Gamma-ray Burst 211106A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Notice

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Sat 06 Nov 21 04:38:13 UT
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    9504,   Sub_Num: 0
GRB_INTEN:      9.74 [sigma]
GRB_TIME:       16651.23 SOD {04:37:31.23} UT
GRB_DATE:       19524 TJD;   310 DOY;   21/11/06
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.  
COMMENTS:       Time_Scale=2.0000 and Time_Error=1.0000.  
COMMENTS:       The SPIACS lightcurve can be found at:  
COMMENTS:       ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2021-11/2021-11-06T04-37-31.0287-26706-11152-0.lc

GCN Circular #31049
Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), James DeLaunay (UAlabama), Jamie A. Kennea (PSU), report:
Swift/BAT did not trigger on GRB 211106A (T0: 2021-11-06T04:37:31.2 UTC, INTEGRAL/SPI-ACS #9504).
The INTEGRAL notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 90 seconds of BAT event-mode data from [-45,+45] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu, arXiv:2111.01769), confidently detects the burst in a 0.512 s analysis time bin with a sqrt(TS) of 19.1. Estimated T90 in the detector is 1.75 +/- 0.05 s (15-350 keV).
A candidate localization is found with DeltaLLHOut of 7.2 and a DeltaLLHPeak of 6.7. For this reason we can confidently claim detection, and preference for an in FOV origin, but the best fit arcmin localization is not strongly preferred over other positions. Conventional imaging does not find a location for this burst.
See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
The BAT position is RA, Dec = 343.643 -53.236 deg which is
```
   RA(J2000)  = 22h 54m 34.32s
   Dec(J2000) =  -53d 14′ 0.9″
```
with an estimated uncertainty of 7 arcmin. The partial coding fraction at this position is 3.9%.
XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular #31050
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT-GUANO GRB 211106A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021466
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Swift/BAT-GUANO event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.

GCN Circular #31051
V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Swift/BAT-GUANO-detected burst GRB 211106A, collecting 5.0 ks of Photon Counting (PC) mode data between T0+39.2 ks and T0+58.2 ks.
Eight uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below:
Source 2:

  RA (J2000.0):  343.5852  =  22:54:20.45
  Dec (J2000.0): -53.2303  =  -53:13:49.0
  Error: 3.4 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: (8.7 +/- 1.6)e-3 ct s^-1	 
  Distance: 126 arcsec from Swift/BAT-GUANO position.
  Flux: (4.42 +/- 0.81)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 3:

  RA (J2000.0):  343.7780  =  22:55:6.71
  Dec (J2000.0): -53.3150  =  -53:18:53.9
  Error: 5.9 arcsec (radius, 90% conf.)
  Count-rate: (2.24 [+1.04, -0.81])e-3 ct s^-1	 
  Distance: 406 arcsec from Swift/BAT-GUANO position.
  Flux: (9.8 [+4.5, -3.5])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 4:

  RA (J2000.0):  343.7223  =  22:54:53.36
  Dec (J2000.0): -53.1215  =  -53:07:17.5
  Error: 5.5 arcsec (radius, 90% conf.)
  Count-rate: (3.18 [+1.21, -0.98])e-3 ct s^-1	 
  Distance: 445 arcsec from Swift/BAT-GUANO position.
  Flux: (1.42 [+0.54, -0.44])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
The source position is 1" away from an AGN candidate (Assef et al,
2018, ApJS, 234, 23; Guo et al., 2018, A&A, 618, 144).

Source 5:

  RA (J2000.0):  343.6827  =  22:54:43.86
  Dec (J2000.0): -53.1372  =  -53:08:14.1
  Error: 5.8 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: (5.5 +/- 1.5)e-3 ct s^-1	 
  Distance: 365 arcsec from Swift/BAT-GUANO position.
  Flux: (2.23 +/- 0.59)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 6:

  RA (J2000.0):  343.7423  =  22:54:58.14
  Dec (J2000.0): -53.2260  =  -53:13:33.6
  Error: 7.3 arcsec (radius, 90% conf.)
  Count-rate: (1.62 [+0.86, -0.66])e-3 ct s^-1	 
  Distance: 216 arcsec from Swift/BAT-GUANO position.
  Flux: (7.5 [+4.0, -3.0])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)
The source position is 7" away from an AGN candidate (Assef et al,
2018, ApJS, 234, 23).

