GRB 130420B

S. R. Oates (UCL-MSSL), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
V. D'Elia (ASDC), N. Gehrels (NASA/GSFC), S. T. Holland (STScI),
N. P. M. Kuin (UCL-MSSL), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), M. H. Siegel (PSU) and
E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift
Team:

At 12:56:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130420B (trigger=553996).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 183.120, +54.386 which is 
   RA(J2000) = 12h 12m 29s
   Dec(J2000) = +54d 23' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 12:57:25.6 UT, 54.5 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. About 8 seconds of data were obtained in WT mode before Swift 
slewed away from the field, indicating a bright X-ray source in the field, 
but no position is available from the WT data. No XRT position will be 
available until data from the second orbit are processed. 

UVOT took a finding chart exposure of	8 seconds with the White filter
starting 57 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 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
Results from the list of sources generated on-board are not available at this
time. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.02. 

Burst Advocate for this burst is S. R. Oates (samantha.oates AT 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.)

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

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

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

V.Krushinski, I.Zalozhnih,  A. Popov
Ural Federal University, Kourovka

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

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 Blagoveschensk was pointed to the  GRB130420B (Oates et. al 
GCN 14411
Loading...
 
 )  44 sec s after notice time and 63 sec after GRB time at 
2013-04-20 12:57:34.948 UT in two polarizations. On 
our first (10s exposure) set we haven`t found optical transient  within 
SWIFT error-box (ra=12 12 28 dec=+54 23 24 r=0.050000).
The 5-sigma upper limit has been about 16.0 mag.
The message may be cited.

A. Melandri (INAF-OAB), C. Guidorzi (U. Ferrara) and C. G. Mundell  
(Liverpool) report on behalf of a larger collaboration:

The 2-m Faulkes Telescope North (FTN) automatically began observing  
GRB130420B (Oates et al., GCN 14411
Loading...
 
 ) on April 20, 12:59:50 UT  
corresponding to ~200 seconds after the burst event.

We detect no new, uncatalogued source in the BAT error circle down to  
the following limiting magnitudes:

Mid time from   Exp    Filter   Mag limit
trigger (min)   (sec)
---------------------------------------------------
28.62           540      R       > 20.5
32.75           520      I        > 20.0
---------------------------------------------------

The magnitudes are calibrated against nearby USNO-B1.0 stars.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),  W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), S. R. Oates (UCL-MSSL),
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+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130420B (trigger #553996)
(Oates et al., GCN 14411
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 183.095, 54.376 deg which is
    RA(J2000)  =  12h 12m 22.7s
    Dec(J2000) = +54d 22' 33.2"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
  
The mask-weighted light curve shows a single gradual peak beginning at about
T-5 seconds and detectable to T+12 seconds.  T90 (15-350 keV) is 10.2 +- 5.4 sec
(estimated error including systematics).
  
The time-averaged spectrum from T-1.0 to T+16.0 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.28 +- 0.52,
and Epeak of 71.3 +- 14.0 keV (chi squared 42.36 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.0 +- 0.5 x 10^-07 erg/cm2
and the 1-sec peak flux measured from T+0.91 sec in the 15-150 keV band is
1.4 +- 0.1 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.45 +- 0.10 (chi squared 61.94 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/553996/BA/

K.L. Page, P.A. Evans and M.R. Goad (U. Leicester) report
on behalf of the Swift-XRT team:

Using 1436 s of XRT Photon Counting mode data and 3 UVOT images, 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 =
183.12805, 54.39054 which is equivalent to:

RA (J2000):  12 12 30.73
Dec (J2000): +54 23 25.9

with an uncertainty of 2.0 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.

X.-H. Zhao (YNAO and PSU), J. Mao (RIKEN and YNAO), J.-M. Bai
(YNAO) report on behalf of a larger collaboration:

We observed the field of GRB 130420B (Page et al., GCN 14421
Loading...
 
 ; Oates et al., GCN 14411
Loading...
 
 ) with 2.4m Gao-Mei-Gu (GMG) telescope. Observations
started at 13:21:14 UT on 2013-04-20 (i.e., 0.4 hrs after the burst). The observations lasted for ~10min. The afterglow was not found at
the XRT position, down to a upper limit of R>22.6.

We thank the GMG staff, especially Yu-Xin Xin, Gui-Hua He and Jian-Duo He for
performing these observations.

[GCN OPS NOTE(20apr13):  I hav removed their copy-paste double TITLE block.]

