[vsnet-grb-info 16383] GRB 150402A: results of Swift observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17664
SUBJECT: GRB 150402A: results of Swift observations
DATE:    15/04/03 21:38:20 GMT
FROM:    Hans Krimm at NASA-GSFC  <hans.a.krimm at nasa.gov>

H. A. Krimm (CRESST/GSFC/USRA), M. De Pasquale (INAF-IASFPA),
N. P. M. Kuin (UCL-MSSL), J. R. Cummings (CPI), J. Kennea (PSU),
A. Y. Lien (GSFC/UMBC),  K. Page (U. Leicester)
report on behalf of the Swift team

Further observations of GRB 150402A (Cummings and Palmer, GCN 17661) were 
carried out by the Swift observatory (Evans, GCN 17662).  We collected 4.8 ks of 
Photon Counting (PC) mode data between T0+108.4 ks and T0+121.6 ks, where T0 is 
the time of the BAT trigger.  One uncatalogued X-ray source has been detected 
inside or close to the Swift/BAT error region, it is below the RASS limit and 
shows no definitive signs of fading. Therefore, at the present time we cannot 
confirm this as the afterglow. Details of this source are given below:

   RA (J2000.0):  173.5883  =  11h 34m 21.19s
   Dec (J2000.0): +40.9398  =  +40 56′ 23.3′′
   Error: 4.6 arcsec (radius, 90% conf.)
   Count-rate: (3.5 ± 1.1)e-3 ct s^-1
   Flux: (1.7 ± 0.5)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

One catalogued source was also detected too far from the BAT GRB position
to be a likely afterglow candidate.
     The UVOT observed in the uvw1 filter.  Close to the XRT position a star is 
seen in the DSS, which shows no evidence of an additional fading source 
contributing to the emission. The GRB upper limit is uvw1 > 18.63.
     Revised analysis of the BAT data yields a refined position of

   RA (J2000):  173.604 = 11h 34m 25.1s
   Dec (J2000): +40.988 = 40d 59' 18"

with an estimated uncertainty radius of 3.0 arcmin (90% containment). 
Mask-weighted data is available from T-2.0 to T+8.0 sec, which does not cover 
the entire burst, but we estimate T90 from the un-weighted data to be 14.4 +- 
1.6 sec (estimated error including systematics).  The available light curve 
shows two peaks, each about 4 seconds long. The time-averaged spectrum from 
T+0.0 to T+8.1 sec is best fit by a simple power-law model.  The power law index 
of the time-averaged spectrum is 2.29 +- 0.47.  The fluence in the 15-150 keV 
band is 1.5 +- 0.4 x 10^-7 erg/cm2. All the quoted errors are at the 90% 
confidence level.
     No further observations of this source are currently planned.