GRB 230815A

N. J. Klingler (GSFC/UMBC/CRESSTII), C. Gronwall (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
T. M. Parsotan (GSFC/UMBC/CRESSTII) report on behalf of the Neil
Gehrels Swift Observatory Team:

At 10:49:55 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230815A (trigger=1185505).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 184.772, -58.065 which is 
   RA(J2000) = 12h 19m 05s
   Dec(J2000) = -58d 03' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 2 sec.  The peak count rate
was ~6000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 10:52:04.0 UT, 128.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 184.72347, -58.05386 which
is equivalent to:
   RA(J2000)  = 12h 18m 53.63s
   Dec(J2000) = -58d 03' 13.9"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
position may be improved as more data are received; the latest position
is available at https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.94 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 7.8
(+3.75/-3.24) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 2.07e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 155 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 100% of
the XRT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. Data from the list of sources generated on-board are not available
at this time. No correction has been made for the large, but uncertain,
extinction expected. 

Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu). 
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/)

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

Using 927 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 230815A, 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 = 184.72225, -58.05290 which is equivalent
to:

RA (J2000): 12h 18m 53.34s
Dec (J2000): -58d 03' 10.4"

with an uncertainty of 2.2 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.

V. Lipunov, V.Kornilov, E.Gorbovskoy, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, D. Vlasenko, 
G.Antipov, D.Zimnukhov, V.Senik, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov,  D.Cheryasov, Ya.Kechin
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile 
(Observatorio Astronomico Felix Aguilar OAFA),

R. Rebolo, M. Serra 
(The Instituto de Astrofisica de Canarias),

D. Buckley 
(South African Astronomical Observatory),

O.A. Gres, N.M. Budnev
(Irkutsk State University, API),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez 
(INAOE, Guillermo Haro Astrophysics Observatory),

A. Tlatov, D. Dormidontov 
(Kislovodsk Solar Station of the Pulkovo Observatory),

A. Gabovich, V.Yurkov 
(Blagoveschensk Educational State University)


MASTER-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 230815A ( N. J. Klingler et al., GCN 34434
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 ) errorbox  27081 sec after notice time and 28191 sec after trigger time at 2023-08-15 18:41:55 UT, with upper limit up to  17.4 mag. The observations began at zenith distance = 58 deg. The sun  altitude  is -32.4 deg. 

The galactic latitude b =  4 deg., longitude l = 299 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2254590

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   28282 |         MASTER-SAAO |   C |   180 | 16.8 |        
   29125 |         MASTER-SAAO |   C |   180 | 17.4 |        
   29335 |         MASTER-SAAO |   C |   180 | 17.3 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

B. Mailyan (Florida tech), A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 10:49:54.66 UT on 15 August 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230815A (trigger 713789399/230815451).
which was also detected by Swift BAT (N. J. Klingler et al. 2023, GCN 34434
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 ).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 159 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 5.2 s (50-300 keV). The time-averaged spectrum
from T0+0.002 to T0+3.264 s is best fit by
a Band function with Epeak = 235 +/- 25 keV,
alpha = -0.6 +/- 0.1, and beta = -2.22 +/- 0.09.

The event fluence (10-1000 keV) in this time interval is
(1.20 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.1 s in the 10-1000 keV band is 27 +/- 2 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/"

E. Fernandez-Garcia, Y.-D. Hu, I. Perez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, SouthAfrica), A. Martin-Carrillo and L. Hanlon (UCD, Ireland) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report:

Following the detection of GRB 230815A by Swift (Klingler et al. GCNC 34434) and Fermi (Mayland et al. GCNC 34440), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) automatically observed the GRB location starting on Aug. 15, 19:21 UT (~ 8.5 h after trigger). No new optical source is detected on the co-added image (5 x 60 s, clear filter) within the enhanced Swift/XRT error region (Beardmore et al. GCNC 34437) down to 19.5 mag.

We thank the staff at Boyden Observatory for their excellent support.

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

We have analysed 6.0 ks of XRT data for GRB 230815A, from 117 s to 45.2
ks after the  BAT trigger. The data comprise 574 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 late-time light curve (from T0+6.1 ks) can be modelled with a
power-law decay with a decay index of alpha=1.94 (+0.25, -0.29).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.92 (+0.06, -0.05). The
best-fitting absorption column is  7.4 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 4.9 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.94 (+0.18, -0.17)
and a best-fitting absorption column of 9.1 (+1.7, -1.5) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.9 x 10^-11 (8.5 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.1 (+1.7, -1.5) x 10^21 cm^-2
Galactic foreground: 4.9 x 10^21 cm^-2
Excess significance: 4.5 sigma
Photon index:	     1.94 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
1.94, the count rate at T+24 hours will be 2.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (2.1 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/01185505.

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

A. A. Breeveld (UCL-MSSL) and N. J. Klingler (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230815A 155 s after the BAT trigger (Klingler et al., GCN Circ. 34434
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 ).
No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 34437
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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 summed exposures are:

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

white_FC           155          305        147           >20.1
white              513         1531        242           >20.3
v                  390         1582        136           >18.5
b                  489         1506        114           >19.3
u                  464         6300        293           >19.4
uvw1               439         1632        136           >18.6
uvm2               761         1606         97           >18.3
uvw2               365         1557        136           >18.8

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.73 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-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 230815A (trigger #1185505)
(Klingler, et al., GCN Circ. 34434
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 ). The BAT ground-calculated position is
RA, Dec = 184.760, -58.067 deg which is
RA(J2000) = 12h 19m 02.4s
Dec(J2000) = -58d 03' 59.5"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 11%.


