GRB 241010A

S. Dichiara (PSU), P. A. Evans (U Leicester), C. Gronwall (PSU),
J. A. Kennea (PSU), 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 10:05:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 241010A (trigger=1259578).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 153.365, +11.544 which is 
   RA(J2000) = 10h 13m 28s
   Dec(J2000) = +11d 32' 38"
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 40 sec.  The peak count rate
was ~10000 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 10:06:56.3 UT, 102.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 153.38152, 11.53521 which is equivalent
to:
   RA(J2000)  = 10h 13m 31.56s
   Dec(J2000) = +11d 32' 06.8"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 66 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 (3.87 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.8
(+3.64/-2.97) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 105 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	10:13:31.54 = 153.38141
  DEC(J2000) = +11:32:03.4  =  11.53429
with a 90%-confidence error radius of about 0.77 arc sec. This position is 4.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.33 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.040.

Burst Advocate for this burst is S. Dichiara (sbd5667 AT psu.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/)

L. Izzo (INAF-OACn and DARK/NBI) and D. B. Malesani (DAWN/NBI and Radboud Univ.) report:

We observed the field of the GRB 241010A (Dichiara et al., GCN #37755
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 ) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located at the McDonald Observatory, TX, United States. Observations started on 2024 October 10th at 11:47:59 UT (1.74 hr after the GRB trigger). We obtained a series of 3x180 s images in the SDSS-r filter.

In the stacked r-band, we detect the optical afterglow within the error box of the Swift-UVOT afterglow (Dichiara, GCN #37755
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 ). We measure a preliminary magnitude of r = 19.64 +/- 0.11 mag (AB), calibrated against nearby stars from the Pan-STARRS catalog.
  
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 101004719.

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

Using 624 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 241010A, 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 = 153.38132, +11.53445 which is equivalent
to:

RA (J2000): 10h 13m 31.52s
Dec (J2000): +11d 32' 04.0"

with an uncertainty of 2.1 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.

Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (MIT), Viraj Karambelkar (Caltech), Danielle Frostig (CfA), Robert Stein (Caltech), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:

We observed the field of GRB 241010A (Dichiara et al., GCN 37755
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 ; Evans et al., GCN 37757
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 ) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). 

Observations were triggered automatically and began at 2024-10-10T11:50:36 UTC (~1.8 hours after the GRB), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565
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 ). 

We do not detect a source at the optical and refined Swift/XRT counterpart location (Dichiara et al., GCN 37755
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 ; Izzo et al., GCN 37756
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 ; Evans et al., GCN 37757
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 ). We obtain the following 5-sigma upper limit: J ~ 18.0 mag (AB).

WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.

V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik,  D. Vlasenko,
G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij
(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. Gress, N.M. Budnev, O.Ershova
(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),

V. Yurkov, A. Gabovich
(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 241010A ( S. Dichiara et al., GCN 37755
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 ) errorbox  59814 sec after notice time and 59836 sec after trigger time at 2024-10-11 02:42:31 UT, with upper limit up to  15.6 mag. The observations began at zenith distance = 81 deg. The sun  altitude  is -17.5 deg. 

The galactic latitude b = 50 deg., longitude l = 229 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2633103

We obtain a following upper limits.  

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

   59927 |         MASTER-SAAO |   C |   180 | 13.9 |        
   60126 |         MASTER-SAAO |   C |   180 | 15.6 |        
Filter C is a clear (unfiltred) band. 


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

S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A.
D'Ai (INAF-IASFPA), D.N. Burrows (PSU) and P.A. Evans report on behalf
of the Swift-XRT team:

We have analysed 8.7 ks of XRT data for GRB 241010A, from 86 s to 68.0
ks after the  BAT trigger. The data comprise 9 s in Windowed Timing
(WT) mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode. 

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.3 (+4.0, -0.9). At T+154 s  the decay
flattens to an alpha of 0.1 (+0.3, -0.4). The light curve breaks again
at T+535 s to a decay with alpha=5.2 (+2.8, -3.4),  and  again at T+677
s s to alpha=-0.6 (+0.4, -0.9),  before a final break at T+3672 s s
after which the decay index is 0.92 (+0.14, -0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.91 (+/-0.13). The
best-fitting absorption column is  2.0 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 3.9 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 3.8 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.0 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 3.9 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     1.91 (+/-0.13)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01259578.

