GRB 230427A
GCN Circular 33722
Subject
GRB 230427A: Swift-BAT refined analysis
Date
2023-05-03T22:26:28Z (2 years ago)
From
Sibasish Laha at GSFC <sibasish.laha@nasa.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC),
T. Sakamoto (AGU), (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 230427A (trigger #1165948)
(Troja et al., GCN Circ. 33687). The BAT ground-calculated position is
RA, Dec = 153.339, 48.231 deg which is
RA(J2000) = 10h 13m 21.5s
Dec(J2000) = +48d 13' 52.3"
with an uncertainty of 3.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 86%.
The BAT light curve showed a complex structure with a duration of about 20 sec.
T90 (15-350 keV) is 4.00 +- 1.41 sec (estimated error including systematics).
The time-averaged spectrum from T-0.17 to T+3.83 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.36 +- 0.47. The fluence in the 15-150 keV band is 9.5 +- 2.9 x 10^-08 erg/cm2.
The 1-sec peak photon flux measured from T-0.17 sec in the 15-150 keV band
is 0.7 +- 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/1165948/BA/
GCN Circular 33712
Subject
GRB 230427A: NOT optical upper limit
Date
2023-04-29T15:45:11Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Z.P. Zhu (NAOC, HUST), D. B. Malesani (Radboud Univ. and DAWN/NBI), X. Liu, D. Xu (NAOC), report on behalf of a larger collaboration:
We observed the field of GRB 230427A detected by Swift (Troja et al., GCN 33687) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 23:06:58 UT on 2023-04-27, i.e., ~12.6 hr after the Swift/BAT trigger, and 3x300 s Sloan r-filter images and 5x200 s Sloan z-filter images were obtained, respectively.
No new source is detected in our stacked images at the Swift/UVOT position (Troja et al., GCN 33687), and preliminary photometric results are as follows:
T_mid-T0 (hr) Filter Upper_Limit (3-sigma)
12.7 r >23.5
13.0 z >22.5
calibrated with the nearby Pan-STARRS field and not corrected for Galactic extinction.
GCN Circular 33711
Subject
GRB 230427A: TSHAO, SAO RAS, AbAO optical upper limit
Date
2023-04-28T21:28:46Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
I. Reva (FAP), A. S. Moskvitin (SAO RAS), O. A. Maslennikova (SAO RAS), R. Ya. Inasaridze (AbAO), A. Volnova (IKI), A. Pozanenko (IKI), N. Pankov (HSE), S. Belkin (IKI) report on behalf of GRB IKI FuN:
We observed the field of Swift GRB 230427A (Troja et al., GCN 33687) in R-filter on 2023-04-27 starting (UT) 15:09:59 with with Zeiss-1000 telescope of TSHAO observatory, (UT) 17:21:56 with Zeiss-1000 telescope of SAO RAS, (UT) 21:56:16 with AS-32 telescope of Abastumani observatory. We do not detect the optical counterpart of GRB 230427A (Troja et al., GCN 33687; Hu et al., GCN 33695; Agui Fernandez et al., GCN 33704; Klingler et al., GCN 33710). Preliminary photometry of stacked images is following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma) Obs.
(mid, days) (s)
2023-04-27 15:09:59 0.22388 37*120 R n/d n/d 21.8 TSAHO
2023-04-27 17:21:56 0.30117 4*300 R n/d n/d 21.4 SAO RAS
2023-04-27 21:56:16 0.51140 104*60 R n/d n/d 21.0 AbAO
The photometry is based on nearby USNO-B1.0 stars.
USNO-B1.0 R2
1381-0248742 15.71
1381-0240666 16.93
1381-0240629 16.83
GCN Circular 33710
Subject
GRB 230427A: Swift/UVOT Detection
Date
2023-04-28T18:03:41Z (2 years ago)
From
N. Klingler at NASA-GSFC/UMBC/CRESST II <noelklingler@gmail.com>
N. J. Klingler (GSFC/UMBC/CRESTII) and E. Troja (UToV) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 230427A 98 s after the BAT trigger (Troja et al., GCN Circ. 33687). A source consistent with the XRT position (Evans et al. 2023, GCN Circ. 33688) is detected in the initial UVOT exposures.
