- GCN Circular #32506
TITLE: GCN CIRCULAR
NUMBER: 32506
SUBJECT: GRB 220831A: Swift/BAT-GUANO localization of a short burst
DATE: 22/09/01 01:55:51 GMT
FROM: Aaron Tohuvavohu at U Toronto
Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU), James DeLaunay
(UAlabama), Gayathri Raman (PSU), report:
Swift/BAT did not successfully trigger on GRB 220831A (T0: 2022-08-31
13:56:33 UTC).
10 seconds of serendipitous event data is available covering the time
of this burst, associated with BAT failed trigger #1122435. This data
was produced due to an unrelated event that occurred close in time to
this burst. There is no long duration GUANO data available for this
burst due to lack of prompt notice from other instruments.
The duration of the burst, as seen by BAT, is ~1 second.
In ground analysis of the available event data, we find the position of
the burst with SNR 15.0 in the image domain.
The BAT position is
RA, Dec = 24.2550 -41.5818, which is:
RA (J2000) 01h 37m 01.2s
Dec (J2000) -41d 34' 54.5"
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.
- GCN Circular #32508
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT GRB 220831A.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021512
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.
- GCN Circular #32510
S. Dichiara (PSU), A.P. Beardmore (U. Leicester), E. Ambrosi
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),
J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P.
Osborne (U. Leicester) 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 220831A (Tohuvavohu et al. GCN Circ.
32506), collecting 5.0 ks of Photon Counting (PC) mode data between
T0+51.2 ks and T0+78.8 ks.
No X-ray sources have been detected consistent with being within 98
arcsec of the Swift/BAT position. The 3-sigma upper limit in the field
ranges from ~0.002 to ~0.003 ct s^-1, corresponding to a 0.3-10 keV
observed flux of 8.1e-14 to 1.1e-13 erg cm^-2 s^-1 (assuming a typical
GRB spectrum).
We report, however, the presence of a low-significance source, at the
following position:
RA (J2000.0): 24.25359 = 01:37:00.86
Dec (J2000.0): -41.59325 = -41:35:35.70
Error: 6.8 arcsec (radius, 90% conf.)
Distance: 41 arcsec from Swift-BAT position.
Given the low-significance detection, we cannot state at the present
stage if this detection is real or spurious.
Six uncatalogued sources were detected too far from the GRB position to
be likely afterglow candidates.
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/00021512.
This circular is an official product of the Swift-XRT team.
- GCN Circular #32511
J. Wood (NASA/MSFC) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 13:56:32.93 UT on 31 Aug 2022, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 220831A (trigger 683646997 / 220831581).
which was also detected by the Swift/BAT-GUANO (A. Tohuvavohu et al. 2022, GCN 32506)
The GBM on-ground location is consistent with the Swift position.
The on-ground calculated location, using the GBM trigger
data, is RA = 28.1, DEC = -45.1 (J2000 degrees,
equivalent to 01h 52m, -45d 06'), with an uncertainty
of 7.9 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32]).
The angle from the Fermi LAT boresight is 102.0 degrees.
The GBM light curve consists of a single pulse
with a duration (T90) of about 1.7 s (50-300 keV).
The time-averaged spectrum from T0-0.5 s to T0+1.3 s is
best fit by a Band function with Epeak = 46 +/- 8 keV,
alpha = -0.67 +/- 0.45, and beta = -2.7 +/- 0.4
The event fluence (10-1000 keV) in this time interval is
(5.0 +/- 0.5)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.2 s in the 10-1000 keV band
is 9.4 +/- 1.7 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/"
- GCN Circular #32513
P. D'Avanzo (INAF/OABr), A. Rossi (INAF/OAS), D. B. Malesani (Radboud
and DAWN/NBI), S. Campana (INAF/OABr), A. J. Levan (Radboud univ.)
report on behalf of the Stargate collaboration:
Following the report of the Swift/BAT/GUANO GRB 220831A (Tohuvavohu et
al., GCN 32506; see also Wood & Meegan, GCN 32511) we observed the BAT
error circle with the ESO Very Large Telescope, equipped with the HAWK-I
near-infrared camera. Observations consisted in 20 min exposure in the J
band, with a mean time of 19.4 hr after the GRB.
Lacking a deep reference image to check for variability, no claim of a
new object can be made based solely on our data. Within the BAT error
circle, several objects are apparent in the HAWK-I image which are not
visible in the the Legacy survey (z and r bands), which are likely due
to color effects.
