- GCN/BACODINE POSITION NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 04 May 21 13:58:56 UT
NOTICE_TYPE: Swift-XRT Nack-Position
TRIGGER_NUM: 1046782, Seg_Num: 0
POINT_RA: 222.296d {+14h 49m 11s} (J2000)
POINT_DEC: -30.538d {-30d 32' 14"} (J2000)
IMG_START_DATE: 19338 TJD; 124 DOY; 21/05/04
IMG_START_TIME: 50308.12 SOD {13:58:28.12} UT, 73135.1 [sec] since BAT Trigger Time
COUNTS: 134 Min_needed= 20
STD_DEV: 0.00 Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER: 4 Max_iter_allowed= 4
ERROR_CODE: 2
COMMENTS: SWIFT-XRT Nack Position.
COMMENTS: Algorithm did not converge; too many iterations.
- red DSS finding chart
ps-file
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 04 May 21 14:01:35 UT
NOTICE_TYPE: Swift-UVOT Source List
TRIGGER_NUM: 1046782, Seg_Num: 0
POINT_RA: 222.296d {+14h 49m 11s} (J2000)
POINT_DEC: -30.538d {-30d 32' 15"} (J2000)
POINT_ROLL: 178.096d
IMG_START_DATE: 19338 TJD; 124 DOY; 21/05/04
IMG_START_TIME: 50310.97 SOD {13:58:30.97} UT, 73137.9 [sec] since BAT Trigger Time
FILTER: 10, White
BKG_MEAN: 2.580
N_STARS: 153
X_OFFSET: 279 [pixels]
Y_OFFSET: 99 [pixels]
X_MAX: 1238 [pixels]
Y_MAX: 1058 [pixels]
DET_THRESH: 13
PHOTO_THRESH: 7
SL_URL: sw01046782000msufc159537.fits
SUN_POSTN: 41.87d {+02h 47m 28s} +16.14d {+16d 08' 11"}
SUN_DIST: 165.50 [deg] Sun_angle= 12.0 [hr] (West of Sun)
MOON_POSTN: 327.53d {+21h 50m 08s} -18.41d {-18d 24' 30"}
MOON_DIST: 92.82 [deg]
MOON_ILLUM: 42 [%]
GAL_COORDS: 330.99, 25.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS: 229.04,-13.63 [deg] ecliptic lon,lat of the pointing direction
COMMENTS: SWIFT-UVOT Source List.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 04 May 21 14:01:55 UT
NOTICE_TYPE: Swift-UVOT Processed Source List
TRIGGER_NUM: 1046782, Seg_Num: 0
POINT_RA: 222.296d {+14h 49m 11s} (J2000)
POINT_DEC: -30.538d {-30d 32' 15"} (J2000)
POINT_ROLL: 178.096d
IMG_START_DATE: 19338 TJD; 124 DOY; 21/05/04
IMG_START_TIME: 50310.97 SOD {13:58:30.97} UT, 73137.9 [sec] since BAT Trigger Time
FILTER: 10, White
BKG_MEAN: 2.580
N_STARS: 153
X_OFFSET: 279 [pixels]
Y_OFFSET: 99 [pixels]
X_MAX: 1238 [pixels]
Y_MAX: 1058 [pixels]
DET_THRESH: 13
PHOTO_THRESH: 7
SL_URL: sw01046782000msufc159537.fits
SUN_POSTN: 41.87d {+02h 47m 29s} +16.14d {+16d 08' 12"}
SUN_DIST: 165.50 [deg] Sun_angle= 12.0 [hr] (West of Sun)
MOON_POSTN: 327.53d {+21h 50m 08s} -18.41d {-18d 24' 27"}
MOON_DIST: 92.83 [deg]
MOON_ILLUM: 42 [%]
GAL_COORDS: 330.99, 25.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS: 229.04,-13.63 [deg] ecliptic lon,lat of the pointing direction
COMMENTS: SWIFT-UVOT Processed Source List.
