GRB 210517A

Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Gu Lim (SNU
ARC/SNU), on behalf of GECKO collaboration

 We searched for the optical counterpart of GRB 210517A (V. E'Elia et al.
GCN #30032
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 ) with the 0.36-m class KCT (KIAS Chamnun Telescope) in
DeepSkyChile, one of the facilities of the GW EM-Counterpart Korean
Observatory (GECKO).

 We observed the center of Swift/XRT localization (RA, Dec = 358.2245
-39.1020) +2.94 hours after report, but could not find any possible
transient within the field of view and at the reported location of optical
afterglow (N. R. Tanvir et al. GCN 30037
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 ). We calibrated flux with the
APASS catalog and used an AB magnitude system. Depth means 5 sigma upper
limit for a point source detection. The magnitudes are not corrected for
galactic extinction.

------
Filter Date-obs[UT] Exp.time[s] Depth
I 2021-05-17T08:24:35.583 180*3 18.435
R 2021-05-17T08:37:00.750 180*3 19.581
V 2021-05-17T08:49:25.333 180*3 20.005
B 2021-05-17T09:01:50.250 180*3 20.047

Gravitational-wave EM Counterpart Korean Observatory (GECKO) is a network
of 10+ 0.5m to 1m class telescopes over the world.

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),  V. D'Elia (SSDC & INAF-OAR), 
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-240 to T+659 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210517A (trigger #1048783)
(D'Elia, et al., GCN Circ. 30032
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 ).  The BAT ground-calculated position is
RA, Dec = 358.190, -39.104 deg which is 
   RA(J2000)  =  23h 52m 45.5s 
   Dec(J2000) = -39d 06' 15.0" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.

The mask-weighted light curve shows a single peak of three-second duration
near the trigger time.  T90 (15-350 keV) is 3.06 +- 1.4 sec (estimated error including 
systematics).

The time-averaged spectrum from T-0.17 to T+3.13 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.85 +- 0.25.  The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.18 sec in the 15-150 keV band
is 1.5 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The position of this burst on the BAT T90-Hardness diagram suggests that it is a 
long GRB.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1048783/BA/

K.L. Page (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &
INAF-OAR), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU),
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and V. D'Elia
report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 210517A (D'Elia et al. GCN
Circ. 30032
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 ), from 85 s to 40.6 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Beardmore et al. (GCN Circ. 30034
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.90 (+/-0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.71 (+0.18, -0.14). The
best-fitting absorption column is  1.4 (+7.0, -1.4) x 10^21 cm^-2, at a
redshift of 2.486, in addition to the Galactic value of 1.3 x 10^20
cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 3.7 x
10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.3 x 10^20 cm^-2
Intrinsic column:    1.4 (+7.0, -1.4) x 10^21 cm^-2 at z=2.486
Photon index:	     1.71 (+0.18, -0.14)

If the light curve continues to decay with a power-law decay index of
0.90, the count rate at T+24 hours will be 3.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (1.2 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01048783.

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

GRB 210517A: Swift/UVOT Upper Limits

S. J. LaPorte (PSU) and V. D'Elia (SSDC & INAF-OAR)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 210517A
69 s after the BAT trigger (D'Elia et al., GCN Circ. 30032
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 ).
No optical afterglow consistent with the optical position
(Tanvir et al. GCN Circ. 30037
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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            69          219          147         >19.4
u_FC               282          531          246         >19.7
white               69         1356          373         >19.9
v                  611         5047          274         >19.0
b                  537         1332           78         >19.5
u                  282         1307          304         >19.7
w1                 661         1109           39         >18.4
m2                5052         5070           18         >18.7
w2                4642         4841          197         >21.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.011 in the direction of the burst
(Schlegel et al. 1998).

N. R. Tanvir (Univ. Leicester), D. Xu (NAOC/CAS), L. Izzo (DARK/NBI), D. 
A. Kann (HETH/IAA-CSIC), D. B. Malesani (DTU space), J.-B. Vielfaure 
(APC), P. Jakobsson (Univ. Iceland), A. de Ugarte Postigo (HETH/IAA-CSIC 
and DARK/NBI), K. E. Heintz (Univ. Iceland and DAWN/NBI), V. D'Elia 
(ASI/SSDC), A. J. Levan (Radboud Univ.), S. D. Vergani (CNRS, Paris 
Obs.), S. Campana (INAF/Brera), G. Pugliese (Amsterdam), report on 
behalf of the Stargate collaboration:

We observed the field of GRB 210517A (D'Elia et al., GCN 30032
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 ; Ursi et 
al., GCN 30036
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 ) using the ESO VLT UT3 (Melipal) equipped with the 
X-shooter spectrograph. Our spectra cover the wavelength range 
3000-21000 AA, and consist of 4 exposures by 600 s each. The observation 
mid time was 2021 May 17.387 UT (3.82 hr after the GRB).

