GRB 121001A

M. Andreev,  A. Sergeev (Terskol Branch of Institute of Astronomy), A. 
Pozanenko (IKI) on behalf of larger GRB follow up collaboration report:

We observed field of the Swift  GRB 121001A = Swift trigger 535026 (D'Elia 
et al. GCN  13831
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 ) with Zeiss-600 telescope of Mt.Terskol observatory in R 
filter starting on Oct. 01 (UT) 18:39:20.  In a stacked image of first 13x60 
exposures we detect optical source in coordinates (J2000) RA=18 24 07.8 
Dec=-05 39 55.3 which is consistent with XRT error circle (GCN  13831
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 ). The 
optical source is absent in DSS2 plates. However at that time we cannot 
determine if the source is variable. Preliminary photometry of the source 
against nearby USNO B1.0 stars is 19.5R.  Finding chart can be found at
http://grb.rssi.ru/GRB121001A/GRB121001A_R_Z600_fc_1.png

E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, N.Tyurina, 
N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov,  V.V.Chazov, 
A.Sankovich, D.Denisenko
Moscow Lomonosov State University, Sternberg Astronomical Institute,

K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk
Irkutsk State University

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

V.Krushinski, I.Zalozhnich,  A. Popov, A. Bourdanov, A. Punanova
Ural Federal University

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Kislovodsk was pointed  to the Swift  GRB121001A 43 s after 
notice time and 209  sec after GRB time at  2012-10-01 18:26:31 UT in a 
two  polarizations.

We haven`t found optical transient  within  SWIFT error-box (D'Elia
et al. GCN  13831
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 )  on our first (20 s exposure) set.

The 5-sigma upper limit has been about 15.8  mag

Observations were carried out under the full moon and  on high zenith 
distance (~70 deg). Also a high  stars density  complicates the analysis.

The data reduction is continued.

The message may be cited.

T. Sakamoto (AGU), 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),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
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-60 to T+243 sec from the recent telemetry 
downlink, we report that Swift trigger #535026 (D'Elia, et al., GCN 
Circ. #13831
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 ) is consistent with being a GRB.  We follow the designation 
of previous authors for the trigger as GRB 121001A (Zheng et al. GCN 
Circ. #13832
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 ; Andreev et al. GCN Circ. #13833
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 ; Gorbovskoy et al. GCN 
Circ. #13834
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 ).

Based on the analysis below, the burst has strong emission up to 100 
keV, and a FRED-like light curve profile with duration longer than 
100sec.  Neither of these is consistent with a neutron star 
thermonuclear X-ray burst (which would be blackbody emission with 
temperature kT ~ few keV).  The soft emission we reported in GCN Circ. 
#535026
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  is associated with an X-ray burst from HETE J1900.1-2455, 
another active X-ray binary in the BAT field of view.  Thus, we conclude 
that trigger #535026 is consistent with a GRB interpretation.

We report further BAT analysis of GRB 121001A (trigger #535026).
The BAT ground-calculated position is
RA, Dec = 276.029, -5.667 deg which is
      RA(J2000)  =  18h 24m 06.9s
      Dec(J2000) = -05d 40' 01.0"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The light curve shows a FRED-like profile, starting near T-25sec, rising 
to maximum at T-15sec, and gradually decaying to background near 
T+130sec.  T90 (15-350 keV) is 147 +- 24 sec (estimated error including 
systematics).

The time-averaged spectrum from T-30 to T+143 sec is best fit by a 
simple power-law model.  The power law index of the time-averaged 
spectrum is 1.34 +- 0.15.  The fluence in the 15-150 keV band is 1.7 +- 
0.2 x 10^-6 erg/cm2.  The 1-sec peak photon flux measured from T+3.27 
sec in the 15-150 keV band is 0.5 +- 0.1 ph/cm2/sec.  All the quoted 
errors are at the 90% confidence level.

