GRB 210321A
GCN Circular 29677
Subject
GRB 210321A: Swift detection of a burst
Date
2021-03-21T07:22:33Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. Dichiara (NASA/GSFC/UMCP), C. Gronwall (PSU), H. A. Krimm (NSF),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 07:13:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210321A (trigger=1037828). Swift did not immediately slew
due to an observing constraint.
The BAT on-board calculated location is
RA, Dec 87.874, +70.119 which is
RA(J2000) = 05h 51m 30s
Dec(J2000) = +70d 07' 09"
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 15 sec. The peak count rate
was ~1300 counts/sec (15-350 keV), at ~1 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+43.3
minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is S. Dichiara (dichiara AT umd.edu).
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/)
GCN Circular 29678
Subject
GRB 210321A: Swift-XRT observations
Date
2021-03-21T08:24:08Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M. Perri (SSDC & INAF-OAR), 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 210321A at 07:59:21.6 UT,
2730.6 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 87.89627, 70.13042
which is equivalent to:
RA(J2000) = 05h 51m 35.10s
Dec(J2000) = +70d 07' 49.5"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 49 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 (1.13 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 4
(+3.35/-2.86) x 10^21 cm^-2 (90% confidence).
GCN Circular 29679
Subject
GRB 210321A: Swift/UVOT Detection
Date
2021-03-21T13:35:49Z (4 years ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
M.. H. Siegel (PSU) and S. Dichiara (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210321A
2735 s after the BAT trigger (Dichiara et al., GCN Circ. 29677).
A source consistent with the XRT position (Perri et al., GCN Circ. 29678)
is detected in the initial UVOT exposures.
Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 2735 2837 100 18.76 +/- 0.11
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.116 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 29680
Subject
GRB 210321A: DDOTI Afterglow Confirmation
Date
2021-03-21T14:54:00Z (4 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
Nat Butler (ASU), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Simone
Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM),
Oc��lotl Lopez (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM),
Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report:
We observed the field of the Swift/BAT GRB 210321A (Dichiara et al., GCN
Circ. 29677) with the DDOTI wide-field imager at the Observatorio
Astron��mico Nacional on Sierra San Pedro Martir (
http://ddoti.astroscu.unam.mx) starting at 2021-03-21 08:56 UTC (from 1.7
hours after the trigger).
We observed a region covering approximately 7 degrees in RA and 10 degrees
in declination (about 70 square degrees) centered on the XRT position
(Perri et al., GCN 29678) in the w filter.
Compared to the USNO-B1, Pan-STARRS DR1, and APASS DR10 catalogs, we detect
a bright source at 08:39:50.04 +60:12:18.9 (J2000) fading from about w =
18. This confirms the afterglow reported in UVOT observations by Siegel et
al. (GCN Circ. 29679).
We thank the staff of the Observatorio Astronomico Nacional in San Pedro
Martir.
GCN Circular 29681
Subject
GRB 210321A: Enhanced Swift-XRT position
Date
2021-03-21T15:54:59Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1720 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 210321A, 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 = 87.89579, +70.13057 which is equivalent
to:
RA (J2000): 05h 51m 34.99s
Dec (J2000): +70d 07' 50.1"
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.
GCN Circular 29683
Subject
GRB 210321A: MASTER optical observation
Date
2021-03-21T20:49:00Z (4 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
V. Lipunov, V.Kornilov, E.Gorbovskoy,N.Tiurina,P.Balanutsa,F.Balakin,
V.Vladimirov, A.Kuznetsov,K.Zhirkov,D. Vlasenko, I.Gorbunov, D.Zimnukhov,
V.Senik, A.Chasovnikov,A.Pozdnyakov,V.Topolev, D.Cheryasov(Lomonosov Moscow State University, SAI, Physics Department),
D. Buckley (South African Astronomical Observatory),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA),
R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias),
O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L)
started Swift GRB 210321A (BAT:Dichiara et al. GCN 29677,Ttrig=07:13:51;
XRT:Perri et al. GCN 29678,Beardmore et al. GCN29681;
UVOT: Siegel GCN29679),
optical observations at MASTER-Tavrida at 2021-03-21 16:55:20UT, ~9.7h after trigger time,
with mlim=20.8m.