A source is visible in the HAWK-I image which is consistent with the
weak X-ray source reported by Dichiara et al. (GCN 32510), at
coordinates (J2000):
RA = 01:37:00.95
Dec = -41:35:34.37
Its Vega magnitude is J = 21.9 +- 0.09, calibrated against one 2MASS
star, and is not detected in the Legacy survey down to limiting
magnitudes z > 23.1, r > 24 (all AB).
We also note the presence of the nearby galaxy NGC 625, with a NED
distance ~4 Mpc, which is 23.6 arcmin (~30 kpc in projection) away from
the BAT coordinates of GRB 220831A.
We acknowledge the support of the observing staff at Paranal. Further
observations are planned.
- GCN Circular #32516
GRB 220831A: DECam detection of a possible optical counterpart
J. Freeburn, N. Van Bemmel, D. Dobie, A. Moller, J. Cooke (Swinburne/OzGrav), M. Suhr (Swinburne/ASTRO 3D) report on behalf of the Deeper Wider Faster Collaboration
We have observed the Swift/BAT-GUANO localisation of GRB 220831A (GCN 32506) with the Dark Energy Camera (DECam) on the V. M. Blanco 4-m telescope. Imaging in g, r, i were carried out on UT dates 2022-08-31 and 2022-09-01 as part of an ongoing Deeper, Wider, Faster (DWF) program observing run.
We detect a source that is spatially coincident with the X-ray (GCN 32510) and near-infrared (GCN 32513) candidate counterpart and is not detected in archival imaging of the field.
RA = 01:37:0.965
DEC = -41:35:34.60
We measure:
59823.3 i = 23.13 +/-0.15
59824.3 i = 24.12 +/-0.28
59823.3 r = 23.06 +/-0.12
59824.3 r = 24.32 +/-0.20
59823.1 g < 23.9
59824.3 g < 24.6
Deep spectroscopy is encouraged. We will continue to monitor this source with DECam as part of DWF.
- GCN Circular #32521
N. J. Klingler (NASA-GSFC/UMBC/CRESST II) reports on behalf of the
Swift-UVOT team:
Swift-UVOT has performed follow-up observations of the Swift-BAT-detected
burst GRB 220831A (Tohuvavohu et al. GCN 32506), collecting 4.7 ks of
observations with the White filter between T0+51.2 ks and T0+78.8 ks. No
source was detected in the UVOT data at the position of the X-ray source
reported by Dichiara et al. (GCN 32510), which is also positionally
coincident with the candidate near-infrared and optical counterparts
reported by D'Avanzo et al. (GCN 32513) and Freeburn et al. (GCN 32516),
respectively.
3-sigma upper limits using the UVOT photometric system (Breeveld et al.
2011, AIP Conf. Proc. 1358, 373) are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 51227 78844 4712 >23.39
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.0161684 in the direction of the burst
(Schlegel et al. 1998).
- GCN Circular #32529
G. E. Anderson (Curtin), M. E. Bell (UNewcastle), P. J. Hancock (Curtin),
J. C. A. Miller-Jones (Curtin), M. D. Aksulu (UvA), A. Bahramian (Curtin),
A. J. van der Horst (GWU), S. D. Ryder (Macquarie), A. Rowlinson (UvA, ASTRON),
R. A. M. J. Wijers (UvA)
We used the Australia Telescope Compact Array (ATCA) to perform a radio
observation of the short GRB 220831A at 5.5 and 9 GHz. The scheduled observations
began on 2022 Sept 14 UT for 5 hours (4 days post-burst; Fermi GBM Team
GCN 32511, which had been localised by Swift/BAT-GUANO; A. Tohuvavohu et al.,
GCN 32506). No radio source was detected at the candidate Swift-XRT, VLT/HAWK-I
and DECam afterglow position (S. Dichiara et al., GCN 32510; P. D’Avanzo et al.,
GCN 32513; A. Moller et al., GCN 32516), with 3 sigma upper-limits of 39 microJy
and 36 microJy at 5.5 and 9 GHz, respectively.
We thank the ATCA and CSIRO Astronomy and Space Science (CASS) staff for
scheduling these observations.
Gemma Anderson
Senior Research Fellow | Curtin Institute of Radio Astronomy (CIRA)
International Centre for Radio Astronomy Research (ICRAR)
My work days are Monday, Wednesday, Thursday and Friday
Curtin University
Tel | +61 8 9266 3785
Email | gemma.anderson@curtin.edu.au
Pronouns | She/Her
[signature_930817360]
CRICOS Provider Code 00301J
- GCN Circular #32535
A. C. Gordon (Northwestern U.), N. Tejos (PUCV), and C. D. Kilpatrick (Northwestern U.) report on behalf of the F4 Collaboration:
"We observed the Swift/BAT-GUANO localization of GRB 220831A (Tohuvavohu et al., GCN #32506) with Gemini South/GMOS in follow-up to the DECam observation (Freeburn et al., GCN #32516). Imaging in r- and i-band were carried out starting at UT 2022-09-05 04:05:49.
