Gamma-ray Burst 240411B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:39:15 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.569d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
POINT_ROLL:      76.892d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56155.41 SOD {15:35:55.41} UT,   1320.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.304
N_STARS:         35
X_OFFSET:        442 [pixels]
Y_OFFSET:        612 [pixels]
X_MAX:           1401 [pixels]
Y_MAX:           1571 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    6
SL_URL:          sw01221183000msufc260520.fits
SUN_POSTN:        20.57d {+01h 22m 16s}   +8.66d {+08d 39' 29"}
SUN_DIST:        148.19 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.78d {+03h 55m 07s}  +24.19d {+24d 11' 41"}
MOON_DIST:       157.05 [deg]
MOON_ILLUM:      11 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:39:32 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.569d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
POINT_ROLL:      76.892d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56155.41 SOD {15:35:55.41} UT,   1320.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.304
N_STARS:         35
X_OFFSET:        442 [pixels]
Y_OFFSET:        612 [pixels]
X_MAX:           1401 [pixels]
Y_MAX:           1571 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    6
SL_URL:          sw01221183000msufc260520.fits
SUN_POSTN:        20.57d {+01h 22m 16s}   +8.66d {+08d 39' 30"}
SUN_DIST:        148.19 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.78d {+03h 55m 08s}  +24.20d {+24d 11' 44"}
MOON_DIST:       157.05 [deg]
MOON_ILLUM:      11 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:40:38 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.569d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
ROLL:            76.892d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56155.41 SOD {15:35:55.41} UT,   1320.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     734542588
X_OFFSET:        761 [pixels]
Y_OFFSET:        931 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       921
Y_GRB_POS:       1091
BINNING_INDEX:   1
IM_URL:          sw01221183000msuni260554.fits
SUN_POSTN:        20.57d {+01h 22m 16s}   +8.66d {+08d 39' 31"}
SUN_DIST:        148.19 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.79d {+03h 55m 11s}  +24.20d {+24d 11' 54"}
MOON_DIST:       157.04 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:40:49 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.569d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
ROLL:            76.892d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56155.41 SOD {15:35:55.41} UT,   1320.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     734542588
X_OFFSET:        761 [pixels]
Y_OFFSET:        931 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       921
Y_GRB_POS:       1091
BINNING_INDEX:   1
IM_URL:          sw01221183000msuni260554.fits
SUN_POSTN:        20.57d {+01h 22m 16s}   +8.66d {+08d 39' 31"}
SUN_DIST:        148.19 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.80d {+03h 55m 11s}  +24.20d {+24d 11' 56"}
MOON_DIST:       157.04 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:46:55 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.568d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
POINT_ROLL:      76.891d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56313.57 SOD {15:38:33.57} UT,   1479.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.580
N_STARS:         53
X_OFFSET:        202 [pixels]
Y_OFFSET:        372 [pixels]
X_MAX:           1641 [pixels]
Y_MAX:           1811 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01221183000msufc260678.fits
SUN_POSTN:        20.57d {+01h 22m 17s}   +8.66d {+08d 39' 36"}
SUN_DIST:        148.19 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.86d {+03h 55m 26s}  +24.21d {+24d 12' 53"}
MOON_DIST:       157.01 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:47:03 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.568d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
POINT_ROLL:      76.891d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56313.57 SOD {15:38:33.57} UT,   1479.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.580
N_STARS:         53
X_OFFSET:        202 [pixels]
Y_OFFSET:        372 [pixels]
X_MAX:           1641 [pixels]
Y_MAX:           1811 [pixels]
DET_THRESH:      7
PHOTO_THRESH:    3
SL_URL:          sw01221183000msufc260678.fits
SUN_POSTN:        20.57d {+01h 22m 17s}   +8.66d {+08d 39' 37"}
SUN_DIST:        148.19 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.86d {+03h 55m 27s}  +24.22d {+24d 12' 55"}
MOON_DIST:       157.00 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:48:17 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.568d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
ROLL:            76.891d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56313.57 SOD {15:38:33.57} UT,   1479.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     734542746
X_OFFSET:        761 [pixels]
Y_OFFSET:        931 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       921
Y_GRB_POS:       1091
BINNING_INDEX:   1
IM_URL:          sw01221183000msuni260712.fits
SUN_POSTN:        20.57d {+01h 22m 18s}   +8.66d {+08d 39' 38"}
SUN_DIST:        148.20 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.87d {+03h 55m 30s}  +24.22d {+24d 13' 06"}
MOON_DIST:       157.00 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 11 Apr 24 15:48:31 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1221183,   Seg_Num: 0
POINT_RA:        231.568d {+15h 26m 16s} (J2000)
POINT_DEC:        -2.147d {-02d 08' 48"} (J2000)
ROLL:            76.891d
IMG_START_DATE:  20411 TJD;   102 DOY;   24/04/11
IMG_START_TIME:  56313.57 SOD {15:38:33.57} UT,   1479.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     734542746
X_OFFSET:        761 [pixels]
Y_OFFSET:        931 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       921
Y_GRB_POS:       1091
BINNING_INDEX:   1
IM_URL:          sw01221183000msuni260712.fits
SUN_POSTN:        20.57d {+01h 22m 18s}   +8.66d {+08d 39' 38"}
SUN_DIST:        148.20 [deg]   Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN:       58.88d {+03h 55m 30s}  +24.22d {+24d 13' 08"}
MOON_DIST:       157.00 [deg]
MOON_ILLUM:      12 [%]
GAL_COORDS:        1.04, 42.60 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      229.73, 16.08 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN Circular #36063
T. M. Parsotan (GSFC), S. Dichiara (PSU), R. A. J. Eyles-Ferris (U Leicester), C. Gronwall (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB), M. H. Siegel (PSU) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 15:32:54 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 240411B (trigger=1221183). Swift slewed immediately to the burst. No further BAT information is available at this time due to a telemetry gap. Further information will be available after the next telemetry pass over a ground station.