Source 7: RA (J2000.0): 343.7343 = 22:54:56.22 Dec (J2000.0): -53.3579 = -53:21:28.5 Error: 6.0 arcsec (radius, 90% conf.) Count-rate: (2.98 [+1.18, -0.94])e-3 ct s^-1 Distance: 481 arcsec from Swift/BAT-GUANO position. The source position is 5" away from an AGN candidate (Assef et al, 2018, ApJS, 234, 23).
Source 8:

  RA (J2000.0):  343.7230  =  22:54:53.51
  Dec (J2000.0): -53.2861  =  -53:17:10.0
  Error: 6.9 arcsec (radius, 90% conf.)
  Count-rate: (2.72 [+1.12, -0.90])e-3 ct s^-1	 
  Distance: 249 arcsec from Swift/BAT-GUANO position.
  Flux: (9.7 [+4.0, -3.2])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)
The source position is 9.5" away from an AGN candidate (Assef et al,
2018, ApJS, 234, 23).

Source 9:

  RA (J2000.0):  343.8707  =  22:55:28.96
  Dec (J2000.0): -53.2028  =  -53:12:10.2
  Error: 5.3 arcsec (radius, 90% conf.)
  Count-rate: (2.17 [+1.02, -0.79])e-3 ct s^-1	 
  Distance: 504 arcsec from Swift/BAT-GUANO position.
  Flux: (6.3 [+3.0, -2.3])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)

A catalogued source was also detected.
The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021466.
This circular is an official product of the Swift-XRT team.

