GRB 240102A

Amit K. Ror, Rahul Gupta, Amar Aryan, and Shashi B. Pandey (ARIES) report:

We observed the field of GRB 240102A detected by Swift (Gropp et al. 2024,
GCN 35461
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 ) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located
at the Devasthal Observatory of the Aryabhatta Research Institute of
Observational Sciences (ARIES), India. The observations were started on
2024-01-02 at 18:23:56 UT, i.e., ~ 49 minutes after the BAT trigger. We
have taken multiple frames with an exposure time of 300 s in the R filter.
We stacked the images after the alignment. We did not detect any optical
afterglow in our stacked image within the enhanced Swift-XRT error box
(Goad et al., 2024, GCN 35471
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 ). We obtain the following preliminary 3-sigma
upper limit in the stacked image:


Date Start_UT T_start-T0 (minutes) Filter  Exp time (s)  Limiting magnitude
=========================================================
2024-01-02 18:23:56    ~49     R     300*20     > 21.5


Our non-detection is consistent with the observations of Hu et al. 2024,
GCN 35465
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 ; Strausbaugh et al. 2024, GCN 35467
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 ; and Belles et al. 2024, GCN
35475
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 .

The magnitude is not corrected for the Galactic extinction in the direction
of the burst. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalog. This circular may be cited.

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

Using the data set from T-60 to T+243 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 240102A (trigger #1205899)
(Gropp et al., GCN Circ. 35461
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 ).  The BAT ground-calculated position is
RA, Dec = 96.848, -20.011 deg which is
   RA(J2000)  =  06h 27m 23.5s
   Dec(J2000) = -20d 00' 39.0"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve show some weak emission that starts at ~T+8 s
and ends at ~T+140 s. T90 (15-350 keV) is 119.00 +- 30.59 sec
(estimated error including systematics).

The time-averaged spectrum from T+8.00 to T+142.00 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
2.00 +- 0.22.  The fluence in the 15-150 keV band is 8.5 +- 1.3 x 10^-7
erg/cm2.
The 1-sec peak photon flux measured from T+65.00 sec in the 15-150 keV band
is 0.4 +- 0.1 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/1205899/BA/

A. Belles (PSU) and J. D. Gropp (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240102A
113 s after the BAT trigger (Gropp et al., GCN Circ. 35461
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 ).
No optical afterglow consistent with the XRT position
(Goad et al., GCN Circ. 35471
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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           135          285          147         >20.7
u_FC               294          544          246         >19.9
white              135         1196          353         >21.1
v                  113         1246           90         >18.8
b                  550         1172           58         >19.5
u                  294         1314          299         >20.0
w1                 676         1295           78         >19.0
m2                 823         1270           58         >18.7
w2                 600         1221           78         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.176 in the direction of the burst
(Schlegel et al. 1998).

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

Using 4654 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 240102A, 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 = 96.83931, -20.04096 which is equivalent
to:

RA (J2000): 06h 27m 21.43s
Dec (J2000): -20d 02' 27.5"

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.

J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU) and P.A. Evans report
on behalf of the Swift-XRT team:

We have analysed 6.6 ks of XRT data for GRB 240102A, from 113 s to 28.3
ks after the  BAT trigger. The data comprise 91 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 best available XRT position
 (using the promptly downlinked event data, the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec =
96.83800, -20.04076 which is equivalent to:

RA (J2000): 06 27 21.12
Dec(J2000): -20 02 26.7

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The late-time light curve (from T0+4.7 ks) can be modelled with a
power-law decay with a decay index of alpha=0.5 (+/-0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.74 (+0.11, -0.10). The
best-fitting absorption column is  3.3 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 2.3 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.3 x 10^-11 (5.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     3.3 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 2.3 x 10^21 cm^-2
Excess significance: 3.1 sigma
Photon index:	     1.74 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
0.5, the count rate at T+24 hours will be 9.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x
10^-13 (5.6 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/01205899.

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 240102A (Gropp et al., GCN 35461
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 ) field with the LCOGT 1-meter Sinistro instrument at the Teide Observatory, Tenerife site, on January 2, from 23:34 to January 3 00:07 UT (corresponding to 6.00 to 6.55 hours after the GRB trigger time) with the sdss r and i filters.

We performed a series of 3x300s exposures in each band.  We do not detect an uncatalogued source within the XRT error region in either band.  This result is consistent with other optical upper limits (Hu et al., GCN 35465
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 ).

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

r > 22.9
i > 22.3

These magnitudes are not corrected for galactic extinction.

Y.-D. Hu, E. Fernandez-Garcia, I. Perez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy, S.-Y. Wu and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), 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 240102A by Swift (Gropp et al. GCNC 35461), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) observed the GRB location starting on Jan. 2, 18:41 UT (~ 1.1 hours after trigger) in different optical bands. No new optical source is detected on the co-added images (2 x 60 s, clear-filter) within the Swift/XRT error box down to 20.2 mag. Further imaging is ongoing.

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

J.D. Gropp (PSU), S. Dichiara (PSU), J. A. Kennea (PSU),
K. L. Page (U Leicester) and M. A. Williams (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 17:34:55 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240102A (trigger=1205899). Swift slewed immediately to the 
burst. The BAT on-board calculated location is 
RA, Dec 96.846, -20.024 which is 
   RA(J2000) = 06h 27m 23.0s
   Dec(J2000) = -20d 01' 26.4"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). We currently have no information regarding the
BAT light-curve. 

The XRT began observing the field at 17:37:00.6 UT, 125 seconds
after the BAT trigger. Using promptly downlinked data we find an
uncatalogued X-ray source with an enhanced position: RA, Dec 96.83800,
-20.04076 which is equivalent to:
   RA(J2000)  = 06h 27m 21.12s
   Dec(J2000) = -20d 02' 26.7"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This 
position is 66 arc-seconds from the BAT localization. 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 consistent with the Galactic value of 2.34
x 10^21 cm^-2 (Willingale et al. 2013). 

No afterglow is detected in the initial UVOT data products. 

Burst Advocate for this burst is J.D. Gropp (jdg44 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/)