- GCN Circular #29844
M. J. Moss (GWU), P. A. Evans (U Leicester), C. Gronwall (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:
BAT triggered on GRB 210420B (trigger 1044382) at some time before 18:50
UT. Due to telemetry gaps, we have only XRT data for this burst and
therefore at the present time cannot give a precise trigger time, or
information about the BAT light curve. The most likely trigger time is
between 18:20 and 18:50 UT. Once the full dataset has been downlinked we
will be able to derive a precise trigger time and analyse the BAT light
curve.
Using promptly downlinked data we find an uncatalogued X-ray source
located at RA, Dec 254.32245, 42.56951 which is equivalent to:
RA(J2000) = 16h 57m 17.39s
Dec(J2000) = +42d 34' 10.2"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). 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 (2.09 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.1
(+1.75/-1.59) x 10^21 cm^-2 (90% confidence).
Burst Advocate for this burst is M. J. Moss (mikejmoss3 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/)
- GCN Circular #29845
V. Lipunov, V.Kornilov, E.Gorbovskoy, A.Chasovnikov, P.Balanutsa,V.Vladimirov, A.Kuznetsov,
D. Vlasenko, N.Tiurina, I.Gorbunov, D.Zimnukhov, V.Senik,V.Topolev,
F.Balakin, D.Cheryasov (Lomonosov Moscow State University,SAI, PhysicsDepartment),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev (Irkutsk State University, API),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias),
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 etal.,2010,Advances in Astronomy,2010,30L)
started GRB 210420B (Swift trigger 1044382 Moss et al. GCN 29844,Ttrigger=2021-04-20 18:20-50UT)
at MASTER-Kislovodsk at 2021-04-20 20:01:24UT
There is optical counterpart (changing)
at RA,Dec(2000)= 16h 57m 18.23s ,+42d 34m 11s.8 +-1"
MASTER OT J165718.23+423411.8
found by MASTER auto-detection system
with m_OT~19 at 2021-04-20 20:05:23TU
Observation started at alert altitude 45deg.
- GCN Circular #29846
A. Oksanen (Hankasalmi observatory) report on behalf a larger collaboration:
We observed the field of the Swift GRB 210420B (Page et al., GCN 29844)
using the 0.40 m remote controlled RC telescope of Hankasalmi observatory
equipped with the SBIG STX-16803 CCD camera. Total of 25 exposures of 60 s
each were secured in the clear filter, starting on 2021 April 19:44:58 UT.
A candidate afterglow is clearly detected in the XRT error circle with
coordinates (J2000):
RA = 16:57:18.0
DEC = +42:34:12.6
Its magnitude is r = 17.97 +- 0.05 , calibrated against a nearby star
from SDSS. This object is not visible in the Digitized Sky Survey R band
images.
We consider this object as a viable afterglow candidate to GRB 210420B,
but a confirmation is necessary to assess variability. Further
observations are planned.
- GCN Circular #29847
Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), S. Guziy (Univ. of Nikolaev) and D. R. Xiong, Y. F. Fan, J. M. Bai, C. J. Wang, Y. X. Xin, X. H. Zhao (Yunnan Observatories of CAS) on behalf of a larger collaboration, report:
Following the detection of GRB 210420B by Swift (Moss et al. GCNC 29844), we triggered the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) in order to follow up this event, starting on Apr 20, 19:51 UT. A series of images in clear filter was obtained. An uncatalogued optical source is found within the XRT position (Moss et al. GCNC 29844), for which we measure a magnitude of 17.9 +/- 0.1, calibrated against nearby stars in the USNO-B2 catalogue. This is consistent with the findings from MASTER (Lipunov et al, GCNC 29845) and Hankasalmi (Oksanen et al, GCNC 29846). Further observations are ongoing.
We thank the staff at Lijiang observatory for their excellent support.
- GCN Circular #29848
Tianrui Sun(Purple Mountain Observatory), Lei Hu, Maokai Hu, Xuefeng Wu, Lei Liu, Kelai Meng, Xiaoyan Li(Nanjing Institute of Astronomical Observation Technology), Zhengyang Li, Xiangyan Yuan, Lifan Wang(TAMU), Xiaofeng Wang (Tsinghua University), report on behalf the AST3 Team:
Following the detection of GRB210420B by Swift (Moss et al. GCN 29844), we use Antarctic Survey Telescope 3-3 at YaoAn Astronomy Observation(China, Yunnan) to follow up. We observed 80 images in the g-band and exposure time in 60 seconds. The observation started at 2021-04-20T20:07:30.596 and ends at 2021-04-20T21:42:43.897. Within the candidate position (A. Oksanen et al. GCN 29846), we detected the source with 16.9 mag at 2021-04-20T20:07:30.596 and 17.5 mag at 2021-04-20T21:42:43.897.
