[vsnet-grb-info 1852] Swift-BAT trigger 147918 is not a real GRB

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3692
SUBJECT: Swift-BAT trigger 147918 is not a real GRB
DATE:    05/07/28 02:10:37 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

S. Barthelmy (GSFC) and D. Palmer (LANL)
on behalf of the Swift-BAT team:

The Swift-BAT trigger (trigger=147918) at 06:31:44.34 UT on 27 July 2005
is not due to a real GRB.  A retraction Notice was issued at 07:16:16 UT;
45 min after the trigger (appended below in the full email format).
We note that the KAIT and RTT150 teams (GCN 3689 and 3691, resp)
have issued Circulars on this BAT trigger.  We apologize for the
inconvenience to these, and any other follow-up observers on this trigger.
It will now be Swift-BAT policy to issue retraction Circulars
in addition to the retraction Notices to insure the maximum possible
distribution of this information.

After further analysis, we confirm that the cause of the incorrect
BAT trigger was due to a momentary loss in the Star Tracker lock
and that this incorrect spacecraft attitude information resulted
in the point source found in the BAT image not matching the approrpriate
source in the BAT on-board catalog.

S. Barthelmy (of GCN) further notes that the retraction Notice
was distributed to 228 recipients, whereas the original Notice
was distributed to 243 recipients.  The difference is due
to those sites that have Trigger_ID enabled in their GCN configurations.
Since the retraction Notice has the "non-GRB" flag set, the GCN filtering code
does not send this Notice to sites with Trigger_ID filtering enabled.
The Retraction flag should override the non-GRB flag in these delayed
(non-realtime) Notices that are paired with original Notices.
This is clearly a mistake in the design of the GCN filtering code
and will be rectified soon.  We apologise for the inconvenience
this has caused on this 147918 trigger and the other retraction Notices
the Swift-BAT team has issued in the past.


TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 27 Jul 05 07:16:16 UT
NOTICE_TYPE:     Swift-BAT GRB Position RETRACTION
TRIGGER_NUM:     147918,   Seg_Num: 0
GRB_RA:          238.256d {+15h 53m 01s} (J2000),
                 238.338d {+15h 53m 21s} (current),
                 237.522d {+15h 50m 05s} (1950)
GRB_DEC:         -21.768d {-21d 46' 04"} (J2000),
                 -21.784d {-21d 47' 02"} (current),
                 -21.620d {-21d 37' 11"} (1950)
GRB_ERROR:       4.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=1308 [image_cnts]
TRIGGER_DUR:     64.000 [sec]
TRIGGER_INDEX:   20000     E_range: 15-50 keV
BKG_INTEN:       0 [cnts]
BKG_TIME:        0.00 SOD {00:00:00.00} UT
BKG_DUR:         0 [sec]
GRB_DATE:        13578 TJD;   208 DOY;   05/07/27
GRB_TIME:        23504.34 SOD {06:31:44.34} UT
GRB_PHI:          57.31 [deg]
GRB_THETA:        34.52 [deg]
SOLN_STATUS:     0x33
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    7.98 [sigma]
MERIT_PARAMS:     +1  +0  +0  +6  +1  -2  +0  +0 +44  +1 
SUN_POSTN:       126.67d {+08h 26m 41s}  +19.17d {+19d 10' 27"}
SUN_DIST:        116.47 [deg]
MOON_POSTN:       21.77d {+01h 27m 06s}   +9.68d {+09d 40' 47"}
MOON_DIST:       142.90 [deg]
MOON_ILLUM:      59 [%]
GAL_COORDS:      349.43, 24.29 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      240.74, -1.50 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is an image trigger.  (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.)  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is not a GRB.  
COMMENTS:        This is a RETRACTION of a previous notice that identified this as a GRB -- it is NOT a GRB.  
COMMENTS:        This Notice was ground-reprocessed from flight-data.  
COMMENTS:          
COMMENTS:        This is NOT a real GRN, nor is it a Transient.  
COMMENTS:        The s/c attitude information was not valid at the time of the trigger.  
COMMENTS:        So it is very likely this is a known source misidentified due to incorrect pointing information.