COMMENTS: All 4 attachments are included.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 04 May 21 14:03:25 UT
NOTICE_TYPE: Swift-UVOT Image
TRIGGER_NUM: 1046782, Seg_Num: 0
POINT_RA: 222.296d {+14h 49m 11s} (J2000)
POINT_DEC: -30.538d {-30d 32' 15"} (J2000)
ROLL: 178.096d
IMG_START_DATE: 19338 TJD; 124 DOY; 21/05/04
IMG_START_TIME: 50310.97 SOD {13:58:30.97} UT, 73137.9 [sec] since BAT Trigger Time
FILTER: 10, White
EXPOSURE_ID: 641829537
X_OFFSET: 598 [pixels]
Y_OFFSET: 418 [pixels]
WIDTH: 160 [pixels]
HEIGHT: 160 [pixels]
X_GRB_POS: 758
Y_GRB_POS: 578
BINNING_INDEX: 1
IM_URL: sw01046782000msuni159564.fits
SUN_POSTN: 41.87d {+02h 47m 29s} +16.14d {+16d 08' 13"}
SUN_DIST: 165.50 [deg] Sun_angle= 12.0 [hr] (West of Sun)
MOON_POSTN: 327.55d {+21h 50m 11s} -18.40d {-18d 24' 12"}
MOON_DIST: 92.84 [deg]
MOON_ILLUM: 42 [%]
GAL_COORDS: 330.99, 25.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS: 229.04,-13.63 [deg] ecliptic lon,lat of the pointing direction
COMMENTS: SWIFT-UVOT Image.
COMMENTS: The GRB Position came from the Window Position in the Mode Command.
COMMENTS: The image has 2x2 binning (compression).
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Tue 04 May 21 14:03:34 UT
NOTICE_TYPE: Swift-UVOT Processed Image
TRIGGER_NUM: 1046782, Seg_Num: 0
POINT_RA: 222.296d {+14h 49m 11s} (J2000)
POINT_DEC: -30.538d {-30d 32' 15"} (J2000)
ROLL: 178.096d
IMG_START_DATE: 19338 TJD; 124 DOY; 21/05/04
IMG_START_TIME: 50310.97 SOD {13:58:30.97} UT, 73137.9 [sec] since BAT Trigger Time
FILTER: 10, White
EXPOSURE_ID: 641829537
X_OFFSET: 598 [pixels]
Y_OFFSET: 418 [pixels]
WIDTH: 160 [pixels]
HEIGHT: 160 [pixels]
X_GRB_POS: 758
Y_GRB_POS: 578
BINNING_INDEX: 1
IM_URL: sw01046782000msuni159564.fits
SUN_POSTN: 41.87d {+02h 47m 29s} +16.14d {+16d 08' 13"}
SUN_DIST: 165.50 [deg] Sun_angle= 12.0 [hr] (West of Sun)
MOON_POSTN: 327.55d {+21h 50m 12s} -18.40d {-18d 24' 11"}
MOON_DIST: 92.84 [deg]
MOON_ILLUM: 42 [%]
GAL_COORDS: 330.99, 25.84 [deg] galactic lon,lat of the pointing direction
ECL_COORDS: 229.04,-13.63 [deg] ecliptic lon,lat of the pointing direction
COMMENTS: SWIFT-UVOT Processed Image.
COMMENTS: The GRB Position came from the Window Position in the Mode Command.
COMMENTS: The image has 2x2 binning (compression).
COMMENTS: All 4 attachments are included.
- GCN Circular #29929
A. P. Beardmore (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU),
N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
B. Sbarufatti (PSU) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:
Swift Burst Alert Telescope (BAT) triggered and located GRB 210504A
(trigger=1046782), with the trigger time most likely between 13:40
and 13:58 UT. No BAT information is available at this moment.
XRT began observing the field of the new trigger at 13:58:28 UT.
In a promptly-downlinked image we find an X-ray source at
RA,Dec = 222.3933, -30.5322 which is equivalent to
RA (J2000) = 14:49:34.4
Dec (J2000) = -30:31:56
with an estimated uncertainty of about 10".
We currently have very limited data products and are awaiting the
full data after a ground station pass to further characterise
this object.
UVOT took a finding chart exposure of 150 seconds with the white filter.
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 extinction in the Milky Way.
Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk).
