GRB 120724A

P. D'Avanzo (INAF-OAB), W. H. Baumgartner (GSFC/UMBC),
V. D'Elia (ASDC), H. A. Krimm (CRESST/GSFC/USRA),
B. Sbarufatti (INAF-OAB/PSU) and M. Stamatikos (OSU/NASA/GSFC) report
on behalf of the Swift Team:

At 06:39:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120724A (trigger=528443).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 245.190, +3.509 which is 
   RA(J2000) = 16h 20m 46s
   Dec(J2000) = +03d 30' 33"
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 about 40 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 06:40:52.0 UT, 109.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 245.18192, 3.50750 which
is equivalent to:
   RA(J2000)  = 16h 20m 43.66s
   Dec(J2000) = +03d 30' 27.0"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 29 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 4.29
x 10^20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 5.14e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 117 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
0.05. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.it). 
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.)

C. Guidorzi (U. Ferrara), A. Melandri (INAF-OAB),
J. Japelj (U. Ljubljana) on behalf of a large
collaboration report:

The 2-m Faulkes Telescope North automatically began observing
GRB 120724A (D'Avanzo et al. GCN Circ. 13510
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 ) on July 24 2012,
06:42:31 UT corresponding to 209 seconds post burst trigger
with BVRi' filters. Within the XRT error circle we found the
following uncatalogued fading source,

R.A. = 16:20:43.21
Dec = +03:30:29.3   (J2000)

with an uncertainty of about 1" with a magnitude of
20.5 +/- 0.3 in the i band at 13.8 minutes, calibrated
against nearby USNOB-1 stars. The source is also visible
in stacked R-band frames.

A. Cucchiara (UCSC/UCO Lick), N.R. Tanvir (U. Leicester), 
D. Perley (Caltech), and A. J. Levan (U. Warwick) report 
on behalf of a larger collaboration:

We observed the afterglow of GRB 120724A (Guidorzi et al. 
GCN 13511
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 ; D'Avanzo et al. GCN 13510
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 ) using the GMOS-N 
spectrograph on the Gemini-North telescope under very good 
seeing conditions (0.5").

Observations began at 2012-7-24 08:31 UT, about 2 hr post-burst.
Two spectra of 900s each were acquired, covering the
6000-10000 Angstrom wavelength range.

A preliminary analysis of some of the absorption features
identified suggests that the GRB redshift is z = 1.48, 
based on identification of MgII2796,2803 doublet, 
MnII2606, FeII2600, and MnII2594.

We thank the Gemini staff, in particular J. Holt and 
J. Kemp, for making these observations possible.

P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli  (INAF-IASFPA),
J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), A.P. Beardmore
(U. Leicester), P.A. Evans (U. Leicester), and O.M. Littlejohns (U.
Leicester) report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 120724A (D'Avanzo  et al.
GCN Circ. 13510
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 ), from 115 s to 13.0 ks after the  BAT trigger. The
data comprise 40 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The best available XRT position  (using the
promptly downlinked event data, the XRT-UVOT alignment and matching
UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 245.1800,
3.5081 which is equivalent to:

RA (J2000): 16 20 43.19
Dec(J2000): +03 30 29.0

with an uncertainty of 2.2 arcsec (radius, 90% confidence).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.78 (+/-0.22), followed by a break at T+851 s to an
alpha of 0.48 (+0.18, -0.79).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.88 (+0.20, -0.09). The
best-fitting absorption column is  consistent with the Galactic value
of 4.3 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 3.7 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 4.3 x 10^20 cm^-2
Intrinsic column:    0 (+9.3, -0) x 10^20 cm^-2 at z=1.48
Photon index:	     1.88 (+0.20, -0.09)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00528443.

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

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

Using 2299 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 120724A, 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 = 245.18020, +3.50793 which is equivalent
to:

RA (J2000): 16h 20m 43.25s
Dec (J2000): +03d 30' 28.6"

with an uncertainty of 1.5 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.

