GRB 100606A

S. R. Oates (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), S. Campana (INAF-OAB),
P. A. Curran (UCL-MSSL), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), J. M. Gelbord (PSU),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), O. M. Littlejohns (U Leicester),
C. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), A. Rowlinson (U Leicester),
T. Sakamoto (NASA/UMBC), B. Sbarufatti (INAF-OAB/IASFPA),
M. H. Siegel (PSU), R. L. C. Starling (U Leicester),
E. Troja (NASA/GSFC/ORAU), T. N. Ukwatta (GSFC/GWU) and
L. Vetere (PSU) report on behalf of the Swift Team:

At 19:12:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100606A (trigger=424031).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA, Dec 350.603, -66.236 which is 
   RA(J2000) = 23h 22m 25s
   Dec(J2000) = -66d 14' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of at least 30 sec.  The peak count rate
was ~6000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 19:14:18.2 UT, 96.4 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 350.6246, -66.2434 which is equivalent to:
   RA(J2000)  = 23h 22m 29.90s
   Dec(J2000) = -66d 14' 36.2"
with an uncertainty of 5.2 arcseconds (radius, 90% containment). This
location is 41 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 1.70e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 106 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 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
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
0.03. 

Burst Advocate for this burst is S. R. Oates (sro AT mssl.ucl.ac.uk). 
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.)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using 1374.0 ks of promptly downlinked XRT event data for GRB 100606A,
we find an enhanced XRT position of the afterglow: RA, Dec: 350.6265,
-66.2411 which is equivalent to:
   RA (J2000)  = 23 22 30.37
   Dec (J2000) = -66 14 28.1
with an uncertainty of 2.0 arc sec (radius, 90% confidence). Analysis
of the promptly available data is online at
http://www.swift.ac.uk/sper/424031.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1354 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 100606A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 350.62704, -66.24127 which is equivalent
to:

RA (J2000): 23h 22m 30.49s
Dec (J2000): -66d 14' 28.6"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), C. B. Markwardt (GSFC/UMD),
S. R. Oates (UCL-MSSL), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 100606A (trigger #424031)
(Oates, et al., GCN Circ. 10824
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 350.617, -66.234 deg, which is 
   RA(J2000)  =  23h 22m 28.1s 
   Dec(J2000) = -66d 14' 03.3" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 25%.
 
The mask-weighted light curve shows an initial FRED peak starting at ~T-0.2 sec,
peaking at ~T+0.5 sec.  Then there are two peaks at ~T+12 and ~T+20 sec
followed by a roughly exponential decay out to ~T+180 sec.  Another, weak peak
occurs at ~T+200 followed by some very weak emission out to ~T+370 sec,
and possibly out to ~T+500 sec.  T90 (15-350 keV) is 480 +- 150 sec
(estimated error including systematics).
 
The time-averaged spectrum from T+0.3 to T+672.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.35 +- 0.10.  The fluence in the 15-150 keV band is 6.4 +- 0.4 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+7.82 sec in the 15-150 keV band
is 1.6 +- 0.4 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/424031/BA/

O. Littlejohns, P. A. Evans, J. P. Osborne (U. Leicester) and S. R.
Oates (UCL-MSSL) report on behalf of the Swift-XRT team:

We have analysed 4.9 ks of XRT data for GRB 100606A (Oates et al. GCN
Circ. 10824
Loading...
 
 ), from 86 s to 19.1 ks after the BAT trigger. The data
comprise 313 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Evans et al.
(GCN. Circ 10825).

The light curve can be modelled with a series of power-law decays. The
light curve initially shows some flaring with an underlying decay index
of 1.69 (+0.14, -0.10) from T+138 s to T+455 s. The light curve then
breaks at T+455 s to a decay with alpha=0.88 (+0.15, -0.26), flares may
also be present in this interval, before a final break at T+1641 s after
which the decay index is 2.09 (+1.28, -0.16).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.61 (+/-0.08). The
best-fitting absorption column is 2.06 (+0.29, -0.28) x 10^21 cm^-2, in
excess of the Galactic value of 2.4 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.91 (+0.15, -0.14)
and a best-fitting absorption column of 2.2 (+0.5, -0.4) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 4.4 x 10^-11 (6.2 x 10^-11) erg cm^-2
count^-1.