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 #29930
A. Y. Lien (GSFC/UMBC), A. P. Beardmore (U Leicester),
and K. L. Page (U Leicester) report on behalf of the Neil Gehrels
Swift Observatory Team:
We received further data from recent telemetry downlink.
The trigger time for GRB 210504A (Swift trigger #1046782;
Beardmore et al., GCN Circ. 29929) is
2021-05-04T13:54:53 UTC.
Based on currently available data from T-60 to T+63 sec,
the burst duration is longer than 50 seconds.
- GCN Circular #29931
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-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 GRB210504.58 (trigger No 1046782,14h 49m 34.40s , -30d 31m 56.0s, R=0.05) errorbox 12678 sec after notice time and 16835 sec after trigger time at 2021-05-04 18:39:03 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 50 deg. The sun altitude is -34.4 deg.
The galactic latitude b = 25 deg., longitude l = 332 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=1606655
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
16926 | MASTER-SAAO | C | 180 | 19.3 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
- GCN Circular #29932
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 210504A by Swift (Beardmore et al. GCNC 29929), we triggered the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) in order to follow up this burst, starting on May 4, 16:05 UT (~2.2 hr after the BAT trigger, according to Lien et al. GCNC 29930). No optical source is detected within the XRT error box (Beardmore et al. GCNC 29929) down to 19.1 mag in the co-added image (630 s in total, clear filter). This non-detection is consistent with the UVOT (Beardmore et al. GCNC 29929) and MASTER (Lipunov et al. GCNC 29931) limits.
We thank the staff at Lijiang observatory for their excellent support.
- GCN Circular #29933
A. A. Breeveld (UCL-MSSL) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210504A 218 s after the BAT trigger
(Beardmore et al., GCN Circ. 29929). A fading source is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 14:49:34.03 = 222.39179 (deg.)
Dec (J2000) = -30:32:02.2 = -30.53395 (deg.)
with an estimated uncertainty of 0.6 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 218 368 147 19.75 0.19
white 1168 1877 97 20.08 0.31
v 374 739 58 >18.26
b 473 837 58 >19.29
b 1144 1852 97 19.17 0.25
u 448 812 58 >18.89
uvw1 424 788 58 >18.49
uvm2 399 418 20 >17.24
uvw2 523 1040 59 >18.60
- GCN Circular #29934
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 GRB 210504A by Swift (Beardmore et al. GCNC 29929), we use Antarctic Survey Telescope 3-3 at YaoAn Astronomy Observation (China, Yunnan) for follow-up. Our observation started on 2021-05-04T16:02:29.850 (about 2 hours after the trigger of BAT, according to Lien et al. GCNC 29930). No optical source was detected within the XRT error box down to 21.0 +/- 0.6 mag in the coadded image (total 2100s, g-band). Our non-detection result is consistent with the UVOT (Beardmore et al. GCNC 29929), MASTER (Lipunov et al. GCNC 29931), and the BOOTES-4/ MET (Hu et al. GCNC 29932) limits.
- GCN Circular #29936
R. Hosokawa, K. L. Murata, M. Niwano, N. Ito, H. Takamatsu, Y. Imai,
S. Sato, M. Takaku, R. Noto, R. Yamaguchi, Y. Yatsu, and N. Kawai
(TokyoTech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 210504A (Beardmore et al. GCN Circular #29929, Lien
et al. GCN Circular #29930) 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 2021-05-04 14:55:16 UT (1.0 hour after the BAT
trigger, Lien et al. GCN Circular #29930). We stacked the images with
good conditions. We did not detect any uncatalogued sources within the
XRT error circle (Beardmore et al. GCN Circular #29929) 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
------------------------------------------------------------------------------------------------
1.1 2021-05-04 15:01 300 g’>15.9, Rc>16.2, Ic>15.9
2.8 2021-05-04 16:42 2580 g’>18.3, Rc>18.7, Ic>18.3
------------------------------------------------------------------------------------------------
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 #29937
K. E. Heintz (Univ. of Iceland and DAWN/NBI), D. A. Perley (LJMU), D. B.
Malesani (DTU Space), and A. A. Djupvik (NOT) report on behalf of a
larger collaboration:
We observed the location of the optical and X-ray afterglow of GRB
210504A (Beardmore et al., GCN 29929; Breeveld & Beardmore, GCN 29933)
using the Nordic Optical Telescope (NOT) equipped with the ALFOSC
camera. We obtained 3x300 s frames in the Sloan r-band filter, followed
by 5x200s frames in the z-band filter. Observations were carried out on
2021-05-04 UT between 23:10 and 23:35 (9.3 hours after the BAT trigger
time given by Lien et al. (GCN 29930).