Swift optical counterpart (87.8947 +70.1305) isn't visible yet.
This message may be cited.
GCN Circular 29684
Subject
GRB 210321A: NOT optical afterglow detection and redshift limit
Date
2021-03-21T22:41:10Z (4 years ago)
From
Kasper Elm Heintz at Univ. of Iceland and DAWN/NBI <keh14@hi.is>
Kasper E. Heintz (Univ. of Iceland, DAWN/NBI), Johan P. U. Fynbo (DAWN/NBI), and Tapio Pursimo (NOT), report on behalf of a larger collaboration:
We observed the field of the Swift/BAT-detected GRB 210321A (Dichiara et al., GCN #29677), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Starting at 20:26:25.6 UTC on March 21, we obtained 3x300 sec exposures in the Sloan r-band. The observations were carried out under good conditions, with seeing around 0.8". We confirm the optical afterglow reported by Siegel et al. (GCN #29679), and measure r = 21.6 +/- 0.15 mag at 13.5 hr post-burst, calibrated against nearby field stars in the Pan-STARRS catalog.
Following the imaging sequence, we obtained spectroscopy of the afterglow with ALFOSC using grism 4 (320 to 960 nm) and for 4x1200 sec total integration. A faint trace is detected but we do not identify any particular absorption or emission features to infer the redshift from. However, since the continuum is detected down to 380 nm, we put a limit on the redshift of z < 2.
GCN Circular 29685
Subject
GRB 210321A: Redshift from OSIRIS/GTC
Date
2021-03-21T22:57:51Z (4 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D.A. Kann,
C. Thoene, M. Blazek, J.F. Agui Fernandez (all HETH/IAA-CSIC),
S. Geier (GTC, IAC), A. Tejero (GTC) report:
We observed the afterglow of GRB 210321A (Dichiara et al. GCN
29677; Perri et al. GCN 29678; Siegel et al. GCN 29679; Butler et
al. GCN 29680; Heintz et al. GCN 29684) with OSIRIS at the
10.4m GTC telescope at Roque de los Muchachos Observatory,
in La Palma (Spain). The observation started at 20:28 UT (0.5517
days after the burst), and consisted in 3x900s with grism R1000B,
covering the spectral range from 3700 to 7800 AA.
The 30s acquisition image, with a seeing of 0.75���, shows the
afterglow at a magnitude of r��� = 21.39+/-0.03, using a nearby
PanSTARRS field star as photometric reference.
The spectral continuum is well detected above 3900 AA, and
shows very weak lines consistent with several features of FeII, MgII
and MgI at a common redshift of z = 1.487, which we assume to be
the likely redshift of the GRB. However, we note that strictly
speaking this would be a lower limit, with the upper limit being z ~< 2,
as already noted by the NOT spectroscopy (Heintz et al. GCN 29684).
GCN Circular 29686
Subject
GRB 210321A: Swift-XRT refined Analysis
Date
2021-03-21T23:16:40Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M.
Capalbi (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A.
Kennea (PSU) and S. Dichiara report on behalf of the Swift-XRT team:
We have analysed 6.7 ks of XRT data for GRB 210321A (Dichiara et al.
GCN Circ. 29677), from 2.7 ks to 44.2 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.
29681).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.59 (+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 1.99 (+0.20, -0.19). The
best-fitting absorption column is 2.3 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 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 3.6 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 2.3 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 2.9 sigma
Photon index: 1.99 (+0.20, -0.19)
If the light curve continues to decay with a power-law decay index of
1.59, the count rate at T+24 hours will be 2.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 x
10^-14 (1.1 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/01037828.
This circular is an official product of the Swift-XRT team.
