GRB 251024A

M. H. Siegel and M. J. Moss (GSFC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251024A 132 s after the BAT trigger (Moss et al., GCN Circ. 42426
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 ). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 42430
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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           132          282          147         >21.0
u_FC               290          540          246         >19.9
white              132          591          167         >21.0
v                  622          641           19         >18.0
b                  547          567           20         >19.8
u                  290          540          246         >19.9
w2                 597          617           20         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.044 in the direction of the burst
(Schlegel et al. 1998).

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), 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), D. Sadaula
(GSFC/UMBC) (i.e. the Swift-BAT team):

Using the data set from T-240 to T+613 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 251024A (trigger #1406589)
(Moss et al., GCN Circ. 42426
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 ).  The BAT ground-calculated position is
RA, Dec = 306.666, -68.576 deg which is
   RA(J2000)  =  20h 26m 39.7s
   Dec(J2000) = -68d 34' 34.3"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.

The mask-weighted light curve shows a weak pulse structure that starts at
~T+1 s and peaks at ~T+3 s. The main pulse structure ends at ~T+25 s, and
there are some tail emissions that last till ~T+100 s. T90 (15-350 keV) is
82.66 +- 23.27 sec (estimated error including systematics).

The time-averaged spectrum from T+1.16 to T+97.28 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 1.68 +- 0.30.  The fluence in the 15-150 keV band is 6.5 +- 1.2 x 10^-07
erg/cm2. The 1-sec peak photon flux measured from T+2.16 sec in the 15-150
keV band is 0.5 +- 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/1406589

S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C.
Salvaggio (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A.
Evans report on behalf of the Swift-XRT team:

We have analysed 4.4 ks of XRT data for GRB 251024A, from 113 s to 56.4
ks after the   trigger. The data comprise 30 s in Windowed Timing (WT)
mode (the first 10 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.  The late-time light curve
(from T0+4.5 ks) is consistent with a constant source of mean count
rate 4.5e-01 ct/sec. A power-law fit gives an index of -0.14 (+0.15,
-0.14).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.06 (+0.16, -0.11). The
best-fitting absorption column is  consistent with the Galactic value
of 3.7 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 3.2 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.7 (+/-2.8) x 10^20 cm^-2
Galactic foreground: 3.7 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.06 (+0.16, -0.11)

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01406589.

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

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

Using 1910 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 251024A, 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 = 306.59782, -68.57239 which is equivalent
to:

RA (J2000): 20h 26m 23.48s
Dec (J2000): -68d 34' 20.6"

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 https://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.

R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:

We observed the Swift GRB 251024A field (Moss et al., GCN 42426
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 )  with the LCOGT 1-meter Sinistro instrument at the South African Astronomical Observatory site, on October 24, from 18:18 to 18:50 UT (corresponding to 0.51 to 1.05 hours after the GRB trigger time) with the Bessel I and R filters.

We performed a series of 3x300s exposures in I-band and R-band.  We detect an uncatalogued source in the XRT error region in both bands, which we propose to be the afterglow.

The following magnitudes are calculated using the USNO-B1.0 catalog as reference:

R = 21.2 +/- 0.1
I = 21.2 +/- 0.2

These magnitudes are not corrected for galactic extinction.

M. J. Moss (GSFC), S. Dichiara (PSU),
R. A. J. Eyles-Ferris (U Leicester), R. Gupta (NASA GSFC),
J. A. Kennea (PSU), A. Y. Lien (U Tampa), K. L. Page (U Leicester) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 17:47:02.25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251024A (trigger= 1406589).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 306.622, -68.574 which is 
   RA(J2000) = 20h 26m 29s
   Dec(J2000) = -68d 34' 25"
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 ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 17:49:11.3 UT, 129.1 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 306.59743,
-68.57225 which is equivalent to:
   RA(J2000)  = 20h 26m 23.38s
   Dec(J2000) = -68d 34' 20.1"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 32 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.73 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3
(+2.09/-1.77) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 132 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. The typical 3-sigma upper limit has been about 19.6 mag.
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
0.044.

Burst Advocate for this burst is M. J. Moss (mikejmoss3 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/)

V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, 
G.Antipov,  A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

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 GRB251024.74 (trigger No 1406589,20h 26m 29.26s , -68d 34m 26.4s, R=0.05) errorbox  10 sec after notice time and 73 sec after trigger time at 2025-10-24 17:48:15 UT, with upper limit up to  16.5 mag. Observations started at twilight.  The observations began at zenith distance = 38 deg. The sun  altitude  is -11.1 deg. 

The galactic latitude b = -34 deg., longitude l = 327 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3022698

We obtain a following upper limits.  

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

      78 |         MASTER-SAAO |  P\ |    10 | 16.2 |        
      78 |         MASTER-SAAO |   C |    10 | 16.1 |        
     112 |         MASTER-SAAO |  P\ |    20 | 16.5 |        
     112 |         MASTER-SAAO |   C |    20 | 16.3 |        
Filter C is a clear (unfiltred) band. 


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