Notice and the Position Notice.
The Alert Notice provides a heads-up warning when a BATSE-detected GRB is determined to be in the ASM FOV based on the spacecraft observing schedule. It is available within a minute after the GRB -- a full 2-4 hours warning before the RXTE-ASM Initial Position Notice is available. This allows people to start planning a potential follow-up observation based on the rough location in the sky. To minimize the number of false positives (BATSE says yes, but the ASM does not or can not detect the burst), (a) intensity and fluence threshold tests are applied to the BATSE GRBs to match the sensitivity of the ASM, and (b) a test is made to see if the Earth is occulting the BATSE location as seen from the ASM. If an Alert is issued and there is no subsequent ASM detection or localization, then a second Alert Notice is distributed that announces the null result -- this allows people to stand-down. [ALERT NOTICES ARE NOT YET IMPLEMENTED]
The Position Notice gives the RA,Dec location of the GRB as detected by the ASM and as calculated by the ASM team along with the size and boundaries of the error box and the burst intensity. Ther will always be an "Initial" notice, and some times there will be "Updated" and "Final" versions of the notice as the location calculation is refined. The Position Notice comes in two sub-types: the "Box" and the "Line". The difference is explained in the 'Error Box' section below.
There are a total of four sub-type Notices for the RXTE-ASM program. There is one sub-type for the Alert Notice and three sub-types for the Position Notice. The Alert sub-type provides a heads-up service to let potential follow-up observsers that the ASM may be producing a GRB location. The three Position sub-types are (1) RXTE-ASM detected a GRB and the error 'box' coordinates are listed, or (2) RXTE-ASM detected a GRB and the error 'line' coordinates are listed, or (3) RXTE-ASM was not able localize the GRB. Samples of the E-mail, Pager and Short-form Pager distribution methods of the three GCN/RXTE-ASM Position Notice sub-types are attached below. The format is very similar to that of the other sources of GRB locations distributed by the GCN system. Please note that for this source 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. The Alert Notice is type=28 and the Position Notice is type=29.
Sites can elect to receive either the Alert Notices or the Position Notices or both. There is a separate dis/enable flag for each the Alerts and the Positions. (This is different than the four RXTE-PCA notice subtypes, which have only a single dis/enable flag controlling the distribution of all four subtypes.) This filtering applies to all distribution methods/media.
The uncertainty in the location will depend on the burst intensity, its duration, and its position relative to the ASM FOV. Because of the shape of the FOV for the three individual ASM detectors, the error boxes tend to be long and thin. If the burst is sufficiently long in duration for the burst to be detected in two sequential dwell intervals or if the burst is in the region where two of the cameras overlap, then the length of the error box will be shortened. Typical error boxes are ??x??arcmin for a single-camera single-dwell detection and ??-??arcmin for a dual-camera and/or a dual-dwell interval detection. The systematic uncertainty is about ?? arcmin. The errors quoted in the Position Notices includes both the statistical and the systematic contributions. The confidence level for that error is also specified in the Notice (it is typically 90-99%).
Sites should include Don Smith, ????, & ???? (MIT for RXTE-ASM); and Scott Barthelmy & Paul Butterworth (GSFC for GCN) in the author list of IAU Circulars, journal papers and conference presentations discussing the follow-up observations using these GCN/RXTE-ASM locations.
For further information on this, please contact
Don Smith (for RXTE-ASM issues), or
Scott Barthelmy (for GCN issues),
or see the
RXTE-ASM
and
these GCN web pages.
Examples of the four sub-types of the e-mail formats are shown below.
Note that for the ALERT Notice, the time of the burst is listed,
and the RA,Dec listed for the POSITION Notice is the RXTE-ASM 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_ASM_GRB_ALERT
2) GCN/RXTE_ASM_GRB_POSITION
3) GCN/RXTE_ASM_GRB_POSITION
4) GCN/RXTE_ASM_GRB_POSITION
"alert" is tbd -- it's not yet implimented.
