GRB 130912A

V. D'Elia (ASDC), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
D. Malesani (DARK/NBI), C. B. Markwardt (NASA/GSFC),
K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of
the Swift Team:

At 08:34:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130912A (trigger=570465).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 47.615, +13.974 which is 
   RA(J2000) = 03h 10m 28s
   Dec(J2000) = +13d 58' 28"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a short spike
with substructure with a duration of about 0.5 sec.  The peak count rate
was ~11000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 08:36:31.7 UT, 93.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 47.59060, 13.99546 which is equivalent
to:
   RA(J2000)  = 03h 10m 21.74s
   Dec(J2000) = +13d 59' 43.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 115 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.24 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 2.1
(+1.66/-1.48) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 98 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 0.28. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)

WeiKang Zheng, Alexei V. Filippenko, Adam Morgan (UC Berkeley), and
S. B. Cenko (NASA/Goddard Space Flight Center) report on behalf of the
KAIT GRB team:

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to the short-duration GRB 130912A
(D'Elia et al., GCN 15212
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 ) starting at 08:48:04 UT, ~13 minutes after
the burst. Observations were performed with an automatic sequence
in V, I, and clear filters (20 s exposure for each image). Due to
a technical issue, the first useful image begain ~35 minutes after the
burst. We do not detect any new source in the XRT error circle.
The estimated limiting magnitude in our first clear-band (close to R)
image is about 19.6 (calibrated to USNO B1.0) at a midtime of ~36
minutes after the burst.

M. Tanga (MPE Garching), S. Klose (TLS Tautenburg), V. Sudilovsky
(MPE Garching), R. Filgas (IEAP Prague), J. Greiner (MPE Garching)
report on behalf of the GROND team:

We observed the field of GRB 130912A (Swift trigger 570465; D'Elia et al.
2013, GCN #15212
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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 MPG/ESO telescope at La Silla
Observatory (Chile).

Observations started at 08:50 UT on 12 Sep 2013, 16 min after the GRB
trigger. At the northern edge of the r=2.2 arcsec XRT error circle (D'Elia
et al., GCN #15173
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 ) we detect a faint source at coordinates

RA (J2000)   = 03:10:22.23
Dec. (J2000) = 13:59:48.7

with an error of 0".3 arcseconds.

However, the object seems to be constant over the first hour of
our observations, with a preliminary magnitude of r' = 22.0+-0.2 mag,
calibrated against the GROND zeropoint. Given the constant flux,
this might be the host galaxy of GRB 130912A.

P. D'Avanzo, D. Fugazza, A. Melandri (INAF-OAB), V. D'Elia (ASI/ASDC) report on behalf of the REM team:

We observed the field of the short GRB 130912A (D'Elia et al., GCN 15212
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 ) simultaneously in the optical and near infrared with the the 60-cm robotic telescope REM at La Silla Observatory (Chile). The observations started at 08:47:33 UT, 12.6 min after the GRB.

No source is detected within the XRT error circle nor at the position of the possible host galaxy reported by Tanga et al. (GCN 15214
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 ). The limiting magnitudes are r'=19.6 and H=16.1 (Vega; calibrated against the USNOB1 and the 2MASS catalogue, respectively) at a mid t-t0=17.5 minutes.

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC),  W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), V. D'Elia (ASDC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), 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-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130912A (trigger #570465) (D'Elia, et al.,
GCN Circ. 15212
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 ).  The BAT ground-calculated position is
RA, Dec = 47.606, 13.999 deg which is
    RA(J2000)  =  03h 10m 25.6s
    Dec(J2000) = +13d 59' 55.7"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 31%.
  
The mask-weighted light curve shows two overlapping peaks.  T90 (15-350 keV) is
0.28 +- 0.03 sec (estimated error including systematics).
  
The time-averaged spectrum from T+0.00 to T+0.32 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.20 +- 0.20.  The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.34 sec in the 15-150 keV band
is 2.2 +- 0.3 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/570465/BA/

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

Using 1499 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 130912A, 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 = 47.59265, +13.99703 which is equivalent
to:

RA (J2000): 03h 10m 22.24s
Dec (J2000): +13d 59' 49.3"

with an uncertainty of 1.6 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.

A. Trotter, D. Reichart, J. Haislip, A. LaCluyze, A. B. Smith, D. Caton, 
L. Hawkins, V. Hoette, K. Cudworth, D. Harper, R. Kron, T. Linder, R. 
Russell, E. Struble, T. Berger, H. T. Cromartie, R. Egger, A. Foster, N. 
Frank, K. Ivarsen, M. Maples, J. Moore, M. Nysewander, and J. A. Crain 
report:

Skynet observed the Swift/XRT localization of GRB 130912A (D'Elia et 
al., GCN 15212
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 , Swift trigger 570465) with the 14" telescope at the 
Appalachian State University Dark Sky Observatory (DSO-14) in NC, USA (R 
and I bands), the 41" telescope of Yerkes Observatory in WI, USA (r' and 
i' bands), and with four 16" telescopes of the PROMPT array at CTIO, 
Chile (B, V, R, and I bands).

