GRB 100424A

E. A. Hoversten (PSU), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
W.B Landsman (GSFC), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
C. Pagani (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
M. A. Stark (PSU) report on behalf of the Swift Team:

At 16:32:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100424A (trigger=420367).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 209.453, +1.513 which is 
   RA(J2000)  =  13h 57m 49s
   Dec(J2000) = +01d 30' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT lightcurve shows nothing as is usual
for an image trigger. 

The XRT began observing the field at 16:34:42.1 UT, 119.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 209.4467, +1.5366 which is equivalent to:
   RA(J2000)  = 13h 57m 47.20s
   Dec(J2000) = +01d 32' 11.7"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). 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 2.09e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 128 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 E. A. Hoversten (hoversten 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.)

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

Using 1.4 ks of promptly downlinked XRT data and 1 promptly available UVOT image
we find an enhanced position of the XRT afterglow of GRB 100424A (Hoversten et
al., GCN Circ. 10667
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 ) of RA, Dec 209.4478, 1.5386 which is equivalent to:
   RA(J2000)  = 13h 57m 47.44s
   Dec(J2000) = +01d 32' 18.8"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). Analysis of the
promptly available data is online at http://www.swift.ac.uk/sper/420367.

Position enhancement 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 1406 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 100424A, 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 = 209.44775, +1.53897 which is equivalent
to:

RA (J2000): 13h 57m 47.46s
Dec (J2000): +01d 32' 20.3"

with an uncertainty of 1.7 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),
E. E. Fenimore (LANL), N. Gehrels (GSFC), E. A. Hoversten (PSU),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), 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 100424A (trigger #420367)
(Hoversten et al., GCN Circ. 10667
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 ).  The BAT ground-calculated position
is RA, Dec = 209.453, 1.512 deg which is
    RA(J2000)  =  13h 57m 48.6s
    Dec(J2000) = +01d 30' 44.2"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 88%.

The mask-weighted lightcurve shows a single broad peak from about T+20
to T+150 sec.  T90 (15-350 keV) is 104 +- 15.5 sec (estimated error
including systematics).

The time-averaged spectrum from T+22.3 to T+148.5 sec is best fit by
a simple power-law model.  The power law index of the time-averaged
spectrum is 1.83 +- 0.13.  The fluence in the 15-150 keV band is
1.5 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from
T+58.28 sec in the 15-150 keV band is 0.4 +- 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/420367/BA/

D. Malesani (DARK/NBI), D. Xu (Weizmann Inst.), A. J. Levan (Univ. 
Warwick), P. Jakobsson (Univ. Iceland), T. Pursimo (NOT), report on 
behalf of a larger collaboration:

We observed the field of GRB 100424A (Hoversten et al., GCN 10667
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 ) with 
the NOT equipped with ALFOSC in the R, I, and z filters. Observations 
started on April 24 at 22:38, 23:05, and 23:31 UT in R, I, z, 
respectively (6.30, 6.74, and 7.21 hr after the GRB), and were affected 
by the closeby bright Moon (42 deg away, 85% full) and some clouds.

We do not detect any new object within the refined XRT error circle 
(Evans, GCN 10668
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 ; Evans et al., GCN 10669
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 ). The limiting magnitudes are 
R(Vega) = 22.5 and z(AB) = 21.9, calibrated against the USNO-B1 and SDSS 
catalogs, respectively.

Given the relatively large X-ray flux, we encourage NIR observations.

A.J. Levan, C. Copperwheat, E. Breedt (U. Warwick), D. Malesani
(DARK/NBI) report on behalf of a larger collaboration:

"We observed the localization of GRB 100424A (Hoversten et al. GCN
10667
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 ) using the WHT and ACAM. Observations begin at April 25 00:18,
approximately 9 hours after the burst. We obtained 4x200s exposures
in the z-band. No source is visible within the enhanced XRT location
(Evans et al. GCN 10669
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 )  to a limiting magnitude of z>23.2, calibrated
against SDSS. 

The deep z-band limit, coupled with apparently bright early X-ray
afterglow is suggestive of either a highly extinguished, or high
redshift burst."

M. C. Stroh, D. Grupe and E. A. Hoversten (PSU) report on behalf of the Swift-XRT team:

We have analysed 641 s of XRT data for GRB 100424A (Hoversten  et al.
GCN Circ. 10667
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 ), from 126 s to 769 s after the  BAT trigger. The data
comprise 509 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The light curve can be modelled with a
series of power-law decays. The initial decay index is alpha=0.63
(+/-0.14). At T+288 s the decay steepens to an alpha of 1.41 (+0.27,
-0.19) before breaking again at T+526 s to a final decay with index
alpha=2.8 (+0.9, -0.6).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.26 (+/-0.06). The
best-fitting absorption column is 1.62 (+0.22, -0.21) x 10^21 cm^-2,
in excess of the Galactic value of 2.3 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 5.8 x 10^-11 (6.5 x 10^-11) erg
cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of
2.8, the count rate at T+24 hours will be 5.1 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-16 (3.3 x 10^-16) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00420367.