The optical afterglow is detected in the combined images. We report a
refined position (J2000) of:
RA: 14:49:34.04
Dec: -30:32:02.6
No source is visible at this location in Pan-STARRS reference imaging.
The r-band magnitude of the afterglow at the time of the observation is
measured to be 20.95 +/- 0.05.
- GCN Circular #29939
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), J. R. Cummings (CPI),
H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (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 210504A (trigger #1046782)
(Beardmore et al., GCN Circ. 29929). The BAT ground-calculated position is
RA, Dec = 222.379, -30.557 deg which is
RA(J2000) = 14h 49m 31.0s
Dec(J2000) = -30d 33' 23.5"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 53%.
The mask-weighted light curve shows several overlapping pulses
that start at ~T-30 s and end at ~T+150 s. There might be additional
burst emission before the GRB came into the BAT FOV at ~T-43 s.
T90 (15-350 keV) is 135.06 +- 9.57 sec (estimated error including
systematics).
The time-averaged spectrum from T-27.55 to T+134.76 sec is best fit
by a simple power-law model. The power law index of the time-averaged
spectrum is 1.64 +- 0.13. The fluence in the 15-150 keV band is
2.7 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from
T+87.68 sec in the 15-150 keV band is 0.9 +- 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/1046782/BA/
- GCN Circular #29942
D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), A. Melandri (INAF-OAB), T.
Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and A.P. Beardmore report
on behalf of the Swift-XRT team:
We have analysed 6.7 ks of XRT data for GRB 210504A (Beardmore et al.
GCN Circ. 29929), from 218 s to 24.9 ks after the BAT trigger. The
data comprise 146 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 2804 s of PC mode data and 3 UVOT
images, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
222.39118, -30.53345 which is equivalent to:
RA (J2000): 14h 49m 33.88s
Dec(J2000): -30d 32' 00.4"
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
The late-time light curve (from T0+11.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.9 (+/-0.8).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.00 (+0.13, -0.11). The
best-fitting absorption column is 1.50 (+0.41, -0.20) x 10^21 cm^-2,
consistent with the Galactic value of 1.3 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 2.11 (+0.25,
-0.16) and a best-fitting absorption column of 1.35 (+0.75, -0.06) x
10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.1 x 10^-11 (4.2 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.35 (+0.75, -0.06) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.11 (+0.25, -0.16)
If the light curve continues to decay with a power-law decay index of
1.9, the count rate at T+24 hours will be 1.1 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.3 x
10^-14 (4.4 x 10^-14) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01046782.
This circular is an official product of the Swift-XRT team.
- GCN NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Wed 05 May 21 04:55:02 UT
NOTICE_TYPE: Swift-UVOT Position
TRIGGER_NUM: 1046782, Seg_Num: 0
GRB_RA: 222.3917d {+14h 49m 34.00s} (J2000),
222.7126d {+14h 50m 51.02s} (current),
221.6417d {+14h 46m 34.01s} (1950)
GRB_DEC: -30.5338d {-30d 32' 01.6"} (J2000),
-30.6213d {-30d 37' 16.7"} (current),
-30.3270d {-30d 19' 37.0"} (1950)
GRB_ERROR: 0.7 [arcsec radius, statistical only]
GRB_MAG: 19.87 +/- 0.17 [mag]
FILTER: 10, White
IMG_START_DATE: 19338 TJD; 124 DOY; 21/05/04
IMG_START_TIME: 50307.00 SOD {13:58:27.00} UT, 73133.9 [sec] since BAT Trigger Time
SUN_POSTN: 42.47d {+02h 49m 52s} +16.31d {+16d 18' 49"}
SUN_DIST: 165.69 [deg] Sun_angle= 12.0 [hr] (West of Sun)
MOON_POSTN: 335.36d {+22h 21m 27s} -15.81d {-15d 48' 31"}
MOON_DIST: 100.37 [deg]
MOON_ILLUM: 36 [%]
GAL_COORDS: 331.07, 25.81 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 229.12,-13.60 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT UVOT Position Notice.
