TABLE OF CONTENTS:
The GCN system has been modified to incorporate the distribution of locations of GRBs detected by the Wide Field Camera (WFC) and the MECS/LECS narrow field instruments (NFI) on the BeppoSAX spacecraft. It has been doing this since late 1997 in a semi-manual procudure, which incurred some extra delay time, but now (as of Nov 99) the procedure is fully automated (from the SAX Ops center in Italy all the way through to the outgoing portion of GCN) so the delay times are as small as possible.
About 6-15 times a year, there is a GRB in the FOV of the WFC instrument that is bright enough for the WFC to produce a location. Some of the detected GRBs are followed-up with a ToO observation with the NFI (MECS & LECS) instruments.
Like all the other sources of GRB locations within the GCN system, users can elect to receive (or not) these SAX-WFC and -NFI sources as well.
The GCN/SAX Notices are archived within the GCN website in the Table of SAX GRBs.
The sequence of activities for a typical burst follows:
1) SAX Science Operations (SSO) continuously analyzes the GRBM data
looking for a burst.
2) When there is a GRBM trigger, the SSO does a quick-look in the WFC data
(at T+2-3 hrs):
If the WFC detected the burst, then SSO sends a SAX_WFC_SRC to GCN:
This would be an Initial "saw" something subtype.
This would be an "~10 arcmin" (diameter) location.
The SSO also decides if the burst can be followed-up with an NFI observation.
3) In the meantime, the SSO will probably continue to analyze the WFC detection
and issue an improved location notice (2-5 hrs):
SSO sends a SAX_WFC_SRC to GCN with Subtype "Updated".
This would be a "~6 arcmin" (diameter) location.
There could be more than one of these "Updated" notices, or there
could be none, and the sequence jumps from the "Initial" to the "Final" notice.
4) SSO does a quick-look on the NFI data when it becomes available (10-24 hrs).
If the NFI detected the burst, then SSO sends a SAX_NFI_SRC to GCN:
This would be an "Initial" "saw" subtype.
If nothing was detected, then it is likely no Notice will be generated/distributed.
However, a Circular may be generated/distributed.
5) The SSO continues to analyze the NFI detection and issues an improved
location notice (24-48 hrs):
SSO sends a SAX_NFI_SRC to GCN with Subtype "Updated".
There could be more than one of these "Updated" notices, or there
could be none, and the sequence jumps from the "Initial" to the "Final" notice.
The total time delay is 2-3 hours for the WFC Initial and ~5 hours
for the WFC Update, and ~12-24 hours for an NFI Initial location.
Notice Types, Content, and Purpose
There are two notice types for the SAX-WFC program. There is the Alert Notice (not yet implimented) and the Position Notice (implimented).
The Position Notice (either Initial, Updated, or Final) gives the RA,Dec location of the GRB as detected by the WFC. The SAX-WFC Initial Position, Update, and Final Position Notices come out 2 to 5 hours after the burst.
For NFI there are only Notices (there are no Alerts). However, the Initial, Updated and Final forms exist.
The Alert Notice types are yet to be implemented, and are intended to provide a way to give a heads-up for CGRO-BATSE bursts determined to be in the FOV of the WFC and a heads-up for future NFI follow-up observations.
Samples of the E-mail, Pager, Short-form Pager, etc distribution methods of the two GCN/SAX-WFC and -NFI Notice types are attached below. The format is very similar to the other spacecraft/instrument sources of GRB locations. Many of the fields are the same except the intensity is now in mCrab units. Also note that if the intensity is not determined at the time of the Notice (particularly true for Initial Notices), the the intensity field will contain the string "unknown" instead of a numerical value.
The socket packet contents and format is similar to the other packet types and are described in detail in the socket definition document. The Alert Notices are type=33 & 35 and the Position Notices are type=34 & 36.
Sites can elect to receive either the WFC Notices or the NFI Notices or both types. There is a separate dis/enable bit for each type and subtype. Currently, there is no filter bits for the "saw" vs "no_saw" scenarios, because the rate of issuance of no_saw Notices is so low. This filtering applies to all distribution methods/media.
The uncertainty in the location will depend on (a) the burst intensity, (b) its position relative to the WFC FOV, and (c) the relative locations and intensities of other sources in the FOV. The typical error for the Initial Notice is ~10 arcmin, and ~6 arcmin (diameter) for the Update and Final Notices. The systematic uncertainty depends on the satellite attitude (whether startrackers or gyros or sunsensor are in use) and varies from 0 arcmin to 1 deg in the worst situations. 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 1-sigma).
The errors for the x-ray afterglow counterparts detected by the NFI instruments are typically 2 arcmin (diameter).
Sites are encouraged to acknowledge SAX and GCN in their publications based on follow-up observations using these GCN/SAX-WFC/-NFI locations.
For further information on this, please contact
Luigi Piro (for SAX issues),
John Heise (for WFC issues), or
Scott Barthelmy (for GCN issues),
or see the
BeppoSAX web page,
SAX-WFC web page,
these GCN web pages, and
GCN/SAX GRB table.
Examples of the two notice types of the e-mail formats are shown below.
The "/////" divider bars are NOT part of the messages.
The RA,Dec listed for the POSITION Notices is the SAX-WFC or -NFI
RA,Dec position.