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

A. N. Morgan and J. S. Bloom (UC Berkeley) report:

We observed the field of GRB 100424A (Hoversten et al., GCN 10667
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 )
with the 1.3m PAIRITEL located at Mt. Hopkins, Arizona. Observations
began at 2010-04-25 03:51:19 UT, ~11.3 hours after the Swift Trigger,
under high airmass.  In  mosaics (effective exposure time of 0.74
hours) taken simultaneously in the J, H, and Ks filters, we do not
detect any source within the enhanced XRT error circle (Evans et al.,
GCN 10669
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 ).

The preliminary photometry yields:

post burst
t_mid (hr) exp.(hr) filt  U. Limit (3 sig)
11.81      0.74     J     > 19.3
11.81      0.74     H     > 18.4
11.81      0.74     Ks    > 17.0

Further observations are ongoing to obtain a deeper limit.  All
magnitudes are given in the Vega system, calibrated to 2MASS. No
correction for Galactic extinction has been made to the above reported
values.

F. Olivares, T. Kruehler and J. Greiner (all MPE Garching) report on 
behalf of the GROND team:

We observed the field of GRB 100424A (Swift trigger 420367; Hoversten et 
al., GCN 10667
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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 00:16 UT on April 25, 7.7 hours after the GRB 
trigger, and continued for 3 hours. The observations were severely 
affected by passing cirrus clouds.

In our first stacked images of 24 min total integration time in g'r'i'z' 
and 20 min in JHK, we do not (see also Malesani et al., GCN 10671
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 , Levan 
et al., GCN 10672
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 , Morgan & Bloom GCN 10675
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 ) detect a source within the 
enhanced Swift/XRT error circle (Evans et al., GCN 10669
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 ) down to the 
following preliminary 3 sigma limiting magnitudes (all in the AB system):

g' > 23.03
r' > 23.37
i' > 22.96
z' > 23.04
J > 21.77
H > 21.21
K > 20.29

Later images do not increase these limiting magnitudes due to worse sky 
conditions. These limits were derived by calibrating the images against 
SDSS/2MASS field stars and are not corrected for the Galactic foreground 
extinction corresponding to a reddening of E_(B-V)= 0.03 in the 
direction of the burst (Schlegel et al. 1998).

K.Y. Huang (ASIAA), Y. Urata, P. Tsai (NCU) on behalf of EAFON report;

We observed the field of GRB 100424A (Hoversten et al., GCN 10667
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 ) in
r' and z'-band with the LOT. Observations started at 17:52 UT on April 24, 
~80 min after the Swift Trigger. In our z'-band stacked image shows
no new object within the enhanced Swift/XRT position (Evans et al.,
GCN 10669
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 ) down to the following preliminary limiting magnitudes,

----------------------------
Time(hr)  Filter   Limit(AB)
----------------------------
2.16      z'       20.6
----------------------------

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:


We observed the field of GRB 100424A (Hoversten et al. GCNC 10667)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2010-04-24 16:34:56 UT (~2.2 min after
the burst). We did not find any new point source within the XRT
error circle (Evans, GCNC 10668; Evans et al., GCNC 10669) in all
the three bands.

Three sigma upper limits of the OT are listed below. We used SDSS
catalog for flux calibration.


T0+[day]   MID-UT   T-EXP[sec]    g'     Rc     Ic
------------------------------------------------------
0.00527    16:40:18   540.0     >18.4  >18.5  >17.7
0.04356    17:35:26  5940.0     >19.6  >20.0  >19.4
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

Jan Strobl (1), Martin Jelinek (2), Cyril Polasek (1), Petr Kubanek (2,3),
Martin Nekola (1), Matus Kocka (1), Michal Jakubec (1) and Rene Hudec (1)
(1. ASU AVCR Ondrejov, 2. IAA Granada, 3. GACE Valencia)

We observed the field of Swift GRB 100424A (Hoversten et al., GCNC 10667) 
with the 0.5m telescope D50 in Ondrejov (Czech Republic), starting at 
23:27:02 UT, i.e. 06:54:20 after the trigger. A sequence of 20s unfiltered 
images was obtained. We coadded 60x20s exposure, obtaining an image with a 
limitting magnitude Rc~19.3, with an effective exposure time 7.35h after 
the trigger (23:54UT). We do not detect any new source within the XRT 
localization (Evans et al., GCN10699
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 ).

This message can be cited.

