GRB 201221A

K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 07:09:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201221A (trigger=1013852).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 214.477, -45.411 which is 
   RA(J2000) = 14h 17m 55s
   Dec(J2000) = -45d 24' 38"
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 50 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~10 sec after the trigger. 

The XRT began observing the field at 07:11:17.8 UT, 136.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 214.47885, -45.41606 which
is equivalent to:
   RA(J2000)  = 14h 17m 54.92s
   Dec(J2000) = -45d 24' 57.8"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 18 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 (9.32 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.3
(+4.59/-3.72) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 141 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
0.11. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.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/)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 201221A, we find an
enhanced XRT position of the afterglow: RA, Dec: 214.4805, -45.4166
which is equivalent to:
   RA (J2000)  = 14 17 55.31
   Dec (J2000) = -45 24 59.9
with an uncertainty of 2.3 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/1013852.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

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 201221A ( K. L. Page et al., GCN 29096
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 ) errorbox 76 sec after trigger time at 2020-12-21 07:10:17 UT, with upper limit up to  17.6 mag. The observations began at zenith distance = 65 deg. The sun  altitude  is -23.8 deg. 

The galactic latitude b = 14 deg., longitude l = 319 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1507781

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      86 |         MASTER-OAFA |   C |    20 | 17.3 |        
     126 |         MASTER-OAFA |   C |    20 | 17.2 |        
     170 |         MASTER-OAFA |   C |    30 | 17.5 |        
     225 |         MASTER-OAFA |   C |    40 | 17.6 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

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

report:

The 30cm robotic telescope FRAM-Auger in Malargue (Argentina) reacted
robotically to the Swift/BAT alert of GRB201221A (Page et al., GCNC 29096,
Evans et al., GCNC 29097), starting with a series of 20 s R-band images at
07:10:13 UT, i.e. 72 s post trigger.

We do not detect any new or strongly variable source at or around the
reported gamma-ray errorbox in single frames nor in a combined 20 x 20 s
image spanning the period from 1.2 min to 12.1 min after the initial
trigger. The combined exposure has a 3-sigma limiting magnitude R(Vega) ~
17.5.

D. B. Malesani (DTU Space), J.-B. Vielfaure (APC, Paris University), L. 
Izzo (DARK/NBI), S. D. Vergani (GEPI, Observatoire de Paris), D. 
Burgarella (AMU, CNRS, CNES, LAM), V. D'Elia (ASI/SSDC), A. de Ugarte 
Postigo (HETH/IAA-CSIC, DARK/NBI), J. P. U. Fynbo (DAWN/NBI), A. J. 
Levan (Radboud Univ.), B. Milvang-Jensen (DAWN/NBI), D. A. Kann 
(HETH/IAA-CSIC), E. Palazzi (INAF/OAS), G. Pugliese (API, Univ. 
Amsterdam), N. R. Tanvir (Univ. Leicester), K. Wiersema (Univ. Warwick), 
report on behalf of the Stargate consortium:

We observed the field of GRB 201221A (Page et al., GCN 29096
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 ) using the 
ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.

Using the acquisition camera, multi-band imaging was secured. Within the 
XRT error circle (Evans, GCN 29097
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 ), no source is detected in an r-band 
image (taken at mean epoch of 42 min after the GRB) down to limiting 
magnitude r > 23.5 (AB). However, a source is clearly visible in the 
z-band image with z = 19.76 +- 0.04 AB (mean time 35 min after the GRB). 
The corresponding color r-z > 3.7 is exceptionally red. The coordinates 
of the object are (J2000, 0.3" error):

RA = 14:17:55.26
Dec = -45:24:58.0

Spectroscopy of the z-band source was executed covering the wavelength 
range 3000-25000 AA. Unfortunately due to visibility constraints, only 
two spectra by 600 s each were secured, plus two extra exposures during 
twilight which have lower quality. We report on the analysis of the 
first set only, which has a mean time of 1.65 hr after the GRB.

Continuum is well detected in the infrared arm, as well as in the red 
part of the visible arm. A clear break is detected around 8150 AA, 
which, if interpreted as the Lyman break, corresponds to z = 5.70. Weak 
continuum is detected blueward of the break, until it vanishes 
completely at the corresponding location of the Lyman limit. We thus 
conclude that z = 5.70 is the redshift of GRB 201221A.

Further analysis is undergoing.

We acknowledge support from the ESO observing staff at Paranal, in 
particular Zahed Wahhaj.