The mask-weighted light curve shows a strong peak at trigger time with precursor emission
At T-14 sec from trigger. T90 (15-350 keV) is 17.00 +- 7.62 sec (estimated error including systematics).


The time-averaged spectrum from T-14.78 to T+9.22 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.19 +- 0.10. The fluence in the 15-150 keV band is 5.2 +- 0.3 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+0.22 sec in the 15-150 keV band
is 13.7 +- 1.1 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/1185505/BA/

C. D. Kilpatrick (Northwestern), C. R. Bom (CBPF), A. Santos (CBPF/Fermilab), S. Panda (LNA), Felipe Navarete (NOIRLab/SOAR) on behalf of a larger collaboration, report:

Following the detection of GRB230815A (Klingler et al., GCN 34434
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 , Mailyan et al., GCN 34440
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 ), we triggered observations with the Goodman high-throughput imaging spectrograph on the SOAR 4.1m telescope at Cerro Pachón, Chile.  Targeting the site of the reported Swift/XRT counterpart (Beardmore et al., GCN 34437
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 ), we obtained 6x180s exposures in SDSS i-band and 7x180s in SDSS z-band at start times of 2023-08-15 23:17:36 and 2023-08-15 23:50:48 UTC, respectively.  We did not detect a counterpart in either stacked image, with the limiting magnitude in both frames significantly affected by poor atmospheric transparency.  Performing forced photometry at the site of the XRT counterpart (R.A.=12:18:53.34, Decl.=-58:03:10.4), we derive limits on an optical counterpart of:

MJD Filter Maglimit
60171.97055 i 20.5
60171.99361 z 17.9

Both magnitude limits are on the AB magnitude system calibrated from SkyMapper DR2 standard stars (Onken et al. 2019) and are not corrected for the significant Galactic extinction along this sight line (A_i=1.25 mag, A_z=0.93 mag).

Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia e Inovações do Brasil (MCTI/LNA), the US National Science Foundation’s NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

B. Schneider (MIT), A. Chrimes (Radboud), D. B. Malesani (Radboud and DAWN/NBI), 
A. J. Levan (Radboud), N. R. Tanvir (U. Leicester), A. de Ugarte Postigo (OCA/CNRS), 
report on behalf of the Stargate collaboration:

We observed the field of GRB 230815A (Klingler et al., GCN 34434
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 ; 
Mailyan et al. GCN 34440
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 ) with the ESO Very Large Telescope, equipped 
with the HAWK-I near-infrared camera. Observations consisted of two 
epochs of 20 min exposure in the H band at 23:19:53 UT on 2023-08-15 
(~12.5 hr after trigger) and 23:15:46 UT on 2023-08-16 (~36.4 hr after 
trigger).

In both epochs, we clearly detected two sources consistent with the XRT 
error circle (Beardmore et al., GCN 34437
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 ). One of the sources has 
significantly faded (~2 mag) between the two epochs, evolving from 
AB mag = 20.11 +/- 0.02 to AB mag = 22.01 +/- 0.08. This corresponds 
to a power-law decay index of 1.65,  similar to the X-ray decay rate, 
suggesting a small host contribution to the NIR flux. The proposed 
afterglow of the burst is detected at coordinates:

RA (J2000) = 12:18:53.24
DEC (J2000) = -58:03:09.45

with an uncertainty of 0.3".

We acknowledge the excellent support provided by the Paranal staff, 
in particular Joe Anderson.

J. K. Leung (USyd), G. E. Anderson (Curtin), S. D. Ryder (Macquarie),
A. J. van der Horst (GWU), A. Gulati (USyd), L. Rhodes (Oxford), 
S. Chastain (UNM) on behalf of the PanRadio GRB collaboration

The Australia Telescope Compact Array (ATCA) observed long GRB 230815A 
(Klingler et al., GCN 34434
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 ; Mailyan et al., GCN 34440
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 ) as part of the 
ATCA "PanRadio GRB" follow-up Large Project C3542 (PI. Anderson) on 
2023-08-17 UT and 2023-08-18 UT. 

No radio sources were detected at the GRB location in the first 
observation conducted from 2023-08-17 02:00 UT for 10 hrs at 5.5, 9.0, 
16.7 and 21.2 GHz. The 3-sigma upper limits were 75, 69, 324, 741 
microJy/beam, respectively. Note the higher than usual rms was due to 
bad weather during the observation.

The second observation was conducted from 2023-08-18 22:00 UT for 6 hrs 
at 5.5, 9.0 and 44 GHz. In our preliminary analysis, we detect a radio 
counterpart with a flux density of 70+/-10 microJy at 9 GHz. The fitted 
position is:

RAJ2000  = 12:18:53.2
DECJ2000 = -58:03:09.0
with an uncertainty of ~0.3". 

This is in broad agreement with previously reported Swift/XRT (Beardmore
et al., GCN 34437
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 ) and VLT/HAWK-I (Schneider et al., GCN 34467
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 ) 
afterglow positions. There was also a marginal ~3 sigma detection at 
5.5 GHz (rms=14 microJy/beam) and a non-detection at 44 GHz with a
3-sigma upper limit of 111 microJy/beam.

Further observations are planned.

We thank the CSIRO Space and Astronomy staff for supporting these 
observations. We acknowledge the Gomeroi people as the traditional
owners of the Observatory site. The Australia Telescope Compact Array is
part of the Australia Telescope National Facility 
(https://ror.org/05qajvd42) which is funded by the Australian Government
for operation as a National Facility managed by CSIRO.