GRB 230826A

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

At 19:32:44 UT on 26 Aug 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230826A (trigger 714771169.528076 / 230826814).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 82.8, Dec = 67.1 (J2000 degrees, equivalent to J2000 05h 31m, 67d 05'), with a statistical uncertainty of 2.0 degrees.

The angle from the Fermi LAT boresight is 117.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230826814/quicklook/glg_skymap_all_bn230826814.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230826814/quicklook/glg_healpix_all_bn230826814.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230826814/quicklook/glg_lc_medres34_bn230826814.gif

R. A. J. Eyles-Ferris (U Leicester), S. Dichiara (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), D. M. Palmer (LANL),
T. M. Parsotan (GSFC/UMBC/CRESSTII), M. H. Siegel (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 19:32:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230826A (trigger=1187463).  Swift slewed immediately to
the location.  The BAT on-board calculated location is 
RA, Dec 83.012, +66.125 which is 
  RA(J2000) = 05h 32m 03s
  Dec(J2000) = +66d 07' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Preliminary quicklook data suggests that the
light curve is doubly peaked with a T90 of ~50 sec and background 
subtracted peak count rate of ~4000 counts/sec at T0+3 sec. 

The XRT began observing the field at 19:34:03.7 UT, 76.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 83.05920, 66.12506 which
is equivalent to:
   RA(J2000)  =  5h 32d 14.2s,
   Dec(J2000) = 66h 07d 30.2s
with an uncertainty of 10.0 arcseconds (radius, 90% containment). This
location is 69 arcseconds from the BAT onboard position, within the BAT
error circle. 

Due to a telemetry gap, no further information is available at
this time.  However a simultaneous Fermi trigger (GCN #34564
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 ) 
confirms the GRB. 

Burst Advocate for this burst is R. A. J. Eyles-Ferris (raje1 AT leicester.ac.uk). 
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/)

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

We observed the field of GRB 230826A detected by Fermi GBM (Fermi GBM Team, GCN 34564
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 ) and Swift (Eyles-Ferris et al, 34565) with AZT-33IK telescope of Sayan observatory (Mondy).  Observations started on 2023-08-26 220:06:00  (UT) (i.e. ~33 min since trigger). We obtained  
series of images in R-filter. We do not detect evident candidate within XRT error  circle (Swift-XRT Position: +05h 32m 14.20s +66d 07' 30.0" 5.3 arcsec, radius) in a stacked image.  Preliminary photometry is following:

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

2023-08-26 20:06:00   0.038345  R     44*60  n/d  n/d   22.0

We note the presence of the object USNO-B1.0 1561-0095652 at 8.8 arces from the Swift-XRT Position. Measured brightness of the object is R = 18.1 +/- 0.01 what is brighter than USNO-B1.0 R2=18.22 magnitude.

All photometry is based on nearby USNO-B1.0 stars, R2 magnitudes

J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), M. Capalbi (INAF-IASFPA), M.
Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), D.N. Burrows
(PSU) and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 8.3 ks of XRT data for GRB 230826A, from 65 s to 29.5
ks after the  BAT trigger. The data comprise 56 s in Windowed Timing
(WT) mode (the first 8 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. The refined XRT position is RA,
Dec = 83.0642, +66.1244 which is equivalent to:

RA (J2000): 05 32 15.41
Dec(J2000): +66 07 27.9

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.44 (+0.25, -0.24). At T+213 s  the decay
flattens to an alpha of -0.06 (+0.24, -0.26) before breaking again at
T+1264 s to a final decay with index alpha=1.39 (+0.22, -0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.93 (+0.32, -0.29). The
best-fitting absorption column is  4.7 (+1.0, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 1.5 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.15 (+0.22, -0.21)
and a best-fitting absorption column of 4.4 (+1.1, -1.0) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (6.3 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.4 (+1.1, -1.0) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: 4.8 sigma
Photon index:	     2.15 (+0.22, -0.21)

If the light curve continues to decay with a power-law decay index of
1.39, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x
10^-13 (1.8 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/01187463.

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

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

Using 1910 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 230826A, 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 = 83.06410, +66.12384 which is equivalent
to:

RA (J2000): 05h 32m 15.38s
Dec (J2000): +66d 07' 25.8"

with an uncertainty of 2.0 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.

O.J. Roberts (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 19:32:44.53 UT on 26 August 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230826A (trigger 714771169/230826814),
which was also detected by Swift-BAT (R.A.J. Eyles-Ferris  et al. 2023, GCN 34565
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 ).
The Fermi GBM Final Real-time Localization (GCN 34564
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 ) is consistent with the Swift-BAT position.