S. B. Cenko, J. S. Bloom, A. N. Morgan, and B. E. Cobb (UC Berkeley)
report on behalf of a larger collaboration:

We have imaged the field of GRB 100424A (Hoversten et al., GCN 10667
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 ) with
the Near-InfraRed Imager and Spectrometer mounted on the 8 m Gemini North
telescope.  Observations were taken in the J and K filters beginning at
6:28 UT on 25 April 2010 (~ 14 hours after the burst).

At the edge of the refined XRT error circle (Evans et al., GCN 10669
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 ) we
identify a faint point source in both filters.  Referencing both the
astrometry and photometry to the 2MASS source 13574681+0131477, we
measure a position (J2000.0) of

	RA: 13:57:47.43		Dec: +01:32:18.9

and approximate magnitudes of K = 19.9, J = 22.1 (both Vega magnitudes).
The J-K color indicates a red afterglow, though does not necessarily
require a high-redshift origin (e.g., Levan et al., GCN 10672
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 ).  No
other objects are detected inside the XRT error circle.

Without evidence for variability, we cannot definitively confirm if this
source is the afterglow of GRB 100424A.  Further observations are planned
to search for fading.

We wish to thank the staff at Gemini Observatory, in particular Kristin
Chiboucas, for promptly executing these observations.

Z. Cano, A. Melandri (Liverpool JMU), C. Guidorzi (U. Ferrara), C.
Mundell, R.J. Smith, D. Bersier, I.A. Steele, S. Kobayashi, C.J. Mottram,
(Liverpool JMU), A. Gomboc (U. Ljubljana) report, on behalf of a larger
collaboration:

We observed the field of GRB 100424A (Hoversten et al. GCNC 10667) with
the Liverpool Telescope starting 20:54 UT on April 24, 2010.  We do not
detect the NIR afterglow discovered by Cenko et al. (GCN 10682
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 ), nor any
other object within the enhanced XRT error circle (Evans, GCN 10668
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 ; Evans
et al., GCN 10669
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 ) down to the following limits:

-------------------------------------------------------------------
 Mid Exposure        Total
  T-To (hrs)   Exposure Time (min)     Filter          upper limit
-------------------------------------------------------------------
     6.91              30                 B              >21.5
     6.92              50                 I              >21.8
     8.38              20                 R              >21.7
-------------------------------------------------------------------

The upper limits are for an isolated object in our images and are
calibrated using nearby stars in the USNO-B1 catalogue.  No correction for
Galactic extinction has been made.

P.A. Curran (MSSL-UCL) and E. Hoversten (PSU) report on behalf of the
Swift/UVOT team:


The Swift/UVOT began settled observations of the field of GRB 100424A 
128 s after the BAT trigger (Hoversten et al., GCN Circ. 10667
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 ). No 
optical afterglow consistent with the refined XRT position (Evans et 
al., GCN Circ. 10669
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 ) or the proposed NIR counterpart (Cenko et al. (GCN 
Circ. 10682
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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 initial finding charts (FC) 
and exposures are:

Filter   T_start(s) T_stop(s)   Exp(s)   Mag
----------------------------------------------
white    128         278        147      >20.8 (FC)
u        288         537        246      >20.0 (FC)
white    128        2046        444      >21.2
v        618        1930        156      >19.2
b        543        2028        156      >20.1
u        288        2003        382      >20.1
w1       668        1979        156      >19.7
m2       642        1955         97      >19.1
w2       594        5584        193      >20.0


The values quoted above are not corrected for the Galactic extinction 
due to the reddening of E(B-V) = 0.08 in the direction of the burst 
(Schlegel et al. 1998).

S. B. Cenko, A. N. Morgan, and J. S. Bloom (UC Berkeley) report on behalf
of a larger collaboration:

We have obtained further imaging of the field of GRB 100424A (Hoversten et
al., GCN 10667
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 ) with the Near InfraRed Imager and Spectrometer mounted on
the 8 m Gemini North telescope.  Following our report of a detection of a
candidate afterglow in the J and K filters (Cenko et al., GCN 10682
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 ), we
obtained a sequence of H-band images beginning at 9:29 UT on 25 April 2010
(~ 17 hours after the burst).

The candidate afterglow is also detected in the H-band.  Using the
PAIRITEL imaging of the field for photometric calibration (Morgan and
Bloom, GCN 10675
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 ), we measure a magnitude of H = 20.9 (Vega) at this time.

Combined with our previous J and K photometry (and assuming the afterglow
decays in time like a power-law with index alpha=-1), the candidate
infrared afterglow appears consistent with a relatively steep spectral
power-law index of beta ~ 2.5-3.0 across all three bands.  This suggests
the afterglow is reddened due predominantly to dust in the host galaxy of
the GRB, and not an extremely high-redshift (z > 7) origin, as would be
suggested by the presence of host galaxy extinction from the X-ray
afterglow spectrum (Stroh et al., GCN 10674
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 ).

