Gamma-ray Burst 240418A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:25:00 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1222885,   Seg_Num: 0
GRB_RA:          239.322d {+15h 57m 17s} (J2000),
                 239.582d {+15h 58m 20s} (current),
                 238.786d {+15h 55m 09s} (1950)
GRB_DEC:         +23.607d {+23d 36' 26"} (J2000),
                 +23.539d {+23d 32' 19"} (current),
                 +23.750d {+23d 45' 02"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       26027 [cnts]    Image_Peak=506 [image_cnts]
TRIGGER_DUR:     8.192 [sec] 
TRIGGER_INDEX:   453     E_range: 15-50 keV
BKG_INTEN:       186097 [cnts]
BKG_TIME:        73358.70 SOD {20:22:38.70} UT
BKG_DUR:         64 [sec]
GRB_DATE:        20418 TJD;   109 DOY;   24/04/18
GRB_TIME:        73448.17 SOD {20:24:08.17} UT
GRB_PHI:         -109.52 [deg]
GRB_THETA:        20.38 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.64 [sigma]
IMAGE_SIGNIF:    7.96 [sigma]
MERIT_PARAMS:     +1  +0  +0  +3  +1  -2  +0  +0 +68  +0 
SUN_POSTN:        27.23d {+01h 48m 56s}  +11.22d {+11d 13' 10"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.35d {+10h 25m 25s}  +13.76d {+13d 45' 41"}
MOON_DIST:        78.46 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      230.33, 42.91 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 139.75,15.53 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:26:16 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.326d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.610d {+23d 36' 35"} (J2000)
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73570.42 SOD {20:26:10.42} UT,   122.2 [sec] since BAT Trigger Time
COUNTS:          2    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        1    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:28:00 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1222885,   Seg_Num: 0
GRB_RA:          239.322d {+15h 57m 17s} (J2000),
                 239.582d {+15h 58m 20s} (current),
                 238.786d {+15h 55m 09s} (1950)
GRB_DEC:         +23.607d {+23d 36' 26"} (J2000),
                 +23.539d {+23d 32' 19"} (current),
                 +23.750d {+23d 45' 02"} (1950)
GRB_DATE:        20418 TJD;   109 DOY;   24/04/18
GRB_TIME:        73448.17 SOD {20:24:08.17} UT
TRIGGER_INDEX:   453
GRB_PHI:         -109.52 [deg]
GRB_THETA:        20.38 [deg]
DELTA_TIME:      12.00 [sec]
TRIGGER_DUR:     8.192 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.64 [sigma]
IMAGE_SIGNIF:    7.96 [sigma]
LC_URL:          sw01222885000msb.lc
SUN_POSTN:        27.23d {+01h 48m 56s}  +11.22d {+11d 13' 12"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.38d {+10h 25m 30s}  +13.75d {+13d 45' 03"}
MOON_DIST:        78.45 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      230.33, 42.91 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 139.75,15.53 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:29:00 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.326d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.610d {+23d 36' 36"} (J2000)
POINT_ROLL:      45.550d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73573.93 SOD {20:26:13.93} UT,   125.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.490
N_STARS:         22
X_OFFSET:        457 [pixels]
Y_OFFSET:        558 [pixels]
X_MAX:           1416 [pixels]
Y_MAX:           1517 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    7
SL_URL:          sw01222885000msufc0125.fits
SUN_POSTN:        27.23d {+01h 48m 56s}  +11.22d {+11d 13' 13"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.38d {+10h 25m 32s}  +13.75d {+13d 44' 50"}
MOON_DIST:        78.45 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:29:14 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.326d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.610d {+23d 36' 36"} (J2000)
POINT_ROLL:      45.550d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73573.93 SOD {20:26:13.93} UT,   125.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.490
N_STARS:         22
X_OFFSET:        457 [pixels]
Y_OFFSET:        558 [pixels]
X_MAX:           1416 [pixels]
Y_MAX:           1517 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    7
SL_URL:          sw01222885000msufc0125.fits
SUN_POSTN:        27.24d {+01h 48m 56s}  +11.22d {+11d 13' 13"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.38d {+10h 25m 32s}  +13.75d {+13d 44' 47"}
MOON_DIST:        78.44 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [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 18 Apr 24 20:30:28 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.326d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.610d {+23d 36' 36"} (J2000)
ROLL:            45.550d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73573.93 SOD {20:26:13.93} UT,   125.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     735164807
X_OFFSET:        776 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       936
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01222885000msuni0159.fits
SUN_POSTN:        27.24d {+01h 48m 57s}  +11.22d {+11d 13' 14"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.39d {+10h 25m 35s}  +13.74d {+13d 44' 32"}
MOON_DIST:        78.44 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [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 18 Apr 24 20:30:43 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.326d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.610d {+23d 36' 36"} (J2000)
ROLL:            45.550d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73573.93 SOD {20:26:13.93} UT,   125.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     735164807