In a 30 s image taken with the acquisition camera on May 17.364 UT, we 
detect a single object consistent with the UVOT-enhanced XRT position 
(Beardmore et al., GCN 30034
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 ), at J2000 coordinates:

RA = 23:52:53.95
Dec = -39:06:08.3

We measure for this target an AB magnitude r = 22.3 +- 0.1 (calibrated 
against the Legacy Survey, but only very few, faint stars are present in 
the acquisition camera field of view). We note that at the same 
position, to within the uncertainties, there is a faint object visible 
in the Legacy Survey, with AB magnitude r ~ 23.7. We conclude that the 
above source is the optical afterglow of GRB 210517A, and the archival 
object is its host galaxy.

In our spectra, continuum is detected over the whole observed range. A 
prominent emission line is detected around 4236 AA, which we identify as 
Ly alpha in emission. This interpretation is confirmed by the detection 
of both emission lines in the near-infrared arm (corresponding to [O II] 
and [O III]), and a plethora of metallic absorption features, among them 
Si II, Si IV, O I, C IV, C II, all at a common redshift z = 2.486. 
Consistent with the detection of bright Ly alpha in emission, the 
observed HI absorption column density is low.

We note that at z = 2.486 the galaxy is a particularly bright GRB host, 
with an absolute AB magnitude M(1800 AA) ~ -21.5.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Luca Sbordone, Francisco Caceres, and Boris 
Haeussler.

A. Ursi (INAF/IAPS), C. Pittori (SSDC, and INAF/OAR), G. Piano (INAF/IAPS),
M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Argan, M. Cardillo,
C. Casentini, Y. Evangelista (INAF/IAPS), F. Lucarelli, F. Verrecchia
(SSDC, and INAF/OAR), A. Bulgarelli, A. Di Piano,  V. Fioretti, F.
Fuschino, N. Parmiggiani (INAF/OAS-Bologna), M. Marisaldi
(INAF/OAS-Bologna, and Bergen University), M. Pilia, A. Trois
(INAF/OA-Cagliari), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN
Trieste), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team:

The AGILE satellite detected the long GRB 210517A at T0 = 2021-05-17
05:28:01 s (UTC), reported by Swift (GCNs #30032
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 , #30034
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 ).

The burst is visible in the AGILE scientific ratemeters of the SuperAGILE
(SA; 20-60 keV) and MiniCALorimeter (MCAL; 0.4-100 MeV) detectors. The
event lasted ~6 s and released a total number of 663 counts in the SA
detector (above a background rate of 77 Hz) and 8759 counts in the MCAL
detector (above a background rate of 1200 Hz). The AGILE ratemeter light
curves can be found at
http://www.agilescienceapp.it/notices/GRB210517A_AGILE_RM.png .

Additional analysis of AGILE data is in progress.

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

Using 1271 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 210517A, 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 = 358.22445, -39.10218 which is equivalent
to:

RA (J2000): 23h 52m 53.87s
Dec (J2000): -39d 06' 07.9"

with an uncertainty of 2.2 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.

V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, 
V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva,
D.Kuvshinov,  D. Cheryasov
(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. Gres, N.M. Budnev, O.Ershova 
(Irkutsk State University, API),

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

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




MASTER-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB210517.23 (trigger No 1048783,23h 52m 41.76s , -39d 06m 18.0s, R=0.05) errorbox  40 sec after notice time and 254 sec after trigger time at 2021-05-17 05:32:16 UT, with upper limit up to  16.2 mag. The observations began at zenith distance = 83 deg. The sun  altitude  is -71.9 deg. 

The galactic latitude b = -73 deg., longitude l = 344 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1614656

We obtain a following upper limits.  

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

     280 |         MASTER-OAFA |   C |    50 | 16.2 |        
     486 |         MASTER-OAFA |   C |    90 | 15.4 |        
     784 |         MASTER-OAFA |   C |   140 | 15.8 |        
Filter C is a clear (unfiltred) band. 


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

V. D'Elia (SSDC & INAF-OAR), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), J.D. Gropp (PSU), H. A. Krimm (NSF),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL),
B. Sbarufatti (PSU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 05:28:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210517A (trigger=1048783).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 358.174, -39.105 which is 
   RA(J2000) = 23h 52m 42s
   Dec(J2000) = -39d 06' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT lightcurve shows a peak at least
2 seconds long and a maximum count rate of ~2200 counts/s (15-350 keV). 

The XRT began observing the field at 05:29:08.6 UT, 67.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 358.2245,
-39.1020 which is equivalent to:
   RA(J2000)  = 23h 52m 53.88s
   Dec(J2000) = -39d 06' 07.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 141 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.30 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.2
(+2.58/-2.26) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 69 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 expected
extinction corresponding to E(B-V) of 0.011. 

Burst Advocate for this burst is V. D'Elia (valerio.delia AT ssdc.asi.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/)