The BAT results for this circular represent a limited time window.  The 
results may be revised if additional downlinked data show more emission.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/535026/BA/

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

Using 2340 s of XRT Photon Counting mode data and 3 UVOT images of GRB 
121001A (D'Elia et al., GCN Circ. 13831
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 ), 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 = 276.03227, -5.66587 
which is equivalent to:

RA (J2000):  18 24 07.74
Dec (J2000): -05 39 57.1

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 is an official product of the Swift-XRT team.

V. D'Elia (ASDC) and P. Evans (U. Leicester)  report on behalf of the
Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 121001A (D'Elia et al. GCN
Circ. 13831
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 ), from 111 s to 41.8 ks after the  BAT trigger. The data
comprise 93 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. Using 2340 s of PC mode data and 3 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 276.03227, -5.66587
which is equivalent to:

RA (J2000): 18h 24m 07.74s
Dec(J2000): -05d 39' 57.1"

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

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.30 (+/-0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.28 (+0.25, -0.24). The
best-fitting absorption column is  7.6 (+2.4, -2.0) x 10^21 cm^-2, in
excess of the Galactic value of 4.5 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 7.6 x 10^-11 (9.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.6 (+2.4, -2.0) x 10^21 cm^-2
Galactic foreground: 4.5 x 10^21 cm^-2
Excess significance: 2.5 sigma
Photon index:	     1.28 (+0.25, -0.24)

If the light curve continues to decay with a power-law decay index of
1.30, the count rate at T+24 hours will be 2.1 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (2.1 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00535026.

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

F. E. Marshall (NASA/GSFC) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 121001A
130 s after the BAT trigger (D'Elia et al., GCN Circ. 13831
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 ).
No optical afterglow consistent with the optical position
(Tello et al. GCN Circ. 13835
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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           130          280          147         >21.0
u_FC               288          538          246         >20.0
white              130         7415          824         >22.4
v                  618         6390          352         >20.2
b                  544         7210          526         >21.2
u                  288         7005          756         >20.7
w1                 668         6800          529         >20.4
w2                 767         7608          439         >21.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.36 in the direction of the burst
(Schlegel et al. 1998).

S. Schmidl (TLS Tautenburg), D. A. Kann (MPE Garching), S. Klose (TLS
Tautenburg), and J.Greiner (MPE Garching) report on behalf of the GROND
team:

We observed the field of GRB 121001A (Swift trigger 535026, D'Elia et al.,
GCN # 13831) 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 on October 01, 2012, at 23:37 UT, 5.23 hr after the
GRB trigger. They were performed at an average seeing of 2".7 (in r') and
at an average airmass of 1.2.

We found a source in the z', J, H and K bands at coordinates (J2000):

RA   =  18:24:07.84

Dec. = -05:39:55.30

with an error of 0".3 in each coordinate.

This is consistent with the afterglow positions reported by Andreev et al.
(GCN # 13833) and Tello et al. (GCN # 13835), but slightly outside the
refined XRT position reported by Evans et al. (GCN # 18837).

Based on 1380 s of total exposures in g'r'i'z' (mean time 0.2415 days
after the trigger) and 1920 s in JHK (mean time 0.2363 days after the
trigger) we estimate preliminary AB magnitudes (upper limits are 3 sigma) of

g' > 23.6,

r' > 22.9,

i' > 22.2,

z' = 21.7 +/- 0.2,

J  = 19.5 +/- 0.4,

H  = 18.4 +/- 0.1 and

K  = 17.94 +/- 0.06.

Given magnitudes are calibrated against GROND zeropoints in the optical as
well as 2MASS field stars in the NIR and are not corrected for the high
Galactic foreground reddening of E_(B-V) ~ 1.3 mag (Schlegel et al. 1998).

Our r'- and i'-band non-detections vs. the detections reported by Andreev
et al. (GCN # 13833) and Tello et al. (GCN # 13835) confirm that this is
the afterglow of GRB 121001A. Furthermore, the bright source we detect in
K is not detected in 2MASS, while nearby sources of similar magnitude are
clearly visible in 2MASS.