For those sites/people that use daemons and/or incoming e-mail filters,
the "Subject" lines for the two notices are fixed, and the strings are:
1) GCN/SAX_WFC_POSITION
2) GCN/SAX_NFI_POSITION
/////////////////////////////////e-mail format/////////////////////////////////
TITLE: GCN/SAX_WFC BURST POSITION NOTICE
NOTICE_DATE: Sun 05 Jan 98 21:23:00 UT
NOTICE_TYPE: SAX-WFC Initial {or Updated or Final}
GRB_DATE: 10576 TJD; 128 DOY; 97/05/08
GRB_TIME: 78060.00 SOD {21:41:00.00} UT
GRB_SAX_RA: 102.950d {+06h 51m 48s} (J2000),
102.840d {+06h 51m 22s} (current),
100.867d {+06h 43m 28s} (1950)
GRB_SAX_DEC: +79.280d {+79d 16' 48"} (J2000),
+79.283d {+79d 16' 60"} (current),
+79.337d {+79d 20' 15"} (1950)
GRB_SAX_ERROR: 0.170 [deg radius (stat+sys), 1-sigma]
GRB_SAX_INTEN: 2000.00 [mCrab]
SUN_POSTN: 45.86d {+03h 03m 27s} +17.28d {+17d 17' 01"}
SUN_DIST: 67.13 [deg]
MOON_POSTN: 73.70d {+04h 54m 48s} +17.58d {+17d 34' 51"}
MOON_DIST: 63.15 [deg]
COMMENTS: SAX-WFC GRB Coordinates.
COMMENTS:
COMMENTS: On May 8, around 21.41 UT the GRBM instrument aboard BEPPOSAX
COMMENTS: detected a gamma-ray burst that was simultaneously seen
COMMENTS: in the WFC.
COMMENTS:
COMMENTS: Preliminary coordinates, as derived by the analysis carried
COMMENTS: out by the PI of the program (E. Costa) and the team
COMMENTS: of the Science Operation Center are:
COMMENTS: alpha(2000)=102.95 deg
COMMENTS: delta= +79.28
COMMENTS: (error radius about 10 arcmin)
COMMENTS:
COMMENTS: We will circulate a refined position (estimated error radius of
COMMENTS: about 3 arcmin) as soon as it will available from the off-line
COMMENTS: analysis of the data carried out by the PI team.
COMMENTS:
COMMENTS: Observations in all wavelenghts are urged.
//////////////////////////////e-mail format////////////////////////////////////
TITLE: GCN/SAX_NFI BURST POSITION NOTICE
NOTICE_DATE: Sun 05 Jan 98 21:23:00 UT
NOTICE_TYPE: SAX-NFI Initial
GRB_DATE: 10576 TJD; 128 DOY; 97/05/08
GRB_TIME: 78060.00 SOD {21:41:00.00} UT
GRB_SAX_RA: 102.950d {+06h 51m 48s} (J2000),
102.840d {+06h 51m 22s} (current),
100.867d {+06h 43m 28s} (1950)
GRB_SAX_DEC: +79.280d {+79d 16' 48"} (J2000),
+79.283d {+79d 16' 60"} (current),
+79.337d {+79d 20' 15"} (1950)
GRB_SAX_ERROR: 0.017 [deg radius (stat+sys), 1-sigma]
GRB_SAX_INTEN: 150.00 [mCrab]
SUN_POSTN: 45.86d {+03h 03m 27s} +17.28d {+17d 17' 01"}
SUN_DIST: 67.13 [deg]
MOON_POSTN: 73.70d {+04h 54m 48s} +17.58d {+17d 34' 51"}
MOON_DIST: 63.15 [deg]
COMMENTS: SAX-NFI GRB Coordinates.
COMMENTS:
COMMENTS: On May 8, around 21.41 UT the GRBM instrument aboard BEPPOSAX
COMMENTS: detected a gamma-ray burst that was simultaneously seen
COMMENTS: in the WFC. It was decided to perform an NFI follow-up
COMMENTS: observation on this burst (starting at T+8 hrs).
COMMENTS:
COMMENTS: The data analysis is continuing and a refined location
COMMENTS: may be forthcoming.
//////////////////////////////////////////////////////////////////////////////
Examples of the two 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 RA,Dec position listed is that carried over from the previous BATSE Notice (to allow for planning of the follow-up observation), and the RA,Dec listed in the POSITION Notice is the SAX-WFC RA,Dec position.
////////////////////////////////////////////////////////////////////////////// GCN/SAX_WFC GRB Initial RA=102.840d DEC=+79.283d TIME: 21:41:00.00 UT I=2000.00 mCrab SAX-WFC GRB Coordinates. ////////////////////////////////////////////////////////////////////////////// GCN/SAX_NFI GRB Initial RA=102.843d DEC=+79.238d TIME: 21:41:00.00 UT I=2400.00 mCrab SAX-NFI GRB Coordinates. //////////////////////////////////////////////////////////////////////////////
Examples of the four 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.
////////////////////////////////////////////////////////////////////////////// SAX-WFC RA=100.867 DEC=+79.337d ////////////////////////////////////////////////////////////////////////////// SAX-NFI RA=100.931 DEC=+79.310d //////////////////////////////////////////////////////////////////////////////
The two forms of the Subject-only format exist for the SAX-WFC/-NFI Notices.
////////////////////////////////////////////////////////////////////////////// SAX-WFC RA=100.867 DEC=+79.337d ////////////////////////////////////////////////////////////////////////////// SAX-NFI RA=100.931 DEC=+79.310d ////////////////////////////////////////////////////////////////////////////// SAX-WFC RA=06h43m28.1 DEC=79d20m13.2s E=0.02 T=21:41:00.00 I=2000 ////////////////////////////////////////////////////////////////////////////// SAX-NFI RA=06h43m28.1 DEC=79d20m13.2s E=0.01 T=21:41:00.00 I=2400 //////////////////////////////////////////////////////////////////////////////