The angle from the Fermi LAT boresight is 116 degrees.

The GBM light curve consists of a single FRED peak with a duration (T90)
of about 37 s (50-300 keV). The time-averaged spectrum
from T0-4.1 to T0+46.1 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.75 +/- 0.12 and the cutoff energy,
parameterized as Epeak, is 87 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is
(6.012 +/- 0.246)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.9 s in the 10-1000 keV band is 4.9 +/- 0.4 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/"

M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Kolar, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal,  A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), yyT. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory),  T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.

The long-duration GRB 230826A (Fermi/GBM detection: GCN 34564
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 ; Swift/BAT detection: GCN 34565
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 ) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023; arXiv:2302.10048
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 ).

The detection was confirmed at the peak time 2023-08-26 19:32:45 UTC. The T90 duration measured by GRBAlpha is 18 s and the overall significance during T90 reaches 8.3 sigma.

The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB230826A_GCN.pdf

All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ 
GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. 

A. A. Breeveld (UCL-MSSL) and R. A. J. Eyles-Ferris (U Leicester) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230826A 114 s after the BAT trigger (Eyles-Ferris et al., GCN Circ. 34565
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 ).
No optical afterglow consistent with the enhanced XRT position (Osborne et al., GCN Circ. 34569
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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           114          263        147           >20.0
white              606         5452        312           >20.4
v                  657         1105         58           >17.8
b                  582         5339        255           >19.6
u                  327         5134        481           >19.5
uvw1               707         1320         71           >18.4
uvm2               682         1303         78           >18.4
uvw2               632         1254         78           >18.6

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.243 in the direction of the burst (Schlegel et al. 1998).

M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory),  N. Werner  (Masaryk U.), M. Ohno (Hiroshima U.),  L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory),  T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU)  -- the VZLUSAT-2/GRB payload collaboration.

The long duration GRB 230826A (Fermi/GBM detection: GCN 34564
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 ; Swift/BAT detection: GCN 34565
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 ; GRBAlpha detection: GCN 34572
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 ) was detected by the GRB detectors on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).

The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2023-08-26 19:32:48 UTC. The T90 duration is 17 s (18 s) and the significance during T90 reaches 11 sigma (17 sigma) for detector unit no. 0 (no. 1).

The light curve obtained by VZLUSAT-2 is available here:
https://vzlusat2.konkoly.hu/static/share/GRB230826A_GCN_VZLUSAT2.pdf

All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/
The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral.

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


Using the data set from T-61 to T+1091 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 230826A (trigger #1187463)
(Eyles-Ferris, et al., GCN Circ. 34565
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 ). The BAT ground-calculated position is
RA, Dec = 83.048, 66.129 deg which is
RA(J2000) = 05h 32m 11.5s
Dec(J2000) = +66d 07' 43.9"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 87%.


The mask weighted light curve shows two main emission episodes where the first has
enhanced structure. T90 (15-350 keV) is 41.07 +- 2.36 sec (estimated error including systematics).


The time-averaged spectrum from T-4.26 to T+56.79 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.20 +- 0.22,
and Epeak of 122.3 +- 70.2 keV (chi squared 44.78 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 3.6 +- 0.1 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T+2.44 sec in the 15-150 keV band is
3.0 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index
of 1.55 +- 0.05 (chi squared 52.29 for 57 d.o.f.). 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/1187463/BA/ <http://gcn.gsfc.nasa.gov/notices_s/1187463/BA/>

M. Kerr, C.C. Cheung, J. E. Grove, R. Woolf (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge (MSFC), and M.S. Briggs (UAH) report:

The Glowbug gamma-ray telescope [1,2], operating on the International Space Station, reports the detection of GRB 230826A, which was also detected by Fermi/GBM, Swift/BAT, GRBAlpha, and VZLUSAT-2 (GCN 34564
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 , 34565
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 , 34572
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 , 34586
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 ).

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2023-08-26 19:32:44.336 with a duration of 12.3 s and a total significance of about 29.9 sigma. The light curve comprises a single peak.

Using a standard power-law function with an exponential high-energy cutoff [3] to model the emission over this duration results in a poorly constrained power-law index and a cutoff energy ("Epeak") of 138 keV. The modeled 10-10000 keV fluence is 1.5e-06 erg/cm^2.

The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.

Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS. The detector comprises 12 large-area (15 cm x 15 cm) CsI:Tl panels covering the surface of a half cube, and two hexagonal (5-cm diameter, 10-cm length) CLLB scintillators, giving it a large field of view (instantaneous FoV ~2/3 sky) over a wide energy band of 50 keV to >2 MeV.

[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
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[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv :1909.03006

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