GCN Circular #31054
A. Ridnaia, D. Frederiks, S. Golenetskii, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report:
The short-duration GRB 211106A (Swift/BAT-GUANO localization: Tohuvavohu et al., GCN 31049) triggered Konus-Wind at T0=16652.485 s UT (04:37:32.485).
The burst light curve shows a single pulse started at ~T0-0.3 s with a total duration of ~0.5 s. The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB211106_T16652/
As observed by Konus-Wind, the burst had a fluence of 6.09(-1.22,+1.41)x10^-7 erg/cm2, and a 16-ms peak flux, measured from T0+0.070 s, of 3.37(-1.59,+1.68)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The spectrum of the burst (measured from T0 to T0+0.192 s) is best fit in the 20 keV - 2 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.02(-0.80,+1.13) and Ep = 196(-45,+78) keV (chi2 = 27/23 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.2 (chi2 = 27/22 dof).
All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
GCN Circular #31055
C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team:
Swift/BAT-GUANO detected GRB 211106A at 04:37:31.2 UT (GCN 31049). This event was also detected by INTEGRAL/SPI-ACS #9504 and Konus-Wind (GCN 31054). 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 no counterparts.
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals identified a transient most significantly on the 0.256 s timescale, with a location consistent with the Swift/BAT-GUANO event, using the standard search protocol with a S/N of 22. This event was detected ~10 s after GBM exited SAA. The GBM targeted search event was found with the highest significance with a "normal" spectrum (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB.
[1] Goldstein et al. 2019 arXiv:1903.12597
GCN Circular #31063
S. de Wet (UCT), P.M. Vreeswijk (Radboud), A.J. Levan (Radboud),
P.J. Groot (Radboud/UCT/SAAO) report on behalf of the MeerLICHT
consortium and the Stargate collaboration:
We observed the field of the Swift/BAT-GUANO short GRB candidate
GRB211106A (Tohuvavohu et al., GCN 31049) with the 0.6m wide-field
MeerLICHT optical telescope located at Sutherland, South Africa,
taking 10x60s exposures in the q-band starting at 2021-11-06,
18:37:17 UT, approximately 14 hours after the GRB trigger.
We co-added the images to reach a full-frame 5-sigma AB limiting
magnitude of q = 21.90. An archival reference image with limiting
magnitude of q = 20.54 was used to perform image subtraction
through our transient detection pipeline. The MeerLICHT field-of-view
fully covers the BAT-GUANO error box and includes all the X-ray
sources found through Swift-XRT follow-up observations
(D'Elia et al., GCN 31051).
Our transient pipeline finds 1 candidate in the BAT-GUANO error
box, at the same position as the XRT source coincident with a known
X-ray source. The coordinates of the transient coincide with a star
with brightness G = 17.49 in the Gaia EDR3 catalogue, spatially
very close to galaxy LEDA 432583. We believe the transient detection
is due to the star showing variable behaviour rather than a transient
in the galaxy, owing to an increase in brightness of the star from
q = 17.73 mag in the reference image to q = 17.47 in the new image.
We detect no source in our images at the position of the known X-ray
source 1RXS J225507.9-531312.
No other promising transient candidates are found in the error boxes
of the 9 XRT sources nor the BAT-GUANO error box, down to a transient
limiting magnitude of 20.34.
There is one other potential transient candidate in our FOV, but it
is 15.6’ away from the centre of the BAT-GUANO error box, so unlikely
to be associated with GRB 211106A. The coordinates are
RA, Dec (J2000) = 22:54:17.88, -52:58:35.22. The Legacy Survey DR9
images show a spiral galaxy at this position, which could be showing
variable behaviour or may be due to a transient near the galaxies' core.
MeerLICHT is built and run by a consortium consisting of Radboud
University, University of Cape Town, the South African Astronomical
Observatory, the University of Oxford, the University of Manchester
and the University of Amsterdam.
GCN Circular #31068
V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the Swift/BAT-GUANO-detected burst GRB 211106A (Ridnaia et al. GCN Circ. 31054). The observations now extend from T0+39.3 ks to T0+290.7 ks.