If the light curve continues to decay with a power-law decay index of
2.09, the count rate at T+24 hours will be 2.9 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-14 (1.8 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00424031.

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

S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 100606A 107s after the BAT trigger (Oates et al., GCN Circ. 10824
Loading...
 
 ).
We do not detect any source at the enhanced Swift XRT position
(Evans et al. GCN Circ. 10827
Loading...
 
 ).

The 3-sigma upper limits for the finding chart exposures (FC)
and summed images are:

Filter   T_start   T_stop   Exp(s)  Mag (3-sigma upper limit)
-------------------------------------------------------------
white (FC) 107      256      147        > 21.08
u     (FC) 319      568      246        > 20.35
white      598      6542     461        > 21.70
v          648      6952     333        > 19.86
b          574      6337     312        > 20.76
u     	   722      7567     487        > 20.47
uvw1   	   698      7362     490        > 20.54
uvm2  	   673      7157     274        > 19.93
uvw2       1030	    6748     255        > 20.27
-------------------------------------------------------------

The quoted upper limits have not been corrected for the expected
Galactic extinction due to the reddening of E_(B-V) = 0.03 mag
along the line of sight. All photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383, 627).

A.J. Levan (U. Warwick) and N.R. Tanvir (U. Leicester) report for
a larger collaboration:

We imaged the location of GRB 100606A (Oates et al. GCN 10824
Loading...
 
 )
using GMOS-S on Gemini South. Observations began at 06:02 UT on June 7th,
approximately 11 hours after the burst, and were obtained in the r, i and 
z-bands, with a total of 900s exposure in each band. Within the refined 
XRT error circle (Evans et al. GCN 10827
Loading...
 
 ) we find a faint, and apparently
extended source, with r~25 (using archival zero point), which is barely 
visible in our i and z-band observations, suggesting a relatively blue 
colour. Although it is plausible that this object contains some 
contribution from a faint afterglow, the extended source is apparently 
dominating, and we suggest that this is the host of GRB 100606A.

The faint afterglow (r>25), combined with the apparently high X-ray
column density (Littlejohns et al. GCN 10829
Loading...
 
 ) is consistent with
GRB 100606A as a highly extinguished burst.

We thank the staff of Gemini South, especially Peter Pessev, for
the help in acquiring these data.

S. Golenetskii, R. Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long GRB 100606A (Swift-BAT trigger=424031;
Oates et al., GCN 10824
Loading...
 
 ; Krimm et al., GCN 10828
Loading...
 
 )
triggered Konus-Wind at T0=69163.712s UT (19:12:43.712)

The total duration of the burst is ~100 s.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB100606_T69163/

As observed by Konus-Wind the burst
had a fluence of 3.9(+/-0.5)x10-5 erg/cm2,
and a 256-ms peak flux measured from T0+0.256s
of 2.5(+/-0.25)x10-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+82.176 s) is best fit
in the 20 keV - 2 MeV range by a power law
with exponential cutoff model, for which
alpha = -1.05(+/-0.14),
and Ep = 945(-266, +551) keV;
chi2 = 49/58 dof.

The spectrum at the maximum count rate
(measured from T0 to T0+8.448 s) is best fit
in the 20 keV - 2 MeV range by a power law
with exponential cutoff model, for which
alpha = -0.68(+/-0.15),
and Ep = 767(-126, +175) keV;
chi2 = 72/58 dof.

All the quoted results are preliminary.
All the quoted errors are at the 90% confidence level.

A. Nicuesa (TLS Tautenburg), T. Kruehler and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 100606A (Oates et al., GCN 10824
Loading...
 
 )
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 04:27 UT on June 07, 9.2 hours after the
GRB trigger.

Within the enhanced XRT error circle (Evans et al. GCN 10827
Loading...
 
 )
we confirm the presence of the blue and extended source reported by
Levan et al. (GCN 10831
Loading...
 
