GCN Circular 13405

T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), Gehrels (GSFC),
E. Sonbaas (GSFC)   (for the Swift-BAT team);
O. Littlejohns (U. Leicester)  (for the Swift-XRT team);
S. R. Oates (MSSL-UCL) (of the Swift-UVOT team):
 
Using the data set from T-60 to T+243 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120630A (trigger #525451).
There was no initial set of GCN Notices nor a rapid-response circular
because of the power outage at GSFC when this burst occurred.
Swift slewed immediately to the burst location.

The BAT ground-calculated position is RA, Dec = 352.300, 42.495 deg, which is 
   RA(J2000)  =  23h 29m 12.0s 
   Dec(J2000) = +42d 29' 41.5" 
with an uncertainty of 2.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 65%.
 
The mask-weighted light curve shows a single spike starting at ~T-0.05 sec
and ending at ~T+0.65 sec.  T90 (15-350 keV) is 0.6 +- 0.2 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-0.1 to T+0.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.04 +- 0.43.  The fluence in the 15-150 keV band is 6.1 +- 1.4 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.25 sec in the 15-150 keV band
is 0.7 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence level. 

Given the short duration and the hard spectrum of this burst,
it is very likely a short GRB.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/525451/BA/ .


We have analysed 1.4 ks of XRT data for GRB 120630A from 97 s to 1.5 ks
after the BAT trigger.  The data are entirely in Photon Counting (PC) mode.
The refined XRT position is RA, Dec = 352.29481, 42.55483 which is equivalent to:
   RA (J2000): 23 29 10.75
   Dec(J2000): +42 33 17.4
with an uncertainty of 3.9 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay index
of alpha=1.7 (+/-0.5).

A spectrum formed from the PC mode data can be fitted with an absorbed power-law
with a photon spectral index of 1.7 (+/-0.4).  The best-fitting absorption column
is consistent with the Galactic value of 8.8 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 4.2 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
   Total column:        0 (+2.2, -0) x 10^21 cm^-2
   Galactic foreground: 8.8 x 10^20 cm^-2
   Excess significance: <1.6 sigma
   Photon index:        1.7 (+/-0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00525451 .


The Swift/UVOT began settled observations of the field of GRB 120630A
150 s after the BAT trigger (trigger #525451).  No optical afterglow
consistent with the refined XRT position nor with the candidate optical
afterglow (Xu et al., GCN Circ. 13403
Not found
 
 
) is detected in the initial UVOT
exposures.  Preliminary 3-sigma upper limits using the UVOT photometric
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
v                  457          1409         117         >19.0
b                  406          1508         156         >20.0
u_FC               150          400          246         >20.2
u                  150          1032         393         >20.3
uvw1               506          1458         117         >19.3
uvm2               481          1434          97         >19.0
uvw2               432          1530         131         >19.5

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.106 in the direction of the burst
(Schlegel et al. 1998).