GRB 160411A

A.J. Levan (U. Warwick), W. Fong (Arizona) and N.R. Tanvir (Leicester) report on behalf of a larger collaboration:

���We obtained a second epoch of i-band observations of the short-GRB 160411A (Page et al. GCN 19279
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 ) on 2016 April 13, 10:01 UT. Photometry suggests that our previously identified source B (Levan & Fong GCN 19293
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 ) has faded by approximately 0.9 magnitudes between the two epochs obtained 48 hours apart, although a source close to this location is still faintly detected in our imaging. We therefore suggest this source may be the optical afterglow of GRB 160411A.

We thank the Gemini staff, in particular Bryan Miller and Rodolfo Angeloni for assistance with these observations.���

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (AGU), 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 downlinks,
we report further analysis of BAT short GRB 160411A (trigger #682339)
(Page, et al., GCN Circ. 19279
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 ).  The BAT ground-calculated position is
RA, Dec = 349.370, -40.258 deg, which is 
   RA(J2000)  =  23h 17m 28.8s 
   Dec(J2000) = -40d 15' 30.3" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 27%.
 
The mask-weighted light curve shows two overlapping peaks starting at
~T+0.0 and ending at ~T+0.5 sec.  T90 (15-350 keV) is 0.36 +- 0.08 sec
(estimated error including systematics).
 
The time-averaged spectrum from T+0.06 to T+0.46 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.43 +- 0.28.  The fluence in the 15-150 keV band is 8.0 +- 1.8 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.24 sec in the 15-150 keV band
is 1.5 +- 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/682339/BA/

A.J.Levan (U. Warwick), W. Fong (Arizona) report on behalf of a larger collaboration:

���We observed the location of GRB 160411A (Page et al. GCN 19279
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 , Evans et al. GCN 19283
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 ) with Gemini-S and GMOS starting at 09:35 UT on 2016 April 11. Observations were taken in the i-band and began 9 hours after the BAT trigger. They were taken at the start of morning twilight as the source was rising, because of this the seeing is poor (1.4���) and depth relatively shallow. 

The region around the enhanced XRT position is relatively complex, with multiple sources in the surrounding area. Two obvious sources are located just outside the Eastern and Western edge of the XRT circle at locations of

Source A: 
RA(J2000) 23:17:25.99
DEC(J2000) -40:14:32.0

Source B: 
RA(J2000) 23:17:25.37
DEC(J2000) -40:14:30.5

The sources have comparable magnitude and appear to be marginally extended, although the poor seeing and signal to noise complicates such analyses. 

With thank the Gemini staff, in particular Bryan Miller, for their assistance with these observations���

R Yates, T-W Chen, and J Greiner (all MPE Garching) report on behalf of
the GROND team:

We observed the field of GRB 160411A (Swift trigger 682339; Page et al.,
GCN #19279
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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 telescope at ESO La Silla
Observatory (Chile).

Observations started at 09:14 UT on 11-04-2016, 7 hr 45 min after the GRB
trigger. They were performed at an average seeing of 1.9" in the r'-band
and at an average airmass of 1.8.

Based on the first 49 min of total exposures, we do not detect a source
within the 4.0" Swift-XRT error circle reported by Perri et al. (GCN
#19281
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 ) down to (all in the AB system):

g' > 23.7 mag,
r' > 23.9 mag,
i' > 23.1 mag,
z' > 22.9 mag,
J > 21.3 mag,
H > 20.8 mag, and
K > 19.9 mag.

The given limits are derived based on calibrating the images against GROND
zeropoints and 2MASS field stars and are not corrected for the Galactic
foreground extinction corresponding to a reddening of E_(B-V)=0.02 mag in
the direction of the burst (Schlafly & Finkbeiner 2011).

