GRB 211107B

Swift/BAT did not successfully trigger on GRB 211107B (T0: 2021-11-07
17:27:10 UTC).

Swift/BAT triggered in real-time onboard in the rates domain (trigger
#1082818), but no strong source was found to be associated in the
onboard imaging. This 'failed trigger' resulted in 10s of BAT TTE data
being saved and sent to the ground.

The duration of the burst, as seen by BAT, is ~15 seconds.

In ground analysis of the available TTE data, we find the position of
the burst with SNR 12.6 in the image domain.
The BAT position is
RA, Dec = 65.7949 -27.5524, which is:
    RA (J2000)     04h 23m 10.78s
    Dec (J2000)  -27d 33' 8.6"
with an estimated uncertainty of 2 arcminutes.

XRT and UVOT follow-up has been requested. Results of follow-up
observations will be reported in future circulars.

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

Swift has initiated a ToO observation of the Swift/BAT GRB 211107B. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021467

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 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.

A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A.
Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.
Melandri (INAF-OAB), T. Sbarrato (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-detected burst GRB 211107B (Swift/BAT did not successfully
trigger on GRB 211107B et al. GCN Circ. 31057
Loading...
 
 ), collecting 1.7 ks of
Photon Counting (PC) mode data between T0+124.3 ks and T0+131.0 ks. 

One uncatalogued X-ray source has been detected consistent with being
within 197 arcsec of the Swift/BAT position, it is below the RASS limit
and shows no definitive signs of fading. Therefore, at the present time
we cannot confirm this as the afterglow. Details of this source are
given below:

Source 1:
  RA (J2000.0):  65.80807  =  04:23:13.94
  Dec (J2000.0): -27.56097  =  -27:33:39.5
  Error: 2.9 arcsec (radius, 90% conf. [Enhanced position])
  Count-rate: 0.0220 +/- 0.0042 ct s^-1   
  Distance: 52 arcsec from Swift/BAT position.
  Flux: (5.15 +/- 0.98)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

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/00021467.

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

A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU), J. D. Gropp (PSU), J.A.
Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.
Melandri (INAF-OAB), T. Sbarrato (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-detected burst GRB 211107B (Swift/BAT did not successfully
trigger on GRB 211107B et al. GCN Circ. 31057
Loading...
 
 ). The observations now
extend from T0+124.3 ks to T0+147.5 ks. The source previously reported
by D'Ai et al. (GCN Circ. 31064
Loading...
 
 ), "Source 1", is fading with 1.8 sigma
significance and thus is believed to be the GRB afterglow. Using 2958 s
of PC mode data and 4 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 = 65.80812, -27.56084 which is equivalent
to:

RA (J2000): 04h 23m 13.95s
Dec(J2000): -27d 33' 39.0"

with an uncertainty of 2.7 arcsec (radius, 90% confidence). This
position is 51 arcsec from the Swift/BAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.84 (+0.04, -2.67).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.5 (+0.9, -0.7). The
best-fitting absorption column is  1.6 (+2.5, -1.2) x 10^21 cm^-2,
consistent with the Galactic value of 4.3 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 2.7 x 10^-11 (4.5 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+2.5, -1.2) x 10^21 cm^-2
Galactic foreground: 4.3 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.5 (+0.9, -0.7)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00021467.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021467.

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

D. Svinkin, S. Golenetskii, D. Frederiks, M. Ulanov,
A. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 211107B
(Swift-BAT detection: Tohuvavohu, GCN Circ. 31057
Loading...
 
 )
triggered Konus-Wind at T0=62836.647 s UT (17:27:16.647).

The burst light curve shows the initial pulse,
which starts at ~T0-3.7 s and has a total duration of ~24 s,
followed by a weaker emission seen up to T0+205 s.
The emission is seen up to ~1 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB211107_T62836/

As observed by Konus-Wind, the burst
had a fluence of 8.95(-1.76,+1.88)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0-0.108 s,
of 1.42(-0.68,+0.69)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The spectrum of the initial pulse
(measured from T0 to T0+16.640 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 = -0.88(-0.40,+0.47)
and Ep = 152(-26,+41) keV (chi2 = 51/56 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 51/55 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.