Starting at 2013-09-12, 08:47 UT and continuing until 10:26 UT 
(t=12m-111m post-trigger), Skynet took a total of 72 160s exposures. In 
stacked images, we do not detect an optical source in any band in or 
near the XRT error circle.  Our 3-sigma limiting magnitudes are 
tabulated below:

==================================
tmid  scope   expos  fil  limit
==================================
21m  DSO-14   2x160s  I  >18.7
24m  DSO-14   2x160s  R  >19.6
61m  Prompt5 10x160s  I  >20.6
61m  Prompt4 10x160s  R  >21.0
61m  Prompt1 10x160s  V  >21.3
61m  Prompt3 10x160s  B  >21.1
63m  Y-41    11x160s  i' >21.6
60m  Y-41     9x160s  r' >21.9
66m  Y-41     8x160s  g' >21.8
==================================

BVRI magnitudes are in the Vega System, and g'r'i' magnitudes are in the 
AB system, calibrated to 4 APASS stars in the field.  Magnitudes have 
not been corrected for line-of-sight Milky Way dust extinction, with 
expected E(B-V)=0.28 (Schlegel et al. 1998).

No further Skynet observations are scheduled.

Bin-Bin Zhang (UAH), Suzanne Foley (UCD) and Narayana Bhat (UAH) 
report on behalf of the Fermi GBM Team:

"At 08:34:58.00 UT on 12 September 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located a short GRB 130912A (trigger 400667700 / 130912358),
which was also detected by the Swift (D'Elia et al., GCN 15212
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 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 102 deg from Swift/XRT 
position (Beardmore et al. GCN 15217
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 ).

The GBM light curve consists of a single pulse with of multiple peaks
with a duration (T90) of about 0.5 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.448 s is
well fit by a Band function with alpha = -1.0 +/- 0.1, beta = -1.9 +/- 0.2
and Epeak= 1225 +/- 599 keV. The event fluence (10-1000 keV) in this time interval is
(2.29 +/- 0.14)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.13 s in the 10-1000 keV band is 4.5 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

J.A. Kennea (PSU), B.P. Gompertz (U. Leicester), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A. Maselli  (INAF-IASFPA), A.
Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), V. Mangano (PSU),
M.C. Stroh (PSU) and V. D'Elia report on behalf of the Swift-XRT team:

We have analysed 6.6 ks of XRT data for GRB 130912A (D'Elia  et al. GCN
Circ. 15212
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 ),  from 104 s to 13.1 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Beardmore et al. (GCN. Circ 15217).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.24 (+/-0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.49 (+0.20, -0.12). The
best-fitting absorption column is  1.29 (+0.67, -0.05) x 10^21 cm^-2,
consistent with the Galactic value of 1.2 x 10^21 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 5.0 x 10^-11 (5.8 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.29 (+0.67, -0.05) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.49 (+0.20, -0.12)

If the light curve continues to decay with a power-law decay index of
1.24, the count rate at T+24 hours will be 1.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x
10^-14 (9.2 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/00570465.

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

S. B. Cenko (NASA/GSFC), V. Sudilovsky, M. Tanga, and J. Greiner (MPE
Garching), report on behalf of a larger collaboration:

We have imaged the field of the Swift short GRB130912A (D'Elia et al., GCN
15212
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 ) with the robotic Palomar 60 inch telescope in the r', i', and z'
filters.  Observations began at 8:48 UT on 2013 September 12 (13 min after
the Swift trigger).

Within the enhanced XRT error circle (Beardmore et al., GCN 15217
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 ) we
detect the faint source reported by Tanga et al. (GCN 15214
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 ) in all three
filters.  Using calibration stars from GROND, we measure an AB magnitude
of r' = 21.77 +/- 0.20 mag at a mean time of 8:58 UT and r' = 22.09 +/-
0.25 at 09:28 UT (23 and 53 min after the Swift trigger, respectively).
The lack of significant variability implies either a shallow afterglow
decay index, or this source may be the host galaxy of GRB130912A, as
suggested by Tanga et al. (GCN 15214
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 ).

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

"We observed the location of GRB 130912A (D'Elia et al. GCN 15212
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 ) with the William Herschel Telescope, beginning at approximately 05 UT on 13 September 2013,  roughly 20 hours after the burst trigger. At this epoch we obtained observations in the g,i and J-bands utilising ACAM and LIRIS.

At the location of the counterpart identified by Tanga et al. (GCN 15214
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 ) and Cenko et al. (GCN 15222
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 ) we detect no source in our g-band observations (limiting magnitude g~25), and a source which is only weakly detected in the i-band and J-band (i~24). This implies that the light observed at earlier epochs when the source was measured at r=22 was due to a significant contribution from the optical transient, and that any underlying host galaxy is faint."