GCN Circular 29687
Subject
GRB 210321A: Xinglong GWAC-F60A optical observation
Date
2021-03-22T03:41:33Z (4 years ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
L. P. Xin(NAOC), C. Gao(GXU), X. H. Han(NAOC), J. Y. Wei(NAOC),
J. Wang(GXU), G. W. LI(NAOC), L. H. Li(NAOC), C. Wu(NAOC),
X. G. Wang(GXU), E. W. Liang (GXU), Y. L. Qiu(NAOC), and J. S. Deng(NAOC) report:
We began to observe GRB 210321A (Dichiara et al. GCN
29677; Perri et al. GCN 29678; Siegel et al. GCN 29679; Butler et
al. GCN 29680; Heintz et al. GCN 29684; Ugarte Postigo et al., GCN 29685)
with Xinglong GWAC-F60A telescope, China, at 11:30:49 (UT),
21th. Mar. 2021, about 4.28 hours after the burst.
A series of R, I images were obtained.
The optical counterpart ( Siegel et al. GCN 29679; Butler et al. GCN 29680;
Heintz et al. GCN 29684; Ugarte Postigo et al., GCN 29685)
was clearly detected in the stacked R-band image
observed during 11:30:49 and 12:48:17 UT.
The brightness was estimated to be 18.98 +/-0.13 mag at the mean
time of 4.88 hours after the burst, calibrated to USNO B1.0 R2 mag,
This result is consistent with the previous report (Zhu et al., GCN 29530).
GCN Circular 29689
Subject
GRB 210321A: Mondy optical observations
Date
2021-03-22T11:15:29Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI)
report on behalf of GRB IKI FuN:
We observed the field of GRB 210321A (Dichiara et al., GCN 29677) with
AZT-33IK telescope of Sayan observatory (Mondy) starting on 2021-03-21
(UT) 14:20:37. The optical afterglow (Siegel et al., GCN 29679; Butler
et al., GCN 29680; Lipunov et al., GCN 29683; Heintz et al., GCN
29684; de Ugarte Postigo et al., GCN 29685; Xin et al. GCN 29687) is
clearly detected in a combined image. Preliminary photometry of the
afterglow in the combined image is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2021-03-21 14:20:37 0.31199 R 45*60 20.1 0.14 20.5
The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1601-0068003 15.84
1600-0068970 16.18
1601-0068018 16.54
1601-0067995 16.23
GCN Circular 29691
Subject
GRB 210321A: Swift-BAT refined analysis
Date
2021-03-22T18:12:52Z (4 years ago)
From
Hans Krimm at NSF/NASA-GSFC <hkrimm@nsf.gov>
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), S. Dichiara (NASA/GSFC/UMCP),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), (i.e. the Swift-BAT team):
Using the data set from T-240 to T+700 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210321A (trigger #1037828)
(Dichiara, et al., GCN Circ. 29677). The BAT ground-calculated position is
RA, Dec = 87.887, 70.109 deg which is
RA(J2000) = 05h 51m 32.8s
Dec(J2000) = +70d 06' 33.4"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 30%.
The mask-weighted light curve shows a single, fairly symmetrical peak from
approximately T-8 to T+4 sec. T90 (15-350 keV) is 8.21 +- 0.50 sec
(estimated error including systematics).
The time-averaged spectrum from T-7.00 to T+1.84 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.15 +- 0.20. The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-6.99 sec in the 15-150 keV band
is 1.7 +- 0.4 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/1037828/BA/
GCN Circular 29692
Subject
GRB 210321A: CrAO optical upper limit
Date
2021-03-22T19:02:33Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE), S. Nazarov (CrAO), A. Pozanenko (IKI), S. Belkin (IKI)
report on behalf of GRB IKI FuN:
We observed the field of GRB 210321A (Dichiara et al., GCN 29677) with
AZT-8 telescope of CrAO observatory starting on 2021-03-21 (UT)
19:04:11. The optical afterglow (Siegel et al., GCN 29679; Butler et
al., GCN 29680; Lipunov et al., GCN 29683; Heintz et al., GCN 29684;
de Ugarte Postigo et al., GCN 29685; Xin et al. GCN 29687; Pankov et
al., GCN 29689) is not detected in a combined image. Preliminary
photometry of the field is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2021-03-21 19:04:11 0.51238 R 55*60 n/d n/d 20.8
The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1601-0068003 15.84
1600-0068970 16.18
1601-0068018 16.54
1601-0067995 16.23
GCN Circular 29694
Subject
GRB 210321A: DDOTI Position Correction
Date
2021-03-22T19:42:51Z (4 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
The afterglow position quoted by Butler et al. (GCN 29680) was typed
incorrectly. The correct position is 05:51:34.82, +70:07:50.4 (J2000).