COMMENTS: This Notice was ground-generated -- not flight-generated.
COMMENTS: Result based on Genie data.
COMMENTS: Notice generated automatically.
- GCN Circular #29944
D. Xu (NAOC), P. Schady (Univ. Bath), K. E. Heintz (Univ. Iceland and
DAWN/NBI), D. B. Malesani (DTU Space), B. Sbarufatti (PSU), G. Pugliese
(API, Univ. Amsterdam), D. A. Perley (LJMU), V. D'Elia (ASI/SSDC,
INAF/OAR), D. A. Kann (HETH/IAA-CSIC), and J. P. U. Fynbo (DAWN/NBI/DTU)
report on behalf of the Stargate consortium:
We observed the optical afterglow (Breeveld & Beardmore, GCN 29933;
Heintz et al., GCN 29937) of GRB 210504A (Beardmore et al., GCN 29929;
Lien et al., GCN 29330) 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 of 1200 s each (8 x 600 s in
the NIR). The observation mid-time was 2021 May 05.06 UT (11.6 hr after
the GRB).
In a 60 s image taken with the acquisition camera on May 05.02 UT, we
detect the optical afterglow, for which we measure an AB magnitude r' =
21.11 +- 0.04 mag (calibrated against nearby stars from the Pan-STARRS
catalog).
We clearly detect continuum over the wavelength range of the entire
spectrum. A trough is visible around 3740 AA, which we identify as due
to H I. From the detection of several absorption features, which we
interpret as due to Si II, C II, C IV, Fe II, Al II, Mg II, among
others, as well as the Lyman forest, we infer a redshift z = 2.077.
We acknowledge excellent support from the observing staff at Paranal, in
particular Steffen Mieske, Ditte Slumstrup and Diego Parraguez.
- GCN Circular #29946
B. O'Connor (UMD, GWU), S.Dichiara (UMD, NASA-GSFC), E. Troja
(UMD, NASA-GSFC), P. Gatkine (Caltech), J.M. Durbak (UMD), S.B. Cenko
(NASA-GSFC), A. Kutyrev (UMD, NASA-GSFC), S. Veilleux (UMD) report:
We observed the field of the GRB 210504A (Beardmore et al., GCN 29929;
Lien et al., GCN 29930) using the Large Monolithic Imager (LMI) on the
4.3m Lowell Discovery Telescope (LDT) at Happy Jack, AZ. Observations
started on May 5, 2021 at 06:32:14 UT (about 16.6 hours after the Swift
trigger) using the SDSS g, r, i, and z filters. Observations were taken at
an
airmass of 2.5 and seeing of about 1.5".
We detect the optical counterpart identified by the Swift/UVOT
(Breeveld et al., GCN 29933), the NOT (Heintz et al., GCN 29937),
and VLT (Xu et al., GCN 29944). The afterglow has magnitude r ~ 21.66
+/- 0.04 AB mag and i ~ 21.43 +/- 0.03 AB mag.
Magnitudes are calibrated against the PanSTARRS catalog and are not
corrected for Galactic extinction.
We thank the staff of the Lowell Discovery Telescope for assistance
with these observations.
- GCN Circular #30027
R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:
We observed Swift GRB 210504A (Beardmore, et al., GCN 29929) with the LCO 1-m Sinistro instrument at the South African Astronomical Observatory site, on May 5, from 18:49 to 18:56 UT (corresponding to 4.92 to 5.03 hours from the GRB trigger time) with the Bessel R filter.
We performed a series of 3x180s exposures in R. We detect an uncatalogued optical source in the coadded images consistent with the UVOT position (Breeveld, et al., GCN 29933). Using the USNO-B.1 catalog as reference, we calculate the following magnitude:
R=20.29+/-0.18
These magnitudes are not corrected for galactic extinction.
R.S. is funded by NSF AST grant #1831682
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