- GCN Circular #29851
Simone Leonini, M. Conti, P. Rosi and L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy) report:
We observed the field of GRB 210420B (Swift trigger 1044382, M.J. Moss et al., GCN Circ. 29844) with the automatic 0.53m RC telescope + U47 detector at Montarrenti Observatory (Siena, Italy, IAU code C88).
The observations were started under good weather conditions at 2021-04-20 23:46:05 UT (approximately 4 hours after notice) stacking 5x60s R filter CCD exposures for each run.
The optical afterglow was clearly detected as follows:
2021 Apr 20.99207 UT (23:48:35 mid-time) R=19.0 +/-0.13
2021 Apr 21.03089 UT (00:44:29 mid-time) R=19.2 +/-0.14
Preliminary magnitudes were obtained using Astrometrica software using USNO-B1 catalogue for positions and photometry. An ensemble between 83 and 76 stars were used for the magnitude and astrometric comparison. Measures are not corrected for galactic dust extinction.
The position of the GRB (within the error box given by Swift) is the following:
RA (J2000.0) 16h 57m 18.05s +/-0.14
Decl. (J2000.0) +42° 34' 12.0" +/-0.13
Our detection is consistent with these reported by MASTER-Net (Lipunov et al, GCNC 29845), Hankasalmi Observatory (Oksanen, GCNC 29846), BOOTES-4 (Hu. et al., GCN 29847) and AST3-3 (Sun et al., GCN 29848).
Further observations are ongoing.
- GCN Circular #29852
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. B. Malesani (DTU
Space), E. Knudstrup (NOT, Aarhus Univ.) report on behalf of a larger
collaboration:
We observed the afterglow of GRB 210420B (Moss et al. GCN 29844;
Lipunov et al. GCN 29845; Oksanen GCN 29846; Hu et al. GCN 29847;
Sun et al. GCN 29848; Leonini et al. GCN 29851) with ALFOSC at the
2.5 m Nordic Optical Telescope at Roque de los Muchachos Observatory
(La Palma, Spain). The observation consisted of 3x100 s imaging in g, r
and i bands, and 5x100 s in z-band and started at 00:13 UT.
The afterglow is well detected in individual images in all bands at
the following coordinates (J2000) calibrated with Gaia, and with an
uncertainty estimated at 0.3":
R.A. = 16:57:18.00
Dec. = +42:34:12.1
In a preliminary analysis we measure the following AB magnitudes, as
compared with 3 field stars from the SDSS catalogue:
g = 19.45 +/- 0.04
r = 19.32 +/- 0.04
i = 19.18 +/- 0.04
z = 19.03 +/- 0.07
- GCN Circular #29853
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), M. Blazek,
C. Thoene, D. A. Kann, J. F Agui Fernandez (all HETH/IAA-CSIC),
and S. Geier (GTC, IAC) report:
We observed the afterglow of GRB 210420B (Moss et al. GCN
29844; Lipunov et al. GCN 29845; Oksanen GCN 29846; Hu et al.
GCN 29847; Sun et al. GCN 29848; Leonini et al. GCN 29851;
de Ugarte Postigo GCN 29852) with OSIRIS at the 10.4m GTC
telescope, at the Roque de los Muchachos Observatory (La Palma,
Spain). Observations consisted of 2x600 s spectroscopy with grism
R1000B, covering the spectral range between 3700 and 7800 AA.
The spectrum shows a strong continuum with weak absorption
features that we identify as due to FeII, MgII and MgI at a common
redshift of z = 1.400, which we interpret as the redshift of the GRB.
- GCN Circular #29854
A. Y. Lien (GSFC/UMBC), M. J. Moss (GWU),
and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift
Observatory Team:
We received further data from recent telemetry downlink,
The trigger time for GRB 210420B (Swift trigger #1044382;
Moss et al., GCN Circ. 29844) is
2021-04-20T18:34:37 UTC.
The burst duration is at least 30 seconds, the full data
products will allow a complete duration estimate.
- GCN Circular #29858
Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Simone Dichiara
(GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl 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 210420B (Moss et al., GCN Circ.