Of the sources reported by D'Elia et al. (GCN Circ. 31051), "Source 2" is fading with 2.5 sigma significance and thus is believed to be the GRB afterglow. Using 2766 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 343.58521, -53.23028 which is equivalent to:
```
RA (J2000): 22h 54m 20.45s
Dec(J2000): -53d 13' 49.0"
```
with an uncertainty of 3.4 arcsec (radius, 90% confidence). This position is 2.1 arcmin from the Swift/BAT-GUANO position.
The light curve can be modelled with a power-law decay with a decay index of alpha=0.7 (+0.5, -0.4).
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021466. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021466.
This circular is an official product of the Swift-XRT team.
GCN Circular #31069
A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg), and A. Rau (MPE Garching) report:
We observed the field of the short GRB 211106A (Tohuvavohu et al., GCN 31049; D'Elia et al., GCN 31051; Ridnaia et al., GCN 31054; Fletcher, GCN 31055; de Wet et al., GCN 31063) centered at the location of the X-ray source #2 (D'Elia et al., GCN 31051, 31068) with GROND mounted at the 2.2m MPG telescope at La Silla Observatory (Chile).
Inside the XRT error circle of 'Source #2' no object is detected. At a midtime of November 9, 2021, 02:10 UT, we measure the following 3-sigma AB upper limits:
```
g' > 24.8,
r' > 25.0,
i' > 24.0,
z' > 22.0,
J  > 21.7,
H  > 21.1,
K  > 19.8.
```
Magnitudes are calibrated against the SkyMapper catalog (Wolf et al., 2018, PASA 35, e010) in g'r'i'z' and 2MASS field stars in JHK (Skrutskie et al., 2006, AJ 131, 1163).
We thank Paul Eigentaler for excellent support and for performing the observations.
GCN Circular #31070
Daniele B. Malesani (Radboud Univ. and DAWN/NBI), Paolo D'Avanzo (INAF/OABr), Andrew J. Levan (Radboud Univ.), Ana Nicuesa Guelbenzu (TLS Tautenburg), report on behalf of the Stargate consortium:
We observed the location of XRT source #2 (D'Elia et al., GCNs 31051, 31068), indicated as the X-ray afterglow of the short GRB 211106A (Tohuvavohu et al., GCN 31049; Ridnaia et al., GCN 31054; Fletcher, GCN 31055) using the ESO VLT UT1 equipped with the FORS2 camera. A total of 20 minutes on source were obtained in the R band, with mid time 2021 Nov 9.116 UT (that is, 2.92 days after the GRB).
No bright sources are detected inside the XRT error circle, down to R > 26.2 (Vega, preliminary calibration based on faint USNO-B1 stars). However, there are two extended (FWHM ~ 2") objects at the following coordinates:
```
RA = 22:54:21.31
Dec = -53:13:47.2

RA = 22:54:20.29
Dec = -53:13:53.6
```
The second one is partially blended with a brighter star. These two galaxies are 7.9" and 4.8" away, respectively, from the center of the XRT position (which has currently a 90% uncertainty radius of 3.4"). A faint extension of the most nearby object, or a separate, very faint source, is also marginally detected inside the XRT error circle.
Should the GRB be associated with one of the closeby galaxies, this would indicate a relatively low redshift. Lacking a reference image, we cannot yet ascertain whether a faint transient could be present, superposed on top of the galaxy light. Chandra X-ray observations would help pinpoint the precise location of the source.
We acknowledge excellent support from the ESO staff at Paranal, still operating at reduced capacity because of the COVID pandemic, in particular Eleonora Sani, Aleksandra Solarz, Rodrigo Palominos, Pedro Figuera and Thomas Rivinius.
GCN Circular #31075
L. Christensen (DAWN/NBI), L. Izzo (DARK/NBI), P. Schady (Univ. Bath), D. B. Malesani (Univ. Radboud and DAWN/NBI), P. D'Avanzo (INAF/OABr), A. J. Levan (Radboud Univ.), S. Campana (INAF/OABr), D. Alexander Kann (HETH, IAA/CSIC), report on behalf of the Stargate consortium:
We observed the field surrounding the candidate afterglow (source #2) of the short GRB 211106A (Tohuvavohu et al., GCN 31049; D'Elia et al., GCNs 31051, 31068) with the ESO VLT equipped with the MUSE panoramic integral-field spectrograph, covering a square 1'x1' region around the XRT position. Spectra of each spaxel cover the wavelength range 4750-9350 AA. The mean time of our observation was November 10.03 UT (3.84 days after the GRB).
We report the redshift of three galaxies close to the XRT error circle (D'Elia et al., GCN 31068; see also Malesani et al., GCN 31070):
```
#1)
RA = 22:54:20.29
Dec = -53:13:53.6
z = 0.097 as inferred by the detection of the [O iii] doublet and Hbeta 
in emission.
