GRB 241006A

R. Gupta (NASA GSFC), M. J. Moss (GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 21:51:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 241006A (trigger=1258721).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 304.794, -40.796 which is 
   RA(J2000) = 20h 19m 11s
   Dec(J2000) = -40d 47' 44"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 30 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~-1 sec after the trigger.

The XRT began observing the field at 21:54:23.5 UT, 145.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 304.74258,
-40.80514 which is equivalent to:
   RA(J2000)  = 20h 18m 58.22s
   Dec(J2000) = -40d 48' 18.5"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 143 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 (4.92 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5
(+3.24/-2.77) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.75e-10 erg cm^-2 s^-1 (0.2-10
keV).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 349 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 0.065.

Burst Advocate for this burst is R. Gupta (rahulbhu.c157 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/)

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

Using 391 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 241006A, 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 = 304.74263, -40.80500 which is equivalent
to:

RA (J2000): 20h 18m 58.23s
Dec (J2000): -40d 48' 18.0"

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.

SVOM/VT commissioning team: Y. L. Qiu, L. P. Xin, H. L. Li, C. Wu, X. H. Han, W. J. Xie,  H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang (NAOC), J. Zhang, L. J.  Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM), D. Turpin (CEA), Z. P. Jin, H. Zhou (PMO)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)

report on behalf of the SVOM team:

During the commissioning phase of SVOM mission, we observed the GRB 241006A detected by Swift/BAT (Gupta et al. GCN 37722
Loading...
 
 ) with SVOM/VT telescope in ToO mode. The observation started at 2024-10-07T03:15:07 UT, approximately 5.38 hours after the burst, with a total exposure time of 5220 seconds. The VT telescope conducted observations simultaneously in two channels: VT_B (400nm-650nm) and VT_R (650nm-1000nm).

Preliminary analysis shows that, no any source was detected within the error circles of XRT (Beardmore et al., GCN 37724
Loading...
 
 ) with the 3 sigma limit magnitudes of about 24.0 mag for VT_B and 23.8 mag for VT_R in the AB magnitude system, after stacking the images for both bands separately.

More observations with inferred wavelengths are encouraged to investigate the nature of the burst. 

The SpaceVariable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.

N.P.M. Kuin and R. Gupta (NASA GSFC) report on behalf of
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 241006A   350 s after the BAT trigger (Gupta et al.,
GCN Circ. 37722
Loading...
 
 ). No optical afterglow consistent with the XRT
position has been 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           350          499          147         >21.0
white              350          625          167         >21.0
v                  656          676           19         >17.4
b                  580          600           19         >19.0
u                  556          575           19         >17.9
w1                 531          715           28         >18.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.065 in the direction of the burst
(Schlegel et al. 1998).

J. Durbak (UMD), O. Guiffreda (UMD), S. Atri (U Rome), A. S. Kutyrev (NASA/GSFC), E. Troja (U Rome), K. De (MIT), S. B. Cenko (NASA/GSFC)

Following the Swift BAT detection (GCN 37722
Loading...
 
 ), we observed the transient field in J-filter with PRIME ~45 minutes after Swift BAT detection in cloudy conditions.

At the enhanced XRT position (GCN 37728
Loading...
 
 ), we detect no uncatalogued sources in J-band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive a limiting magnitude of <18.7 AB, not corrected for Galactic extinction.  

PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024).

We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.

B. Sbarufatti (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S.
Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB) and P.A. Evans report on
behalf of the Swift-XRT team:

We have analysed 7.8 ks of XRT data for GRB 241006A, from 295 s to 50.5
ks after the  BAT trigger. The data comprise 23 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=3.3 (+0.4, -0.3).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.73 (+0.28, -0.20). The
best-fitting absorption column is  6.4 (+8.3, -1.5) x 10^20 cm^-2,
consistent with the Galactic value of 4.9 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 3.9 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.4 (+8.3, -1.5) x 10^20 cm^-2
Galactic foreground: 4.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.73 (+0.28, -0.20)

If the light curve continues to decay with a power-law decay index of
3.3, the count rate at T+24 hours will be 3.1 x 10^-8 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-18 (1.3 x 10^-18) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01258721.

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

T. Hussenot-Desenonges (IJCLAB), Y. Rajabov (UBAI), M. Tanasan (NARIT), I. Abdi (AUS), R.Strausbaugh (EIU), S. Antier (OCA), S. Karpov (FZU), M. Coughlin (UMN), C. Andrade (UMN), I. Tosta e Melo (UniCT-DFA), P. Hello, N. Leroy (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), L. De Almeida, W. Corradi, N. Sasaki, F. Navarete, L. Braga (LNA), K. Noysena (NARIT)
on behalf of the GRANDMA collaboration.

We performed observations with the GRANDMA network on the field of GRB 241006A, detected by Swift-BAT (GCN 37722
Loading...
 
 ).
The first images were taken at OPD starting from 2024-10-07T01:01:42, 3 hours after the GRB trigger, in the I and R filters. TRT-SBO also observed the field in R and I filters starting from 2024-10-07T09:26:52, 11.5 hours after the trigger.