The XRT began observing the field at approximately 15:35:54 UT, around 180 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 231.54236, -2.14609 which is equivalent to:
```
   RA(J2000)  = 15h 26m 10.17s
   Dec(J2000) = -02d 08' 45.9"
```
with an uncertainty of 1.9 arcseconds (radius, 90% containment). 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 1.11 x 10^21 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 190 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 none of the XRT error circle. 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 0.138.
Burst Advocate for this burst is T. M. Parsotan (parsotat AT umbc.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/)
GCN Circular #36064
L. Izzo (INAF-OACn & DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud Univ.), M. Della Valle and R. Martone (INAF-OACn) report:
We observed the field of GRB 240411B (Parsotan et al., GCN 36063) with the Sinistro instrument mounted on the 1-m telescope of the LCO network, located at Siding Spring Observatory, Australia. Observations started on April 11 at 17:02:54 UT (1.5 hours after the GRB trigger). We obtained a series of 3x180 s images in the r filter.
In the stacked image, we detect a new source within the XRT position, at the coordinates:
```
RA(J2000) = 15:26:10.17
Dec(J2000) = -02:08:46.8
```
We measure a preliminary magnitude of r = 21.66 +- 0.22 (AB), calibrated against nearby stars from the Pan-STARRS catalog.
This source is not visible in the Pan-STARRS catalog and is thus very likely the optical afterglow of GRB 240411B.
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 730890.
GCN Circular #36065
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team.
Using 373 s of XRT Photon Counting mode data and 1 UVOT images for GRB 240411B, 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 = 231.54213, -2.14640 which is equivalent to:
```
RA (J2000): 15h 26m 10.11s
Dec (J2000): -02d 08' 47.0"
```
with an uncertainty of 2.6 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.
GCN Circular #36067
B. Schneider (MIT), C. Adami (LAM/Pytheas/AMU), E. Le Floc=E2=80=99h (CEA Paris-Saclay), A. Saccardi (GEPI/Obs. de Paris) report on behalf of a larger collaboration:
We observed the field of the GRB 240411B (Parsotan et al., GCN 36063; Goad et al., GCN 36065) and its afterglow candidate (Izzo et al., GCN 36064) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. A total of 10 exposures (8x600s + 2x720s) were obtained in the r-band at 00:44:01.5 UT on 2024-04-12 (~9.2h after the trigger). In the combined frame, we detect a source consistent with the optical afterglow reported by Izzo et al. (GCN 36064).
The preliminary magnitude derived for that source is
r = 23.1 +/- 0.3 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction.
We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Jean-Pierre Troncin for the MISTRAL observations.
GCN Circular #36069
Amit K. Ror, Anshika Gupta, Rahul Gupta, Amar Aryan, Saurabh, and Shashi B. Pandey (ARIES) report:
We observed the field of GRB 240411B detected by Swift (Parsotan et al., 2024 GCN 36063) 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 2024-04-11 at 19:06:28 UT, i.e., ~ 3.56 hours 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 clearly detected an optical afterglow (Izzo et al., 2024, GCN 36064; Schneider et al., 2024, GCN 36067) in our final stacked image within the error box of enhanced Swift-XRT observation (Goad et al., 2024, GCN 36065). The estimated preliminary magnitude is as follows:
Date Start_UT T_start-T0 (hours) Filter Exp time (s) Limiting magnitude
=======================================================
2024-04-11 19:06:28 UT 3.56 R 300*15 22.34 +/- 0.11
The detection of the afterglow is consistent with the observations of Izzo et al. 2024, GCN 36064, and Schneider et al. 2024, GCN 36067.
The given magnitude value is not corrected for the Galactic and host extinctions in the direction of the GRB afterglow. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalog. This circular may be cited.
GCN Circular #36071
P. D'Avanzo (INAF-OAB), J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 3.9 ks of XRT data for GRB 240411B, from 160 s to 74.6 ks after the BAT trigger. The data comprise 10 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 power-law decay with a decay index of alpha=0.66 (+0.12, -0.11).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.13 (+0.38, -0.20). The best-fitting absorption column is consistent with the Galactic value of 1.1 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 3.2 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     1.1 (+/-1.0) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.13 (+0.38, -0.20)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01221183.