The projected separation from the center of the XRT error circle is 
4.8", or 8.6 kpc at z = 0.097.
A bright, pointlike object (RA = 22:54:20.32, Dec = -53:13:56.7) is 
spatially blended with this galaxy, which we confirm to be a star thanks 
to the detection of Balmer and Ca II absorption at z = 0.

#2)
RA = 22:54:21.31
Dec = -53:13:47.2
z = 0.294 as inferred by the detection of the [O iii] doublet and Hbeta 
in emission.
The projected separation from the center of the XRT error circle is 
7.9", or 34.9 kpc at z = 0.294.

#3)
RA = 22:54:20.34
Dec = -53:13:40.8
z = 1.012 as inferred by the detection of the (resolved) [O ii] doublet 
in emission.
The projected separation from the center of the XRT error circle is 
8.3", or 67.0 kpc at z = 1.012.
```
While the association of these sources with GRB 211106A cannot be confirmed based on our data, object #1 has the smallest chance association probability. With R ~ 21.5, using the formula by Bloom et al. (2002, AJ, 123, 1111), we compute a chance association probability of ~5%.
Stacking the MUSE cube along the wavelength axis, faint emission is also detected inside the XRT error circle, consistent with our FORS2 image (Malesani et al., GCN 31070). The S/N is too low to extract any spectral information, and no emission lines are identified.
An image showing the position of the three galaxies can be viewed at the following link:
https://www.astro.ru.nl/~dmalesani/GRB/211106A/GRB211106A_galaxies.jpg
We acknowledge expert support from the observing staff at Paranal, in particular Thomas "Rivi" Rivinius, Thomas Wevers, Israel Blanchard, Juan Carlos Olivares, and Joe Anderson.
GCN Circular #31078
D. Svinkin, S. Golenetskii, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team,
K. Hurley, on behalf of the IPN,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu on behalf of the Swift-BAT team,
A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
and
A. Goldstein, M. S. Briggs, and C. Wilson-Hodge on behalf of the Fermi GBM team, report:
The short-duration GRB 211106A (Swift-BAT-GUANO detection: Tohuvavohu et al., GCN 31049; Konus-Wind detection: Ridnaia et al., GCN 31054; Fermi-GBM sub-threshold detection: Fletcher et al., GCN 31055) was detected by INTEGRAL (SPI-ACS), Swift (BAT), Konus-Wind, and Fermi (GBM) at about 16651 s UT (04:37:31).
We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:
```
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   342.487 (22h 49m 57s) -52.039 (-52d 02' 19")
  Corners:
   359.734 (23h 58m 56s) -61.384 (-61d 23' 04")
   333.528 (22h 14m 07s) -40.998 (-40d 59' 52")
   331.989 (22h 07m 57s) -42.431 (-42d 25' 51")
     0.415 (00h 01m 40s) -63.951 (-63d 57' 05")
  ---------------------------------------------
```
The error box area is 45.2 sq. deg, and its maximum dimension is 27.7 deg (the minimum one is 1.7 deg). The Sun distance was 95 deg.
The Swift-BAT position reported in Tohuvavohu et al. is consistent with the IPN error box.
This box may be improved.
A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB211106_T16652/IPN/
The Swift (BAT) event data used for the IPN localization came from the GUANO system (https://www.swift.psu.edu/guano/).
GCN Circular #31079
N Paul Kuin (UCL-MSSL) and Aaron Tohuvavohu (U Toronto) report on behalf of the Swift/UVOT team:
The Swift/UVOT observed the field of the Swift/BAT-GUANO localisation ( Tohuvavohu et al, GCN Circ. 31049) of the INTEGRAL/SPI-ACS #9504 discovery of the short GRB211106A using the white filter. The GRB was also reported by Fermi GBM (Fletcher, GCN Circ. 31055), Konus-Wind (Ridnaia et al., GCN Circ. 31054). Ground-based follow up on XRT Source 2 by MeerLicht (de Wet et al, GCN Circ. 31063) at 17 hours past trigger found an upper limit of q = 21.90; GROND around seventy hours after the trigger while mounted on the 2.2m MPG telescope find upper limits only ranging from g' > 24.8 to K > 19.8 (GCN Circ. 31069); Malesani et al used the VLT UT1/FORS2 also at 70 hours after triggger to place a limit R > 26.2.
Here we report on upper limits for the XRT Source number 2 (see D'Elia et al, GCN Circ. 31051) which is the candidate afterglow (D'Elia et al, GCN Circ. 31068).
Swift UVOT observed discontinuously starting day 0.45-0.67d, then day 1.45-1.97, 2.6-3.7, 4.6-5.0 for a total of 19.5 ks. For these periods, the 3-sigma UVOT upper limits are white > 23.2, 22.4, 22.7, 22.9 mag (Vega, Breeveld et al. 2011).
