GRB 201209A

J.D. Gropp (PSU), H. A. Krimm (NSF), F. E. Marshall (NASA/GSFC),
M. J. Moss (GWU), D. M. Palmer (LANL), T. Sakamoto (AGU),
B. Sbarufatti (PSU), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 05:44:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201209A (trigger=1011980).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 23.106, -1.763 which is 
   RA(J2000) = 01h 32m 25s
   Dec(J2000) = -01d 45' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 30 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~7 sec after the trigger. 

The XRT began observing the field at 05:46:44.1 UT, 111.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 23.09079, -1.75347 which
is equivalent to:
   RA(J2000)  = 01h 32m 21.79s
   Dec(J2000) = -01d 45' 12.5"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 64 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 3.60
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 6.48e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 121 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 J.D. Gropp (jdg44 AT psu.edu). 
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/)

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 GRB201209A (Gropp et al., GCNC
29005), starting with a series of 20 s R-band images at 05:45:40 UT, i.e.
48 s post trigger.

We do not detect any new or strongly variable source at or around the
reported X-ray error box in single frames nor in a combined 20 x 20 s image
spanning the
period from 0.8 min to 11.9 min after the initial trigger. The combined
exposure has a 3-sigma limiting magnitude R(Vega) ~ 17.4.

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 201209A (Gropp et al.,
GCN 29005
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 ) starting at 05:48:09 UT, 197 s after the burst under
cloudy condition. Observations were performed with an automatic
sequence in the clear (roughly R), V, and I filters, and the
exposure time was 20 s per image. We do not detect any optical
afterglow candidate within the XRT position error circle (Gropp
et al., GCN 29005
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 ), neither in single image, nor in the co-add images.
The typical limiting magnitude of our single clear image is about
15.0 mag calibrated to the USNOB1.0 catalog.

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

Using 1536 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 201209A, 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 = 23.09069, -1.75468 which is equivalent
to:

RA (J2000): 01h 32m 21.77s
Dec (J2000): -01d 45' 16.8"

with an uncertainty of 1.7 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.

D. Nadella (NITK), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta
(IUCAA), P. Sawant (IUCAA), V. Bhalerao (IITB), D. Bhattacharya
(IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on
behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al,
2020, arxiv:2011.07067) showed detection of a long GRB 201209A, which
was also detected by Swift-BAT (GCN #29005
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 ).

The source was clearly detected in the 20-200 keV energy range. The
light curve showed multiple peaks of emission with the strongest peak
at 2020-12-09 05:44:56.500 UT. The measured peak count rate associated
with the burst is 456 (+51, -54) cts/s above the background in the
combined data of four quadrants, with a total of 3215 (+719, -885)
cts. The local mean background count rate was 557 (+4, -3) cts/s.
Using cumulative rates, we measure a T90 of 23 (+14, -12) s.

It was also clearly detected in the CsI anticoincidence (Veto)
detector in the 100-500 keV energy range. The light curve showed
multiple peaks of emission with the strongest peak at 2020-12-09
05:44:56.336 UT. The measured peak count rate is 697 (+81, -89) cts/s
above the background in the combined Veto data of four quadrants, with
a total of 4866 (+1506, -1667) cts. The local mean background count
rate was 1856 (+6, -7) cts/s. We measure a T90 of 25 (+26, -15) s from
the cumulative Veto light curve.

CZTI GRB detections are reported regularly on the payload site at
http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led
consortium of institutes across India, including VSSC, ISAC, IUCAA,
SAC and PRL. The Indian Space Research Organisation funded, managed
and facilitated the project.

Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu, D. Xu (NAOC) report on behalf of 
a larger collaboration:

We observed the field of GRB 201209A (Gropp et al., GCN 29005
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 ) using the 
2.16-m optical telescope located at Xinglong, Hebei, China, equipped 
with the BFOSC camera. Observations started at 13:05:43 UT on 
2020-12-09, and 2x360 s, 3x600 s R-band frames were obtained.

An uncatalogued source is detected in our stacked image at coordinates

R.A. (J2000) = 1:32:21.76
Dec. (J2000) = -1:45:17.13

with an uncertainty of ~0.5 arcsec, being fully consistent with the 
Enhanced XRT position (Goad et al., GCN 29009
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 ). Calibrated with nearby 
PS1 stars, the source has m(R) = 22.05 +/- 0.16 mag at a median time of 
0.321 days post-burst, whereas PS1 is deeper but no object is present at 
the position. We thus conclude that the source is likely the optical 
afterglow of the burst.

We acknowledge excellent support from the Xinglong-2.16m observing 
staff, in particular Aiying Zhou and Jie Zheng.

