GCN/Fermi-GBM Subthreshold Notices

This page gives some of the technical details of the content
of the Fermi-GBM Subthreshold transients notices.


The Notices contain the date, time, transient number,
the RA,Dec of the largest location probability, and
the uncertainty of that location.
The measure of the duration of the transient which is the delta_time
for the interval for which the search algorithm found the
highest statistical significance.

A "type_class" flag indicating if the event is "short" or "long".
A "spectral class" flag indicating if the event spectrum is "hard" or "soft".
This field is only really defined for events with sufficient signal and otherwise has
the default value of "1" hard. Events of reliability 2 and some events of
higher reliability have insufficient signal for the evaluation. A soft flag
indicates that the transient is most likely not a GRB.
A "reliability" value (running from 1 to 10) indicating the likeliness
that this transient is astrophysical.

Over the 3.2 months of April to July 2017, there were 144 Notices produced, of which:
All 144 had "type_class" of "short", and "spectral class" of "hard". This is because
the analysis pipeline producing the "longs" is not yet ready for release
so all 144 "shorts" have come from the "short" pipeline. The "long" pipeline
is expected to be ready in a few months.
And 80% had reliability "2" (low), 10% had "5" (medium), and 10% were "8" (high reliability).

Included are URLs for (a) a Healpix FITS file of the location probability on the sky,
(b) a PNG file showing that map, and (c) a URL the lightcurve of the transient.
(The URLs point to the GCN website where they can be downloaded via wget/curl/etc.)

The expected rate will be about 70 per month. (During periods
of Cyg X-1 activity, the rate will be ~270/month.)

Given that the ground processing of the batched downlinked data,
the time delays for this notice type will range from 0.5 to 6 hours.

The location uncertainties are in the 10-40 deg range (radius, stat+sys, 68% containment).
This uncertainty represents the quality of the online position reconstruction, and
it is computed in real time for each transient.

The GCN/FERMI_GBM_SUBTHRESHOLD Notices are archived
in the Table of GBM SUBTHRESHOLD Notices.

Can be found at the GCN/Fermi page.

Here is an example of a full-format email Fermi-GBM_SUBTHRESHOLD:

///////////////////////// Fermi-GBM e-mail format //////////////////////////////
NOTICE_DATE:     Tue 04 Jul 17 14:45:26 UT
NOTICE_TYPE:     Fermi-GBM SubThreshold
TRANS_NUM:       520865109
FULL_ID_NUM:     520865109.040000
TRANS_RA:        304.080d {+20h 16m 19s} (J2000),
                 304.306d {+20h 17m 13s} (current),
                 303.435d {+20h 13m 44s} (1950)
TRANS_DEC:        -1.030d {-01d 01' 47"} (J2000),
                  -0.975d {-00d 58' 30"} (current),
                  -1.185d {-01d 11' 04"} (1950)
TRANS_ERROR:     25.64 [deg radius, stat+sys, 68% containment]
TRANS_DURATION:  0.703 [sec]
TRANS_DATE:      17938 TJD;   185 DOY;   17/07/04
TRANS_TIME:      45904.04 SOD {12:45:04.04} UT
EARTH_ANGLE:     124.50 [deg]
SPECTRAL_CLASS:  1    (0=soft, 1=hard)
TYPE_CLASS:      0    (0=short, 1=long)
RELIABILITY:     2    (2=low, 5=medium, 8=high)
HEALPIX_URL:     https://gcn.gsfc.nasa.gov/notices_gbm_sub/gbm_subthresh_520865109.040000_healpix.fits
MAP_URL:         https://gcn.gsfc.nasa.gov/notices_gbm_sub/gbm_subthresh_520865109.040000_map.png
LC_URL:          https://gcn.gsfc.nasa.gov/notices_gbm_sub/gbm_subthresh_520865109.040000_lc.pdf
SUN_POSTN:       103.92d {+06h 55m 42s}  +22.82d {+22d 49' 09"}
SUN_DIST:        150.52 [deg]   Sun_angle= 10.6 [hr] (West of Sun)
MOON_POSTN:      231.84d {+15h 27m 21s}  -13.51d {-13d 30' 33"}
MOON_DIST:        72.73 [deg]
MOON_ILLUM:      82 [%]
GAL_COORDS:       42.02,-19.29 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      306.15, 18.24 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Subthreshold.
COMMENTS:        This Notice was ground-generated -- not flight-generated.

The socket packets contents can be found at sock_pkt_def_doc.

Return to GCN/TAN homepage.
This file was last modified on 17-Jul-17.