29844) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional
on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-21 04:36
to 08:15 UTC (from 10.0 to 13.7 hours after the trigger) and obtained 10380
seconds of exposure in the w filter.
We observed a region covering aproximately 7 degrees in RA and 10 degrees in
declination (about 70 square degrees), including the XRT position. We calibrated
our images against the APASS catalog.
We detect a source at 16:57:17.97 +42:34:12.3 J2000 with an AB magnitude of w =
21.47 +/- 0.09.
This source is outside the XRT error region reported by Moss et al. (GCN Circ.
29844), but is not present in the Pan-STARRS DR1 g image of the field and is
consistent with the afterglow coordinates reported by Oksanen (GCN Circ. 29846),
Lipunov et al. (GCN Circ. 29845), Leonini et al. (GCN Circ. 29851), and de
Ugarte Postigo et al. (GCN Circ. 29852).
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
- GCN Circular #29861
WeiKang Zheng and Alexei V. 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 the Swift GRB 210420B (Moss et al.,
GCN 29844) starting at ~0.61 days after the Swift trigger (Lien et al.
GCN 29854). A total of 30x60s images were obtained in the clear (roughly R)
filters. We detect the optical afterglow (Lipunov et al., GCN 29845;
Oksanen,
GCN 29846; Hu et al., GCN 29847; Sun et al., GCN 29848; Leonini et al.,
GCN 29851; de Ugarte Postigo et al., GCN 29852; Watson et al., GCN 29858)
in the coadd image with a mag of 19.9 +/- 0.2, calibrated to the
Pan-STARRS1 catalog.
- GCN Circular #29862
A. A. Breeveld (UCL-MSSL) and M. J. Moss (GWU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210420B 147s after the BAT trigger
(Moss et al., GCN Circ. 29844 and updated in Lien et al., GCN Circ. 29854).
A fading source consistent with the optical counterpart reported by Lipunov et al. GCN Circ. 29845,
Oksanen GCN Circ. 29846, Hu et al. GCN Circ. 29847, Tianrui et al. GCN Circ. 29848, Leonini et al.
GCN Circ. 29851, de Ugarte Postigo et al. GCN Circ. 29852 and Watson et al. GCN Circ. 29858, 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 first finding chart (_fc) exposure and other early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u_fc 147 391 240 16.2 ± 0.04
u 18793 19317 512 18.6 ± 0.1
v 447 467 20 16.7 ± 0.2
b 397 417 19 17.1 ± 0.1
w1 496 516 20 16.5 ± 0.2
m2 620 1121 39 17.2 ± 0.2
w2 1201 1371 39 17.6 ± 0.2
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of
E(B-V) = 0.022 in the direction of the burst (Schlegel et al. 1998).
- GCN Circular #29863
B. Stecklum, A. Nicuesa Guelbenzu, S. Klose, S. Melnikov, and U. Laux
(all Tautenburg) report:
We observed the field of GRB 210420B (Moss et al., GCN 29844) with the
Tautenburg 1.34m Schmidt telescope equipped with the TAUKAM 6k x 6k CCD
camera. Observations started on April 20 at 20:13:21 UT, 99 min after the
BAT trigger (Lien et al., GCN 29854). Altogether four observing runs (5x5
min each) were performed (Sloan r'). The afterglow (Lipunov et al., GCN
29845; Oksanen, GCN 29846; Hu et al., GCN 29847; Sun et al., GCN 29848;
Leonini et al., GCN 29851; de Ugarte Postigo et al., GCNs 29852, 29853;
Watson et al., GCN 29858) was clearly detected in all frames. Magnitudes
were calibrated against SDSS.
The data show that between the first (mean time: 20:26:10 UT; r' = 18.30
+/- 0.03) and the second observing run (mean time: 21:47:07 UT; r' = 18.75
+/- 0.03) ) the light curve was steepening to a decay with alpha2 = 0.99
+/- 0.04 (break time tb = 0.091 +/- 0.017 days). Before the break the
decay index is not well constrained (alpha1 = 0.35 +/- 0.33).
- GCN Circular #29864
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), Jesús
González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report:
We observed the field of GRB 210420B (Moss, et al., GCN 29844) with the
Reionization and Transients Infrared Camera (RATIR) on the 1.5m Harold
Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San
Pedro Mártir from 2021/04 21.39 to 2021/04 21.49 UTC (13.73 to 16.08 hours
after the BAT trigger), obtaining a total of 1.47 hours exposure in the r
and i bands and 0.55 hours exposure in the Z, Y, J, and H bands.
