Gamma-ray Burst 121025A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Notice
  

  TITLE:           GCN/MAXI NOTICE
  NOTICE_DATE:     Thu 25 Oct 12 08:37:10 UT
  NOTICE_TYPE:     MAXI Unknown Source Position 
  EVENT_ID_NUM:    225258354
  EVENT_RA:        248.84d {+16h 35m 22s} (J2000),
                   248.97d {+16h 35m 53s} (current),
                   248.34d {+16h 33m 21s} (1950)
  EVENT_DEC:       +27.97d {+27d 57' 58"} (J2000),
                   +27.94d {+27d 56' 25"} (current),
                   +28.07d {+28d 04' 03"} (1950)
  EVENT_ERROR:     1.0 [deg radius, stat+sys, 90% containment] 
  EVENT_FLUX:      208.0 +- 0.0 [mCrab] 
  EVENT_DATE:      16225 TJD;   299 DOY;   12/10/25 
  EVENT_TIME:      28001.00 SOD {07:46:41.00} UT
  EVENT_TSCALE:    30s
  EVENT_EBAND:     Medium, 4-10 keV
  SUN_POSTN:       210.15d {+14h 00m 36s}  -12.28d {-12d 16' 58"}
  SUN_DIST:         55.05 [deg]  
  MOON_POSTN:      341.17d {+22h 44m 40s}   -2.46d {-02d 27' 29"}
  MOON_DIST:        93.09 [deg]
  MOON_ILLUM:      82 [%]
  GAL_COORDS:       47.63, 40.81 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      240.74, 49.28 [deg] ecliptic lon,lat of the burst (or transient)
  COMMENTS:        MAXI Unknown Source Position. GRB or unknown X-ray Transient.
  

• GCN Circular #13895
  M. Asada, H. Negoro (Nihon U.), M. Serino (RIKEN), M. Morii (Tokyo Tech), Nakahira (JAXA), K. Yamaoka (Waseda U.), S. Ueno, H. Tomida, M. Ishikawa (JAXA), T. Mihara, M. Sugizaki, T. Yamamoto, J. Sugimoto, M. Matsuoka (RIKEN), N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech), A. Yoshida (AGU), H. Tsunemi, M. Kimura (Osaka U.), M. Nakajima (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.) M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.) report on behalf of the MAXI team:
  At 2012-10-25T07:46:30 UT, the MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source. The transient emission lasted at least 20 seconds within the 44 second long triangular transit response of MAXI/GSC. We identify this event as GRB 121025A.
  Assuming that the source flux was constant over the transit, we obtain the source position at
  (R.A., Dec) = (248.75 deg, +27.73 deg) = (16 35 00, +27 44 05)(J2000)
  with a 90% C.L. statistical error of 0.27 deg and an additional systematic +uncertainty of 0.1 deg (90% containment radius). The 4-10 keV flux was 129 (+26/-22) mCrab.
  Within the scan transit, the variability of the source was marginally detected +with a chance probability of 0.084 for 4 - 10 keV band.
  There was no significant excess flux in the previous transit at 06:13 UT and in the next transit at 09:18 UT with an upper limit of 20 mCrab for each.
  Follow-up observations are encouraged.
• GCN Circular #13909
  K.L. Page, R.L.C. Starling and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
  Swift performed a Target of Opportunity observation of the MAXI-detected GRB 121025A (Asada et al., GCN Circ. 13895), starting 26.1 ks after the trigger. A series of four tiled pointings was performed, in order to cover the MAXI error circle. Within these fields, one > 3 sigma uncatalogued source was detected, at RA, Dec = 248.38182, 27.67189, which is equivalent to:

  RA(J2000)  = 16h 33m 31.64s
  Dec(J2000) = 27d 40' 18.8"
  

  with an uncertainty of 3.8 arcsec (radius, 90% containment). This source has a mean count rate of 0.022 +/- 0.004 count s^-1. A spectrum formed from the 1.8 ks of data can be fitted with an absorbed power-law with a photon spectral index of 2.36 (+0.57,-0.56). The best-fitting absorption column is consistent with the Galactic value of 3.8 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1.
  It is not possible to determine whether this source is fading at this time and, therefore, whether it is the X-ray afterglow.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #13941
  K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team:
  Swift performed a follow-up observation of the possible X-ray afterglow of MAXI-detected GRB 121025A (Asada et al., GCN Circ. 13895) announced in GCN Circ. 13909 (Page, Starling & Evans). This second observation took place on 2012-10-31, 5.8 days after the burst. The source has now faded by at least an order of magnitude, with an upper limit on the count rate of 0.002 count s^-1 (corresponding to an observed flux of 8.1 x 10^-14 erg cm^-2 s^-1). This source is therefore confirmed as the X-ray afterglow of GRB 121025A.
  This circular is an official product of the Swift-XRT team.
• GCN Report 399.1
  GCN_Report 399.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_399_1.pdf by K.L. Page at U. Leicester titled: "Swift Observations of GRB 121025A"