GRB 170318A

B. Sbarufatti (INAF-OAB/PSU), D. N. Burrows (PSU), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 12:11:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170318A (trigger=743065).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 305.645, +28.409 which is 
   RA(J2000) = 20h 22m 35s
   Dec(J2000) = +28d 24' 32"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 30 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 12:13:44.4 UT, 108.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 305.66565,
28.40652 which is equivalent to:
   RA(J2000)  = 20h 22m 39.76s
   Dec(J2000) = +28d 24' 23.5"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 65 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 4.45
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 6.78e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 116 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 large, but uncertain extinction expected. 

Burst Advocate for this burst is B. Sbarufatti (boris.sbarufatti 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.)

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

Using  promptly downlinked XRT event data for GRB 170318A, we find an
enhanced XRT position of the afterglow: RA, Dec: 305.6668, 28.4066
which is equivalent to:
   RA (J2000)  = 20 22 40.03
   Dec (J2000) = +28 24 23.7
with an uncertainty of 2.1 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/743065.

Position enhancement is 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.

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

Using 2006 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 170318A, 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 = 305.66732, +28.40600 which is equivalent
to:

RA (J2000): 20h 22m 40.16s
Dec (J2000): +28d 24' 21.6"

with an uncertainty of 1.9 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.

J. R. Cummings (CPI),S. D. Barthelmy (GSFC), N. Gehrels (GSFC),
H. A. Krimm (NSF/USRA),A. Y. Lien (GSFC/UMBC),C. B. Markwardt (GSFC),
D. M. Palmer (LANL),T. Sakamoto (AGU),B. Sbarufatti (INAF-OAB/PSU),
M. Stamatikos (OSU),T. N. Ukwatta (LANL)(i.e. the Swift-BAT team):

Using the data set from T-239 to T+483 sec from the recent telemetry 
downlink,
we report further analysis of BAT GRB 170318A (trigger #743065)
(Sbarufatti, et al., GCN Circ. 20904
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 ). The BAT ground-calculated 
position is
RA, Dec = 305.662, 28.408 deg which is
    RA(J2000)  =  20h 22m 38.9s
    Dec(J2000) = +28d 24' 30.5"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 43%.

The mask-weighted light curve shows a single FRED-shaped pulse that starts
approximately T+20 sec, peaks at T+2 sec and decays to background by
T+100 sec.  T90 (15-350 keV) is 133.7 +- 42.8 sec (estimated error 
including systematics).

The time-averaged spectrum from -21.544 to 175.788 sec is best fit by a 
simple
power-law model.  The power law index of the time-averaged spectrum is
1.35 +- 0.11.  The fluence in the 15-150 keV band is 3.7 +- 0.3 x 
10^-06erg/cm2.
The 1-sec peak photon flux measured from T+1.87 sec in the 15-150 keV band
is 1.2 +- 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/743065/BA/

A. A. Breeveld (UCL-MSSL) and B. Sbarufatti (INAF-OAB/PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170318A
117 s after the BAT trigger (Sbarufatti et al., GCN Circ. 20904
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 ).
No optical afterglow consistent with the XRT position (Evans et al. GCN 
Circ. 20907
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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           117          266          147         >20.4
u_FC               329          552          220         >19.6
white              117         6605          363         >20.8
v                 2222         2241           19         >17.0
b                 2147         6400          216         >19.8
u                  329         6195          417         >20.1
w1                5790         5990          197         >19.4
m2                5585         5784          197         >19.3
w2                2197        11766          560         >20.4

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.97 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 (UVI), Eleonora
Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes��s
Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 170318A (Sbarufatti, et al., GCN 20904
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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 2017/03 18.51 to 2017/03 18.53 UTC (3.0 to
27.6 minutes after the BAT trigger), obtaining a total of 0.24 hours
exposure in the r and i bands and 0.11 hours exposure in the Z, Y, J, and H
bands.

We do not detect a source within the Swift-XRT error circle (Evans, et al.,
GCN 20907
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 ).  In comparison with the USNO-B1 and 2MASS catalogs, we obtain
the following upper limits (3-sigma):

 r > 23.39
 i > 22.82
 Z > 21.72
 Y > 21.56
 J > 21.12
 H > 20.73

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  We note that this field suffers
large Galactic extinction (A_V~3).

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

S. J. LaPorte (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester),
P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti
(INAF-OAB/PSU) and  report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 7.0 ks of XRT data for GRB 170318A, from 98 s to 41.1
ks after the  BAT trigger. The data comprise 94 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 light curve can be modelled with an initial power-law decay with an
index of alpha=1.09 (+0.51, -0.29), followed by a break at T+208 s to
an alpha of 2.74 (+0.76, -0.17).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 0.84 (+0.20, -0.19). The
best-fitting absorption column is  6.3 (+2.7, -1.9) x 10^21 cm^-2,
consistent with the Galactic value of 4.4 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 0.92 (+0.35,
-0.30) and a best-fitting absorption column of 6.4 (+4.6, -1.9) x 10^21
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 8.3 x 10^-11 (9.3 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.4 (+4.6, -1.9) x 10^21 cm^-2
Galactic foreground: 4.4 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     0.92 (+0.35, -0.30)

If the light curve continues to decay with a power-law decay index of
2.74, the count rate at T+24 hours will be 4.0 x 10^-7 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.4 x
10^-17 (3.8 x 10^-17) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00743065.

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

Max Genecov, WeiKang Zhang, and Alex Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 170318A (Sbarufatti, et al.,
GCN 20904
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 ) starting at 12:33:14 UT, ~23 minutes after the burst.
The target was at low elevation but rising. Observations were performed
with an automatic sequence in the clear (roughly R) and I filters, and
the exposure time was 20 s per image. We do not detect any optical
source within the XRT error circle (Evans, et al., GCN 20907
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 ).
The limiting magnitude of the co-added clear band image is ~17.6 at
a mid-time of 39.7 minutes after the burst.

K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender 
(Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D. 
Titterington, S. H. 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 
170318A (Sbarufatti et al., GCN 20904
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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 18.55 and Mar 21.50 
(UT) do not reveal any radio source at the XRT location (Evans et al., 
GCN 20907
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 ), with 3sigma upper limits of 159 uJy and 93 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/.