GRB 201026A

S. B. Cenko (GSFC), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), M. J. Moss (GWU),
D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 22:37:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201026A (trigger=1002103).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 196.664, +83.761 which is 
   RA(J2000) = 13h 06m 39s
   Dec(J2000) = +83d 45' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex peak
structure with a duration of about 30 sec.  The peak count rate
was ~1700counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 22:38:53.0 UT, 78.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 196.7408, 83.7849 which is equivalent to:
   RA(J2000)  = 13h 06m 57.79s
   Dec(J2000) = +83d 47' 05.6"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 91 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 7.01e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 87 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
0.18. 

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/)

L. Izzo (DARK/NBI), D. B. Malesani (DTU Space), T. Kuutma (NOT), report 
on behalf od a larger collaboration:

We observed the optical afterglow of GRB 201026A (Cenko et al., GCN 
28784
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 ) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC 
imaging camera. A set of 2x300 s and 5x200 s images was secured in the 
SDSS r and z bands, respectively. The mid time of the observation was 
Oct 26.968 (36.2 min after the GRB). Observations were conducted at high 
airmass under moderate seeing conditions (1.4").

No new object is detected consistent with the XRT position, down to a 
limiting magnitude r= 21.5, z = 21.4 AB (3 sigma), calibrated against 
nearby stars from the Pan-STARRS catalog.

We note the presence of a faint, possibly extended object visible in the 
archival Pan-STARRS images, at a position consistent (RA = 13:06:58.71, 
Dec = +83:46:58.5) with that of the X-ray afterglow. This object could 
be the host galaxy of GRB 201026A, but we caution that the currently 
available uncertainty radius of the XRT position is still relatively 
large (3.9"), hence the association not robust.

Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC), X. Gao (Urumqi 
No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of GRB 201026A (Cenko et al., GCN 28784
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 ) using the 
NEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. 
Observations automatically started at 22:49:35 UT on 2020-10-26, i.e., 
12 min after the BAT trigger. We obtained 3x40 s, 4x60 s and 12x90 s 
frames in the Sloan r-filter.

No new optical source is detected in our stacked image at the XRT 
position, down to a limiting magnitude of r = 20.5, calibrated with the 
nearby Pan-STARRS field.

Martin Jelinek and Jan Strobl (ASU CAS Ondrejov, CZ),
Sergey  Karpov, Martin  Masek,  Petr  Janecek, Jakub  Jurysek,
Jan  Ebr, Ronan  Cunniffe, Petr  Travnicek and  Michael Prouza
(Institute of Physics, Prague, CZ)

report:

The  25cm  robotic  telescope  FRAM-ORM at  La  Palma  (Spain)
reacted robotically  to the alert  of GRB201026A (Cenko  et al
GCNC  28784), obtaining  a series  of 20  s unfiltered  images
starting at 22:50:58.9 UT, i.e. 13.4 min post trigger.

We  do not  detect  any  new source  within  or  near the  XRT
errorbox  neither in  single  images  (3-sigma limit  R>~17.1,
(Vega), calibrated  by the  Atlas catalog)  nor in  a combined
15x20s frame  (mean exp time  21.15 min post  trigger, 3-sigma
limit R>~18.5) similarly to Lipunov  et al. (GCNC 28783), Izzo
et al. (GCNC 28785) and Zhu et al. (GCNC 28786)

M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 466 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 201026A, 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 = 196.74662, +83.78196 which is equivalent
to:

RA (J2000): 13h 06m 59.19s
Dec (J2000): +83d 46' 55.0"

with an uncertainty of 1.9 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.

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 201026A 88 s after the BAT trigger 
(Cenko et al., GCN Circ. 28784
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 ).
No optical afterglow consistent with the XRT position (Goad et al., GCN Circ. 28791
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 ) 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            88          238          147         >20.6
white               88          904          210         >20.9
u_FC               300          550          246         >20.1
v                  630          823           39         >18.3
b                  563          749           32         >19.2
u                  300          724          265         >20.2
w1                 680          873           39         >18.5
w2                4139         4518          197         >19.3

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of 
E(B-V) = 0.18 in the direction of the burst (Schlegel et al. 1998).

