GRB 221016A

The Fermi GBM team reports the detection of a likely LONG GRB

At 23:39:22 UT on 16 Oct 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221016A (trigger 687656367.709164 / 221016986).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 37.6, Dec = -32.1 (J2000 degrees, equivalent to J2000 02h 30m, -32d 06'), with a statistical uncertainty of 2.2 degrees.

The angle from the Fermi LAT boresight is 98.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221016986/quicklook/glg_skymap_all_bn221016986.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221016986/quicklook/glg_healpix_all_bn221016986.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221016986/quicklook/glg_lc_medres34_bn221016986.gif

K. L. Page (U Leicester), J. A. Kennea (PSU),
N. J. Klingler (GSFC/UMBC/CRESSTII), A. Y. Lien (U Tampa),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
A. Tohuvavohu (U Toronto) and M. A. Williams (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 23:39:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 221016A (trigger=1129775).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 38.949, -34.624 which is 
   RA(J2000) = 02h 35m 48s
   Dec(J2000) = -34d 37' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
with tail structure with a duration of about 30 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 23:42:24.0 UT, 179.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 38.94479, -34.61039 which is equivalent
to:
   RA(J2000)  = 02h 35m 46.75s
   Dec(J2000) = -34d 36' 37.4"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 50 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 in excess of the Galactic value (3.53 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.8
(+3.14/-2.70) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 97 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 none of
the XRT error circle. 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 0.026. 

Burst Advocate for this burst is K. L. Page (kimlpage1978 AT gmail.com). 
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/)

R. Strausbaugh (University of Minnesota), A. Cucchiara (NASA) report on
behalf of a larger collaboration:

We observed the GRB 221016A (Page et al., GCN 32774
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 ) field with the LCOGT
1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory,
Chile site, on October 17, from 01:39 to 02:06 (corresponding to 2.00 to
2.55 hours from the GRB trigger time) with the Bessel I and R filters.

We performed a series of 3x300s exposures in each band.  We detect an
uncataloged optical source within the XRT error region (Page et al., GCN
32774
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 ), in R band, and marginally in I-band (2-sigma detection).

The following magnitudes are calculated using the USNO-B1.0 catalog as
reference:

R = 21.22 +/- 0.18
I = 20.03 +/- 0.17

These magnitudes are not corrected for galactic extinction.  Gemini
imaging+spectroscopic follow up is ongoing.

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

Using 165 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 221016A, 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 = 38.94459, -34.61073 which is equivalent
to:

RA (J2000): 02h 35m 46.70s
Dec (J2000): -34d 36' 38.6"

with an uncertainty of 2.4 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. B. Malesani (Radboud Univ. and DAWN/NBI), D. A. Kann (Goethe Univ.), 
L. Izzo (DARK/NBI), S. Covino, P. D'Avanzo (INAF/OAB), N. R. Tanvir 
(Univ. Leicester), report on behalf of the Stargate consortium:

We observed the field of GRB 221016A (Page et al., GCN 32774
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 ) with the 
ESO VLT UT3 (Melipal), using the acquisition camera of the X-shooter 
spectrograph. A single 30 s image is available to us, taken on 2022 Oct 
17.034 UT (1.17 hr after the trigger). The image seeing was rather poor, 
about 2.2".

No source is detected at the position of the optical counterpart 
discovered by Strausbaugh & Cucchiara (GCN 32775
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 ), down to a 3-sigma 
limit z > 20.8 (AB; calibrated against one nearby SkyMapper star). 
Comparison between our limit and the magnitudes reported by Strausbaugh 
& Cucchiara (GCN 32775
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 ) seems to indicate a brightening of the afterglow 
between ~1 and ~2 hr after the trigger.

We acknowledge the ESO staff for a quick reaction to our request, in 
particular Matias Jones and Felipe Gaete.

E. Bissaldi (Politecnico and INFN Bari), P. Veres (UAH)
and C. Meegan (UAH) report on behalf of the Fermi GBM Team:


"At 23:39:22.71 UT on 16 October 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 221016A (trigger 687656367/221016986),
which was also detected by the Swift/BAT (Page et al. GCN 32774
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 ).
The Fermi GBM Final Real-time Localization (GCN 32773
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 )
is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 98 degrees.