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.09 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #31145
E. Berger (Harvard), A. Rouco Escorial, and W. Fong (Northwestern) report on behalf of a larger collaboration:
"We observed the location of the short GRB 211106A (GCNC #31049) with the Chandra X-ray Observatory + ACIS-S starting on 2021 November 16.58 UT (10.38 days post-burst) for 19.8 ksec as part of program 22500107 (PI: Berger). Within the XRT error circle (GCNC #31068) we detect a single X-ray source at (J2000):
RA = 22:54:20.51
Dec = -53:13:51.2
with a preliminary uncertainty of about 0.8 arcsec. This source is located 3.1" from the center of galaxy #1 at z=0.097 identified in earlier VLT observations (GCNC #31070 and #31075). The angular offset corresponds to a projected physical offset of 5.6 kpc at the redshift of the galaxy. The flux of the X-ray source indicates continued fading with a power law index of about -1.
We thank the CXO staff for rapidly scheduling these observations."
GCN Circular #31146
C. D. Kilpatrick (Northwestern), E. Berger (Harvard), and W. Fong (Northwestern) report on behalf of a larger collaboration:
"We observed the location of the short GRB 211106A (GCNC #31049) with the Hubble Space Telescope sta= rting on 2021 November 25.37 (19.17 days post-trigger) using ACS/F814W and = WFC3/F110W for 2 orbits each, as part of program 16303 (PI: Berger). Within= the 0.8-arcsec error circle of the X-ray afterglow detected with Chandra (= GCNC #31145) we detect a single source in both filters at (J2000): RA =3D 2= 2:54:20.54 Dec =3D -53:13:50.6 with an uncertainty of about 0.05 arcsec. Pr= eliminary photometry indicates AB magnitudes of m(F814W) ~ 25.7 and m(F110W= ) ~ 25.6. We note that the source may be slightly extended (northward) in t= he F110W image. The origin of the optical/NIR source is unclear at the pres= ent. If it is the afterglow, then a similar decline rate as observed in the= X-rays (about t^-1; GCNC #31145) would indicate an expected optical magnit= ude of ~23.7 at the time of the VLT/FORS2 observations, over 2 mag brighter= than the limit of R~26 mag listed in GCNC #31070. If the source is a kilon= ova, and the event is associated with the galaxy at z=3D0.097 identified in= VLT data (GCNC #31075), then it is about 2.5 mag (a factor of 10) more lum= inous in J-band than the kilonova associated with GW170817 (Villar et al. 2= 017, ApJ, 851, L21), and moreover significantly bluer, with m(F814W)-m(F110= W) ~ 0 mag. Finally, it is possible that the optical/NIR source is the actu= al host galaxy of GRB 211106A, most likely placing the burst at a higher re= dshift than z=3D0.097. Additional HST observations are planned to shed ligh= t on the nature of the source.
GCN Circular #31150
Y. Q. Zhang, S. L. Xiong, C. Cai, S. Xiao, P. Zhang, C. Y. Li, S. L. Xie, X. Y. Zhao, Y. Huang, X. Y. Song, J. C. Liu, Y. Zhao, Z. W. Guo, C. Zheng, W. C. Xue, C. W. Wang, Q. B. Yi, B. X. Zhang, W. X. Peng, R. Qiao, D. Y. Guo, X. B. Li, X. Ma, L. M. Song, P. Wang, J. Wang, Z. Zhang, S. J. Zheng, W. Chen, J. J. He, G. Y. Zhao, Y. Q. Du, H. Wu, J. Liang, Q. Luo, X. L. Zhang, H. M. Zhang, Z. H. An, M. Gao, K. Gong, B. Li, C. Li, J. H. Li, X. Q. Li, Y. G. Li, X. H. Liang, X. J. Liu, Y. Q. Liu, X. L. Sun, Y. L. Tuo, J. Z. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, S. Yang, C. Y. Zhang, D. L. Zhang, Fan Zhang, Fei Zhang, X. Zhou, F. J. Lu, S. N. Zhang (IHEP) report on behalf of GECAM team:
During the commissioning phase, GECAM-B was triggered by a short burst, GRB 211106A, at 2021-11-06T04:37:31.250 UTC (denoted as T0), which was also observed by Swift/BAT-GUANO (GCN #31049), Fermi/GBM Sub-Threshold (GCN #31055), Konus-Wind (GCN #31054), INTEGRAL/SPI-ACS (TrigID #9504) and IPN (GCN #31078).
According to the GECAM-B light curves, this burst mainly consists of two pulses with duration of about 2 s.
The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_89872651.PNG
GECAM location is consistent with the Swift/BAT position within the error.
The time-integrated spectrum (measured from T0-0.25 s to T0+1.85 s) is best fit by the power law model (in the 20 keV - 5 MeV range): A(E) ~ k * E^(-alpha) with alpha = 1.32 (-0.13, 0.15). The burst had a fluence of 6.35 (3.72, 7.05)x10^-7 erg/cm^2 (20 - 200 keV) during the time interval metioned above. All parameters in parenthesis are for 90% confidence level.