This circular is an official product of the Swift-XRT team.
GCN Circular #36072
A. Y. Lien (U Tampa), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 240411B (trigger #1221183) (Parsotan, et al., GCN Circ. 36063). The BAT ground-calculated position is RA, Dec = 231.562, -2.172 deg which is
```
   RA(J2000)  =  15h 26m 14.8s 
   Dec(J2000) = -02d 10' 20.9" 
```
with an uncertainty of 3.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 53%.
The mask-weighted light curve shows two spikes separated by an interval of ~15 seconds. The estimated T90 (15-350 keV) is 33.26 +- 1.49 sec (estimated error including systematics).
The time-averaged spectrum from T-0.37 to T+33.92 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.69 +- 0.41. The fluence in the 15-150 keV band is 4.9 +- 1.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+32.87 sec in the 15-150 keV band is 0.9 +- 0.3 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/1221183
GCN Circular #36074
A. de Ugarte Postigo (CNRS, OCA, LAM), N. R. Tanvir (U. Leicester), J. F. Agui Fernandez (CAHA), A. Martin-Carrillo (UCD), C. C. Thoene (ASU-CAS), L. Izzo (INAF-OACn & DARK/NBI), J. P. U. Fynbo (DAWN/NBI), G. Lombardi (GRANTECAN), S. Geier (GRANTECAN) report:
We observed the field of GRB 240411B (Parsotan et al. GCN 36063) with HiPERCAM on the 10.4m GTC, at the Roque de Los Muchachos Observatory (Spain). We simultaneously obtained 20x60s exposure in each of the u, g, r, i, and z filters. The transparency was bad due to strong calima and the seeing was also poor. The afterglow (Izzo et al. 36064; Goad et al. GCN 36065; Schneider et al. GCN 36067; Ror et al. GCN 36069) is well detected in g, r, i and z, but not in u-band, where the limit is shallow. Observations had a mean time of 0.4256 days after the burst. We measure an r-band magnitude (AB) of r = 23.21+/- 0.08 mag as compared with field star magnitudes from the SDSS.
GCN Circular #36077
A. Aryan, T.-W. Chen, C.-S. Lin, W.-J. Hou, A. Sankar.K, Y.-C. Pan (all NCUIA), S. Yang (HNAS), M.-H. Lee, C.-H. Lai, H.-Y. Hsiao, C.-C. Ngeow, H.-C. Lin, J.-K. Guo (all NCUIA), S. Srivastav (Oxford), M. Fulton, T. Moore, C. Angus, and A. Aamer (all QUB) report:
We observed the field of GRB 240411B (Parsotan et al., GCN 36063; Goad et al., GCN 36065; D'Avanzo et al., GCN 36071; Lien et al., GCN 36072) using the Lulin One-meter Telescope (LOT) at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen et al., AstroNote 2021-92). The optical afterglow candidate of GRB 240411B was identified (Izzo et al., GCN 36064) and followed with several instruments (Schneider et al., GCN 36067; Ror et al., GCN 36069).
The first LOT epoch of observations started at 16:45 UT on 11 of April 2024. We followed standard IRAF (Tody D., 1993, ASPC, 52, 173) procedure to reduce the images. Further, PSF photometry was performed using DAOPHOT II (Stetson P. B., 1987, PASP, 99, 191) software. The details of the observations and the preliminary magnitudes (in the AB system) of the afterglow are as follows:
```
Telescope | Filter | MJD | t-t0 | Exposure | Magnitude | avg. Seeing | med. Airmass
LOT | r | 60411.698 | 1.25 hrs | 300 sec * 1 | 20.92 +/- 0.12 | 1".16 | 1.17
LOT | i | 60411.715 | 1.65 hrs | 300 sec * 1 | 20.28 +/- 0.15 | 1".0 | 1.13
```
The presented magnitudes are calibrated using the nearby stars from the PanSTARRS catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.14 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
GCN Circular #36078
N. Pankov (HSE,IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), S. Belkin (IKI) report on behalf of IKI GRB FuN:
We observed the field of GRB 240411B (Parsotan et al., GCN 36063; Goad et al., GCN 36065; D'Avanzo et al., GCN 36071; Lien et al., GCN 36072) with ZTSh 2.6m telescope of CrAO observatory starting on 2024-04-11 (UT) 21:18:47. We detect optical afterglow (Izzo et al. GCN 36064; Schneider et al. GCN 36067; Ror et al. GCN 36069; Ugarte Postigo et al. GCN 36074; Aryan et al. GCN 36077).
Preliminary photometry of the afterglow in a combined image is following
Date UT start t-T0 Filter Exp. OT err UL(3sigma) (mid, days) (s) 2024-04-11 21:18:47 0.283257 R 60*120 22.40 0.25 22.8
The photometry is based on several nearby USNO-B1.0 (R2) stars USNO-B1.0

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Jochen Greiner, last update: 13-Apr-2024 [Disclaimer]