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

Using 2103 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 201221A, 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 = 214.48016, -45.41620 which is equivalent
to:

RA (J2000): 14h 17m 55.24s
Dec (J2000): -45d 24' 58.3"

with an uncertainty of 1.5 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.P. Beardmore (U. Leicester), P.A. Evans (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), J.P. Osborne
(U. Leicester) and K.L. Page report on behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 201221A (Page et al. GCN
Circ. 29096
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 ), from 143 s to 23.8 ks after the  BAT trigger. The data
comprise 320 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Beardmore et al. (GCN Circ. 29097
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.71 (+/-0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.39 (+0.16, -0.15). The
best-fitting absorption column is  6.3 (+8.3, -6.3) x 10^22 cm^-2, at a
redshift of 5.7, in addition to the Galactic value of 9.3 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 5.0 x 10^-11
(4.7 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 9.3 x 10^20 cm^-2
Intrinsic column:    6.3 (+8.3, -6.3) x 10^22 cm^-2 at z=5.7
Photon index:	     1.39 (+0.16, -0.15)

If the light curve continues to decay with a power-law decay index of
0.71, the count rate at T+24 hours will be 0.016 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.0 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/01013852.

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

A. A. Breeveld (UCL-MSSL) and K. L. Page (U. Leicester) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 201221A 141 s after the BAT trigger 
(Page et al., GCN Circ. 29096
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 ). No optical afterglow consistent with the optical position (Malesani 
et al. GCN Circ. 29100
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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           141          291          147         >20.0
u_FC               300          549          246         >19.1
white              141          951          257         >20.2
v                  629         4762          236         >18.8
b                  555          748           39         >18.3
u                  300         5271          357         >19.5
w1                 679         5172          236         >19.4
m2                 654         4967          236         >19.2
w2                 605         4557          235         >19.4

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of 
E(B-V) = 0.11 in the direction of the burst (Schlegel et al. 1998).

P. Veres (UAH) reports on behalf of the Fermi-GBM Team:

"At 07:09:01 UT on 21 December, 2020 Swift detected GRB 201221A  (Page
et al. GCN 29096
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 ). There was no Fermi-GBM onboard trigger around the
event.

An automated, blind search for short gamma-ray bursts below the
onboard triggering threshold in Fermi-GBM identified a long
counterpart with high significance.  This was not included in the
public list (https://gcn.gsfc.nasa.gov/gcn/fermi_gbm_subthresh_archive.html),
because the search reports only short candidates.

The GBM targeted search [1], the most sensitive, coherent search for
GRB-like signals identified a transient most significantly on the
8.192 s timescale, with a log likelihood ratio of 52 and a location
consistent with the event.

The GBM light curve consists of a single peak. The time-averaged
spectrum from T0-10 s to T0+47 s is best fit by a power law function
with an exponential high-energy cutoff (T0 is the Swift trigger time).
The power law index is -1.17 +/- 0.21 and the cutoff energy,
parameterized as Epeak, is 129 +/- 28 keV.

The event fluence (10-1000 keV) in this time interval is (3.30 +/-
0.27)E-04 erg/cm^2. Using the redshift z=5.7 reported by Malesani et
al (GCN 29100
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 ),  we derive an isotropic equivalent energy in the
1-10,000 keV range of (2.02 +/- 0.16)E+55 erg.

This analysis is preliminary.

[1] Goldstein et al. 2019 arXiv:1903.12597
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"

[GCN OPS NOTE(22Dec2020): The 5th paragraph contains some errors
in the number results.  Please see Circ 29111 for the correct values.]

P. Veres (UAH) reports:

In GCN 29110
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  we reported the sub-threshold detection of GRB 201221A. The
reported fluence  value contained an error. The corrected paragraph reads:

"
The event fluence (10-1000 keV) in the T0-10 s to T0+47 s time interval (T0
is the Swift trigger time) is (3.6 +/- 0.4)E-06 erg/cm^2. Using the
redshift z=5.7 reported by Malesani et al (GCN 29100
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 ),  we derive an
isotropic equivalent energy in the 1-10,000 keV range of (2.2 +/- 0.2)E+53
erg.
"

We apologize for the confusion this may have caused.

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),
K. L. Page (U Leicester), 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-240 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 201221A (trigger #1013852)
(Page et al., GCN Circ. 29096
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 ).  The BAT ground-calculated position is
RA, Dec = 214.488, -45.406 deg which is
   RA(J2000)  =  14h 17m 57.1s
   Dec(J2000) = -45d 24' 20.8"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 42%.

