{
  "bibcode": "2009GCN..9279....1Z",
  "body": "Bin-Bin Zhang and Bing Zhang (University of Nevada Las Vegas) report:\n\nGRB 090423 is a second, high-z, intrinsically short GRB after GRB \n080913. Following  the similar procedure discussed in Zhang, B et al \n2009, http://arxiv.org/abs/0902.2419 ,  we have simulated a pseudo GRB \nby shifting GRB 090423 to z=1. The following three factors, i.e, \nspecific flux (f_\\nu) amplification due to a smaller luminosity \ndistance, blue-shift of spectrum, and temporal compression of the \nlightcurve (de-dilation), have been considered. We notice that there is \nan early X-ray flare in GRB 090423 (again similar to GRB 080913), which \nshould be harder and observable by BAT if it were at z=1. Following the \nsimilar procedure described in Zhang et al. (2009), we manipulate the \nXRT data of GRB 090423 to simulate the BAT band extended emission of the \npseudo  burst. The constructed BAT band lightcurve of the pseudo GRB at \nz=1 is shown in the  figure at \nhttp://grb.physics.unlv.edu/gcns/090423/pseudo.jpg . This psuedo burst \nappears as a short duration GRB with extended emission.\n\nOn the other hand, both high-z GRBs have high isotropic luminosity and \nenergy, which make them following the Amati/Yonetoku correlation defined \nby GRBs that are of the  massive star origin (Type II or long \npopulation). Although it is possible to have NS-NS and NS-BH mergers \n(Type I or short population) at such a high-z (Belczynski et al. 2009),  \nthe difficulty is to have two such energetic merger events at high-z. \nThe Type I model  has difficulty to accommodate both low-z, low-L Type I \nevents and these events in terms of luminosity function (Zhang et al. \n2009). Based on the multiple criteria analysis, we cannot address the \nphysical category of GRB 090423 and GRB 080913 using more definite \ncriteria (e.g. SN association, host galaxy property, etc). On the other \nhand, one can use less definite criteria (Amati/Yonetoku relation and \nenergetics)  to judge that both bursts are Type II (massive star \ncollapse) candidates. A judging flow chart using Fig. 8 of Zhang et al. \n(2009) is posted at  \nhttp://grb.physics.unlv.edu/gcns/090423/flowchart.jpeg .  We also \nnoticed the interesting discussions by Krimm et al. (GCN 9241) and  Nava \net al. (GCN 9235), which are broadly consistent with our conclusion here.\n\nFinally, using the three samples (Type II Gold,  Type I Gold, and Other \nShort/Hard)  defined in Zhang et al. (2009), we plot the intrinsic \nduration (T_{90}/(1+z)) as a function of z (see \nhttp://grb.physics.unlv.edu/gcns/090423/t90z.png ). It is interesting to \nnote that the two high-z bursts are intrinsically shorter than the  \nmajority of Type II GRBs. If these observations persist in the future, \nit may suggest  an intrinsic trend of short duration for Type II GRBs at \nhigh-z.\n\nThis message can be cited.",
  "circularId": 9279,
  "createdOn": 1240963801000,
  "email": "zbb@physics.unlv.edu",
  "subject": "GRB 090423:  pseudo burst at z=1 and its relation to GRB 080913",
  "submitter": "Binbin Zhang at UNLV  <zbb@physics.unlv.edu>",
  "eventId": "GRB 090423"
}