GRB 210421A
GCN Circular 29849
Subject
GRB 210421A: Swift detection of a burst
Date
2021-04-21T00:39:04Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. J. Moss (GWU), S. D. Barthelmy (GSFC), C. Gronwall (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 00:27:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210421A (trigger=1044426). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 104.908, +4.934, which is
RA(J2000) = 06h 59m 38s
Dec(J2000) = +04d 56' 03"
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 40 sec. The peak count rate
was ~1500 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 00:28:58.1 UT, 87.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 104.87569, 4.92168 which
is equivalent to:
RA(J2000) = 06h 59m 30.17s
Dec(J2000) = +04d 55' 18.0"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 124 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. We cannot determine whether the source
is fading at the present time. No spectrum from the promptly downlinked
event data is yet available to determine the column density.
The initial flux in the 0.1 s image was 1.51e-08 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 96 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 large, but uncertain, extinction expected.
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 29850
Subject
Swift GRB 210421A: Global MASTER-Net observations report
Date
2021-04-21T00:42:22Z (4 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
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 GRB 210421A ( M. J. Moss et al., GCN 29849) errorbox 13 sec after notice time and 47 sec after trigger time at 2021-04-21 00:28:17 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 54 deg. The sun altitude is -30.5 deg.
The galactic latitude b = 5 deg., longitude l = 210 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=1597889
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
52 | MASTER-OAFA | C | 10 | 16.4 |
82 | MASTER-OAFA | C | 10 | 16.4 |
116 | MASTER-OAFA | C | 20 | 16.8 |
160 | MASTER-OAFA | C | 30 | 17.0 |
215 | MASTER-OAFA | C | 40 | 17.1 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 29857
Subject
GRB 210421A: DDOTI Upper Limit
Date
2021-04-21T04:56:00Z (4 years ago)
From
Alan M Watson at UNAM <alan@astro.unam.mx>
Alan M. Watson (UNAM), Nat Butler (ASU), 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 210421A (Moss et al., GCN Circ.
29849) with the DDOTI wide-field imager at the Observatorio Astron��mico Nacional
on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-21 03:05
to 04:33 UTC (from 2.6 to 4.1 hours after the trigger) and obtained 4320 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 do not detect any source in the XRT region to a 3-sigma limiting AB magnitude of
w = 21.1.
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
GCN Circular 29865
Subject
GRB 210421A: Enhanced Swift-XRT position
Date
2021-04-21T15:22:26Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1675 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 210421A, 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 = 104.87443, +4.92232 which is equivalent
to:
RA (J2000): 06h 59m 29.86s
Dec (J2000): +04d 55' 20.4"
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.
GCN Circular 29875
Subject
GRB 210421A: Swift-XRT refined Analysis
Date
2021-04-21T22:39:46Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),
D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), K.L. Page (U.
Leicester) and M.J. Moss report on behalf of the Swift-XRT team:
We have analysed 6.4 ks of XRT data for GRB 210421A (Moss et al. GCN
Circ. 29849), from 91 s to 68.9 ks after the BAT trigger. The data
comprise 130 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 29865).
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.6 (+0.8, -0.9). At T+109 s the decay
steepens to an alpha of 4.96 (+0.17, -0.15) before breaking again at
T+397 s to a final decay with index alpha=0.59 (+0.22, -0.14).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.74 (+/-0.08). The
best-fitting absorption column is 5.3 (+/-0.3) x 10^21 cm^-2, in
excess of the Galactic value of 4.6 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.17 (+0.19, -0.14)
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 3.7 x 10^-11 (6.5 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 4.6 (+0.8, -0.0) x 10^21 cm^-2
Galactic foreground: 4.6 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.17 (+0.19, -0.14)
If the light curve continues to decay with a power-law decay index of
0.59, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.1 x
10^-13 (7.4 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/01044426.
This circular is an official product of the Swift-XRT team.
GCN Circular 29882
Subject
GRB 210421A: MITSuME Akeno optical upper limits
Date
2021-04-22T14:52:20Z (4 years ago)
From
Naohiro Ito at Tokyo Tech <n.ito@hp.phys.titech.ac.jp>
N. Ito, K. L. Murata, R. Hosokawa, M. Niwano, H. Takamatsu, Y. Yatsu,
and N.Kawai (TokyoTech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 210421A (M. J. Moss et al. GCN Circular
#29849, V. Lipunov et al. GCN Circular #29850, Alan M. Watson et al.
GCN Circular #29857, P.A. Evans et al. GCN Circular #29865, P.A. Evans
et al. GCN Circular #29875) with the optical three color (g', Rc, and
Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno
Observatory, Yamanashi, Japan. The observation with a series of 60 sec
exposures started at 2021-04-21 09:51:58 UT (9.4 hours after the Swift
BAT trigger) We stacked the images with good conditions. We did not
detect any sources within the enhanced XRT error region (P.A. Evans et
al. GCN Circular #29865) in all three bands.