We did not detect any optical counterparts of the Swift-XRT afterglow position (RaDec 304.74263 -40.80500, GCN 37724
Loading...
 
 ), with the following 5-sigma upperlimits at its coordinates:

+-------------+-------------+--------+----------+-----------+-------------+
| MJD (start) | T-T0 (days) | Filter | Exposure | Telescope | U.L. (Vega) |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.0429  | 0.1318      | I      | 16x360s  | OPD       | 19.6        |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.0556  | 0.1445      | R      | 9x360s   | OPD       | 20.1        |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.3937  | 0.4826      | R      | 5x300s   | TRT-SBO   | 21.6        |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.4079  | 0.4968      | I      | 5x300s   | TRT-SBO   | 20.0        |
+-------------+-------------+--------+----------+-----------+-------------+

We also searched the Swift-BAT field (RA, Dec 304.794, -40.796, uncertainty 3 arcmin) and did not detect any optical counterpart. The 5-sigma upperlimits on the field are:
+-------------+-------------+--------+----------+-----------+-------------+
| MJD (start) | T-T0 (days) | Filter | Exposure | Telescope | U.L. (Vega) |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.0429  | 0.1318      | I      | 16x360s  | OPD       | 19.4        |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.0556  | 0.1445      | R      | 9x360s   | OPD       | 20.0        |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.3937  | 0.4826      | R      | 5x300s   | TRT-SBO   | 21.5        |
|-------------+-------------+--------+----------+-----------+-------------+
| 60590.4079  | 0.4968      | I      | 5x300s   | TRT-SBO   | 19.9        |
+-------------+-------------+--------+----------+-----------+-------------+



All the data has been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022).

We use the SkyPortal application (skyportal.io) to monitor our observational campaign.

GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518)

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

Using the data set from T-240 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 241006A (trigger #1258721;
Gupta et al., GCN Circ. 37722
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 304.782, -40.806 deg which is
   RA(J2000)  =  20h 19m 07.6s
   Dec(J2000) = -40d 48' 21.7"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 65%.

The mask-weighted light curve shows a single-pulse structure that starts at
~T-7 s, peaks at ~T+10 s, and ends at ~T+50 s. T90 (15-350 keV) is 47.95 +-
9.72 sec (estimated error including systematics).

The time-averaged spectrum from T-7.14 to T+47.82 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 1.52 +- 0.19.  The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-06
erg/cm2. The 1-sec peak photon flux measured from T+9.95 sec in the 15-150
keV band is 0.6 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90%
confidence
level.

The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1258721

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

We observed GRB 241006A (Gupta et al., GCN 37722
Loading...
 
 ) as part of the Australia Telescope Compact Array (ATCA) "PanRadio GRB" Large Project C3542 (PI: G. Anderson) at 5.5 and 9 GHz, 5.2 hours post-merger on 2024-10-07 (03:03-14:32 UT) and 2.25 days post-merger on 2024-10-09 (04:30-08:30 UT). 

No radio sources were detected near the Swift/XRT enhanced position (A.P. Beardmore et al., GCN 37724
Loading...
 
 ) in either observation epoch. The 3-sigma upper limits for the 9 GHz observations are 27 and 39 uJy respectively.

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.

K. Noonan (UVI), P. Gokuldass (ERAU), N. Orange (OrangeWave Innovative Science, LLC), D. Morris (NASA), T. Lombardi (Eckerd College), F. George (ERAU), R. Querrard (UVI), D. Smith (UVI), K. Smith (UVI) report:

We observed the field of GRB241006A (Gupta et al., GCN 37722
Loading...
 
 ) with the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of the Virgin Islands' Etelman Observatory on 2024-10-07 starting at 23:05:40.9 (Tmid+25.7 hrs). We performed a series of exposures in an R filter with a total exposure of 3490s. The weather conditions were partly cloudy during the hours of observation with an average airmass of 1.9. 

We do not detect any source within the enhanced XRT position (Beardmore  et al. GCN 37724
Loading...
 
 ). This non-detection is consistent with the upper limits reported by SWIFT/UVOT (Kuin et al., GCN 37729
Loading...
 
 ), PRIME (Durbak et al., GCN 37730
Loading...
 
 ), GRANDMA (Hussenot-Desenonges et al., GCN 37738
Loading...
 
 ), and SVOM/VT (Qiu et al., GCN 37728
Loading...
 
 ). We report the following 3-sigma upper limit:

T_mid                ||Exposure   ||Filter   ||Limit 
T+ 25.7 hrs          || 3490s     || R       ||>20.46

The limit is estimated from comparison to nearby USNO B1 stars and is not corrected for Galactic extinction. The VIRT is still in the commissioning phase. 

We acknowledge financial support from NASA EPSCoR award 80NNSC22M0063, NSF PAARE award 2319415, and NASA EPSCoR award 80NSSC24M0112. This message can be cited.