{
  "bibcode": "2012GCN.13314....1B",
  "body": "S.D. Barthelmy (GSFC), D.M. Palmer (LANL) and Neil Gehrels (GSFC)\nfor the Swift Team:\n\nPUNCHLINE:\nSwift has started a new campaign structured to detect fainter transients\nin nearby galaxies -- in particular subluminous long GRBs and SGR Superflares.\n(This campaign started ~13:00 UT 14 may 2012.)\n\nINTRO:\nSwift/BAT lowered the triggering threshold for peaks in the image domain\nthat are near locations of known sources in the on-board catalog.\nIt is called the \"interesting source\" threshold.  We are lowering it\nfrom 6.40 sigma (where it has been for years) to 5.80 sigma.\nTo satisfy the interesting source threshold, a peak in the image domain\nmust be greater than 5.80 sigma AND it must be within a 12 arcmin radius\nof one of these sources in the catalog AND the peak intensity minus\nthe current on-board threshold intensity for that source must be\ngreater than 2 sigma.  We have about 600 nearby galaxies (distance < 20 Mpc)\nin the on-board catalog, ~70 tiles covering M31, and ~600 other known\nhard x-ray sources.  For the 670 galaxy entries (nearby and M31),\ntheir thresholds have been set to 0.  For nearly all of the 600\nknown sources, their thresholds are twice their previous trigger level.\nIt is the \"(peak_intensity - threshold_intensity) > 2 sigma\"\nthat inhibits this new Interesting Source trigger from firing\non the many known sources.  We are going after the underluminous\nlong GRBs and SGRs in the nearby galaxies.\n\nDETAILS:\nThe following bullets describe key aspects about the information\nyou will receive for these Interesting Source triggers:\n* The full, normal set of Swift GCN Notices will be produced for these triggers.\nAnd these Notices will have their full set of information content;\nthere is no format or content change for these triggers.\nThese triggers (in the 5.8 - 6.4 sigma range) will still cause BAT to trigger\nand produce the normal set of messages down TDRSS, through GCN, and out to\nthe world, ie BAT_POS, BAT_LC, BAT_SCALEDMAP, FOM, SC_SLEW, XRT_POS_[NACK], etc.\n* If the spacecraft decides it is safe to slew (just like normal),\nthen the spacecraft will slew  and the XRT & UVOT will produce their normal set\nof observations and GCN notices (including updates).  (On rare occaisions,\nthe merit value of the new interesting source will be below the merit value\nof the target currently being observed, and so no slew will occur until\na planned target of lower merit value comes along AND the interesting source\nis still visible.)\n* Since, by definition, these triggers will be spatially coincident with a source\nin the on-board BAT catalog, there will be a COMMENT line in the full-format GCN email\nnotice that says \"this matches source XYZ123 in the on-board catalog;  delta=0.NNN [deg]\".\nAnd a COMMENT line \"this matches source XYZ123 in the ground catalog;  delta=0.NNN [deg]\".\nBecause the matching tolerance (12 arcmin=0.20 deg) is much larger than the typical BAT\nposition error (3 arcmin=0.05 deg), most spurious events will have a delta > 0.07 deg.\nHowever, a large delta can also indicate a true object in the halo of a galaxy\n(35 kpc @ 10 Mpc = 0.2 deg).\n* Because of these catalog matches, GCN will label the trigger as a TRANSIENT\n(not a GRB).  (So there will be the usual two GCN notices go out for these\ncatalog-matching triggers: (a) the BAT_GRB_POS notice, and (b) the BAT_TRANSIENT notice.\n* Other noteworthy pieces of information for these Interesting Sources are:\n(a) these Interesting Source triggers can result from both Rate Triggers (4msec - 32 sec)\nand from Image Triggers (Trigger_Dur > 60 sec).\n(b) the \"IMAGE_SIGNIF:  5.83 [sigma]\" line in the BAT_POS notice\nwill have a value between 5.8 & 6.4.\nThis will also cause a COMMENT line to appear to the effect of \"low image significance...\".\n(c) If the \"TRIGGER_DUR:  0.032 [sec]\" has a small value (probably 4 to ~128 msec),\nthen it is likely an SGR Superflare or a Short GRB in nearby galaxy or noise.\nIf it is a big value, then it is either a long GRB or a hard x-ray transient\nin a nearby galaxy, or noise.\n\nOCCURANCE RATE:\nWe currently estimate that the false positive rate will be ~1 per week.\nIf this turns out to be significantly off, we will adjust the 5.80 value\nhigher or lower accordingly.\nThe rate of reals is somewhat harder to calculate, but is expected\nto be in the 0.5-1 per month range.\n\nRAPID-RESPONSE CIRCULARS:\nThe Swift Team will issue its rapid-response Circular only if the trigger is\na real astrophysical source, but not for noise-caused triggers (this is because\nthe Team is getting smaller and this would increase the work-load).\nThese rapid-response Circulars are typically issued within 30 min of the trigger time.",
  "circularId": 13314,
  "createdOn": 1337615701000,
  "email": "scott@lheamail.gsfc.nasa.gov",
  "subject": "Swift starts a new program to find fainter transients",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>"
}