P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi 
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (ASDC), J.A. Kennea
(PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), K.L. Page (U.
Leicester) and S.B. Cenko report on behalf of the Swift-XRT team:

We have analysed 3.2 ks of XRT data for GRB 201026A (Cenko et al. GCN
Circ. 28784
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 ), from 85 s to 46.3 ks after the  BAT trigger. The data
comprise 361 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 28791
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.90 (+1.12, -0.13).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.82 (+/-0.03). The
best-fitting absorption column is  4.84 (+0.22, -0.21) x 10^21 cm^-2,
in excess of the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.4 x 10^-11 (6.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     4.84 (+0.22, -0.21) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 29.0 sigma
Photon index:	     1.82 (+/-0.03)

If the light curve continues to decay with a power-law decay index of
0.90, the count rate at T+24 hours will be 5.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x
10^-13 (3.6 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/01002103.

This circular is an official product of the Swift-XRT team.

R. Hamburg (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 22:37:33.06 UT on 26 October 2020, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 201026A (trigger 625444658 / 201026943), which
was initially misclassified as a distant particle event by the GBM
flight software. GRB 201026A was also detected by the Swift/BAT and the
Swift/XRT (Cenko et al. 2020, GCN 28784
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 ). The GBM on-ground location
is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 58
degrees.

The GBM light curve shows a main pulse with a duration (T90) of about
35 s (50-300 keV). There is also later emission extending to
approximately T0+280 s. We cannot conclusively confirm it is
related to the main emission episode with GBM data alone;
however, similar late-time emission can be seen in the
Swift-XRT lightcurve (Evans et al. 2020, GCN 28796
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 ).

The time-averaged spectrum of the main pulse from T0-16 s to T0+23 s
is best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.83 +/- 0.10 and
the cutoff energy, parameterized as Epeak, is 68 +/- 3 keV.
A Band function fits the spectrum equally well with
Epeak = 63 +/- 5 keV, alpha = -0.73 +/- 0.14 and beta = -2.84 +/- 0.34.

The event fluence (10-1000 keV) in this time interval is
(3.96 +/- 0.14)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.47 s in the 10-1000 keV band
is 3.04 +/- 0.22 ph/s/cm^2.

For the later emission episode, the time-averaged spectrum
from T0+188 s to T0+237 s is best fit by
a simple power law function with index -1.84 +/- 0.04.
The event fluence (10-1000 keV) in this time interval is
(4.51 +/- 0.29)E-06 erg/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support
Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

GRB 201026A: Swift-BAT refined analysis

S. D. Barthelmy (GSFC), S. B. Cenko (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),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-60 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 201026A (trigger #1002103)
(S. B. Cenko et al., GCN Circ. 28784
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 ).  The BAT ground-calculated position is
RA, Dec = 196.696, 83.807 deg which is
   RA(J2000)  =  13h 06m 47.0s
   Dec(J2000) = +83d 48' 24.3"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 46%.

The BAT light curve showed a complex structure. There are two prominent peaks, at
~ T+0 sec and T+210 sec with a duration of about 50 sec and 60 sec respectively.
There is a small peak at T+140 to T+170 sec, and possibly a precursor at
T-60 to T-40 sec.
T90 (15-350 keV) is 135.38 +- 120.84 sec (estimated error including systematics).

The time-averaged spectrum from T-13 to T+146 sec and T+165 to T+230 sec is best fit by
a simple power-law model.  The power law index of the time-averaged spectrum is
1.94 +- 0.09.  The fluence in the 15-150 keV band is 5.6 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+1.05 sec in the 15-150 keV band
is 2.2 +- 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/1002103/BA/