GRB 240101B

Amit K. Ror, Rahul Gupta, Amar Aryan, and Shashi B. Pandey (ARIES) report:
We observed the field of the GRB 240101B detected by Swift (Cenko et al.
2024, GCN 35449
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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 12:43:55 UT, i.e., ~ 0.68 days 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
(Evans et al., 2024, GCN 35455
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 ). We obtain the following preliminary
3-sigma upper limit in the stacked image:

Date Start_UT T_start-T0 (days) Filter  Exp time (s)  Limiting magnitude
=========================================================
2024-01-02 12:43:55    ~0.68      R     300*12       > 21.7


Our non-detection is consistent with Zheng et al. 2024, GCN 35454
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 ; Kuin et
al. 2024, GCN 35458
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 ; and Peretto 2024, GCN 35463
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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.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),  S. B. Cenko (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC),
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 240101B (trigger #1205744)
(Cenko, et al., GCN Circ. 35449
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 ).  The BAT ground-calculated position is
RA, Dec = 352.147, 51.646 deg which is
   RA(J2000)  =  23h 28m 35.3s
   Dec(J2000) = +51d 38' 46.9"
with an uncertainty of 3.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a single peak from approximately T+0
To T+18 seconds.  There is a possible precursor at T-50 sec.

T90 (15-350 keV) is 43.1 +- 12.6 sec (estimated error including systematics).
The time-averaged spectrum from T+2.18 to T+48.32 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.70 +- 0.26.  The fluence in the 15-150 keV band is 4.6 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+10.28 sec in the 15-150 keV band
is 0.5 +- 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/1205744/BA/

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

We have analysed 6.9 ks of XRT data for GRB 240101B, from 138 s to
126.6 ks after the  BAT trigger. The data comprise 189 s in Windowed
Timing (WT) mode (the first 12 s were taken while Swift was slewing)
with the remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+5.0 ks) can be modelled with a
power-law decay with a decay index of alpha=0.80 (+0.33, -0.29).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.28 (+0.14, -0.13). The
best-fitting absorption column is  6.5 (+/-0.8) x 10^21 cm^-2, in
excess of the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.39 (+0.29, -0.27)
and a best-fitting absorption column of 7.9 (+2.0, -1.8) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.8 x 10^-11 (9.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.9 (+2.0, -1.8) x 10^21 cm^-2
Galactic foreground: 2.9 x 10^21 cm^-2
Excess significance: 4.7 sigma
Photon index:	     2.39 (+0.29, -0.27)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01205744.

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

Ivo Peretto (MarSEC, Marana Space Explorer Center, Marana Di Crespadoro, VI, Italy)

Member of:
UAI/SSV - Unione Astrofili Italiani/Sezione Stelle Variabili, GRB section.
AAVSO (American Association Variable Stars Observers)

In collaboration with: Stefano Lora (MarSEC, Marana Space Explorer Center, Marana di Crespadoro, VI, Italy)

report:
We imaged the field of GRB 240101B detected by SWIFT(trigger=1205744)
with the telescope  14” RC Officine Stellari of MarSEC (Marana Space Explorer Center).

The observations with a series of 120 sec exposures started at 2024-01-01 21:42:43 UT, 77 min. after the GRB trigger, with a Ritchey-Chretien telescope D=360 mm f/ 8.

at the following position:

RA(J2000) = 23h 28m 12s
Dec(J2000) = +51d 38' 43"

Weather conditions were medium with Moon illuminated 70% at 2° from the horizon.

We co-added 30 exposures of 120 sec each.

Start T0+      End T0+       V lim.
 77 min          137 min       20.12

We did not found any optical counterpart in A.R. 23 28 12, DEC. +51 38 43 position and in the error box of the XRT candidate.
ref.: S. B. Cenko (GSFC) et al., GCN Circular 35449
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Magnitudes were estimated with the Gaia DR3  and
are not corrected for galactic dust extinction.

Reference:
https://www.marsec.org/

The message may be cited. 

N. P. M. Kuin (UCL-MSSL) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240101B
110 s after the BAT trigger (Cenko et al., GCN Circ. 35449
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 ).
No optical afterglow consistent with the XRT position
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           134          284          147         >21.1
u_FC               294          543          246         >20.1
white              134         1718          411         >21.8
v                  110         1595          130         >19.2
b                  549         1693          117         >20.5
u                  294         1669          343         >20.2
w1                 675         1644          117         >19.3
m2                 648         1619           97         >21.0
w2                 599         1741          134         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.287 in the direction of the burst
(Schlegel et al. 1998).

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

Using 1510 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 240101B, 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 = 352.09572, +51.63617 which is equivalent
to:

RA (J2000): 23h 28m 22.97s
Dec (J2000): +51d 38' 10.2"

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.

WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on

behalf of the KAIT GRB team:


The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, responded to Swift GRB 240101B (Cenko et al.,

GCN 35449
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 ) starting at 7.38 hours after the burst. A total of

31x60s images were obtained in the clear (roughly R) filters.

We do not detect any optical afterglow candidate within the XRT

position error circle (Cenko et al., GCN 35449
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 ), neither in single

image, nor in the co-add images. The typical limiting magnitude of

our single clear image is about 18.5 mag calibrated to the PS1 catalog.

S. B. Cenko (GSFC), C. Gronwall (PSU), J.D. Gropp (PSU),
H. A. Krimm (NSF), A. Y. Lien (U Tampa) and K. L. Page (U Leicester)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 20:25:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240101B (trigger=1205744).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 352.052, +51.645 which is 
   RA(J2000) = 23h 28m 12s
   Dec(J2000) = +51d 38' 43"
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 ~600 counts/sec (15-350 keV), at ~7 sec after the trigger. 

The XRT began observing the field at 20:27:43.2 UT, 123.9 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 352.0966, 51.6379 which is equivalent to:
   RA(J2000)  = 23h 28m 23.18s
   Dec(J2000) = +51d 38' 16.4"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 102 arcseconds from the BAT onboard position, within the
BAT error circle. 

The initial flux in the 2.5 s image was 2.19e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 134 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
0.286. 

Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/)