We detect the source reported by Oksanen (GCN 29846), Lipunov et al. (GCN
29845), Leonini et al. (GCN 29851), de Ugarte Postigo et al. (GCN 29852),
Watson et al. (GCN 29858), Zheng et al. (GCN 29861), and Breeveld et al.
(GCN 29862). In comparison with the SDSS DR9 and 2MASS catalogs, we obtain:
r = 19.98 +/- 0.02
i = 19.77 +/- 0.02
Z = 19.70 +/- 0.03
Y = 19.48 +/- 0.05
J = 19.31 +/- 0.05
H = 19.26 +/- 0.08
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.
- GCN Circular #29866
M. Jelinek, J. Strobl, R. Hudec, C. Polasek (ASU CAS Ondrejov)
report:
We observed the position of the bright GRB 210420B (Moss et al., GCN 29833
& Lien et al., GCN 29854) with the D50 telescope of the Astronomical
Institute Ondrejov, near Prague, Czech Republic. We performed a series of
120 s unfiltered exposures starting 21:10 UT, between 2.6 and 4.9 h after
the trigger.
The optical afterglow (Lipunov et al., GCNC 29845; Oksanen et al., GCNC
29846; Hu et al., GCNC 29847; Tianrui Sun et al., GCNC 29848; Leonini et
al., GCNC 29851; de Ugarte Postigo et al., GCNC 29852; de Ugarte Postigo et
al., GCNC 29853; Watson et al., GCNC 29858; Zheng et al., GCNC 29861;
Breeveld et al., GCNC 29862; Stecklum et al., GCNC 29863 and Butler et al.,
GCNC 29864) is clearly detected in single 120 s images, at least at the
beginning of the series.
We can confirm a decaying nature of the object - the afterglow faded > 0.4
mag during the course of our observations, providing an alpha decay of 0.69
+- 0.17.
- GCN Circular #29867
There was a transcription error in the DDOTI magnitude reported by Watson et al.
(GCN Circ. 29858) for GRB 210420B. The correct magnitude is w = 20.47 +/- 0.09.
- GCN Circular #29872
Simone Leonini, M. Conti, P. Rosi and L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy) report:
In reference to the GRB 210420B (Moss, et al., GCN 29844), as a follow-up of our early observations already reported in GCN 29851, we kept on imaging the afterglow until 2021-04-21 02:49:13 UT with the same conditions, set-up and analysis. Here our complete set of measurements:
2021 Apr 20.99207 UT (23:48:35 mid-time) R=19.0 +/-0.13
2021 Apr 21.03089 UT (00:44:29 mid-time) R=19.2 +/-0.14
2021 Apr 21.06793 UT (01:37:49 mid-time) R=19.1 +/-0.14
2021 Apr 21.11587 UT (02:46:51 mid-time) R=19.5 +/-0.12
Along the span of our observations we estimate from our measurements a decay rate of 1.02+/-0.35.
- GCN Circular #29876
J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &
INAF-OAR), V. D'Elia (SSDC & INAF-OAR), J. D. Gropp (PSU), J.A. Kennea
(PSU), A. Tohuvavohu (U. Toronto), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester) and M.J. Moss report on behalf of the
Swift-XRT team:
We have analysed 4.8 ks of XRT data for GRB 210420B (Moss et al. GCN
Circ. 29844), from 141 s to 87.5 ks after the BAT trigger. The data
comprise 177 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
254.3227, +42.5696 which is equivalent to:
RA (J2000): 16 57 17.45
Dec(J2000): +42 34 10.6
with an uncertainty of 3.5 arcsec (radius, 90% confidence).
The light curve can be modelled with an initial power-law decay with an
index of alpha=2.23 (+0.11, -0.12), followed by a break at T+425 s to
an alpha of 1.13 (+/-0.07).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.72 (+0.08, -0.07). The
best-fitting absorption column is 9 (+11, -9) x 10^20 cm^-2, at a
redshift of 1.4, in addition to the Galactic value of 2.1 x 10^20 cm^-2
(Willingale et al. 2013). The PC mode spectrum has a photon index of
1.61 (+0.08, -0.07) and a best-fitting absorption column consistent
with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (4.2
x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Galactic foreground: 2.1 x 10^20 cm^-2
Intrinsic column: 2.1 (+6.0, -0.0) x 10^20 cm^-2 at z=1.4
Photon index: 1.61 (+0.08, -0.07)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01044382.
