GRB 100526B

M. H. Siegel (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), D. Grupe (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
D. M. Palmer (LANL), T. A. Pritchard (PSU), P. Romano (INAF-IASFPA),
T. Sakamoto (NASA/UMBC), M. A. Stark (PSU), E. Troja (NASA/GSFC/ORAU)
and L. Vetere (PSU) report on behalf of the Swift Team:

At 19:00:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100526B (trigger=423184).  The slew was delayed due to
an observing constraint.  The BAT on-board calculated location is 
RA, Dec 0.700, -37.902 which is 
   RA(J2000)  =  00h 02m 48s
   Dec(J2000) = -37d 54' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a few weak peaks
with a duration of about ~30 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

Due to an observing constraint, Swift will not slew until 
T0+54 minutes. There will be no XRT or UVOT data until
this time. 

Burst Advocate for this burst is M. H. Siegel (siegel AT astro.psu.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

J. A. Kennea, L. Vetere and M. Siegel (PSU) report on behalf of the Swift 
team:

The XRT began observing the field of GRB 100526B at 19:55:21.1 UT, 3282.6 
seconds after the BAT trigger. Using promptly downlinked data we find an 
uncatalogued X-ray source located at RA, Dec 0.73552, -37.91195 which is 
equivalent to:
   RA(J2000)  = 00h 02m 56.52s
   Dec(J2000) = -37d 54' 43.0"
with an uncertainty of 5.6 arcseconds (radius, 90% containment). This 
location is 107 arcseconds from the BAT onboard position, within the BAT 
error circle. This position may be improved as more data are received; the 
latest position is available at http://www.swift.ac.uk/sper.  We cannot 
determine whether the source is fading at the present time.

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.12e+20 cm^-2 (Kalberla et al. 2005).

UVOT took a finding chart exposure of 150 seconds with the White filter 
starting 3288 seconds after the BAT trigger. No credible afterglow 
candidate has been found in the initial data products. The 2.7'x2.7' 
sub-image covers none of the XRT error circle. The 8'x8' region for the 
list of sources generated on-board covers 100% of the XRT error circle. 
The list of sources is typically complete to about 18 mag. No correction 
has been made for the expected extinction corresponding to E(B-V) of 0.01.

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. H. Siegel (PSU),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 100526B (trigger #423184)
(Siegel, et al., GCN Circ. 10799
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 ).  The BAT ground-calculated position is
RA, Dec = 0.777, -37.913 deg, which is 
   RA(J2000)  =  00h 03m 06.5s 
   Dec(J2000) = -37d 54' 48.4" 
with an uncertainty of 3.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 95%.
 
The mask-weighted light curve shows a broad weak peak starting at ~T-25 sec,
peaking around T+10 sec, and ending around t+50 sec.  The burst location
went out of the BAT FOV at T+240 sec when Swift was forced to slew due 
to an observing constraint.  T90 (15-350 keV) is 64.0 +- 22.6 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-28.4 to T+35.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.47 +- 0.28.  The fluence in the 15-150 keV band is 4.7 +- 0.9 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+11.15 sec in the 15-150 keV band
is 0.1 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/423184/BA/

T. A. Pritchard (PSU) and Siegel (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100526B
3288 s after the BAT trigger (Siegel et al., GCN Circ. 10799
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 ).
No optical afterglow consistent with the XRT position
(Kennea et al., GCN Circ. 10802
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 ) is detected in the initial UVOT
exposures. Preliminary 3-sigma upper limits using the UVOT
photometric system (Poole et al. 2008, MNRAS, 383, 627) for the
first finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
--------------------------------------------------------------
white (FC)        3288         3438          147         >21.3
white             3288         4669          344         >21.7
v                 3445         5080          393         >20.2
b                 4265         5880          372         >20.7
u                 4060         5695          393         >20.5
w1                3855         5491          393         >20.7
m2                3650         3849          197         >19.9
w2                4675         4875          197         >20.3

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).

L. Vetere and M. H. Siegel (PSU) report on behalf of the Swift-XRT team:

We have now collected 5.7 ks of Swift-XRT Photon Counting mode data on  
the GRB 100526B (Siegel et al. GCN Circ. 10799
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 ), from 3289 s to 34.8 ks 
after the BAT trigger.

The source reported by Kennea et al. (GCN Circ. 10802
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 ) is now only
marginally detected, with a count rate of 1.5x10^-3 count s^-1
(corresponding to an observed flux of 7.1x10^-14 erg cm^-2 s^-1).

With this fading, we can confirm that this source is the X-ray
afterglow of GRB 100526B.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00423184.

This circular is an official product of the Swift-XRT team.

GRB 100526B: GROND Upper limits

P. Afonso (MPE), A. Nicuesa (Tautenburg Obs.), R. Filgas and J. Greiner
(all MPE Garching), report on behalf of the GROND team:

We observed the field of GRB 100526B (Swift trigger #423184 ; Siegel et
al., GCN #10799
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla
Observatory (Chile).

Observations started at 09:37 UT on March 27, 14.6 hours after the GRB
trigger, and were performed under strong wind.

We do not detect a source within the Swift-XRT error circle reported by
Kennea et al. (GCN #10802
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 ) in any of the GROND filters.
Stacked images with a total integration time of 28 minutes in JHK and 32
minutes in g'r'i'z' yield the following preliminary 3-sigma upper limits:


g' > 24.1
r' > 24.2
i' > 23.9
z' > 23.8
J  > 22.7
H  > 22.2
K  > 21.3


All magnitudes given above are in the AB system and are based on the GROND
zeropoints and 2MASS field stars. No correction has been applied for the
Galactic foreground extinction corresponding to a reddening of E_(B-V)=
0.012 in the direction of the burst (Schlegel et al. 1998).