The GBM light curve shows a single emission episode
with a duration (T90) of about 13 s (50-300 keV).
The time-averaged spectrum from T0-1.2 s to T0+11 s is
best fit by a Band function with Epeak = 119 +/- 12 keV,
alpha = -0.51 +/- 0.12, and beta = -2.11 +/- 0.11.

The event fluence (10-1000 keV) in this time interval is
(6.3 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.8 s in the 10-1000 keV band
is 7.4 +/- 0.3 ph/s/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/"

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

The long-duration GRB 221016A
(Fermi-GBM detection: Fermi GBM team, GCN#32773
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 ,
Bissaldi et al., GCN#32782
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 ;
Swift-BAT detection: Page et al., GCN#32774
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 )
triggered Konus-Wind at T0=85166.713 s UT (23:39:26.713).

The burst light curve shows a single emission pulse
which starts at ~T0-1.7 s and has a total duration of ~12.5 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/GRB221016_T85166/

As observed by Konus-Wind, the burst
had a fluence of 5.46(-0.74,+1.07)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+0.800 s,
of 1.87(-0.73,+0.74)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.02(-0.33,+0.40)
and Ep = 207(-46,+98) keV (chi2 = 60/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.0
(chi2 = 60/98 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with  alpha = -0.89(-0.30,+0.35)
and Ep = 166(-26,+39) keV (chi2 = 81/96 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.4
(chi2 = 81/95 dof).

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

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne
(U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.
Ambrosi  (INAF-IASFPA) , D.N. Burrows (PSU), J. D. Gropp (PSU), S.
Dichiara (PSU) and K.L. Page report on behalf of the Swift-XRT team:

We have analysed 8.2 ks of XRT data for GRB 221016A (Page et al. GCN
Circ. 32774
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 ), from 76 s to 44.8 ks after the  BAT trigger. The data
comprise 83 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Goad et al.
(GCN Circ. 32776
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 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.20 (+0.22, -0.18), followed by a break at T+254 s to
an alpha of 0.78 (+0.04, -0.05).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.49 (+0.23, -0.21). The
best-fitting absorption column is  7.9 (+4.2, -3.7) x 10^20 cm^-2, in
excess of the Galactic value of 3.5 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.04 (+0.20, -0.19)
and a best-fitting absorption column of 1.5 (+0.6, -0.5) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.3 x 10^-11 (4.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.5 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 3.5 x 10^20 cm^-2
Excess significance: 3.5 sigma
Photon index:	     2.04 (+0.20, -0.19)

If the light curve continues to decay with a power-law decay index of
0.78, the count rate at T+24 hours will be 0.019 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.1 x
10^-13 (8.1 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/01129775.

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

M. H. Siegel (PSU) 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 221016A
97 s after the BAT trigger (Page et al., GCN Circ. 32774
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 ).
A source consistent with the enhanced XRT position (Goad et al. GCN Circ. 32776
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 )
is detected in the initial UVOT exposures.

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white               97          247          147         20.20 +/- 0.23
b                 3736         3861          123        >19.8
u                  309          349           39        >18.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.026 in the direction of the burst
(Schlegel et al. 1998).

S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), 

H. A. Krimm (NSF), A. Y. Lien (U Tampa),

C. B. Markwardt (GSFC), D. M. Palmer (LANL),

T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU),

M. Stamatikos (OSU) (i.e. the Swift-BAT team):

 

Using the data set from T-239 to T+200 sec from the recent telemetry downlink,

we report further analysis of BAT GRB 221016A (trigger #1129775)

(Page, et al., GCN Circ. 32774
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 ).  The BAT ground-calculated position is

RA, Dec = 38.938, -34.615 deg which is 

   RA(J2000)  =  02h 35m 45.2s 

   Dec(J2000) = -34d 36' 54.2" 

with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 53%.

 

The light curve shows a single peaked pulse. T90 (15-350 keV) is 21.86 +- 5.70 sec 

(estimated error including systematics).

 

The time-averaged spectrum from T-3.18 to T+29.18 sec is best fit by a simple

power-law model.  The power law index of the time-averaged spectrum is

1.28 +- 0.08.  The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-06 erg/cm2.

The 1-sec peak photon flux measured from T+0.03 sec in the 15-150 keV band

is 3.4 +- 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/1129775/BA/