GRB 240511A

The Fermi GBM team reports the detection of a likely LONG GRB

At 18:06:20 UT on 11 May 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240511A (trigger 737143585.263482 / 240511754).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 336.8, Dec = 3.8 (J2000 degrees, equivalent to J2000 22h 27m, 3d 47'), with a statistical uncertainty of 3.6 degrees.

The angle from the Fermi LAT boresight is 49.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240511754/quicklook/glg_skymap_all_bn240511754.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240511754/quicklook/glg_healpix_all_bn240511754.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240511754/quicklook/glg_lc_medres34_bn240511754.gif

S. Laha (GSFC/UMBC), A. D'Ai (INAF-IASFPA),
V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R. Gupta (NASA/GSFC),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 18:06:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240511A (trigger=1227767).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 336.664, +8.514 which is 
   RA(J2000) = 22h 26m 39s
   Dec(J2000) = +08d 30' 49"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed multi-peaked
structure with a duration of about 100 sec.  The peak count rate
was ~ 4600 counts/sec (15-350 keV), at ~20 sec after the trigger. 

The XRT began observing the field at 18:08:36.4 UT, 103.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 336.67568, 8.51315
which is equivalent to:
   RA(J2000)  = 22h 26m 42.16s
   Dec(J2000) = +08d 30' 47.3"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 41 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 https://www.swift.ac.uk/sper. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 3.70e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 110 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 expected extinction corresponding to E(B-V) of
0.098. 

Burst Advocate for this burst is S. Laha (sib.laha AT gmail.com). 
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/)

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

Using  promptly downlinked XRT event data for GRB 240511A, we find an
enhanced XRT position of the afterglow: RA, Dec: 336.67568, 8.51317
which is equivalent to:
   RA (J2000)  = 22 26 42.16
   Dec (J2000) = +08 30 47.4
with an uncertainty of 1.9 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/1227767.

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.

V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik,  D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile
(Observatorio Astronomico Felix Aguilar OAFA),

R. Rebolo, M. Serra
(The Instituto de Astrofisica de Canarias),

D. Buckley
(South African Astronomical Observatory),

O.A. Gress, N.M. Budnev, O.Ershova
(Irkutsk State University, API),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez
(INAOE, Guillermo Haro Astrophysics Observatory),

A. Tlatov, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory),

V. Yurkov, A. Gabovich
(Blagoveschensk Educational State University)

MASTER-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 240511A ( S. Laha et al., GCN 36430
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 ) errorbox  24477 sec after notice time and 24510 sec after trigger time at 2024-05-12 00:55:23 UT, with upper limit up to  17.6 mag. The observations began at zenith distance = 79 deg. The sun  altitude  is -55.5 deg. 

The galactic latitude b = -40 deg., longitude l = 74 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2452393

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   24600 |         MASTER-SAAO |   C |   180 | 17.6 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik,  D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile
(Observatorio Astronomico Felix Aguilar OAFA),

R. Rebolo, M. Serra
(The Instituto de Astrofisica de Canarias),

D. Buckley
(South African Astronomical Observatory),

O.A. Gress, N.M. Budnev, O.Ershova
(Irkutsk State University, API),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez
(INAOE, Guillermo Haro Astrophysics Observatory),

A. Tlatov, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory),

V. Yurkov, A. Gabovich
(Blagoveschensk Educational State University)

MASTER-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 240511A ( Fermi GBM team, GCN 36428
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 ) errorbox  24509 sec after notice time and 24543 sec after trigger time at 2024-05-12 00:55:23 UT, with upper limit up to  18.0 mag. The observations began at zenith distance = 79 deg. The sun  altitude  is -55.5 deg. 

The galactic latitude b = -44 deg., longitude l = 70 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2452442

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   24633 | 2024-05-12 00:55:23 |         MASTER-SAAO | (22h 23m 04.05s , +08d 23m 50.7s) |   C |   180 | 17.6 |        
   25535 | 2024-05-12 01:10:25 |         MASTER-SAAO | (22h 24m 51.61s , +08d 10m 11.7s) |   C |   180 | 17.1 |        
   25535 | 2024-05-12 01:10:25 |         MASTER-SAAO | (22h 23m 01.57s , +08d 23m 53.8s) |   C |   180 | 17.9 |        
   25896 | 2024-05-12 01:16:26 |         MASTER-SAAO | (22h 24m 46.54s , +08d 10m 52.2s) |   C |   180 | 17.4 |        
   25896 | 2024-05-12 01:16:26 |         MASTER-SAAO | (22h 22m 56.46s , +08d 24m 32.8s) |   C |   180 | 17.9 |        
   26096 | 2024-05-12 01:19:45 |         MASTER-SAAO | (22h 24m 48.69s , +08d 09m 19.9s) |   C |   180 | 17.5 |        
   26096 | 2024-05-12 01:19:45 |         MASTER-SAAO | (22h 22m 58.61s , +08d 22m 59.7s) |   C |   180 | 18.0 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

Daniele B. Malesani (DAWN/NBI and Radboud Univ.) and Bo Milvang-Jensen (DAWN/NBI) report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 240511A (Laha et al., GCN 36430
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 ; Fermi GBM team, GCN 36428
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 ) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Our observations started on 2024 May 12.186 UT (10.35 hr after the trigger) using the SDSS r and z filters. The seeing was moderate, about 1.5" in the r band.

