GRB 160321A

M. Stamatikos (OSU/NASA/GSFC), S. D. Barthelmy (GSFC),
A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU), S. B. Cenko (GSFC),
P. D'Avanzo (INAF-OAB), P.A. Evans (U Leicester), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL),
L. M. McCauley (PSU), A. Melandri (INAF-OAB), B. Mingo (U Leicester),
K. L. Page (U Leicester), T. G. R. Roegiers (PSU), T. Sakamoto (AGU),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 15:55:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160321A (trigger=680017).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 99.414, +5.715, which is 
   RA(J2000)  =  06h 37m 39s
   Dec(J2000) = +05d 42' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a few weak peaks
with a total duration of about 35 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 15:57:18.0 UT, 110.9 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 99.4192,
5.7474 which is equivalent to:
   RA(J2000)  = 06h 37m 40.60s
   Dec(J2000) = +05d 44' 50.8"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 118 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 consistent with the Galactic value of 7.16
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 114 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 large, but
uncertain extinction expected. 

Due to the proximity of the source to the Galactic plane
(lat = -0.43 degrees) we cannot determine whether this is a
Galactic source or a GRB, based on the immediately available data. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). 
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, N.Tyurina, P.Balanutsa, 
A.Kuznetsov, V.V.Chazov
Lomonosov Moscow State University,
Sternberg Astronomical Institute, Moscow State University

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

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

D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical 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)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Kislovodsk was pointed to the  GRB160321A 6 sec after notice 
time and 68 sec after trigger time at 2016-03-21 15:56:35 UT. We do not 
found optical transient within SWIFT error-box 
(Stamatikos et al., GCN 60321A
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 ) brighter then 13.1.
After Sunset we found:


Pro.type	Date time 	     Exp.time	Limit	Filt.	Tube.
Alert 	      2016-03-21 16:43:44	180	18.6	W	WEST
Alert 	      2016-03-21 16:43:44	180	18.1	W	EAST
Alert 	      2016-03-21 16:40:18	180	18.6	W	WEST
Alert 	      2016-03-21 16:36:45	180	18.6	W	WEST
Alert 	      2016-03-21 16:36:45	180	18.1	W	EAST
Alert 	      2016-03-21 16:33:16	180	18.5	W	WEST
Alert 	      2016-03-21 16:28:25	180	17.6	P	WEST
Alert 	      2016-03-21 16:28:25	180	17.6	P	EAST
Alert 	      2016-03-21 16:21:39	180	17.4	P	EAST

The galaxy latitude is about zero. So this is the optical free GRB.


The message may be cited.

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

Using 1066 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 160321A, 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 = 99.41970, +5.74771 which is equivalent
to:

RA (J2000): 06h 37m 40.73s
Dec (J2000): +05d 44' 51.8"

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.

A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R.
Roegiers (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester) and M. Stamatikos report on
behalf of the Swift-XRT team:

We have analysed 8.9 ks of XRT data for GRB 160321A (Stamatikos et al.
GCN Circ. 19211
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 ), from 96 s to 58.6 ks after the  BAT trigger. The data
comprise 31 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN Circ. 19213
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.36 (+0.13, -0.11).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.45 (+0.33, -0.30). The
best-fitting absorption column is  9.3 (+3.8, -2.1) x 10^21 cm^-2,
consistent with the Galactic value of 7.2 x 10^21 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 6.5 x 10^-11 (8.8 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.3 (+3.8, -2.1) x 10^21 cm^-2
Galactic foreground: 7.2 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.45 (+0.33, -0.30)

If the light curve continues to decay with a power-law decay index of
2.36, the count rate at T+24 hours will be 1.2 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x
10^-17 (1.1 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/00680017.

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

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(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 160321A (trigger #680017)
(Stamatikos, et al., GCN Circ. 19211
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 ).  The BAT ground-calculated position is
RA, Dec = 99.420, 5.753 deg which is
     RA(J2000)  =  06h 37m 40.7s
     Dec(J2000) = +05d 45' 09.3"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.

The mask-weighted light curve shows a single-pulse structure that starts
at ~ T0-22 sec, peaks at ~ T+2 sec, and ends at ~ T+23 sec.
T90 (15-350 keV) is 33.6 +- 4.8 sec (estimated error including systematics).

The time-averaged spectrum from T-20.9 to T+19.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.89 +- 0.19.  The fluence in the 15-150 keV band is 5.3 +- 0.7 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+2.17 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.