GCN Circular 29696
Subject
Konus-Wind detection of GRB 210321A
Date
2021-03-23T12:37:30Z (4 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, S. Golenetskii, A.Lysenko, D. Svinkin, A. Ridnaya,
A. Tsvetkova, M. Ulanov, and T. Cline, report:
The long GRB 210321A (Swift-BAT trigger #1037828, T0(BAT)= 07:13:51.023 UT:
Dichiara, et al., GCN 29677; Ukwatta, et al., GCN 29691)
was detected by Konus-Wind (KW) in the waiting mode.
A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band
reveals a ~10 sigma count rate increase over background in the interval
from ~T0(BAT)-6.430 s to ~T0(BAT)+2.402 s.
A fit to the KW 3-cannel waiting mode spectrum with by a power law with
an exponential cutoff (CPL) yields alpha~-2 and doesn't constrain Ep.
A fit with a simple power law (PL) gives a photon index of (2.19 �� 0.17), chi^2 = 0.78/ 1 dof.
This result is consistent with the Swift-BAT refined analysis (GCN 29691).
In the 10 keV-10 MeV band, standard for the KW spectral analysis, the total burst fluence,
estimated from the PL model, is (1.6 �� 0.3)x10^-6 erg/cm^2,
and the 2.944 s peak energy flux is (2.2 �� 0.4)x10^-7 erg/cm^2.
Assuming the redshift z=1.487 (de Ugarte Postigo, et al., GCN 29685)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the burst isotropic energy release E_iso to ~9.7x10^51 erg
and the isotropic luminosity L_iso to ~3.2x10^51 erg/s.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB210321A/
GCN Circular 29697
Subject
GRB 210321A: Swift/UVOT Detection
Date
2021-03-23T14:17:59Z (4 years ago)
From
Sam LaPorte at PSU <sjl5346@psu.edu>
GRB 210321A: Swift/UVOT Detection
S. J. Laporte (PSU) and S. Dichiara (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210321A
2735 s after the BAT trigger (Dichiara et al., GCN Circ. 29677).
A source consistent with the XRT position
(Beardmore et al. GCN Circ. 29681)
is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 05:51:34.75 = 87.89479 (deg.)
Dec (J2000) = +70:07:49.8 = 70.13051 (deg.)
with an estimated uncertainty of 0.49 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits using the UVOT photometric
system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 2735 2885 147 18.69 +/- 0.09
v 2892 4465 331 18.44 +/- 0.16
b 3713 3913 197 18.64 +/- 0.11
u 3507 3706 197 18.29 +/- 0.12
w1 3302 3502 197 18.48 +/- 0.17
m2 3097 3296 197 >18.9
w2 4124 4324 197 >19.8
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.118 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 29725
Subject
GRB 210321A: OSN Upper Limit
Date
2021-03-24T23:41:30Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui Fernandez (all
HETH/IAA-CSIC), and F. Aceituno (IAA-CSIC) report:
We observed the optical afterglow (Perri et al. GCN #29678; Siegel et
al. GCN #29679; Butler et al. GCN #29680; Heintz et al. GCN #29684; Xin
et al., GCN #29687; Pankov et al., GCNs #29689, #29692; Laporte et al.,
GCN #29697) of GRB 210321A (Swift detection: Dichiara et al., GCN
#29677) with the 1.5m T150 telescope of the Observatorio de Sierra
Nevada (OSN), Granada, Spain. Observations could not be taken due to
high winds in the first night after the GRB. We obtained 11 x 180 s
exposures in Rc starting at 2021-03-22 19:59:44.93 UT, before high winds
shut the telescope down again. The afterglow is not detected in the
combined image.
We determine an upper limit Rc > 23.3 mag (AB mag, vs. a nearby
Pan-STARRS star converted to Rc following the Lupton transformations,
then transformed back to AB mag) at 1.5437 days after the GRB.