TITLE: GCN/RXTE_ASM BURST POSITION NOTICE
NOTICE_DATE: Fri 24 Oct 97 22:41:47 UT
NOTICE_TYPE: RXTE-ASM Initial
TRIGGER_NUM: 6448
GRB_DATE: 10745 TJD; 297 DOY; 97/10/24
GRB_TIME: 41612.00 SOD {11:33:32.00} UT
POSITION_TYPE: Box
GRB_RXTE_RA: 276.257d {+18h 25m 02s} (J2000),
276.243d {+18h 24m 58s} (current),
275.940d {+18h 23m 46s} (1950)
GRB_RXTE_DEC: +49.491d {+49d 29' 27"} (J2000),
+49.490d {+49d 29' 23"} (current),
+49.461d {+49d 27' 41"} (1950)
GRB_RXTE_ERROR: 0.54 [deg radius (stat+sys), 90%]
GRB_ERROR_RA1: 275.584d {+18h 22m 20s} (J2000)
GRB_ERROR_DEC1: 49.180d {+49d 10' 48"} (J2000)
GRB_ERROR_RA2: 276.078d {+18h 24m 19s} (J2000)
GRB_ERROR_DEC2: 49.554d {+49d 33' 14"} (J2000)
GRB_ERROR_RA3: 276.927d {+18h 27m 42s} (J2000)
GRB_ERROR_DEC3: 49.814d {+49d 48' 50"} (J2000)
GRB_ERROR_RA4: 276.421d {+18h 25m 41s} (J2000)
GRB_ERROR_DEC4: 49.435d {+49d 26' 06"} (J2000)
GRB_RXTE_INTEN: 49.00 [mCrab]
SUN_POSTN: 208.96d {+13h 55m 50s} -11.86d {-11d 51' 20"}
SUN_DIST: 84.88 [deg]
MOON_POSTN: 137.10d {+09h 08m 23s} +13.39d {+13d 23' 18"}
MOON_DIST: 107.57 [deg]
COMMENTS: RXTE-ASM GRB Coordinates.
COMMENTS: The intensity (49+-15 mCrab) is averaged over two cameras
COMMENTS: and 90 sec. The actual duration of the
COMMENTS: burst is unknown at this time.
COMMENTS: The diamond represents our best estimate of
COMMENTS: a 90% confidence region.
COMMENTS: The diamond is 1.08 deg in the long direction
COMMENTS: and 0.25 deg in the short direction.
TITLE: GCN/RXTE_ASM BURST POSITION NOTICE
NOTICE_DATE: Mon 15 Dec 97 03:09:37 UT
NOTICE_TYPE: RXTE-ASM Initial
TRIGGER_NUM: 6533
GRB_DATE: 10796 TJD; 348 DOY; 97/12/14
GRB_TIME: 84041.00 SOD {23:20:41.00} UT
POSITION_TYPE: Line
GRB_RXTE_RA: 180.921d {+12h 03m 41s} (J2000),
180.895d {+12h 03m 35s} (current),
180.287d {+12h 01m 09s} (1950)
GRB_RXTE_DEC: +64.912d {+64d 54' 43"} (J2000),
+64.923d {+64d 55' 24"} (current),
+65.190d {+65d 11' 25"} (1950)
GRB_RXTE_ERROR: 2.200 [deg radius (stat+sys), 90%]
GRB_RXTE_LINE_LENGTH: 4.400 [deg]
GRB_RXTE_LINE_WIDTH: 0.200 [deg]
GRB_RXTE_LINE_POS_ANGLE: -89.200 [deg]
GRB_RXTE_INTEN: 400.00 [mCrab]
SUN_POSTN: 262.40d {+17h 29m 36s} -23.26d {-23d 15' 18"}
SUN_DIST: 107.46 [deg]
MOON_POSTN: 94.09d {+06h 16m 21s} +18.71d {+18d 42' 44"}
MOON_DIST: 71.76 [deg]
COMMENTS: RXTE-ASM GRB Coordinates.
COMMENTS: The intensity is ~120 mCrab when averaged over 90 s.
COMMENTS: The error box is long and thin.
COMMENTS: The following are sample points along the "line":
COMMENTS: RA Dec (J2000)
COMMENTS: 185.148d +63.875d
COMMENTS: 182.974d +64.433d
COMMENTS: 180.921d +64.912d
COMMENTS: 178.579d +65.404d
COMMENTS: 176.152d +65.859d
"not_seen" is tbd -- it's not yet implimented.
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 ALERT Notice, the time of the burst is given. and the RA,Dec listed in the POSITION Notice is the RXTE-ASM RA,Dec position. The RA,Dec are Current Epoch.
"alert" is tbd -- it's not yet implimented.
GCN/RXTE_ASM GRB Initial RA=276.243d DEC=+49.490d TIME: 11:33:32.00 UT I=49.00 mCrab RXTE-ASM GRB Box Coordinates.
GCN/RXTE_ASM GRB Initial RA=180.895d DEC=+64.923d TIME: 23:20:41.00 UT I=400.00 mCrab RXTE-ASM GRB Line Coordinates.
"not_seen" is tbd -- it's not yet implimented.
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. The RA,Dec are 1950 Epoch.
"alert" is tbd -- it's not yet implimented.
RXTE-ASM GRB RA=275.940 DEC=+49.461d
GCN/RXTE_ASM GRB RA=180.287 DEC=+65.190d
"not_seen" is tbd -- it's not yet implimented.
Examples of the four sub-types of Subject-only pager/cell_phone format are 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. The RA,Dec are Current Epoch.
"alert" is tbd -- it's not yet implimented.
RXTE-ASM RA=276.243d DEC=+49.490d
RXTE_ASM RA=180.895d DEC=+64.923d
"not_seen" is tbd -- it's not yet implimented.