{
  "bibcode": "2001GCN..1138....1H",
  "body": "J. Heise (SRON, Utrecht), J.J.M. in 't Zand (Utrecht Univ. and SRON),\nS.R. Kulkarni (Caltech), and E. Costa (CNR, IAS, Rome) report:\n\n\"We have carried out further investigations of SAX J2043.6+7717, the X-ray\nrich transient of 30 October, 2001 discovered by BeppoSAX-WFC (GCN 1118).\nThe flash peaks at 0.26 Crab units (2-28 keV), while activity is detected for\nabout 1400 s (but we note that the observations started about 100 s before\nthe first activity from this source was detected). The spectrum is\ncharacterized by a power law with a photon index of -1.9 +/- 0.1. A black\nbody fit is inconsistent with the data at 99.97% confidence. The 2-28 keV\nfluence is estimated at 9E-7 erg/cm2. For X-ray light curve and spectrum,\nwe refer to http://wfc.sron.nl/flash/\n\nWhat could SAX J2043.6+7717 be?\n\nBy several accounts, SAX J2043.6+7717 does not appear to be a traditional\nGRB. First, the absence of detection of the X-ray transient in the Gamma-Ray\nBurst Monitor on BeppoSAX means that the peak energy of the transient must be\nlower than ~40 keV. In contrast, GRBs are distinguished by peaking in the 50\nto 500 keV range. Second, GRBs with such long duration are rare, e.g. the\nlongest T90 listed in the 4th BATSE catalog (Paciesas et al. 2000, ApJS, 122,\n465) out of 1234 bursts is 674 s (trigger 3458) and in general have strong\npulses. In contrast, SAX J2043.6+7717 lasted more than a thousand seconds long.\n\nThe second possibility, especially given the galactic latitude of\nSAX J2043.6+7717 (b=+20.7 degrees), may argue for this source to be a Galactic\ntransient. However, the X-ray spectrum rules out SAX J2043.6+7717 being a type\nI X-ray burst. This then leaves us with the possibility that SAX J2043.6+7717\nis a Fast X-ray Transient (FXT; e.g., Grindlay 1999, ApJ, 510, 710). However,\nFXTs usually last longer than an hour. More importantly, FXTs have been\nidentified with relatively bright quiescent optical/IR counterparts e.g.\nRS CVns, nearby dMe stars, super flares from pre-main sequence stars and\nblack hole transients. However, as noted in GCN 1137, there is no visible\noptical counterpart to the radio source nor was a bright optical or IR\ntransient (GCN 1127) seen following the detection of the X-ray transient.\n\nWe conclude that most likely SAX J2043.6+7717 is a member of the newly\nrecognized class of X-ray flashes (Heise et al. 2001, in Proc. 'Gamma-Ray\nBurst in the Afterglow Era', Rome, Oct. 17-20, 2000, in press).\n\nGiven that we know little about such events (with the 011030 flash possibly\nbeing the first event localized to arcsecond accuracy; see GCN 1136)\nit is not appropriate to call such non-triggered transients as \"X-ray rich,\ngamma-ray poor\" GRBs (or other equally oxymoronic names). Recognizing that\nastronomical research is largely based on empiricism, we suggest that events\nsuch as the one on 011030 characterized by the following criterion be\ntermed as \"X-ray flashes\" (XRF):  \n  (1) Strong non-thermal emission in the X-ray (2-20 keV band;  this\n      criterion distinguishes them from type I bursts);  \n  (2) Weak in the traditional GRB gamma-ray band, 50-250 keV; this explains\n      why typical XRFs do not trigger gamma-ray burst monitors. \n  (3) Durations less than a few thousand seconds; this differentiates XRFs from\n      the so-called fast X-ray transients which have durations  of several\n      hours (many of which are stars with intense coronal activity and some\n      are binaries containing a compact object such as XTE J1819-254).\n  (4) Display no strong quiescent optical/IR counterpart; this criterion\n      distinguishes XRFs from stars with  strong coronal activity (e.g.\n      strong flares from pre-main sequence stars, dMe stars, RSCVn stars,\n      Be stars etc). \n\nThe accurate position of this X-ray flash presents an excellent opportunity\nto understand this new phenomenon which previously has never been detected\noutside the X/gamma-ray regime. We strongly encourage multi-wavelength\nobservations.\"\n\nThis message may be cited.",
  "circularId": 1138,
  "createdOn": 1005323110000,
  "email": "jeanz@sron.nl",
  "subject": "The X-ray Flash 011030 ('GRB 011030')",
  "submitter": "Jean int Zand at SRON  <jeanz@sron.nl>",
  "eventId": "GRB 011030"
}