We wish to thank the staff at Gemini Observatory for assistance in
executing these observations.

S. B. Cenko, J. S. Bloom, D. A. Perley, A. N. Morgan, B. E. Cobb (UC
Berkeley) and A. J. Levan (U. Warwick) report on behalf of a larger
collaboration:

We have obtained a second epoch of K-band imaging of the field of GRB
100424A (Hoversten et al., GCN 10667
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 ) with the Near InfraRed Imager and
Spectrometer mounted on the 8 m Gemini North telescope.  Observations
began at 11:23 UT on 26 April 2010 (~ 43 hours after the burst).

The previously identified candidate in the XRT error circle (Cenko et al.,
GCN 10682
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 ) has faded by 0.9 +/- 0.1 mag, confirming the object is indeed
the NIR afterglow of GRB 100424A.  Assuming negligible contribution from
an underlying host galaxy, the inferred power-law decay index, alpha ~
0.7, is relatively shallow.

We wish to thank the staff at Gemini Observatory, in particular Kristin
Chiboucas, for executing these observations.

V. Rumyantsev, D. Shakhovskoy (CrAO), A. Volnova (SAI MSU), A.
Pozanenko (IKI)  report on behalf of larger GRB  follow-up
collaboration:

We observed the field of the Swift GRB 100424A (Hoversten et al., GCN
10667
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 ) with AZT-11 telescope of CrAO observatory between (UT) Apr. 24
18:01 - 19:18 under seeing of about 3 arcsec. We detected a  probable
source at coordinates (J2000) RA =  13:57:47.64 Dec = +01:32:21.06
with an uncertainty of 0.5 arcsec in both coordinates. The probable
source is located 2.8 arcsec from the enhanced XRT position with an
uncertainty (radius) of 1.7 arcsec (Evans et al., GCN 10669
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 ). Due to
low S/N we cannot confirm the detected source is a real object.

We do not detect any source at the position of afterglow candidate
(Cenko, et al., GCN 10682
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 , Cenko, et al., GCN 10690
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 ).

The photometry of the probable source and upper limit of the
point-like source in a stacked image based on USNO-B1.0 star
(RA(J2000) = 13:57:45.54 Dec(J2000)= +01:33:29.7) and assuming R=17.80
is following:

T0+      Filter, Exposure, mag.           UL
(mid, d)         (s)

0.0882   R       21x180    20.1 +/- 0.3   20.4

The combined image can be found at
http://grb.rssi.ru/GRB100424A/GRB100424a_R_AZT11.gif

Dale A. Frail (NRAO) and Poonam Chandra (RMC) report on behalf of a
larger collaboration:

"We observed the localization of GRB 100424A (Hoversten et al. GCN
10667
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 ) the Expanded Very Large Array (EVLA) on April 27.14 UT at a
center frequency of 8.46 GHz. We do not detect any radio source
anywhere within the refined XRT error circle (Evans et al., GCN 10669
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 )
to a 3-sigma limit of 66 uJy.

The EVLA is still undergoing active commissioning and we caution that
these results should be considered preliminary. The National Radio
Astronomy Observatory is a facility of the National Science Foundation
operated under cooperative agreement by Associated Universities, Inc."

D. Malesani, D. Xu, J. P. U. Fynbo, T. Kruehler (DARK/NBI), D. A. Perley 
(Caltech), S. D. Vergani (CNRS/GEPI), P. Goldoni (APC/IRFU-CEA), report 
on behalf of the GRB GTO X-shooter collaboration:

We observed the field of GRB 100424A (Hoversten et al., GCN 10667
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 ) using 
the Keck-I telescope equipped with the LRIS instrument. Observations 
were carried out on 2010 July 8.2 UT (74.5 days after the burst), 
simultaneously in the g and I bands, for a total exposure time of 35 and 
32 min, respectively.

Consistent with the position of the NIR afterglow (Cenko et al., GCNs 
10682
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 , 10690
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 , 10692
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 ), we detected a source with g = 26 (AB) and I = 24.4 
(Vega). We consider this object to be the host galaxy of GRB 100424A.

A spectrum of this source was taken on 2013 March 11.3 UT with the ESO 
VLT equipped with the X-shooter spectrograph, covering the wavelength 
range 3000-25000 AA. The exposure time was 8x600 s. In the NIR arm, we 
detect four emission lines, that we interpret as [O III](4959), [O 
III](5007), Hbeta, and [O II](3727), all at a common redshift of z = 
2.465. In the UVB arm, we also detect weak Lyalpha in emission at the 
same redshift.

We acknowledge excellent support from the observing staff at Mauna Kea 
and Paranal, in particular Thomas Rivinius and Claudio Melo.