This circular is an official product of the Swift-XRT team.
- GCN Circular #29879
M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), 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+767 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210420B (trigger #1044382)
(Moss et al., GCN Circ. 29844). The BAT ground-calculated position is
RA, Dec = 254.313, 42.558 deg which is
RA(J2000) = 16h 57m 15.1s
Dec(J2000) = +42d 33' 28.1"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 77%.
The BAT light curve showed a complex structure with a duration of about ~160 sec.
T90 (15-350 keV) is 158.8 +- 29.5 sec (estimated error including systematics).
The time-averaged spectrum from T-21.30 to T+160.09 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.49 +- 0.19. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+21.02 sec in the 15-150 keV band
is 0.5 +- 0.2 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/1044382/BA/
- GCN Circular #29883
J. Vinko (Konkoly/ELTE/U Szeged), L. Kriskovics, R. Szakats, A. Pal and K. Vida (Konkoly)
report on behalf of the "Transient Astrophyical Objects" project:
We observed the field of GRB 210420B (Moss et al., GCN 29833; Lien et al., GCN 29854;
Osborne et al. GCN 29876; Stamatikos et al., GCN29879) with the 0.8m RC80 robotic telescope at Piszkesteto Mountain Station of Konkoly Observatory through SDSS r' and i' filters on
2021 Apr 21.85 UT (MJD 59325.85, 1.07 day after the trigger). The total exposure time
was 1800 s in both filters.
The frames were tied to PS1-photometry of local stellar sources. We detect the optical
afterglow (Lipunov et al., GCN 29845; Oksanen et al., GCN 29846; Hu et al., GCN 29847;
Tianrui Sun et al., GCN 29848; Leonini et al., GCN 29851; de Ugarte Postigo et al.,
GCN 29852, 29853; Watson et al., GCN 29858; Zheng et al., GCN 29861; Breeveld et al.,
GCN 29862; Stecklum et al., GCN 29863; Butler et al.,GCN 29864; Jelinek et al., GCN 29866;
Watson, GCN 29867; Leonini et al., GCN 29872) is detected on the stacked r-band images.
Forced photometry at the position of the GRB, tied to the PS1 photometry of nearby stars,
resulted in the following AB-magnitudes:
r = 20.76 +/- 0.33 (5-sigma limit 22.18)
i > 22.09 (5-sigma limit)
GCN Circular #29884
There was a program error to the AST3-3 YaoAn observation:
The two magnitudes reported by Tianrui Sun et al.(GCNC 29848) for GRB 210420B contain an error.
Thus, the correct description should be:
The detected candidate source in g-band was 18.6 mag +/- 0.06 at 2021-04-20T20:07:30.596 and 19.13 mag +/- 0.1 mag at 2021-04-20T21:42:43.897.
- GCN Circular #29890
A. Nicuesa Guelbenzu, S. Klose, S. Melnikov, B. Stecklum, and U. Laux (all
Tautenburg) report:
We continued observing the afterglow of GRB 210420B (Moss et al., GCN
29844) with the Tautenburg 1.34m Schmidt telescope equipped with the
TAUKAM 6k x 6k CCD camera.
Results are:
- run 2: midtime 01:35 UT, April 22: r' = 21.40 +/- 0.20 mag
- run 3: midtime 23:24 UT, April 22: r' > 22.7 (3 sigma)
Magnitudes were calibrated against SDSS stars in the field.
Our data (see Stecklum et al., GCN 29863) imply that between the 2nd and
the 3rd observing run the decay of the light curve has steepened from
alpha = 0.99 +/- 0.04 to alpha = 2.3 +/- 0.9, with a break time at 1.14
+/- 0.29 days. Probably this is the classical jet break time. No further
observations are planned.
- GCN Circular #29894
N. Pankov (HSE, IKI), S. Naroenkov (INASAN), A. Pozanenko (IKI), S.
Belkin (IKI), M. Ibrahimov (INASAN) report on behalf of IKI GRB FuN:
We observed the field of GRB 210420B (Moss et al., GCN 29833; Lien et
al., GCN 29854; Osborne et al. GCN 29876; Stamatikos et al., GCN29879)
with Zeiss-1000 telescope of Koshka observatory (INASAN). We marginally
detect the optical afterglow (Lipunov et al., GCN 29845; Oksanen et
al., GCN 29846; Hu et al., GCN 29847; Tianrui Sun et al., GCN 29848;
Leonini et al., GCN 29851; de Ugarte Postigo et al., GCN 29852, 29853;
Watson et al., GCN 29858; Zheng et al., GCN 29861; Breeveld et al., GCN
29862; Stecklum et al., GCN 29863; Butler et al.,GCN 29864; Jelinek et
al., GCN 29866; Watson, GCN 29867; Leonini et al., GCN 29872; Guelbenzu
et al., GCN 29890).