J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P.
Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB) and J.D. Gropp report on behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 201209A (Gropp et al. GCN
Circ. 29005
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 ), from 117 s to 29.1 ks after the  BAT trigger. The data
comprise 43 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. 29009
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 ).A spectrum formed from the PC mode
data can be fitted with an absorbed power-law with a photon spectral
index of 1.98 (+/-0.08). The best-fitting absorption column is	1.54
(+0.26, -0.25) x 10^21 cm^-2, in excess of the Galactic value of 3.6 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 3.5 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.54 (+0.26, -0.25) x 10^21 cm^-2
Galactic foreground: 3.6 x 10^20 cm^-2
Excess significance: 7.9 sigma
Photon index:	     1.98 (+/-0.08)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01011980.

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

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 201209A (trigger #1011980)
(Gropp, et al., GCN Circ. 29005
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 ).  The BAT ground-calculated position is
RA, Dec = 23.096, -1.762 deg which is 
  RA(J2000)  =  01h 32m 23.0s 
  Dec(J2000) = -01d 45' 43.8" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 11%.

The mask-weighted light curve shows some early emission starting at ~T-20 sec,
and two bright, symmetrical peaks centered at T+0 and T+7 sec.  The burst has
faded to background by T+30 sec.  T90 (15-350 keV) is 48.0 +- 16.0 sec 
(estimated error including systematics).

The time-averaged spectrum from T-31.66 to T+32.34 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.56 +- 0.06.  The fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+7.84 sec in the 15-150 keV band
is 12.2 +- 1.1 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/1011980/BA/

GRB 201209A: Swift/UVOT Upper Limits

K. K. Simpson (PSU) and J. D. Gropp (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 201209A
121 s after the BAT trigger (Gropp et al., GCN Circ. 29005
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 ).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 29009
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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           121          271          147         >20.1
u_FC               334          584          246         >20.3
white              121         1706          412         >20.9
v                  663         1583          117         >19.2
b                  590         1682          117         >19.5
u                  334         1657          343         >20.7
w1                 712         1632           97         >19.8
m2                 688         1260           39         >19.2
w2                1018         1211           39         >19.4

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).

Y. Q. Zhang, C. Cai, J. C. Liu, Q. Luo, S. Xiao, 
W. C. Xue, Q. B. Yi, C. Zheng���Y. Huang, C. K. Li, 
G. Li, X. B. Li, J. Y. Liao, X. Y. Song, S. L. Xiong, C. Z. Liu, 
X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, 
X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), 
T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

At 2020-12-09T05:44:52.53 (T0), Insight-HXMT/HE detected 
GRB 201209A (trigger ID: HEB201209239) in a routine search of the data, 
which also triggered Swift/BAT (Gropp J. et al., GCN #29005
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 ) and 
AstroSat/CZTI ( Nadella D. et al., GCN #29011
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 )..

The Insight-HXMT/HE light curve mainly consists of multiple 
pulses with a duration (T90) of 9.99 s measured from T0-1.09 s. 
The 1-ms peak rate, measured from T0+7.16 s, is 778 cnts/sec. 
The total counts from this burst is 2926 counts. 
URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB201209239_lc.jpg

All measurements above are made with the CsI detectors operating in the 
regular mode with the energy range of about 80-800 keV (deposited energy). 
Only gamma-rays with energy greater than about 200 keV can penetrate 
the spacecraft and leave signals in the CsI detectors installed inside 
of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was 
funded jointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information about it could be found at: 
http://www.hxmt.org.

N. Pankov (HSE), A. Pozanenko (IKI),  A. Volnova (IKI), S. Belkin (IKI), 
  E. Klunko (ISTP)  report  on behalf of IKI GRB FuN:

We observed the field of  GRB 201209A (Gropp et al., GCN 29005
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 ) with 
AZT-33IK telescope of Sayan observatory (Mondy) starting on Dec. 09 (UT) 
  11:41:13 (i.e. 0.28 days) and next epochs later. We detected a weak 
source within enhanced XRT position (Goad et al., GCN 29005
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 ) at ~1.4 
days after GRB 201209A trigger and not detected in other epochs.  Thus 
we confirm the optical afterglow detection on 0.321 days at R = 22.05 
+/- 0.16 (Zhu et al. GCN 29013
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 ).

Preliminary photometry of the field and afterglow is following

Date       UT start   t-T0       Filter Exp.    OT    Err.  UL(3sigma)
                       (mid, days)        (s)

2020-12-09  11:41:13  42*120  R        0.27873   n/d    n/d  21.7
2020-12-10  14:26:13  45*120  R        1.39332   23.4   0.3  23.5
2020-12-12  11:14:21  39*120  R        3.25868   n/d    n/d  22.2
2020-12-13  12:03:41  38*120  R        4.26307   n/d    n/d  22.9

The photometry is based on nearby USNO-B1.0 stars.