 ) in g' and r' at

RA (J2000.0) = 23:22:30.27
Dec (J2000.0) = -66:14:27.1

with typical uncertainties of 0.5" in each coordinate.

Similar to Levan et al. (GCN 10831
Loading...
 
 ) we also do not find evidence of an 
optical/NIR afterglow.

Stacked images of 270 min total integration time in g'r'i'z' and
80 min in JHK yield the following preliminary upper limits
in the AB system, which have been obtained using the GROND zeropoints
and 2MASS field stars as reference:

g' > 25.7 (24.7 +- 0.2)
r' > 25.5 (25.0 +- 0.3)
i' > 24.6
z' > 24.1
J  > 22.2
H  > 21.5
K  > 21.0

Magnitudes in brackets denote the brightness of the putative host galaxy.

Using the r'-band upper limit and the X-ray brightness at a similar 
time, beta_oX is constrained to be smaller than 0.6, implying that the 
burst would not be necessarily 'dark' according to the Jakobsson et al. 
(2004, ApJ, 617, 21) classification. Thus, our limit neither implies 
large redshift nor large extinction.

S. Sugita (Nagoya U.), K. Yamaoka (Aoyama Gakuin U.),
A. Daikyuji, N. Ohmori, Y. Nishioka, M. Yamauchi (Univ. of Miyazaki),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
Y. Terada, M. Tashiro, S. Hong, W. Iwakiri, K. Takahara, T. Yasuda (Saitama
U.),
M. Ohno, M. Kokubun, T. Takahashi (ISAS/JAXA), Y. E. Nakagawa,
M. Suzuki, T. Tamagawa (RIKEN), N. Vasquez (Tokyo Tech.),  Y. Urata,
H. M. Lin, P. P. Tsai (NCU), T. Enoto, K. Nakazawa, K. Makishima
(Univ. of Tokyo) on behalf of the Suzaku WAM team, report:

The long GRB 100606A (Swift/BAT trigger #10824; Oates et al.,)
triggered the Suzaku Wide-band  All-sky Monitor (WAM)
which covers an energy range of 50 keV - 5 MeV at 19:12:41.766 UT (=T0).

The observed light curve shows a multi-peaked structure
lasting from T0-2s to T0+100s with a duration  (T90) of about 65 seconds.
The fluence in 100 - 1000 keV was 2.21 (-0.28, +0.17) x10^-5 erg/cm^2.
The 1-s peak flux measured from T0+1s was 3.40 (-0.41 +0.28)  photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0 to T0+65s is well fitted by a power-law with exponential cutoff model:
dN/dE =  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha       0.63 (-0.30 +0.25), and
Epeak      767 (-121 +172)  keV (chi^2/d.o.f. = 45.2/52).

All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.

The light curves for this burst are available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html

S.Rapoport, J. Scharwaechter, B.P. Schmidt, M.Dopita, M. Bessell
RSAA, The Australian National University report

We observed the afterglow of the Swift GRB 100606A (S.R. Oates
et al. GCN 10824
Loading...
 
 ) with the Australian National University's 
Wide-Field-Spectrograph
(WiFeS)+2.3m telescope located at Siding Spring
Observatory. WiFeS is a high throughput integral field spectrograph 
which covers a FoV of 25"x38"
(Dopita, M., et al, , Ap&SS,310,255).
The spectra  were taken in poor conditions (FWHM 3 arcsec ) at the onset of
twilight, and cover the wavelength region 3200A-9300A
at a resolution of 3000. Data were obtained  in two 900 second exposures
commencing at UT 19:49:20 Jun 6 (35 minutes after GRB trigger).
To maximize image depth, we stacked and remove spectra regions containing
skylines to form g,r,i,z images. We did not detect any source within the XRT
error circle to limiting magnitudes (5-sigma) of

Filter       Mag
       (AB)
===       ===
g          >18.1
r          >19.5
i           >19.1
z          >18.9

calibrated by comparison to a nearby spectrophometric standard star.
The values are not corrected for galactic extinction.