[vsnet-grb 71907] GRBs while Swift is slewing, new GCN Notice type

[Bacodine]

TO:  All GCN Notice recipients
RE:  A new burst notice type is available
DT:  21 Apr 08

INTRO:
There is a new Notice type available within GCN
that has GRBs detected by BAT while the Swift spacecraft
is slewing (BAT_SLEW_POS).  The Harvard group (Antonio Copete
and Josh Grindlay) have developed a technique to process
BAT event-by-event data captured while Swift is slewing
and extract GRB positions during these slew time intervals.

DETAILS:

Data Analysis Method:  Sky images are made from the event data
for each 0.2sec interval during a slew.  Given the slew rate
these 0.2sec intervals result in a slightly less than a 50% increase
in the intrinsic angular resolution on the sky.  Each 0.2-sec image
is added to the total sky image during the slew.  Images are built up
for the 15-50 (Soft) and 50-150 (Hard) keV bands (plus the sum of the two).
These sky images are scanned for point sources above a specified
significance threshold, and each source is compared to a catalog.
Those sources that do not match the catalog are deemed new sources (ie GRBs).

Subclasses:  There are two subcategories of the BAT_SLEW_POS detections:
a) "Gold plated" which are 100% confidence that they are GRBs
   (or at least something astrophysical in gamma-rays).
b) "Silver plated" detections have somewhat lower thresholds
   and a somewhat lower confidence level (tbd%).
The threshold criteria are:
a) Gold:
   >4 sigma in both the Soft  AND  Hard bands.
b) Silver:
   >4 sigma in either Soft OR Hard bands  AND  >4 sigma in Broad band  AND
   at least one of the three bands must be >6 sigma.
(The Broad band is the sum of the Soft and Hard bands, ie 15-150 keV)

Occurance Rate:  Currently, only about 40% of the slews
have event data captured.  This capture efficiency will
likely double within a couple months.  But for now (ie the 40% eff),
the expected rate of the Gold plated detections is ~6/year
and ~50/yr for the Silver plated events.

Time Delay:  Given that these detections are made using
event-by-event data which only comes down the full telemetry
Malindi downlinks, there will be a 0.1 to 8 hr delay
plus an additional 0.5 hrs for the ground processing.
The average delay will be ~3.5 hours.

Location Uncertainty:  Since these events can be weaker than
the normal BAT Rate-trigger or Image-trigger GRBs,
the range of position uncertainties will be slightly larger:
1-7 arcmin.  The uncertainty is given for each detection.

Filtering:  Currently, there is no plan for filtering within the GCN
based on Silver vs Gold plating.  If you have BAT_SLEW_POS enabled,
then you will receive both Gold and Silver.  While it is not known yet
what the GRB-ness confidence level will be for the Silvers, it is epected
to be very high, and if experience should prove otherwaise, the threshold
level (N_sigmas) will be increased to to achieve a high CL.


ACTION ITEM:
If you want to receive this BAT_SLEW_POS notice type,
please send me a request to have it enabled.  You can do this 
by forwarding this email to  scott at milkyway.gsfc.nasa.gov


NOTICE EXAMPLE:
Here is an example of a full-format email BAT_SLEW_POS Notice:

    TITLE:           GCN/SWIFT NOTICE
    NOTICE_DATE:     Thu 17 Apr 08 17:49:31 UT
    NOTICE_TYPE:     Swift-BAT Slew GRB Position
    ID_NUM:          4
    GRB_RA:          223.800d {+14h 55m 12s} (J2000),
                     223.870d {+14h 55m 29s} (current),
                     223.377d {+14h 53m 30s} (1950)
    GRB_DEC:         +48.410d {+48d 24' 36"} (J2000),
                     +48.377d {+48d 22' 36"} (current),
                     +48.612d {+48d 36' 42"} (1950)
    GRB_ERROR:       6.77 [arcmin radius, statistical only]
    GRB_INTEN:       785889 [cnts]    Image_Peak=0 [image_cnts]
    TRIGGER_DUR:     70.596 [sec] 
    TRIGGER_INDEX:   8     Criteria: (S(15-50) OR H(50-150)) > 4.0 sigma  AND  B(15-150) > 4.0 sigma  AND  (S OR H OR B) > 6.0
    ENERGY_RANGE:    15-150 keV
    BKG_INTEN:       0 [cnts]
    BKG_TIME:        0.00 SOD {00:00:00.00} UT
    BKG_DUR:         0 [sec]
    GRB_DATE:        14573 TJD;   108 DOY;   08/04/17
    GRB_TIME:        37993.18 SOD {10:33:13.18} UT
    SOLN_STATUS:     0x4011
    RATE_SIGNIF:     0.00 [sigma]
    IMAGE_SIGNIF:    4.59 [sigma]
    SUN_POSTN:        26.08d {+01h 44m 20s}  +10.79d {+10d 47' 28"}
    SUN_DIST:        118.77 [deg]   Sun_angle= 10.8 [hr] (West of Sun)
    MOON_POSTN:      176.72d {+11h 46m 53s}   -1.54d {-01d 32' 09"}
    MOON_DIST:        64.44 [deg]
    MOON_ILLUM:      93 [%]
    GAL_COORDS:       82.88, 57.97 [deg] galactic lon,lat of the burst (or transient)
    ECL_COORDS:      194.51, 60.34 [deg] ecliptic lon,lat of the burst (or transient)
    COMMENTS:        SWIFT-BAT Slew GRB Coordinates.  
    COMMENTS:        A point_source was found.  
    COMMENTS:        This does not match any source in the ground catalog.  
    COMMENTS:        This is not a GRB.  
    COMMENTS:        Very high confidence of reality (silver-plated).  
    COMMENTS:        This Notice was ground-processed from flight-data.