We detect the source in i-band and an upper limit in r-band at the following position (coincident with GCN #32516) at the coordinates (J2000):
RA = 01:37:00.9864
Dec = -41:35:34.296
From this source, we measure magnitudes (AB mag):
r > 26.4
i = 25.69 +/- 0.31
Our observations confirm that the source presented in GCN #32516 has faded significantly, which supports the hypothesis that it was a transient source associated with GRB 220831A and its weak X-ray counterpart (Dichiara et al., GCN #32510)."
- GCN Circular #32542
B. O'Connor (UMD/GWU), E. Troja (UTV/ASU), S. Dichiara (PSU),
on behalf of a larger collaboration:
We performed target of opportunity observations of GRB 220831A
(Tohuvavohu et al. GCN 32506) with the FLAMINGOS-2 spectrograph
mounted on the Gemini-South telescope. Observations were taken
in the J and Ks filters with total exposure of 1785 and 1635 s,
respectively. The observations began at 2022-09-09 03:27:01 UT,
corresponding to ~8.6 d after the burst. Further observations
were obtained the following night (~9.6 d) in J-band for
2000 s exposure.
At the location of the optical, infrared, and X-ray counterpart
(Dichiara et al. GCN 32510, D'Avanzo et al. GCN 32513, Freeburn
et al. GCN 32516, Gordon et al. GCN 32535), we detect a faint
source with brightness J ~ 24.5 AB mag. This result confirms the
fading of the infrared source reported by D'Avanzo et al.
GCN 32513.
Our measurement implies a very red color, r-J >2, of the late
time emission. At present it is not clear whether this is due
to the onset of a kilonova or to the contribution of an underlying
host galaxy. Assuming a behavior similar to AT2017gfo, the
apparent J-band magnitude implies a distance of ~200 Mpc. However,
the nearby galaxy noted by D’Avanzo et al. GCN 32513 is significantly
closer at only 4 Mpc.
If instead the source is dominated by the host galaxy contribution,
the red color suggests that GRB 220831A was a distant event
(see, e.g., O'Connor et al. 2022, MNRAS, 515, 4890).
Further observations are planned.
Magnitudes are calibrated against stars in the 2MASS catalog
and are not corrected for Galactic extinction.
We thank the staff of the Gemini Observatory, in particular
Joan Font-Serra and Yijung Kang, for rapid scheduling of
these observations.
- GCN Circular #32548
GRB 220831A: DECam optical counterpart follow-up
J. Freeburn, N. Van Bemmel, D. Dobie, A. Moller, J. Cooke (Swinburne/OzGrav), M. Suhr (Swinburne/ASTRO 3D), S. Webb (Swinburne) report on behalf of the Deeper, Wider, Faster Collaboration
We have carried out additional observations further to GCN 32516 of the optical counterpart (RA = 01:37:0.965, DEC = -41:35:34.60) to GRB220831A (GCN 32506). Here we present source observations using the Dark Energy Camera (DECam) on the V. M. Blanco 4-m telescope and revised, forced photometry of our previous observations using NOAO calibrated images. Images were taken in g, r, i on UT dates 2022-08-31 to 2022-09-04 as additional observations during the Deeper, Wider, Faster (DWF) program observing run.
Our photometry, along with those of Gordon et al. (GCN 32535) and D'Avanzo et al. (GCN 32513) are consistent with current short GRB optical afterglow models.
The following detection and upper limits (not corrected for Galactic extinction):
T-start (MJD) filter detection/UL
59823.200 g 23.17 +/- 0.18
59823.203 r 22.885 +/- 0.088
59823.209 i 23.06 +/- 0.13
59823.384 g 23.72 +/- 0.30
59823.395 r 23.37 +/- 0.13
59823.389 i 23.12 +/- 0.13
59824.198 g 24.33 +/- 0.37
59824.203 r 24.69 +/- 0.35
59824.208 i 23.86 +/- 0.22
59824.377 g 24.94 +/- 0.59
59824.390 r 24.13 +/- 0.25
59824.391 i 24.10 +/- 0.25
59825.300 r >24.8
59825.301 i >24.4
59826.306 i >25.0
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