{
  "bibcode": "2011GCN.11843....1C",
  "body": "S. Campana (INAF-OAB), S. Covino (INAF-OAB), G. Tagliaferri (INAF-OAB),\nV. D'Elia (ASI-ASDC), L. Stella (INAF-OAR), R. Salvaterra (Insubria \nUniversity):\n\nGRB 110328A/ Swift J164449.3+573451 is characterized by a very fast\nvariability.  A doubling time less than 500 s can be easily recovered\nfrom the Swift X-ray data. Assuming that the entire source is varying,\nthis poses a limit on the mass of the varying object of M1<5x10^5 solar\nmasses, based on the arguments of Cavallo & Rees (1978) and assuming\na conversion efficiency of ~10%, typical of accretion onto a black hole.\n\nOn the other side if this source is really at z=0.354 (Levan et al. GCN\n11833; Thoene et al. GCN 11834), as confirmed by the radio position\nof the counterpart (Zauderer et al. GCN 11836), its peak flux of ~10^-8\nerg/cm2/s (0.3-10 keV based on the Swift Burst analyser, Evans et al.\n2010, A&A 509 A102) implies a luminosity of ~5x10^48 erg/s.\nIn order not to overcome the Eddington limit a mass of M2>3x10^10\nsolar masses is needed.\n\nThe two mass estimates strongly disagree providing clear evidence for\na highly beamed emission.",
  "circularId": 11843,
  "createdOn": 1301505782000,
  "email": "sergio.campana@brera.inaf.it",
  "subject": "GRB 110328A / Swift J164449.3+573451: beamed emission",
  "submitter": "Sergio Campana at INAF-OAB  <sergio.campana@brera.inaf.it>",
  "eventId": "GRB 110328A"
}