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 98 248 147 20.19 +/- 0.15
v 586 4999 255 >19.3
b 512 1158 58 >19.6
u 256 854 265 >20.5
w1 810 5404 231 >20.0
m2 5004 5204 197 >19.6
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.007 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 33708
Subject
GRB 230427A: Gaoyazi/GOT optical upper limit
Date
2023-04-28T15:42:19Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
S.Y. Fu, S.Q. Jiang, X. Liu, T.H. Lu, D Xu (NAOC), Z.P. Zhu (NAOC, HUST), S.W. Luo, M.M. Yang, Z. K. Feng (GYZO, NAOC) report:
We observed the field of GRB 230427A detected by Swift (Troja et al., GCN 33687) with the GOT-0.5m telescope located at Gaoyazi, Xinjiang, China. Observations started at 16:34:35 UT on 2023-04-27, i.e., 6.05 hr after the Swift/BAT trigger, 5 x 90 s and 10 x 120 s images were obtained in the Sloan r filter.
No optical source is detected in our stacked image at the UVOT position (Troja et al,. GCN 33687), down to a 3-sigma limiting magnitude r > 20.4 (AB) at 6.32 hr post-burst, calibrated with nearby PanSTARRS stars. The magnitude is not corrected for Galactic extinction.
GCN Circular 33707
Subject
GRB 230427A: OHP/T193 spectroscopy observations of WISEA J101316.01+481158.7
Date
2023-04-28T15:40:52Z (2 years ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
C. Adami, M. Garnichey, F. Michel (LAM), B. Schneider (MIT),
S. Basa (LAM), S. D. Vergani (GEPI, Obs. de Paris), D. Turpin,
D. Götz, E. Le Floc'h (CEA Paris-Saclay), report on behalf
of a larger collaboration:
We re-observed the field of GRB 230427A (Troja et al., GCN 33687) using
the T193cm telescope at Observatoire de Haute-Provence (France) equipped
with the MISTRAL spectro-imager. This time, we targeted in spectroscopy
the galaxy close to the GRB line of sight: WISEA J101316.01+481158.7, at
r'SDSS(PSF) = 19.6 (AB). Two exposures of 900s were obtained in the blue
configuration (4200A-8000A) from 2023 28 April 00:25:02 UT to 2023 28 April
00:55:59 UT. The wavelength calibration was performed using the MISTRAL
calibration lamp, exposed just after the science observation. Data were
reduced using the ASPIRED package (https://github.com/cylammarco/ASPIRED)
configured for MISTRAL data.
In the combined frame, we clearly detect the [NII]@6548A, Halpha, [NII]@6583A,
and [SII]@6718A. Halpha is the dominant line of the spectrum. Based on these
lines, we inferred a redshift of z = 0.1524 +/- 0.0005, in good agreement
with the SDSS photometric redshift of z = 0.13 +/- 0.03.
The GRB is at an offset of ~18 arcsec from the WISEA J101316.01+481158.7
center. At the redshift of this galaxy, the burst would have a projected
offset of ~48 kpc and a probability of chance coincidence of ~0.16,
which is not commonly observed for the long GRB population. For this reason,
this object is probably not the host galaxy of GRB 230427A.
We acknowledge the excellent support from Observatoire de Haute-Provence,
in particular Jean Balcaen.
GCN Circular 33706
Subject
GRB 230427A: Nanshan/HMT optical upper limit
Date
2023-04-28T15:38:03Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
S.Q. Jiang, S.Y. Fu, X. Liu, T.H. Lu, D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:
We observed the field of GRB 230427A detected by Swift (Troja et al., GCN 33687) using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. Observations started at 14:50:24 UT on 2023-04-27, i.e., 4.3 hr after the Swift/BAT trigger, and 30x60 s unfiltered frames were obtained.
No optical source is detected in our stacked image at the UVOT position (Troja et al., GCN 33687), down to a 3-sigma limiting magnitude m(r) > 21.1 mag (AB) at 4.7 hr post-burst, calibrated with the nearby PanSTAR field in the Sloan r-filter. The magnitude is not corrected for Galactic extinction.
GCN Circular 33705
Subject
GRB 230427A: Osservatorio Astronomico Nastro verde upper limit
Date
2023-04-28T15:20:54Z (2 years ago)
From
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy - MPC Code C82 <osservatorionastroverde@gmail.com>
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report:
We image the field of GRB 230427A detected by SWIFT(trigger 1165948)
with telescope of Nastro Verde Observatory - Sorrento (Naples), Italy. Member of:
AAVSO - American Association of Variable Star Observers.
UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili.
AstroCampania Associazione
The observations started at 19:04 UT of 2023/04/27, after 8,30 hours after the GRB trigger, at the end of twilight
with principal telescope SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME
I took 32 image of 120 sec each. All images are unfiltered, calibrated with masterdark and masterflat,stacked with Tycho Tracker software
We have not detected any clearly visible sources, up to 20th magnitude with lightly hazy skies and lunar disturbance
Start T0+ End T0+ Rlim
19:04:53 UT 20:22:52 UT 20
We did not found any optical counterpart in the error box of the XRTcandidate.
