GRB 201027A
GCN Circular 28788
Subject
GRB 201027A: Swift detection of a burst
Date
2020-10-27T01:24:01Z (5 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
S. B. Cenko (GSFC), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),
N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Melandri (INAF-OAB), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB)
and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels
Swift Observatory Team:
At 01:07:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201027A (trigger=1002158). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 155.974, -5.515 which is
RA(J2000) = 10h 23m 54s
Dec(J2000) = -05d 30' 53"
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 20 sec. The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 01:09:07.5 UT, 83.4 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 155.9700,
-5.5101 which is equivalent to:
RA(J2000) = 10h 23m 52.81s
Dec(J2000) = -05d 30' 36.2"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 22 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 (4.67 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.6
(+2.14/-1.93) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 86 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 expected extinction corresponding to E(B-V) of
0.04.
Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov).
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 28792
Subject
GRB 201027A: Enhanced Swift-XRT position
Date
2020-10-27T11:11:55Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1722 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 201027A, 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 = 155.96975, -5.51002 which is equivalent
to:
RA (J2000): 10h 23m 52.74s
Dec (J2000): -05d 30' 36.1"
with an uncertainty of 1.8 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 28794
Subject
GRB 201027A: 1.5m OSN optical upper limit
Date
2020-10-27T16:06:00Z (5 years ago)
From
Youdong HU at IAA-CSIC <huyoudong072@hotmail.com>
Y.-D. Hu, F. J. Aceituno, A. J. Castro-Tirado, E. Fernandez-Garcia (IAA-CSIC) on behalf of a larger collaboration, report:
Following the detection of GRB201027A by Swift (Cenko et al. GCNC 28788), optical images in the I-band were obtained at the 1.5m OSN telescope in Granada (Spain) starting at 04:29 (Oct 27), i.e. ~3.4 h post burst. No optical afterglow is detected in the co-added image within the enhanced Swift/XRT error box (Osborne et al. GCNC 28792) down to I=21.9, which is consistent with the non-detection reported by Swift/UVOT (GCNC 28788).
We thank the staff at OSN for their excellent support.
GCN Circular 28798
Subject
GRB 201027A: Swift-XRT refined Analysis
Date
2020-10-28T01:24:03Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC),
V. D'Elia (ASDC), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), D.N.
Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester)
and S.B. Cenko report on behalf of the Swift-XRT team:
We have analysed 4.2 ks of XRT data for GRB 201027A (Cenko et al. GCN
Circ. 28788), from 93 s to 52.6 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Osborne et al. (GCN Circ. 28792).
The light curve can be modelled with an initial power-law decay with an
index of alpha=0.54 (+0.15, -0.21), followed by a break at T+1066 s to
an alpha of 1.36 (+0.38, -0.21).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.81 (+0.23, -0.21). The
best-fitting absorption column is 1.3 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 4.7 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.8 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.3 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 4.7 x 10^20 cm^-2
Excess significance: 2.2 sigma
Photon index: 1.81 (+0.23, -0.21)
If the light curve continues to decay with a power-law decay index of
1.36, the count rate at T+24 hours will be 1.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.9 x
10^-14 (4.7 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/01002158.
This circular is an official product of the Swift-XRT team.
GCN Circular 28799
Subject
GRB 201027A: Swift/UVOT Upper Limits
Date
2020-10-28T14:19:28Z (5 years ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
A. A. Breeveld (UCL-MSSL) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 201027A 87 s after the BAT trigger
(Cenko et al., GCN Circ. 28788). No optical afterglow consistent with the XRT position (Cenko et al.
GCN Circ. 28788) 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 87 236 147 >20.2
u_FC 299 548 246 >19.5
white 87 1721 411 >21.2
v 629 1771 136 >18.3
b 554 1696 117 >19.3
u 299 1671 343 >20.1
w1 678 1818 135 >19.1
m2 653 1795 78 >20.4
w2 604 1574 117 >20.2
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of
E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 28801
Subject
GRB 201027A: Swift-BAT refined analysis
Date
2020-10-29T01:23:20Z (5 years ago)
From
Sibasish Laha at GSFC <sibasish.laha@nasa.gov>
H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), J. R. Cummings (CPI),
S. Laha (GSFC/UMBC), 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 201027A (trigger #1002158)
(S. B. Cenko, et al., GCN Circ. 28788). The BAT ground-calculated position is
RA, Dec = 155.954, -5.499 deg which is
RA(J2000) = 10h 23m 49.0s
Dec(J2000) = -05d 29' 56.8"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 44%.
The BAT light curve showed a complex structure with a duration of about 20 sec.
T90 (15-350 keV) is 546.73 +- 420.95 sec (estimated error including systematics).
The time-averaged spectrum from T-3.86 to T+960 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.50 +- 0.00. The fluence in the 15-150 keV band is 0.0 +- 0.0 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.29 sec in the 15-150 keV band
is 1.4 +- 0.3 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/1002158/BA/
GCN Circular 28802
Subject
GRB 201027A: MITSuME Akeno optical upper limits
Date
2020-10-29T01:29:33Z (5 years ago)
From
Ryohei Hosokawa at Tokyo Institute of Technology <hosokawa@hp.phys.titech.ac.jp>
R. Hosokawa, H. Hara, R. Adachi, M. Niwano, F. Ogawa, K. L. Murata, N.
Nakamura, N. Ito, S. Ogata, H. Takamatsu, Y. Yatsu, and N. Kawai
(TokyoTech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 201027A (V. Lipunov et al., GCN #28787,
S. B. Cenko et al., GCN #28788, Y.-D. Hu et al., GCN #28794 ) 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 2020-10-27
18:43:12 UT(17.2 hour after trigger). Since the first 18 images were
taken under high airmass conditions, we stacked the images with good
conditions. We did not find any new point sources within the enhanced
Swift/XRT circle (J.P. Osborne et al., GCN #28792) 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
------------------------------------------------------------------------------------------------
17.6 19:19:32 3180 g'>19.5,Rc>20.0,Ic>19.1
------------------------------------------------------------------------------------------------
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.,
https://doi.org/10.1093/pasj/psaa091,
https://arxiv.org/abs/2008.11486; https://github.com/MNiwano/Eclaire).