M. H. Siegel (PSU) and K. L. Page (U Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160411A
3139 s after the BAT trigger (Page et al., GCN Circ. 19279
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 ).
No optical afterglow consistent with the XRT position
(Perri et al. GCN Circ. 19281
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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          3139         3289          147         >20.5
white             3139         4521          344         >21.0
v                 3295         4931          393         >19.4
b                 4116         4316          197         >19.9
u                 3910         5546          393         >20.0
w1                3705         5342          393         >20.2
m2                3500         5136          393         >20.1
w2                4527         4726          197         >20.0

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).

O.J. Roberts (UCD), C.M. Hui (NASA/MSFC) report on
behalf of the Fermi GBM Team:

"At 01:28:52.52 UT on the 11th of April 2016, the Fermi
Gamma-Ray Burst Monitor triggered and located GRB 160411A
(trigger 482030936 / 160411062), which was also detected by
Swift (Page et al. 2016, GCN 19279
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 ). The GBM on-ground
location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger
time using the Swift XRT position is about 108 degrees.

The GBM light curve consists of a weak, short burst with a
duration (T90) of about 0.2 s (50-300 keV). The time-averaged
spectrum from T0-0.51 s to T0-0.35 s is best fit by a power
law function with an exponential high-energy cutoff function,
with Epeak = 161 +/- 37 keV and alpha = 0.26 +/- 0.67.

The event fluence (10-1000 keV) in this time interval is
(1.38 +/- 0.30)E-07 erg/cm^2. The 64ms peak photon flux
measured starting from T0-0.51 s in the 10-1000 keV band
is 6.4 +/- 1.4 ph/s/cm^2.

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

C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia
(ASDC), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU)
and K.L. Page report on behalf of the Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 160411A (Page et al. GCN
Circ. 19279
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 ), from 3.1 ks to 22.5 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Evans et al. (GCN Circ. 19283
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.5 (+3.3, -0.9).

If the light curve continues to decay with a power-law decay index of
1.5, the count rate at T+24 hours will be 2.0 x 10^-4 count s^-1

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00682339.

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

V. Lipunov, E. Gorbovskoy,   N.Tyurina, V.Kornilov, P.Balanutsa, 
A.Kuznetsov, D.Kuvshinov
Lomonosov Moscow State University, Sternberg Astronomical Institute

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

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

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

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

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

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 SAAO was pointed to the  GRB160411A 34 sec after notice time 
and 64 sec after trigger time at 2016-04-11 01:30:00 UT. On our first (10s 
exposure)  set we haven`t found optical transient  within SWIFT error-box 
(Page et al GCN 19279
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 , Evans et al GCN 19283
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 ).
The 5-sigma upper limit has been about 16.0 mag  on single (10 sec 
exposure) and 18.5  on coadd (170 sec exposure) image.
The observations made on high zenit distance (z=80 deg).
The message may be cited.

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

Using 1177 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 160411A, 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 = 349.35691, -40.24227 which is equivalent
to:

RA (J2000): 23h 17m 25.66s
Dec (J2000): -40d 14' 32.2"

with an uncertainty of 2.4 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.

M. Perri (ASDC), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU) and G. Cusumano
(INAF-IASF PA) report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 160411A at 02:21:04.2 UT,
3132.3 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 349.35590,
-40.24247 which is equivalent to:
   RA(J2000)  = 23h 17m 25.42s
   Dec(J2000) = -40d 14' 32.9"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 103 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.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.61
x 10^20 cm^-2 (Willingale et al. 2013).

K. L. Page (U Leicester), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 01:28:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160411A (trigger=682339).  Swift could not immediately
slew to the burst due to an observing constraint. 
The BAT on-board calculated location is 
RA, Dec 349.362, -40.271 which is 
   RA(J2000) = 23h 17m 27s
   Dec(J2000) = -40d 16' 14"
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 0.5 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0.2 sec after the trigger. 

Due to an observing constraint, Swift will not slew until T0+50.4
minutes. There will be no XRT or UVOT data until this time. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.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.)