Troja et al., GCN 33687
Magnitudes were estimated with the Gaia DR2 cat. and
are not corrected for galactic dust extinction.
The message may be cited.
GCN Circular 33704
Subject
GRB 230427A: OSIRIS+/GTC observations
Date
2023-04-28T15:05:51Z (2 years ago)
From
J. F. Agui Fernandez at IAA-CSIC <feli@iaa.es>
J. F. Agui Fernandez (IAA-CSIC), A. de Ugarte Postigo
(OCA), C. C. Thoene (ASU-CAS), Fabricio Perez, Alvaro
Tejero and A. L. Cabrera Lavers (GTC, IAC) report:
We observed the afterglow of GRB 230427A at ~ 11.3
hours after burst (Page et al. GCN 33687; Takahashi
et al. GCN 33690; Hu et al. GCN 33695; Tohuvavohu
et al. 33703) with OSIRIS+ at the 10.4m GTC telescope,
at the Roque de los Muchachos Observatory (La Palma,
Spain). Observations consisted of 3x1200 s spectroscopy
with grism R1000B, covering the spectral range between
3700 and 7800 AA under good observing conditions.
From the acquisition image we detect a source at the
GRB location and we measure a magnitude of r ~ 24.2
compared to PanSTARRS field stars. We detect a faint
trace at GRB location above ~3950A which set a limit
for the redshift of z < 3.3.
GCN Circular 33703
Subject
GRB 230427A: Swift-XRT refined Analysis
Date
2023-04-28T12:54:32Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.
Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), J. D. Gropp (PSU) report on behalf of the Swift-XRT team:
We have analysed 4.5 ks of XRT data for GRB 230427A, from 80 s to 75.0
ks after the BAT trigger. The data comprise 7 s in Windowed Timing
(WT) mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode.
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.21 (+0.12, -0.11).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.94 (+0.30, -0.26). The
best-fitting absorption column is 4.0 (+6.6, -3.2) x 10^20 cm^-2,
consistent with the Galactic value of 8.4 x 10^19 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.3 x 10^-11 (3.6 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 4.0 (+6.6, -3.2) x 10^20 cm^-2
Galactic foreground: 8.4 x 10^19 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.94 (+0.30, -0.26)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01165948.
This circular is an official product of the Swift-XRT team.
GCN Circular 33699
Subject
GRB 230427A: GIT optical upper limit
Date
2023-04-28T09:16:24Z (2 years ago)
From
Harsh Kumar at Indian Inst of Tech,Bombay <harshkosli13@gmail.com>
T. Roychowdhury(IITB), V. Swain (IITB), A. Suresh (IITB), H. Kumar(IITB),
D. Raman(IITB), Kaysang (IAO), V. Bhalerao(IITB), G. C. Anupama(IIA), S.
Barway(IIA) report on behalf of the GIT team:
We observed GRB 230427A detected by Swift-BAT (Troja et al., GCN 33687)
with 0.7m GROWTH-India Telescope (GIT). The observations started at
14:20:43 UT on 2023-04-27, 3.8 hours after the Swift-BAT trigger. We
obtained 10 images of 300-sec exposures in the r' filter and 5 images of
300-sec exposures in the i', z' and g' filters. We did not detect any new
source in our stacked image within the 2.4 arcsec circle, around R.A.= 10h
13m 15.16s, DEC.=+48d 12' 14.2". The obtained upper limits follow as:
———————————————————————————————————————————————————————————————————
—————————————
JD (mid) | T_mid-T0(hrs) | Exposure (sec) | Filter | Lim_mag
(5-sigma) |
——————————————————————————————————————————————————————————————————
——————————————
2460062.1148169 | 4.22 | 10 x 300 (stacked) | r' | > 21.70 |
2460062.1433660 | 4.91 | 5 x 300 (stacked) | i' | > 20.76 |
2460062.1604599 | 5.31 | 5 x 300 (stacked) | z' | > 19.42 |
2460062.1775733 | 5.73 | 5 x 300 (stacked) | g' | > 21.35 |
———————————————————————————————————————————————————————————————————
—————————————
Our results are consistent with the upper limit reported by AKO (M. Odeh,
GCN #33693), BOOTES-5/JGT (Y.-D. Hu et al., GCN #33695), OHP/T193 (D.