S. T. Holland (STScI) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:

    The Swift/UVOT observed the field of GRB 120724A starting 99 s
after the BAT trigger (D'Avanzo et al., 2012, GCNC 13510).  Settled
observations started at 120 s.  We detect a faint source with preliminary
coordinates

    RA (J2000)  16:20:43.35  =  245.18062 (deg)
   Dec (J2000) +03:30:27.8   =   +3.50772 (deg)

and an estimated uncertainty of 0.77 arcsec (radius, 90% confidence,
statistical + systematic).  This position is consistent with the
optical source discovered by Guidorzi et al. (2012, GCNC 13511) and is
slightly outside the UVOT-enhanced XRT position (D'Avanzo et al.,
2012, GCNC 13514).  Preliminary magnitiudes for this source, and
3-sigma upper limits for the finding charts (FC) and the co-added
images, are

Filter       TSTART       TSTOP  EXPOSURE       Mag   Err  Sigma
----------------------------------------------------------------
white (FC)      117         267       147     >21.3
   u (FC)      330         580       246     >20.5
white (FC)      609         629        20     >19.8
----------------------------------------------------------------
  v            832        1404        72     >19.2
  b            585        1331        58      20.01 0.41    2.7
  u            330        1461       288      20.50 0.37    3.0
uvw1           1088        1453        59     >19.2
uvm2           1237        1429        39     >18.4
uvw2            635        1380        78     >19.5
white           117        1355       199      21.54 0.45    2.5
----------------------------------------------------------------

   The quoted magnitudes and upper limits have not been corrected for
the Galactic extinction along the line of sight to this burst of
E_{B-V} = 0.05 mag (Schlafly et al. 2011, ApJS, 737, 103).

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), P. D'Avanzo (INAF-OAB), E. E. Fenimore (LANL),
N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 120724A (trigger #528443)
(D'Avanzo, et al., GCN Circ. 13510
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 ).  The BAT ground-calculated position is
RA, Dec = 245.193, 3.535 deg which is
     RA(J2000)  =  16h 20m 46.3s
     Dec(J2000) = +03d 32' 07.2"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 50%.

The mask-weighted light curve shows a single broad peak starting at roughly
T0-30 seconds, peaking at T0 and extending until T0+100 seconds.
T90 (15-350 keV) is 72.8 +- 16.4 sec (estimated error including systematics).

The time-averaged spectrum from -21.3 to 64.5 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.53 +- 1.53,
and Epeak of 27.6 +- 7.5 keV (chi squared 43.55 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.8 +- 1.1 x 10^-07 erg/cm2
and the 1-sec peak flux measured from T+7.51 sec in the 15-150 keV band is
0.6 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.45 +- 0.26 (chi squared 50.75 for 57 d.o.f.).  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/528443/BA/

I.A. Smith (Rice U.), R.P.J. Tilanus (JAC), N.R. Tanvir (U. of Leicester),
D.A. Frail (NRAO) report:

We observed the location of GRB 120724A (D'Avanzo et al., GCN Circ.
13510
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 ) using the SCUBA-2 sub-millimeter continuum camera on the James
Clerk Maxwell Telescope.  The observation started at 07:48 UT on
2012-07-24, corresponding to 69 minutes after the burst trigger.
Exposures totaling 1.7 hours were made in reasonable weather conditions.
No source was detected, with a preliminary RMS of 3.3 mJy/beam at 
850 microns.

We thank Jeff Cox and Antonio Chrysostomou for their prompt support of 
these observations.

A. Pozanenko (IKI), A. Sergeev (Institute of Radio Astronomy of NASU), A. 
Volnova (SAI MSU), O. Burhonov (UBAI), I. Molotov (KIAM) report on behalf 
GRB follow-up collaboration:

We observed  the field of Swift  GRB 120724A (D'Avanzo et al., GCN 13510
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 ) 
with AZT-22 telescope of Maidanak observatory starting on Jul. 24 (UT) 
15:55:51 under mean seeing (FWHM) of about 1.1 arcsec. Totally we obtained 4 
images of 600 s exposure in R  filter. At the edge of the enhanced XRT 
position (Goad et al., GCN 13515
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 ) we detected the object with coordinates 
(J2000) 16 20 43.28  +03 30 27.1 (uncertainty of  0.12 arcsec in both 
coordinates), which is slightly apart from coordinates of the OT reported 
earlier (Guidorzi  et al., GCN 13511
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 ; Holland et al., GCN 13516
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 ).  Since the 
object is also visible in stacked DSS images (R+I) we suggest it is a 
possible host galaxy of GRB 120724A.

A preliminary photometry of the object is based on USNO-B1.0 nearby stars:

T0+        Filter,     Exposure,   OT
(mid, d)                (s)

 0.42252       R    3x600        20.97 +/- 0.09

A finding chart can be found at 
http://grb.rssi.ru/GRB120724A/GRB120724A_AZT22&DSS.png