GRB 241002A

Kasper E. Heintz (DAWN/NBI), Daniele B. Malesani (DAWN/NBI and Radboud Univ.) and Mikael Turkki (NOT and Univ. Helsinki) report on behalf of a larger collaboration:

We observed the field of the Swift GRB 241002A (Caputo et al., GCN 37662
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 ), using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were affected by strong winds, and the delivered seeing was mediocre (1.6-2"). Observations were carried out with mid times Oct 2.204 and Oct 2.217 UT in the SDSS r and z bands, respectively (4.07 and 4.36 hr after the trigger).

No source is detected consistent with the location of the X-ray afterglow (Osborne et al., GCN 37665
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 ), down to limiting magnitudes r > 23.2 and z > 22.5 (both values in the AB system, calibrated against nearby Pan-STARRS point-like sources).

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), 
R. Caputo (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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 241002A (trigger #1257556)
(Caputo, et al., GCN Circ. 37662
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 ).  The BAT ground-calculated position is
RA, Dec = 140.942, 39.829 deg which is 
   RA(J2000)  =  09h 23m 46.1s 
   Dec(J2000) = +39d 49' 44.5" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 69%.
 
The mask-weighted light curve shows an overall single pulse of emission with 
several smaller pulses of emission that can be seen during the main emission.
The T90 (15-350 keV) is 46.81 +- 10.52 sec (estimated error including systematics).
 
The time-averaged spectrum from T-21.34 to T+44.86 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.02 +- 0.10.  The fluence in the 15-150 keV band is 2.1 +- 0.1 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-0.29 sec in the 15-150 keV band
is 1.7 +- 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/1257556

S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.),
N. P. M. Kuin (UCL-MSSL) and R. Caputo (GSFC) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 241002A
116 s after the BAT trigger (Caputo et al., GCN Circ. 37662
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 ).
No optical afterglow consistent with the enhanced XRT position
(Osborne et al., GCN Circ. 37665
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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           116          266          147         >19.9
white		   4616		10268	     1081	 >21.4
v		   5027		16800	     1081	 >19.8
b		   4412		5944	     292	 >19.8
u		   4206		5841	     393	 >19.6
uw1		   5437		5637	     197	 >19.0
uw2		   4822		11104	     1014	 >20.5
um2		   5232		22035	     1477	 >20.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.011 in the direction of the burst
(Schlegel et al. 1998).

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

We have analysed 10 ks of XRT data for GRB 241002A, from 95 s to 38.9
ks after the  BAT trigger. The data comprise 212 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 light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.8 (+1.1, -1.8). At T+122 s  the decay
steepens to an alpha of 5.1 (+/-0.7) before breaking again at T+268 s
to a final decay with index alpha=0.57 (+0.12, -0.18).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.1 (+/-0.3). The
best-fitting absorption column is  1.01 (+0.21, -0.19) x 10^22 cm^-2,
in excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.1 (+0.5, -0.4) and
a best-fitting absorption column of 8.6 (+4.2, -3.4) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.3 x 10^-11 (8.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.6 (+4.2, -3.4) x 10^21 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: 4.1 sigma
Photon index:	     2.1 (+0.5, -0.4)

If the light curve continues to decay with a power-law decay index of
0.57, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.6 x
10^-13 (9.3 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/01257556.

This circular 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 241002A field (Caputo et al., GCN 37662
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 )  with the LCOGT 1-meter Sinistro instrument at the McDonald Observatory, Texas, USA site, on October 2, from 11:23 to 11:55 UT (corresponding to 10.55 to 11.08 hours after the GRB trigger time) with the sdss r and i filters.

We performed a series of 3x300s exposures in i- and r-bands.  We do not detect an uncataloged source within the enhanced Swfit XRT error region (Osborne et al., GCN 37665
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 ) in either band.  This result is consistent with other optical upper limits (Sota et al., GCN 37666
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 ).

The following 5-sigma upper limits are calculated using the PanSTARRS catalog as reference:

r > 22.6
i > 22.2

These magnitudes are not corrected for galactic extinction.

A. Sota, S. Guziy, I. Perez-Garcia, S.-Y. Wu， M. D. Caballero-Garcia, R. Sanchez-Ramirez, A. J. Castro-Tirado (IAA-CSIC) and Y.-D. Hu (INAF-OAB), on behalf of a larger collaboration, report:

Following the detection of GRB 241002A by Swift (Caputo et al. GCNC 37662), we triggered the 1.5m telescope of the Observatiorio Sierra Nevada (OSN) near Granada, Spain. Observations began on Oct 2 at 03:47 UT (~ 2.95 h post burst). No optical afterglow is detected at the coadded I-band image (4 x 600 s) within the enhanced Swift/XRT position (Osborne et al. GCNC 37665) down to 22.0 mag.

We thank the staff at OSN for their excellent support.

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

Using 1737 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 241002A, 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 = 140.94825, +39.83161 which is equivalent
to:

RA (J2000): 09h 23m 47.58s
Dec (J2000): +39d 49' 53.8"

with an uncertainty of 2.9 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.

R. Caputo (GSFC), 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 00:50:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 241002A (trigger=1257556).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 140.955, +39.854 which is 
   RA(J2000) = 09h 23m 49s
   Dec(J2000) = +39d 51' 15"
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 20 sec.  The peak count rate
was ~1900 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 00:52:09.0 UT, 106.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 140.9500, 39.8324 which is equivalent to:
   RA(J2000)  = 09h 23m 48.00s
   Dec(J2000) = +39d 49' 56.6"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). This
location is 78 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 115 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image processing
FAILED because of no aspect solution. Data from the list of sources generated
on-board are not available at this time. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.011.

Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov).
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/)