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

The Swift/UVOT began settled observations of the field of GRB 130420B
57 s after the BAT trigger (Oates et al., GCN Circ. 14411
Loading...
 
 ).
No optical afterglow consistent with the XRT position (Page et al., GCN
circ.
14421
Loading...
 
 ) is detected in the initial and summed UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:

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


white               57         5841          460         >21.7
v                 4707         4907          197         >19.6
b                 4091         5727          393         >20.9
u                 3886         5521          393         >20.6
w1                5117         5317          197         >20.1
m2                4912         5111          197         >19.8
w2                4502         4702          197         >20.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).

Dong Xu (DARK/NBI), Chen Cao, Shaoming Hu, Dayong Ren (SDU) report:

We observed the field of GRB 130420B (Oates et al., GCN 14411
Loading...
 
 ) using
the 1m telescope located in Weihai, Shandong Province, China. We
obtained 12x300s I-band frames with a mean time of 2.973 hr after the
BAT trigger.

No optical source is detected within the enhanced XRT error circle
(Page et al., GCN 14421
Loading...
 
 ) in the stacked image, down to a limiting
magnitude of I>21.2 mag.

K.L. Page (U. Leicester) and S. R. Oates (UCL-MSSL) report on behalf of
the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 130420B (Oates  et al. GCN
Circ. 14411
Loading...
 
 ),  from 39 s to 39.9 ks after the  BAT trigger. The data
comprise 18 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 2638 s of PC mode data and 4 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 = 183.12838, +54.39054
which is equivalent to:

RA (J2000): 12h 12m 30.81s
Dec(J2000): +54d 23' 26.0"

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=1.11 (+0.09, -0.14).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.0 (+/-0.4). The
best-fitting absorption column is  6.8 (+9.6, -5.4) x 10^20 cm^-2,
consistent with the Galactic value of 1.4 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 3.5 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:	     6.8 (+9.6, -5.4) x 10^20 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.0 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
1.11, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.1 x
10^-14 (8.5 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/00553996.

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

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 130420B (Oates et al., GCN 14411
Loading...
 
 ) 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 2013/04 21.15 to 2013/04 21.29 UTC (14.54 to
18.10 hours after the BAT trigger), obtaining a total of 1.32 hours
exposure in the r' and i' bands and 0.55 hours exposure in the Z, Y, J, and
H bands.

For a source within the Swift-XRT error circle (Page et al., GCN 14430
Loading...
 
 ), in
comparison with SDSS DR8 and 2MASS, we obtain the following upper limits
(3-sigma) in the AB magnitude system:

 r'> 23.19
 i'> 22.99
 Z > 21.87
 Y > 21.39
 J > 21.20
 H > 20.53

These magnitudes are not corrected for Galactic extinction in the direction
of the GRB.

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

Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 12:56:32.99 UT on 20 April 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 130420B (trigger 388155395 / 130420539),
which was also detected by Swift/BAT (Oates et al., GCN 14411
Loading...
 
 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is about 50 degrees.

The GBM light curve shows a single pulse with a duration (T90) of
about 16 s (50-300 keV). The time-averaged spectrum from T0-4 s
to T0+4 s is best fit by a power law function with an exponential
high-energy cutoff. The power law index is 0.24 +/- 0.25 and
the cutoff energy, parameterized as Epeak, is 91 +/- 9 keV.

The event fluence (10-1000 keV) in this time interval is
(1.04 +/- 0.08)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band
is 2.6 +/- 0.2 ph/s/cm^2.

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

B. A. Zauderer and E. Berger (Harvard) report on behalf of the
CARMA Key Project "A Millimeter View of the Transient Universe"
and a larger collaboration:

"We observed the position of GRB 130420B (Oates et al.; GCN 14411
Loading...
 
 ) 
beginning 2013 Apr 23.29 UT (dt = 2.75 d) with the Very Large Array 
(VLA) and beginning 2013 Apr 22.91 (dt = 2.37 d) with the Combined Array 
for Research at Millimeter Astronomy (CARMA).  We do not find any 
significant radio emission at the position of the enhanced Swift-XRT 
position (Page et al.; GCN 14421
Loading...
 
 ) at a mean frequency of 5.8 GHz (VLA) 
to a 3-sigma limit of 32 uJy, at 21.8 GHz (VLA) to a 3-sigma limit of 47 
uJy, or at 85 GHz (CARMA) to a 3-sigma limit of 0.78 mJy.

We thank the VLA and CARMA observatories for their support of these 
observations."