The other email-based formats (long/short/subject pager formates)
have the same subset of fields as for the regular BAT_POS Notice type.
The socket packet content can be found at:
http://gcn.gsfc.nasa.gov/gcn/sock_pkt_def_doc.html


Sincerely,
Scott



Scott Barthelmy                      NASA-GSFC, Code 661, Greenbelt, MD   20771
PHONE:  301-286-3106                 (office)       CELL:   301-346-3733
FAX:    301-286-1684                 (1st choice,  -1682 2nd choice)
EMAIL:  scott at lheamail.gsfc.nasa.gov
PAGER:  3013463733 at cingularme.com
WEB:    http://gcn.gsfc.nasa.gov/gcn

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Filter:  ALL
Error_limit=   360.100 [deg, diameter]
Delta_T_limit= 999.900 [hr]
Swift_Trigger_ID_filter:   Disabled
Sources & Notice Types/Subtypes:
    RXTE-PCA_Alert_wont:      Enabled
    RXTE-PCA_Alert_will:      Enabled
    RXTE-PCA_nosaw:           Enabled
    RXTE-PCA_saw:             Enabled
    RXTE-ASM:                 Enabled
    IPN_POS:                  Enabled
    ALEXIS:                   Enabled
    RXTE-ASM_TRANS:           Enabled
    HETE_S/C_ALERT:           Enabled
    HETE_S/C_UPDATE:          Enabled
    HETE_S/C_LAST:            Enabled
    HETE_GND_ANA:             Enabled
    HETE_TEST:                Disabled
    TYPE2_TEST:               Disabled
    INTEGRAL_Test_notices:    Disabled
    SWIFT_BAT_GRB_TEST:       Disabled
    AGILE_GRB_TEST:           Disabled
    GLAST_GBM_TEST:           Disabled
    GLAST_LAT_TEST:           Disabled
    INTEGRAL_POINTDIR:        Disabled
    INTEGRAL_SPIACS:          Enabled
    INTEGRAL_WAKEUP:          Enabled
    INTEGRAL_REFINED:         Enabled
    INTEGRAL_OFFLINE:         Enabled
    GRB_CNTRPART:             Disabled
    MILAGRO_POS:              Disabled
    SWIFT_BAT_GRB_ALERT:      enabled
    SWIFT_BAT_GRB_POS:        enabled
    SWIFT_BAT_GRB_POS_NACK:   enabled
    SWIFT_BAT_SUBTHRESH_POS:  Disabled
    SWIFT_BAT_GRB_LIGHTCURVE: enabled
    SWIFT_FOM_2OBS:           enabled
    SWIFT_SC_2SLEW:           enabled
    SWIFT_XRT_POS:            enabled
    SWIFT_XRT_POS_NACK:       enabled
    SWIFT_XRT_SPECTRUM:       enabled
    SWIFT_XRT_IMAGE:          enabled
    SWIFT_XRT_LIGHTCURVE:     enabled
    SWIFT_UVOT_IMAGE:         enabled
    SWIFT_UVOT_SRCLIST:       enabled
    SWIFT_UVOT_POS:           enabled
    SWIFT_UVOT_POS_NACK:      Disabled
    SWIFT_BAT_GRB_LC_PROC:    enabled
    SWIFT_XRT_SPECTRUM_PROC:  enabled
    SWIFT_XRT_IMAGE_PROC:     enabled
    SWIFT_UVOT_IMAGE_PROC:    enabled
    SWIFT_UVOT_SRCLIST_PROC:  enabled
    SWIFT_FULL_DATA_INIT:     enabled
    SWIFT_FULL_DATA_UPDATE:   enabled
    SWIFT_POINTDIR:           enabled
    SWIFT_BAT_TRANS:          Disabled
    SWIFT_BAT_SLEW_POS:       Disabled


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