GCN Circular 7145

Holland, S. T. (CRESST/USRA/GSFC), de Pasquale, M. (UCL/MSSL), and
Markwardt, C.~B. (CRESST/GSFC/UMD) report on behalf of the Swift/UVOT
team:

      The Swift/UVOT observed the field of the short-hard GRB 070429B
starting 230 s after the BAT trigger (Markwardt, et al., GCN
Circ. 6358
Not found
 
 
).  We have re-examined this data in light of the redshift
for the Antonelli, et al. (GCN Circ. 6372
Not found
 
 
) source "A" reported by
Perley, et al. (GCN Circ. 7140
Not found
 
 
).  We find weak evidence in the UVOT
data for a fading source located inside the refined XRT error circle
(Beardmore, et al., GCN Circ. 6360
Not found
 
 
) at

       RA =  21:52:03.68 (J2000)
      Dec = -38:49:43.6  (J2000)

with an uncertainty of 0.6 arcsec (90% confidence).  This is 0.6
arcsec from the ground-based position of source "A".  For a redshift
of z = 0.904, and (H_0,Omega_M,Omega_Lambda) = (70,0.3,0.7) this
corresponds to 4.7 proper kpc.  This possible source is detected with
a 3.9-sigma significance in a summed image (summed over all seven
filters) between 591 and 2661 s after the BAT trigger.  It is not
detected in subsequent all-filter summed images.  This possible UVOT
source has the following magnitudes and upper limits.  All magnitudes
are on the UVOT system described in Poole, et al. (2007, MNRAS, in
press).

Filter    T_start   T_stop   Exposure    Mag   Err  Significance
    v         2002     2661      94       19.3  0.4      2.5
              6805     7004     393      >20.1  3-sigma upper limit
    b         1460     2598     156       20.5  0.5      2.2
            34,978   35,884     885      >22.0  3-sigma upper limit
    u          403   42,285    2260      >21.8  3-sigma upper limit
   uvw1        379   41,789    3075      >22.4  3-sigma upper limit
   uvm2        354   20,226    2192      >22.0  3-sigma upper limit
   uvw2        456   30,222    2378      >22.4  3-sigma upper limit
  white        591      977     117       21.6  0.5      2.2
              6395     8027     393      >22.1  3-sigma upper limit

      The observations where the suspected source is weakly detected
are all at less than one hour after the BAT trigger.  The earliest
reported ground-based detection of source "A" is Cucchiara, et
al. (GCN Circ. 6368
Not found
 
 
) who find r = 23.18 +/- 0.15 at approximately 4
hours.  Perley, et al. (GCN Circ. 7140
Not found
 
 
) find R = 23.24 +/- 0.05 at
approximately 7 months, which implies that the source did not fade,
and conclude that the "A" source is the host galaxy.  They also find g
= 24.29 +/- 0.14 at this time.  If we assume that the SDSS g band is
approximately similar to the UVOT v band then the expected v magnitude
of the host at 2332 s (assuming a constant magnitude) is v ~= 24.3,
which is 5 mag fainter than the UVOT detection at that time.  This
corresponds to a mean decay index of alpha ~= -2.5.

      The observed decay power-law indices from the UVOT data are
alpha_v <= -0.6 +/- 0.3, alpha_b <= -0.5 +/- 0.2, and alpha_white <=
-0.2 +/- 0.2.  The shallow decay slope in the white filter, and the
faintness of the White detection at early time (t_mid = 784 s)
relative to the b and v detections at later times (t_mid = 2332 (v),
2029 (b)) suggest that the afterglow candidate may have increased in
luminosity at some point between approximately 784 and 2029 s.

      We do not detect any source at the position of source "B"
(Antonelli, et al., GCN Circ. 6372
Not found
 
 
) down to the following limiting
magnitudes.

Filter    T_start   T_stop   Exposure    3-Sigma Upper Limit
    v         230    31,793     2011        >21.5
    b         427    35,115     1463        >22.3
    u         403    42,285     2260        >21.9
  uvw1        379    41,789     3075        >22.4
  uvm2        354    20,226     2192        >22.0
  uvw2        456    30,222     2378        >22.4
  white       247    36,269     1088        >22.7

      The values quoted above are not corrected for the expected
Galactic extinction corresponding to a reddening of E_{B-V} = 0.03 mag
(Schlegel, et al. 1998).