Turpin et al., GCN #33696), GMG (J. Mao et al., GCN #33697) and Bassano
Bresciano Observatory (U.Quadri et al., GCN #33698). The magnitudes are
calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected
for Galactic extinction.
The GROWTH India Telescope (GIT, Kumar et al. 2022) is a 70-cm telescope
with a 0.7-degree field of view, set up by the Indian Institute of
Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB)
with funding from DST-SERB and IUSSTF. It is located at the Indian
Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding
by the IITB alumni batch of 1994, which partially supports the operations
of the telescope. Telescope technical details are available at
https://sites.google.com/view/growthindia/.
GCN Circular 33698
Subject
GRB 230427A: Bassano Bresciano Observatory upper limit
Date
2023-04-28T08:19:17Z (2 years ago)
From
Ulisse Quadri at Bassano Bresciano Obs <oabb@ulisse.bs.it>
U.Quadri and L.Strabla (Bassano Bresciano Astronomical Observatory),
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report:
We imaged the field of GRB 230427A detected by SWIFT(trigger 1165948)
with the robotic telescope of (IAU station 565) Bassano Bresciano
Observatory, Italy. Member of:
AAVSO - American Association of Variable Star Observers.
UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili.
GAC - Gruppo Astrofili Cremonesi.
The observations started 8.72 hour after the GRB trigger, at the end of twilight,
with our Newton telescope D=250 mm F/D=4.8.
Weather conditions were good.
We co-added 2 series of 25 exposures of 60 sec each.
Start T0+ End T0+ Rlim
8.72 hour 9.63 hour 19.5
We did not found any optical counterpart in the error box of the XRTcandidate.
Troja et al., GCN 33687
Magnitudes were estimated with the USNO-B1.0 cat. and
are not corrected for galactic dust extinction.
Reference:
http://www.osservatoriobassano.org/GRB.asp
The message may be cited.
GCN Circular 33697
Subject
GRB 230427A: GMG upper limit
Date
2023-04-28T03:50:39Z (2 years ago)
From
Jirong Mao at Yunnan Obs <jirongmao@mail.ynao.ac.cn>
J. Mao, H.-C. Feng, and J.-M. Bai (YNAO) report:
We observed the field of GRB 230427A (Troja et al. GCN 33687) by the GMG telescope in Yunnan observatories.
The observation began from UT 14:52:28 April 27, 2023, about 4.3 hours from the trigger. We could not observe the optical
afterglow down to a magnitude limit of R~20.6.
GCN Circular 33696
Subject
GRB 230427A : OHP/T193 optical upper limit
Date
2023-04-27T23:52:46Z (2 years ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
D. Turpin (CEA Paris-Saclay), C. Adami (LAM), B. Schneider (MIT),
S. Basa (LAM), E. Le Floc'h, D. Turpin, D. Götz (CEA Paris-Saclay),
S. D. Vergani (GEPI, Obs. de Paris), report on behalf
of a larger collaboration:
We observed the field of GRB 230427A (Troja et al., GCN 33687)
using the T193cm telescope at Observatoire de Haute-Provence (France)
equipped with the MISTRAL spectro-imager. 18 exposures were obtained
in the r-band (16x300s + 2x60s) from 2023 27 April 20:36:47 UT to
2023 27 April 22:59:06 UT (mid time ~11.27h after trigger). In the combined
frame, we do not detect any source at the UVOT position reported by
Troja et al., GCN 33687 and the enhanced XRT position (Beardmore et al.,
GCN 33688) down to the following 3-sigma limit:
r > 22.3 mag (AB)
The photometric calibration was performed using nearby stars from
the PanSTARRS catalog and the magnitude is not corrected for Galactic
extinction.
We acknowledge the excellent support from Observatoire de Haute-Provence,
in particular Jean Balcaen.
GCN Circular 33695
Subject
GRB 230427A: BOOTES-5/JGT afterglow detection
Date
2023-04-27T22:44:56Z (2 years ago)
From
Youdong HU at IAA-CSIC <huyoudong072@hotmail.com>
Y.-D. Hu, E. Fernandez-Garcia, A. J. Castro-Tirado, I. Perez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), D. Hiriart and W. H. Lee (UNAM), C. J. Perez del Pulgar (UMA) and I. M. Carrasco-Garcia (SMA) and I. H. Park (SKKU), on behalf of a larger collaboration, report:
Following the detection of GRB 230427A by Swift (Troja et al. GCNC 33687), the BOOTES-5/JGT 0.6m robotic telescope at observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically observed the GRB location starting on Apr. 27, 10:35:34 UT (~ 282 s after trigger). A series of images in clear filter were gathered. A new optical transient was found within the enhanced Swift/XRT position (Beardmore et al. GCNC 33688) for which we measure a magnitude of 20.6 +- 0.2 on the co-added 10 s x 54 image, which is consistent with the detection of Swfit/UVOT (Troja et al. GCNC 33687).