Preliminary photometry of the afterglow is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2021-04-21 20:02:55 15*180 1.03507 R 21.0 0.3 21.0
2021-04-22 20:16:45 24*180 2.05405 R n/d n/d 20.5
The photometry is based on the nearby USNO-B1.0 stars
USNO_B1.0_id R2
1325-0345119 16.12
1326-0349499 16.57
- GCN Circular #29895
M. Ibrahimov, S. Naroenkov, I. Nikolenko (all from INASAN, Moscow, Russia) and
O. Pons (IGA, Habana, Cuba) report on behalf of a larger team:
Using Zeiss 1m telescope and 4K FLI PL16803 CCD of Simeiz Obserbatory
(Collective Usage Center of INASAN), we observed the field of GRB 210420B
(Moss et al., GCN 29844; Lien et al., GCN 29854; Osborne et al. GCN 29876;
Stamatikos et al., GCN29879). 15x180sec images were acquired through Bessel R
filter on 2021-04-21/20:47:03 UT (midpoint time, 1.09 day after trigger) with
a total exposure time of 2700 sec.
Optical afterglow (Lipunov et al., GCN 29845; Oksanen et al., GCN 29846; Hu et
al., GCN 29847; Tianrui Sun et al., GCN 29848; Leonini et al., GCN 29851; de
Ugarte Postigo et al., GCN 29852, 29853; Watson et al., GCN 29858; Zheng et
al., GCN 29861; Breeveld et al., GCN 29862; Stecklum et al., GCN 29863; Butler
et al., GCN 29864; Jelinek et al., GCN 29866; Watson, GCN 29867; Leonini et
al., GCN 29872; Vinko et al., GCN 29883; Tianrui Sun, GCN 29884; Guelbenzu et
al., GCN 29890) was marginally detected on the stacked R image.
Photometry of the detected optical afterglow, calibrated against USNO-B1
photometry of nearby stars, resulted in: R = 21.8 +/- 0.5 mag.
Research was supported by Project No. RFMEFI61319X0093 (Russian Ministry of
Science and High Education, Agreement No. 075-15-2019-1716 by 2019 Nov 20) and
Project No. 19-29-11013 (Russian Foundation of Fundamental Investigation,
Agreement No. 19-29-11013\20 by 2021 Jan 21).
On behalf of M. Ibrahimov.
- GCN Circular #29901
S. Belkin (IKI), V. Kim (FAI, Pulkovo Observatory), M. Krugov (FAI), A.
Pozanenko (IKI), N. Pankov (HSE, IKI) report on behalf of GRB IKI FuN:
We observed the field of GRB 210420B (Moss et al., GCN 29833; Lien et
al., GCN 29854; Osborne et al. GCN 29876; Stamatikos et al., GCN29879)
with AZT-20 telescope of Assy-Turgen observatory starting on 2021-04-23
(UT) 18:39:00.
We marginally detect the optical afterglow (Lipunov et al., GCN 29845;
Oksanen et al., GCN 29846; Hu et al., GCN 29847; Tianrui Sun et al., GCN
29848; Leonini et al., GCN 29851; de Ugarte Postigo et al., GCN 29852,
29853; Watson et al., GCN 29858; Zheng et al., GCN 29861; Breeveld et
al., GCN 29862; Stecklum et al., GCN 29863; Butler et al.,GCN 29864;
Jelinek et al., GCN 29866; Watson, GCN 29867; Leonini et al., GCN 29872;
Guelbenzu et al., GCN 29890; Pankov et al., GCN 29894; Ibrahimov et al.,
GCN 29895).
Preliminary photometry of the source (afterglow or afterglow + host
galaxy) is following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
(mid, days) (s)
2021-04-23 18:39:00 2.98478 113*60 r' 23.2 0.3 23.3
The photometry is based on the nearby SDSS-DR12 stars
RA DEC r
16:56:42.09384 +42:38:35.9628 15.541
16:57:24.93456 +42:34:14.6388 16.642
16:56:58.03392 +42:33:40.5468 16.987
Previous IAU Circulars 