Based on the ground analysis result, this event is very likely a GRB.
However, given that it is on the Galactic Plane (lat = -0.43 deg.),
we cannot rule out a galactic origin.  We note that the BAT time averaged
spectrum is soft but still in the typical range for BAT GRBs.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/680017/BA/

S.W.K. Emery (UCL-MSSL) and M. Stamatikos (OSU/NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160321A
115 s after the BAT trigger (Stamatikos et al., GCN Circ. 19211
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 ).
No optical afterglow consistent with the XRT position
(Beardmore et al. GCN Circ. 19213
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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) exposure and subsequent exposures are:

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

white_FC           115          265          147         >20.4
u_FC               273          523          246         >19.7
white              115         6458          546         >21.1
v                  603         6870          452         >19.5
b                  529         6253          255         >20.1
u                  273        12683          570         >20.1
w1                 652        12607         1141         >20.2
m2                 627        11700         1205         >20.1
w2                 579         6664          452         >19.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.75 in the direction of the burst
(Schlegel et al. 1998).

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (GSFC/STScI),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
Jos�� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes��s Gonz��lez (UNAM),
Carlos Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC),
John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 160321A (Stamatikos, et al., GCN 19211
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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 Astron��mico Nacional
on Sierra San Pedro M��rtir from 2016/03 22.14 to 2016/03 22.29 UTC (11.32
to 15.08 hours after the BAT trigger), obtaining a total of 2.47 hours
exposure in the r and i bands and 0.82 hours exposure in the Z, Y, J, and H
bands.

For a source within the Swift-XRT error circle (Beardmore, et al., GCN
19213
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 ), in comparison with the USNO-B1 and 2MASS catalogs, we obtain the
following weak detections and upper limits (3-sigma):

 r > 23.84
 i = 22.32 +/- 0.11
 Z = 22.49 +/- 0.34
 Y > 22.19
 J > 21.53
 H > 21.27

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  Further analysis is ongoing.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

E. Mazaeva (IKI), A. Volnova
  (IKI), R. Inasaridze (AbAO), V. Ayvazian (AbAO), I. Molotov (KIAM), A. 
Pozanenko (IKI) report on behalf of larger
GRB follow-up collaboration:

We observed the field of Swift GRB 160321A (Stamatikos et al., GCN 
19211
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 ) with AS-32 (0.7m) telescope of Abastumani Observatory starting on 
Mar. 21 (UT) 16:26:45. We obtained several unfiltered images of the 
field. We do not detect any source within enhanced XRT error circle 
(Beardmore et al., GCN 19213
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 ) down to 21.9m. A probable source (S/N = 2) 
detected 3.5 arcsec South from the center of XRT error circle (Beardmore 
et al., GCN 19213
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 ) in coordinates (J2000) 06:37:40.74 +05:44:48.2 +/- 
0.5 arcsec in both coordinates.

Preliminary photometry of the field is following


Date       UT start   t-T0     Filter  Exp.    UL (3 sigma)
                      (mid, days)       (s)

2016-03-21 16:26:45   0.06839  none    41*120  21.9

Photometry is based on nearby USNO-B1.0 stars
USNO-B1_id   R2
0956-0104166 16.23
0957-0105913 15.38
0957-0106394 14.58
0956-0104566 15.41

K. P. Mooley, T. D. Staley, R. P. Fender (Oxford), G. E. Anderson 
(Curtin), C. Rumsey, D. Titterington, S. Carey, J. Hickish, Y. C. 
Perrott, N. Razavi-Ghods, P. Scott (Cambridge), K. Grainge, A. Scaife 
(Manchester)

The AMI Large Array robotically triggered on the Swift alert for GRB 
160321A (Stamatikos et al., GCN 19211
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 ) as part of the 4pisky program, 
and subsequent follow up observations were obtained up to 10 days 
post-burst. Our observations at 15 GHz on 2016 Mar 21.70, Mar 22.85, Mar 
24.74, Mar 29.66, and Mar 31.68 (UT) do not reveal any radio source at 
the XRT location (Beardmore et al., GCN 19213
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 ), with 3sigma upper limits 
of 195 uJy, 261 uJy, 162 uJy, 207 uJy, and 189 uJy respectively.

We thank the AMI staff for scheduling these observations. The AMI-GRB 
database is a log of all GRB follow up observations with the AMI, and is 
available at http://4pisky.org/ami-grb/.