We obtained the 5-sigma limits of the stacked images as follows.
T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
9.8 11:25 7020 g'>18.8, Rc>18.8, Ic>18.4
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used the PS1 catalog for flux calibration.
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, Vol.73, Issue 1, Pages
4-24; https://github.com/MNiwano/Eclaire).
GCN Circular 29885
Subject
GRB 210421A: Swift/UVOT Upper Limits
Date
2021-04-22T18:53:07Z (4 years ago)
From
Samantha Oates at MSSL <samantha.oates@alumni.ucl.ac.uk>
S. R. Oates (U.Birmingham) and M. J. Moss (GWU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210421A
96 s after the BAT trigger (Moss et al., GCN Circ. 29849).
No optical afterglow consistent with the XRT position
(Evans et al., GCN Circ. 29865).
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 96 246 147 >20.4
white 96 1912 191 >20.6
v 1608 1800 39 >17.9
b 1534 1899 58 >19.2
u_FC 308 484 173 >19.5
u 308 1874 211 >19.6
uvw1 1658 1850 39 >18.1
uvm2 1633 1825 39 >17.9
uvw2 1584 1776 39 >18.3
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.318 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 29889
Subject
GRB 210421A: GECAM detection
Date
2021-04-23T06:37:40Z (4 years ago)
From
QiBin Yi at IHEP, HXMT <yiqb@ihep.ac.cn>
S. L. Xie, X. Y. Song, Q. B. Yi, X. Y. Zhao, Y. Huang, S. L. Xiong,
S. Xiao, C. Cai, Y. Zhao, J. C. Liu, Y. Q. Zhang, W. C. Xue, C. Zheng,
Z. W. Guo, C. W. Wang, D. Y. Guo, P. Wang, X. B. Li, W. X. Peng, R. Qiao,
Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, J. J. He,
B. Li, C. Li, C. Y. Li, J. H. Li, Q. X. Li, X. Q. Li, Y. G. Li, X. H. Liang,
J. Y. Liao, J. C. Liu, X. J. Liu, Y. Q. Liu, F. J. Lu, Q. Luo, X. Ma,
G. Ou, D. L. Shi, J. Y. Shi, L. M. Song, G. X. Sun, X. L. Sun, Y. L. Tuo,
J. Z. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, S. Yang, M. Yao, B. X. Zhang,
C. Y. Zhang, D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang,
P. Zhang, S. N. Zhang, Z. Zhang, S. Y. Zhao, S. J. Zheng, X. Zhou (IHEP),
report on behalf of GECAM team:
During the commissioning phase, GECAM-B triggered a long burst,
GRB 210421A, at 2021-04-21T00:27:32.000 UTC (denoted as T0),
which was also detected by Swift/BAT(GCN #29849).
According to the GECAM-B light curves in about 8 keV - 115 keV,
this burst mainly consists of multiple pulses with duration of about 20 s.
Although in-flight calibration has not been finalized yet,
GECAM-B localized this burst to the following position (J2000):
Ra: 103.56 deg
Dec: 2.26 deg
Err: 3.46 deg (1-sigma,statistical only)
The current systematic error of location is estimated to be several degrees
which could be minimized by the ongoing calibration.
GECAM location is consistent with the Swift/BAT(GCN #29849) position
within the error.
The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/multiLCvsE_2021-04-21T003A273A32.950_.pdf
Please note that all GECAM results here are preliminary. The final analysis
will be published in journal papers or GECAM online catalog.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor
(GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in
Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time),
which was funded by the Chinese Academy of Sciences (CAS).
GCN Circular 29893
Subject
GRB 210421A: Swift-BAT refined analysis
Date
2021-04-23T16:41:44Z (4 years ago)
From
Sibasish Laha at GSFC <sibasish.laha@nasa.gov>
T. N. Ukwatta (LANL), 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), M. Stamatikos (OSU),
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 210421A (trigger #1044426)
(Moss et al., GCN Circ. 29849). The BAT ground-calculated position is
RA, Dec = 104.882, 4.928 deg which is
RA(J2000) = 06h 59m 31.7s
Dec(J2000) = +04d 55' 41.2"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 44%.
The BAT light curve showed a complex structure with a duration of about ~60 sec.
T90 (15-350 keV) is 79.52 +- 26.78 sec (estimated error including systematics).
The time-averaged spectrum from T-21.74 to T+73.22 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.10 +- 0.72,
and Epeak of 35.2 +- 8.5 keV (chi squared 61.93 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T+2.47 sec in the 15-150 keV band is
2.0 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index
of 2.10 +- 0.13 (chi squared 69.44 for 57 d.o.f.). 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/BATbursts/1044426/bascript/top.html