Please note that all GECAM results here are preliminary. The final analysis will be published in journal papers or GECAM online catalog.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time), which was funded by the Chinese Academy of Sciences (CAS).
GCN Circular #31157
C. D. Kilpatrick (Northwestern), E. Berger (Harvard), and W. Fong (Northwestern) report on behalf of a larger collaboration:
"We re-observed the location of the short GRB 211106A (GCNC #31049) with the Hubble Space Telescope starting on 2021 December 1.46 (25.26 days post-trigger; 6.1 days after Visit 1 - GCNC #31146) using WFC3/F110W for 2 orbits, as part of program 16303 (PI: Berger).
The source identified in our first HST observation (GCNC #31146) is still detected, with an unchanged magnitude of m(F110W) ~ 25.6. Digital image subtraction between the two epochs does not reveal any emission at the location of the source to a 5-sigma limit of ~27 mag.
The lack of fading over the 6-day time baseline suggests that this source is not an afterglow or kilonova. Instead, it is likely to be either the host galaxy of GRB 211106A, or an unrelated background galaxy if the GRB itself is associated with the galaxy at z=0.097. The absolute magnitude of the NIR source if it is also located at z=0.097 is M(F110W) ~ -12.7, too luminous to be a globular cluster."
GCN Circular #31259
A. Rouco Escorial, W. Fong, C. D. Kilpatrick, J. Rastinejad, G. Schroeder, A. Nugent (Northwestern), E. Berger (Harvard), and T. Laskar (Radboud) report:
“We initiated our afterglow monitoring campaign, consisting of two EPIC-pn observations, with the XMM-Newton Observatory on the short-duration GRB 211106A (Tohuvavohu et al., GCN #31049) on 2021 November 20 (22:37:51 UT) and 2021 December 8 (19:46:37 UT) UT, with median observation times of ~15 and ~33 days post-trigger. The two XMM-Newton observations were obtained under the Proposal 086286 (PI: Fong), with effective exposure times of ~20 ks and ~47 ks, respectively.
In the combined XMM-Newton dataset, we detect the X-ray counterpart to GRB 211106A at the position:
```
RA(J2000) = 22h54m20.8s
Dec(J2000) = -53d13m50.9s
```
with a total positional uncertainty of 1.7 arcsec (dominated by XMM-Newton’s systematic uncertainty). The XMM-Newton position of the X-ray afterglow and the Chandra position reported by Berger et al. (2021, GCN #31145) are consistent with each other within the errors. The afterglow is detected in both epochs at a significance of ~5.5 sigma and ~3.4 sigma, with total net source counts of ~83 and ~73 (0.3-10 keV), respectively.
The XRT, Chandra and XMM-Newton afterglow unabsorbed flux, starting at ~0.5 days post-burst, can be modeled with a single power-law decline characterized by a decay index (F~t^alpha) of alpha=-1.02 (-0.06,+0.05). Additionally, from our jointly spectral fitting of both data sets, we derive an intrinsic neutral hydrogen absorption column of ~1.4E21 cm^2 for z=0.097 (Malasani et al., GCN #31075; Christensen et al., GCN #31075). We obtain higher inferred intrinsic column density for greater presumed source redshifts (Kilpatrick et al., GCNs #31146, #31157).
We thank the XMM-Newton Project Scientist, Norbert Shartel, and staff for the rapid planning and scheduling of these observations.”
GCN Circular #31300
C. D. Kilpatrick (Northwestern), E. Berger (Harvard), and W. Fong (Northwestern) report on behalf of a larger collaboration:
"We obtained a third observation at the site of the short GRB 211106A (GCNC #31049) with the Hubble Space Telescope starting on 2021 December 24.35 (48.15 days post-trigger, 29.0 days after Visit 1 - GCNC #31146, and 22.9 days after Visit 2 - GCNC #31157) using ACS/F814W for 2 orbits and WFC3/F110W for 2 orbits, as part of program 16303 (PI: Berger).
The source identified in both our previous HST observations and near the reported CXO position of GRB 211106A (GCNC #31145) is still detected, with unchanged magnitudes of m(F110W) ~ 25.6 mag and m(F814W) ~ 25.7 mag. We also detect an extension to the north of the source in stacked F814W imaging (Visit 1 + Visit 3) as previously noted in the F110W imaging (GCNC #31049). The lack of any change over this 29-day baseline, the relatively flat m(F814W)-m(F110W) color, the extension in both bands, and the small offset from the CXO position (GCNC #31145) support the hypothesis that this source is the more likely host galaxy of GRB 211106A."

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Jochen Greiner, last update: 24-Dec-2021 [Disclaimer]