We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for their excellent support.
GCN Circular 33693
Subject
GRB 230427A: AKO Upper Limit
Date
2023-04-27T19:23:20Z (2 years ago)
From
Mohammad Odeh at Al Khatim Observatory M44 <mshodeh@gmail.com>
Mohammad Odeh of Al-Khatim Observatory (AKO) operated by the International
Astronomical Center, in Abu Dhabi, UAE.
As a follow-up for the GRB 230427A detected by Swift (GCN 33687), we
observed the field of the GRB with our 0.35m f/7.7 robotic telescope. The
observation was done on 27 April 2023 from 16:06:55 to 16:13:01 (UT), 5.7
hours after the GRB trigger. We obtained multiple 180-sec exposures in Ic
filter. We did not detect any afterglow within XRT localization. This is
consistent with the report of (Takahashi et al., GCN 33690) and (Lipunov et
al., GCN 33692).
The following upper limit was calculated using Atlas catalogue as a
reference:
-----------------------------------------------------------------------------
JD (mid), T_mid-T0(hrs), Exposure (sec), Filter, Lim_mag
-----------------------------------------------------------------------------
2460062.174630, 5.7, 3 x 180 (stacked), Ic, > 19.0
-----------------------------------------------------------------------------
These magnitudes are not corrected for galactic extinction.
GCN Circular 33690
Subject
GRB 230427A: MITSuME Akeno optical upper limits
Date
2023-04-27T15:34:00Z (2 years ago)
From
Ichiro Takahashi at Tokyo Tech <itakahashi@hp.phys.titech.ac.jp>
I. Takahashi, S. Hayatsu, N. Higuchi, M. Sasada, R. Hosokawa, S. Sato,
M. Niwano, H. Seki, H. Takei, Y. Yatsu (Tokyo Tech), K. L. Murata
(Kyoto U) and N. Kawai (Riken) report on behalf of the MITSuME
collaboration:
We observed the field of GRB 230427A (Troja et al. GCN Circular
#33687, Beardmore et al. GCN Circular #33688) with the optical three
color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm
telescope Akeno.
The observation started at 2023-04-27 10:33:23 UT (91 seconds after
the Swift/BAT trigger). We stacked the images with good conditions. We
did not detect any uncatalogued sources within the error region (Troja
et al. GCN Circular #33687). We obtained the 5-sigma limits of the
stacked images as follows.
T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
263 | 2023-04-27 10:36:15 | 160.0 | g'>17.8, Rc>17.4, Ic>17.0
753 | 2023-04-27 10:44:25 | 540.0 | g'>18.7, Rc>18.7, Ic>18.2
2391 | 2023-04-27 11:11:43 | 2220.0 | g'>19.6, Rc>19.4, Ic>19.0
------------------------------------------------------------------------------------------------
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 33688
Subject
GRB 230427A: Enhanced Swift-XRT position
Date
2023-04-27T13:41:28Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.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 1112 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 230427A, 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 = 153.31316, +48.20393 which is equivalent
to:
RA (J2000): 10h 13m 15.16s
Dec (J2000): +48d 12' 14.2"
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 33687
Subject
GRB 230427A: Swift detection of a burst with an optical counterpart
Date
2023-04-27T10:51:55Z (2 years ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
E. Troja (UToV), P. A. Evans (U Leicester),
R. A. J. Eyles-Ferris (U Leicester), C. Gronwall (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU) and K. L. Page (U Leicester)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 10:31:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230427A (trigger=1165948). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 153.324, +48.180 which is
RA(J2000) = 10h 13m 18s
Dec(J2000) = +48d 10' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). No BAT light-curve is available at this time.
The XRT began observing the field at 10:33:25.9 UT, 94.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 153.31199,
48.20404 which is equivalent to:
RA(J2000) = 10h 13m 14.88s
Dec(J2000) = +48d 12' 14.6"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 91 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 (8.35 x
10^19 cm^-2, Willingale et al. 2013), with an excess column of 3.5
(+2.81/-2.63) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 98 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 10:13:15.05 = 153.31270
DEC(J2000) = +48:12:14.4 = 48.20400
with a 90%-confidence error radius of about 0.74 arc sec. This position is 1.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
20.31 with a 1-sigma error of about 0.20. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.007.
Burst Advocate for this burst is E. Troja (nora.gsfc 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/)