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

S.Q. Jiang, S.Y. Fu, X. Liu, J. An, Z.P. Zhu, D. Xu (NAOC), J.Z. Liu (XAO) report on behalf of a large collaboration:

We observed the field of GRB 241010A detected by Swift (Dichiara et al. GCN 37755
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 ) using the 100C telescope of the JinShan project located at Altay, Xinjiang, China. A series of 300 s frames are obtained in the Sloan r-band, starting at 22:02:29.24 on 2024-10-10, i.e. 11.95 hr after the BAT trigger.

The optical afterglow (Dichiara et al. GCN 37755
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 ; Izzo et al. GCN 37756
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 ) of the burst is clearly detected in our stacked image. We measured a preliminary magnitude of r = 20.46 +/- 0.08 (AB), calibrated with nearby PanSTARRS stars. The magnitude is not corrected for Galactic extinction.

We also note that there exists a known source at the JinShan position in the Legacy Survey at coordinates R.A. (J2000) = 10:13:31.5317, Dec.(J2000) = +11:32:03.116, which is ~ 0.4 arcsec from the center of the UVOT position. The source has g = 23.0 +/- 0.05, r = 22.83 +/- 0.06, z = 22.13 +/- 0.09, a photometric redshfit of z = 0.87 +/- 0.11, and could be the host galaxy of the burst.

We acknowledge the excellent support from X. Yao, S.W. Luo, and Z.K. Feng for enabling these observations.

D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC),
S. Dichiara (PSU),  R. Gupta (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), T. Sakamoto (AGU)
(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 241010A (trigger #1259578)
(Dichiara, et al., GCN Circ. 37755
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 ).  The BAT ground-calculated position is
RA, Dec = 153.367, 11.544 deg which is
   RA(J2000)  =  10h 13m 28.1s
   Dec(J2000) = +11d 32' 40.1"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.
 
The mask-weighted light curve shows multiple emission periods. The first period
lasts ~six seconds and displays three pulses, followed by a quiescent period, and
then a second emission period lasting ~15 seconds with two apparent pulses.
T90 (15-350 keV) is 30.86 +- 1.36 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.04 to T+35.12 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.88 +- 0.08.  The fluence in the 15-150 keV band is 2.0 +- 0.1 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-0.04 sec in the 15-150 keV band
is 4.3 +- 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/1259578

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

We observed the field of GRB241010A (Dichiara et al., GCN 37755
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 ) with the 0.5m Virgin Island Robotic Telescope (VIRT) at the University of the Virgin Islands' Etelman Observatory on 2024-10-11 starting at 08:53:49 (Tmid+ ~23.03 hrs). We performed a series of exposures in R filter with a total exposure of 590s. The weather conditions were partly cloudy during the hours of observation with an average airmass of 1.88. 

We do not detect any source within the enhanced XRT position (Evans et al. GCN 37757
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 ). This non-detection is consistent with detections reported by (Izzo et al. GCN 37756
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 ) and (Jiang et al. GCN 37771
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 ) and upper limits reported by (Mo et al. GCN 37762
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 ) and (Lipunov et al. GCN 37764
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 ). We report the following 3-sigma upper limit:

T_mid                ||Exposure   ||Filter   ||Limit 
T+23.03  hrs         || 590s      || R       ||>19.74

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.

D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Cabrera-Lavers (GTC), J. F. Agui Fernandez (CAHA), A. de Ugarte Postigo (LAM/OCA, CNRS), C. C. Thoene (ASU-CAS, AbAO), J. Rastinejad (Northwestern), B. P. Gompertz (Birmingham), A. J. Levan (Radboud Univ. and Warwick Univ.), W. Fong (Northwestern), N. R. Tanvir (U. Leicester), J. P. U. Fynbo (DAWN/NBI), L. Izzo (INAF-OACn & DARK/NBI), A. Martin-Carrillo (UCD), G. Lombardi (GTC), S. Geier (GTC) report:

At the location of the optical afterglow of GRB 241010A (Dichiara et al., GCN 37755
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 ), an object is visible in the Legacy survey, first noticed by Jiang et al. (GCN 37771
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 ). This is most likely the GRB host galaxy.

On 2024 November 2, once the field became visible to ground-based observatories, we secured spectroscopic observations of the host galaxy using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. Three spectra of 900 s each were obtained, using the R1000R grism, which covers the wavelength range 5150-10200 AA.

On top of clear continuum, a multitude of emission lines are visible, which we interpret as due to [O II], [Ne III] 3869, Hdelta, Hgamma, Hbeta, [O III] 4958 and [O III] 5006, all at a common redshift z = 0.977, which we suggest to be the redshift of GRB 241010A. This value is consistent with the photometric estimate from the Legacy survey (z_ph = 0.87 +- 0.11; Zhou et al. 2021, MNRAS, 501, 3309).