The mask-weighted light curve shows a weak pulse that starts at ~T-7 s
and ends at ~T+40 s. T90 (15-350 keV) is 44.5 +- 6.2 sec (estimated error
including systematics).

The time-averaged spectrum from T-7.63 to T+41.72 sec is best fit by
a simple power-law model.  The power law index of the time-averaged
spectrum is 1.40 +- 0.15.  The fluence in the 15-150 keV band
is 1.9 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured
from T+4.16 sec in the 15-150 keV band is 1.0 +- 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/1013852/BA/

P. D'Avanzo, S. Covino, D. Fugazza, A. Melandri (INAF-OAB), D. B. Malesani (DTU space) 
on behalf of the REM team, report:

We observed the field of GRB 201221A (Page et al., GCN Circ. 29096
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 ) with the REM 60cm robotic 
telescope located at the ESO premise of La Silla (Chile). The observations were performed starting 
on 2020 December 21 at 07:10:33 UT (i.e. 92 seconds after the burst) and were carried in the g, r, i, z 
bands simultaneously. 

From preliminary photometry, we estimate the following magnitudes and 3sigma upper limits for the 
afterglow reported by Malesani et al. (GCN Circ. 29100
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 ):

g > 17.9
r > 17.8
i > 17.7
z = 15.8 +/- 0.3

(AB; calibrated against the APASS catalogues), at a mean time of 97 seconds after the GRB t0. 
By combining our z-band magnitude with the one reported by Malesani et al., we infer an afterglow 
temporal decay (f propto t^(alpha)) of alpha ~ -1.2 between 97 seconds and 2100 seconds after the GRB t0.

D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova, A.Lysenko,
D. Svinkin, A. Tsvetkova,  M. Ulanov, T. Cline, on behalf of the Konus-Wind team,
and A. Lien (GSFC/UMBC), report:

The long GRB 201221A (Swift-BAT trigger #1013852, T0 = T0(BAT)= 07:09:01.4258 UT:
Page et al., GCN 29096
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 ; Breadmore et al., GCN 29108
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 ;
Fermi GBM Sub-Threshold Detection: Veres, GCN 29110
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 , 29111
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 )
was detected by Konus-Wind (KW) in the waiting mode.

A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band
reveals a ~11 sigma count rate increase over background in the interval
from ~T0(BAT)-10 s to ~T0(BAT)+20 s.
The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB201221A/

To derive the broad-band spectral parameters of this burst, we performed
a joint spectral analysis of the Swift/BAT data (15-150 keV) and the Konus-Wind
3-channel spectral data, which cover the energy range from ~20 keV to ~1.5 MeV.

The time-averaged spectrum, measured from T0(BAT)-9.6 s to T0(BAT)+19.8 s,
is best fit in the 15 keV - 1.5 MeV range by the GRB (Band)
function with the following model parameters:
the low-energy photon index alpha = -0.95 (-0.22,+0.31),
the high energy photon index beta = -2.39 (-0.89,+0.38),
and the peak energy Ep = 194 (-63,+81) keV, chi2 = 65/58 dof.

In the 15-1500 keV band, the total burst fluence S is 4.3(-0.4, + 0.7)x10^-6 erg/cm^2,
and the 2.944 s peak energy flux Fp is 2.0 (-0.2, + 0.3)x10^-7 erg/cm^2.
In the 10-10000 keV band, standard for the KW analysis, S = 5.3(-1.0, + 2.3)x10^-6 erg/cm^2
and Fp = 2.4 (-0.4, + 1.0)x10^-7 erg/cm^2.

Assuming the redshift z=5.70 (Malesani et al., GCN 29100
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 )
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the isotropic energy release E_iso to 3.0(-0.5,+1.3)x10^53 erg,
the isotropic luminosity L_iso to 9.0(-1.6,+3.9)x10^52 erg/s,
and the rest-frame peak energy of the time-integrated spectrum Ep,z to 1300(-420,+540) keV.
With these values, GRB 201221A is within 90% prediction bands
for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs
with known redshifts (part I: Tsvetkova et al., ApJ 850 161, 2017;
part II: Tsvetkova et al., ApJ, accepted),
see http://www.ioffe.ru/LEA/GRBs/GRB201221A/GRB201221A_rest_frame.pdf

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.