Gamma-ray Burst 970616

A very bright Gamma-Ray Burst (among the brightest 2%) was detected with BATSE on June 16.757 UT. The burst was multipeaked, with a total duration of about 200 s. Scanning observations with the PCA onboard RXTE 4.0 hr after the burst revealed a source at R.A. = 1h18m.9 +/- 0m.7 (90-percent statistical confidence), Decl. = -5 30' +/- 18' (equinox 2000.0) with a countrate of 4.5 +/- 1.6 counts/s or 1.1 x 10E-11 erg sE-1 cmE-2 in the band 2-10 keV. An ASCA observation during June 20.15-21.44 UT (50 ksec) revealed 4 X-ray sources, two of which are outside the IPN annulus. Though one of these sources is variable, the identification with the GRB afterglow is unclear. Two optical variables have been found, none of which coincides with one of the ASCA sources. A ROSAT observation was performed between June 23-25, 1997 for a total of 22 ksec.

Previous IAU Circulars

• IAUC 6683 Discovery with BATSE; location with RXTE and IPN
  
• IAUC 6687 revised IPN arc; 4 ASCA sources; optical variable
  
• IAUC 6688 no K band variables at K'<17
  
• IAUC 6690 another optical variable
  
• IAUC 6691 photometry of the first optical variable suggest late-type star
  
• IAUC 6696 optical spectrum identifies the first optical as M8.5V-M9V dwarf; no H-alpha
  
• IAUC 6697 no variables down to R = 20 between June 19-25
  
• IAUC 6722 ROSAT fluxes imply fading of 2 ASCA sources
  
• IAUC 6723 4 optical objects at ROSAT source #2, none is variable; variable object of IAUC 6687 withdrawn

• Two of Udalski's images (IAUC 6690):
  

  June 22, 1997

  June 25, 1997

• Some of the McDonald images (Feng Ma)
  The following pictures were taken on June 19.4, 20.4, 21.4 and 23.4 UT. They are centered on 1h18m55.7s, -5d27'23", with size approximately 11.5' x 11.5'. South is up and East is right.
  
  The following are the points of interests, taken on June 19.4, 20.4, 21.4. The object at the upper left corner was reported by Udalski (IAUC 6690) to have an IR transient close to it. The green box is the error box of the X-ray variable reported by Murakami et al. (IAUC 6687), who observed something to fade by a factor of two during June 20.1--June 21.4. Galama's optical variable was close to the bright object at the upper right corner.
  
  The following is the finding chart of the whole PFC field. South is up and East is right. This is a combination of totally 24 frames from 6 nights, with a limiting magnitude of R~21+/-0.5.
  
  
  
• Image of the ROSAT HRI observation with error boxes and various other sources marked: red square = RXTE error box; blue lines = Ulysses/BATSE triangulation arc; red circles = X-ray sources detected in the HRI observation; green circles = X-ray sources detected in the ASCA observation; yellow dots = the two variable optical objects reported.
  
• Keck LRIS image with error circle of ROSAT source #6 = ASCA source #1 overplotted (Groot et al., IAUC 6723).