In the stack of three r-band frames (900 s exposure), a faint object can be seen at a position consistent with the XRT error circle (Evans, GCN 36431
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 ). At the same location a faint source can be glimpsed also in the z images (1000 s exposure). Its coordinates are:

RA = 22:26:42.23
Dec = 08:30:46.6

with an estimated 0.5" uncertainty.

Calibrated against nearby objects from the Pan-STARRS catalog, we measure r = 23.36 +- 0.22 (AB), at a mean epoch of May 12.191 UT. Inspection of the Legacy Survey frames reveals no bright object at the source location, confirming that this is most likely the optical afterglow of GRB 240511A.

C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB),
J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), K.L.
Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 8.5 ks of XRT data for GRB 240511A, from 94 s to 36.0
ks after the  BAT trigger. The data comprise 345 s in Windowed Timing
(WT) mode (the first 6 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. The best available XRT position
 (using the promptly downlinked event data, the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec =
336.67568, 8.51317 which is equivalent to:

RA (J2000): 22 26 42.16
Dec(J2000): +08 30 47.4

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The late-time light curve (from T0+5.2 ks) can be modelled with a
power-law decay with a decay index of alpha=0.76 (+/-0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.07 (+/-0.04). The
best-fitting absorption column is  2.60 (+/-0.16) x 10^21 cm^-2, in
excess of the Galactic value of 8.5 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.08 (+0.16, -0.15)
and a best-fitting absorption column of 1.6 (+0.5, -0.4) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.4 x 10^-11 (4.6 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 8.5 x 10^20 cm^-2
Excess significance: 2.8 sigma
Photon index:	     2.08 (+0.16, -0.15)

If the light curve continues to decay with a power-law decay index of
0.76, the count rate at T+24 hours will be 0.030 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x
10^-12 (1.4 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01227767.

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

M. Niwano, I. Takahashi, M. Sasada, N. Higuchi, S. Hayatsu, H. Seki, S. Joshima, Y. Kubo, H. Hagio, Y. Yatsu and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 240511A (Fermi GBM Team, GCN 36428
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 ) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno.

The observation started at 2024-05-11 18:08:03 UT (103 sec after the Fermi/GBM trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the enhanced Swift/XRT error region (Evans, GCN 36431
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 ), despite the detection report of Daniele et al., (GCN 36442
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 ). We obtained the 5-sigma limits of the stacked images as follows.

T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
258 | 2024-05-11 18:23:31.65 | 970 | g'>18.8, Rc>18.9, Ic>18.5
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the trigger
T-EXP: Total Exposure time

We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire). 

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

Using 1476 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 240511A, 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 = 336.67595, +8.51273 which is equivalent
to:

RA (J2000): 22h 26m 42.23s
Dec (J2000): +08d 30' 45.8"

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.

Geoffrey Mo (MIT), Viraj Karambelkar (Caltech), Danielle Frostig (MIT), Benjamin Schneider (MIT), Robert Stein (Caltech), Nathan Lourie (MIT), Tomas Ahumada (Caltech), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:

We observed the field of GRB 240511A (Fermi GBM team, GCN 36428
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 ; Laha et al., GCN 36430
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 ) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1 square degree WINTER camera (Lourie et al. 2020). 

Observations began at 2024-05-12T10:13:53 UTC (~16 hours after the GRB) and consisted of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline (https://github.com/winter-telescope/mirar). 

We do not detect the optical counterpart discovered by NOT (Malesani et al., GCN 36442
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 ; Lipunov et al., GCN 36435
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 ; Lipunov et al., GCN 36436
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 ; Niwano et al., GCN 36445
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 ) at the Swift-XRT position of the afterglow (Evans et al., GCN 36431
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 ; Salvaggio et al., GCN 36443
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 ; Evans et al., GCN 36446
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 ) setting the following upper limit: J ~ 19.1 mag (AB).

WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucille Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
T. Sakamoto (AGU) (i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 240511A (trigger #1227767)
(Laha et al., GCN Circ. 36430
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 ).  The BAT ground-calculated position is
RA, Dec = 336.669, 8.515 deg which is
   RA(J2000)  =  22h 26m 40.6s
   Dec(J2000) = +08d 30' 54.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.

The mask-weighted light curve shows a major pulse structure that
starts at ~T-50 s and ends at ~T+100 s. There are many smaller pulses
on top of the main pulse structure. The highest peak occurred at
~T+36 s. In addition, there are some weak emissions that start at
~T-100 s and end at ~T+200 s. We note that there are two obvious data
gaps within the T100 duration: (1) ~T+10 s to ~T+20 s and
(2) ~T+155 s to ~T+180 s. These data gaps may be filled by further
data downlink. T90 (15-350 keV) is 148.55 +- 20.07 sec (estimated
error including systematics).