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

The short-duration GRB 130812A (Swift-BAT trigger 570465:
D'Elia et al. GCN 15212
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 , Krimm et al. GCN 15216
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 ;
Fermi-GBM detection: Zhang et al. GCN 15219
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 )
triggered Konus-Wind at T0=30902.290 s UT (08:35:02.290).

The burst light curve shows two peaks in the time
interval from ~T0-0.1 s to ~T0+0.3 s.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130912_T30902/

As observed by Konus-Wind, the burst
had a fluence of (1.6 � 0.2)x10-6 erg/cm2,
and a 16-ms peak flux, measured from T0-0.032,
of (2.2 � 0.6)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The 3-channel time-integrated spectrum
(measured from T0-0.128 to T0+0.256 s)
can be modeled, in the 25 keV - 1.5 MeV range,
by the cutoff power law with the following model parameters:
the photon index alpha = -0.96 � 0.08,
and the peak energy Ep = 580 � 65 keV.

The 3-channel spectrum at the maximum count rate
(measured from T0-0.128 to T0+0.256 s)
can be modeled, in the 25 keV - 1.5 MeV range,
by the cutoff power law with the following model parameters:
the photon index alpha = -1.07 � 0.12,
and the peak energy Ep = 1020 � 320 keV.

All the quoted results are preliminary.

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM),
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC)
report:

We observed the field of GRB 130912A (D'Elia et al., GCN 15212
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 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2013/09 13.30 to 2013/09 13.49 UTC (22.58 to
27.11 hours after the BAT trigger), obtaining a total of 5.33 hours
exposure in the r and i bands and 2.24 hours exposure in the Z, Y, J, and H
bands.

For a source within the Swift-XRT error circle, in comparison with USNO-B1
and 2MASS, we obtain the following upper limits (3-sigma):

  r     > 23.89
  i     > 23.79
  Z     > 22.86
  Y     > 22.38
  J     > 22.30
  H     > 21.78

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.    Our observations confirm that
the source faded
and is therefore the short GRB afterglow.

We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.

W. Fong, B. A. Zauderer and E. Berger (Harvard) report:

"We observed the field of the short-duration GRB 130912A (D'Elia et
al., GCN 15212
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 ; Zhang et al., GCN 15219
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 ; Golenetskii et al., GCN
15225
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 ) with the Karl G. Jansky Very Large Array (VLA) beginning on
2013 Sep 13.26 UT (21.85 hr post-burst) at a mean frequency of 5.8
GHz. In 1 hour of observations, we do not detect any radio source in
coincidence with the optical afterglow (Tanga et al., GCN 15214
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 ; Cenko
et al., GCN 15222
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 ; Tanvir et al., GCN 15224
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 ; Butler et al., GCN 15226
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 )
or within the enhanced XRT position (Beardmore et al., GCN 15217
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 ). We
therefore place a 3-sigma limit of 29 microJy on the radio afterglow
of GRB 130912A at 21.85 hr after the burst.

We thank the VLA staff for quickly executing these observations."

M. M. Chester (PSU) and V. D'Elia (ASDC) report on behalf of the 
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130912A
99 s after the BAT trigger (D'Elia et al., GCN Circ. 15212
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 ).
No optical afterglow consistent with the enhanced XRT position 
(Beardmore et al. GCN Circ. 15217
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 ) is detected in the initial UVOT 
exposures. Preliminary 3-sigma upper limits using the UVOT photometric 
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposures and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            99          249          147         >20.7
u_FC               311          561          246         >20.2
white               99         6848          785         >21.4
v                  640        23984         1395         >20.3
b                  566        30470         1907         >21.6
u                  311        36236         3907         >21.6
w1                 690        35508         3836         >22.1
m2                1070        34601         2827         >21.8
w2                 616        23070         1376         >21.6

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.28 in the direction 
of the burst (Schlegel et al. 1998).

A. Volnova (IKI), R. Inasaridze (AAO), O. Kvaratskhelia (AAO), V. 
Ayvazian(AAO), Yu. Krugly (IA KhNU), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of larger GRB follow-up collaboration:

We observed the field of Swift GRB 130912A (D'Elia et al., GCN 15212
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 )
with AS-32 (0.7m) telescope of Abastumani Observatory starting  Sep., 13 
(UT) 00:18:46. We obtained several unfiltered frames with exposures of 
120 s. On stacked images within the enhanced XRT circle (Beardmore et 
al., GCN 15217
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 ) we did not detect an optical counterpart reported by 
Tanga et al. (GCN 15214
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 ).

The details of the photometry are the following:

t_start, UT   filter exptime,s   t-t0, mid, days  OT    uplim

21:39:21      None   31*120       0.68394         n/d    22.3

The photometry is based 3 USNO-B1.0 stars:

USNO-B1.0 id RA             Dec             R2
1040-0030312 03:10:30.46 +14:01:11.1 19.44
1040-0030310 03:10:29.14 +14:01:21.6 17.38
1040-0030302 03:10:25.12 +14:00:31.6 15.90