The time-averaged spectrum from T-92.012 to T+ 203.704 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.59 +- 0.04.  The fluence in the 15-150 keV band
is 1.06 +- 0.02 x 10^-5 erg/cm2. The 1-sec peak photon flux measured
from T+35.12 sec in the 15-150 keV band is 2.6 +- 0.2 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1227767

L. Scotton (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 18:06:20.26 UT on 11 May 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240511A (trigger 737143585/240511754),
which was also detected by Swift BAT (S. Laha et al. 2024, GCN 36430
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 ).

The Fermi GBM Final Real-time Localization (GCN 36428
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 ) is consistent
with the Swift XRT position (P.A. Evans et al. 2024, GCN 36446
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 ).

The angle from the Fermi LAT boresight is 45.7 degrees.

The GBM light curve consists of a multi-peaked emission episode with a duration (T90)
of about 95 s (50-300 keV). The time-averaged spectrum
from T0-2.0 to T0+104.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.35 +/- 0.03 and the cutoff energy,
parameterized as Epeak, is 250 +/- 20 keV.

The event fluence (10-1000 keV) in this time interval is
(2.54 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+53 s in the 10-1000 keV band is 4.7 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

Lauren Rhodes, Rob Fender (Oxford), Dave Green, Dave Titterington (Cambridge) report:

We observed the field of GRB 240511a (GCN 36428
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 , 36430
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 ) with the Arcminute Microkelvin Imager - Large Array (AMI-LA) at 15.5 GHz beginning at UT 04:33:54 on 15-May-2024 for a total of 4 hours. The flux standard 3c286 was used to calibrate the bandpass response and flux scale of the AMI-LA and J2232+1143 was used as an interleaved complex gain calibrator.

We detected an unresolved radio source at the position of the afterglow candidate (GCN 36442
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 ) with a flux density of about 600uJy/beam. The rms noise in the field is about 70uJy/beam.

More observations are planned.

We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA.

A. de Ugarte Postigo (CNRS, OCA/LAM), J. F. Agui Fernandez (CAHA), N. A. Rakotondrainibe (LAM), C. C. Thoene (ASU/CAS), D. B. Malesani (DAWN/NBI and Radboud Univ.), N. R. Tanvir (U. Leicester), J. P. U. Fynbo (DAWN/NBI), L. Izzo (INAF-OACn & DARK/NBI), S. Geier (GRANTECAN), R. Scarpa (GRANTECAN) report:

We observed the counterpart	of GRB 240511A (Laha et al., GCN 36430
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 ; Scotton & Meegan, GCN 36460
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 ) with OSIRIS+ on the 10.4 m GTC, at the Roque de los Muchachos Observatory (La Palma, Spain). The observations started with acquisition images in the r-band, where the object reported by Malesani et al. (GCN 36442
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 ) is detected as a faint source. The stack of these images, with a total exposure of 320 s and a mean time of 10.42 hr after the burst shows the afterglow at r(AB) = 23.80 +/- 0.16 mag, as compared to field stars of the SDSS catalogue.

We later proceeded to perform long slit spectroscopy with grism R1000B, covering the spectral range between 3600 and 7880 AA at a resolving power of ~600. Unfortunately the observing window was very short and we only managed to obtain 2 exposures of 900 s. The object is detected as a very weak trace, visible redder than 4700 AA, which implies a redshift larger than 4.1 if we consider the Lyman limit as the constraining wavelength.

Two further nearby objects are covered within the slit. The first one, at 5.9" North West of the afterglow and the second 10.4" South East of it. The spectrum of the second object allows us to identify it as a galaxy at redshift of z=0.416 through the detection of the [OII] doublet and H-beta. The first object has an emission feature at a similar wavelength as the [OII] of the other source. If we assume that this is also [OII] the redshift of the first galaxy would be z=0.420. At these redshifts, the afterglow would be at a projected distance of 33 and 58 kpc, making them likely unrelated to the GRB, assuming a collapsar origin.

Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS) report on behalf of a larger collaboration.

We observed the field of GRB 240511A (The Fermi GBM team, GCN 36428
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 ; Laha et al., GCN 36430
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 ; Evans, GCN 36431
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 ; Salvaggio et al., GCN 36443
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 ; Evans et al., GCN 36446
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 ; Krimm et al., GCN 36459
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 ) using the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at SAAO, South Africa. The telescope is equipped with a CCD (FOV: 13 x 13 arcmin, scale: 0.39 arcsec/pixel) and V, R filters. Observations began on May 12, starting 8.8269 hours after the GRB trigger.

We did not detect the optical transient (OT) reported by Malesani and Milvang-Jensen (GCN 36442
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 ) and de Ugarte Postigo et al. (GCN 36498
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 ) in our images. Our non-detection upper limits are consistent with those reported by other teams (Lipunov et al., GCNs 36435
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 , 36436
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 ; Niwano et al., GCN 36445
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 ; Mo et al., GCN 36452
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 ).

UT Start–End	Filter	Exposure (s)	Upper Limit
02:55:57–03:15:57	  R	1200	R_lim = 21.8
09:39:59–10:04:59	  V	1500	V_lim = 22.4
The field was calibrated against nearby SDSS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.