X_OFFSET:        776 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       936
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01222885000msuni0159.fits
SUN_POSTN:        27.24d {+01h 48m 57s}  +11.22d {+11d 13' 15"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.40d {+10h 25m 35s}  +13.74d {+13d 44' 28"}
MOON_DIST:        78.44 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [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 18 Apr 24 20:31:08 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     1222885,   Seg_Num: 0
GRB_RA:          239.3722d {+15h 57m 29.32s} (J2000),
                 239.6327d {+15h 58m 31.84s} (current),
                 238.8364d {+15h 55m 20.73s} (1950)
GRB_DEC:         +23.5957d {+23d 35' 44.5"} (J2000),
                 +23.5271d {+23d 31' 37.3"} (current),
                 +23.7387d {+23d 44' 19.1"} (1950)
GRB_ERROR:       6.5 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73577.00 SOD {20:26:17.00} UT,   128.8 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        27.24d {+01h 48m 57s}  +11.22d {+11d 13' 15"}
SUN_DIST:        132.98 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.40d {+10h 25m 36s}  +13.74d {+13d 44' 23"}
MOON_DIST:        78.48 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.06 [deg] galactic lon,lat of the burst
ECL_COORDS:      230.40, 42.92 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN Circular #36162
M. H. Siegel (PSU), S. Dichiara (PSU), J.D. Gropp (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 20:24:08 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 240418A (trigger=1222885). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 239.322, +23.607 which is
```
   RA(J2000) = 15h 57m 17s
   Dec(J2000) = +23d 36' 26"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of at least 20 sec. The peak count rate was ~700 counts/sec (15-350 keV), at ~7 sec after the trigger.
The XRT began observing the field at 20:26:10.4 UT, 122.2 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 239.37228, 23.59581 which is equivalent to:
```
   RA(J2000)  = 15h 57m 29.35s
   Dec(J2000) = +23d 35' 44.9"
```
with an uncertainty of 6.5 arcseconds (radius, 90% containment). This location is 170 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. We cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 5.26 x 10^20 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 125 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 0.058.
Burst Advocate for this burst is M. H. Siegel (siegel AT swift.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/)
GCN Circular #36163
V. Lipunov, V.Kornilov, E. Gorbovskoy, K. Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, V.Senik, D. Vlasenko, G.Antipov, D.Zimnukhov, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik, A. Sosnovskij (Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gress, N.M. Budnev, O.Ershova (Irkutsk State University, API),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich (Blagoveschensk Educational State University)
MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB240418.85 (trigger No 1222885,15h 57m 17.26s , +23d 36m 26.3s, R=0.05) errorbox 18 sec after notice time and 78 sec after trigger time at 2024-04-18 20:25:26 UT, with upper limit up to 17.8 mag. The observations began at zenith distance = 41 deg. The sun altitude is -34.9 deg.
The galactic latitude b = 48 deg., longitude l = 39 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2426906
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      88 |   MASTER-Kislovodsk |  P| |    20 | 17.0 |        
      98 |   MASTER-Kislovodsk |  P| |    40 | 17.3 |  Coadd 
     171 |   MASTER-Kislovodsk |  P| |    10 | 16.5 |        
     202 |   MASTER-Kislovodsk |  P| |    10 | 16.5 |        
     236 |   MASTER-Kislovodsk |  P| |    20 | 17.0 |        
     275 |   MASTER-Kislovodsk |  P| |    30 | 17.3 |        
     331 |   MASTER-Kislovodsk |  P| |    40 | 17.5 |        
     395 |   MASTER-Kislovodsk |  P| |    50 | 17.5 |        
     470 |   MASTER-Kislovodsk |  P| |    60 | 17.8 |        
```
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:51:08 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.325d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.608d {+23d 36' 31"} (J2000)
POINT_ROLL:      45.549d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73731.75 SOD {20:28:51.75} UT,   283.6 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.865
N_STARS:         47
X_OFFSET:        217 [pixels]
Y_OFFSET:        318 [pixels]
X_MAX:           1656 [pixels]
Y_MAX:           1757 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw01222885000msufc0283.fits
SUN_POSTN:        27.25d {+01h 49m 00s}  +11.23d {+11d 13' 32"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.55d {+10h 26m 12s}  +13.67d {+13d 40' 10"}
MOON_DIST:        78.32 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 18 Apr 24 20:51:24 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.325d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.608d {+23d 36' 31"} (J2000)
POINT_ROLL:      45.549d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73731.75 SOD {20:28:51.75} UT,   283.6 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.865
N_STARS:         47
X_OFFSET:        217 [pixels]
Y_OFFSET:        318 [pixels]
X_MAX:           1656 [pixels]
Y_MAX:           1757 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw01222885000msufc0283.fits
SUN_POSTN:        27.25d {+01h 49m 00s}  +11.23d {+11d 13' 32"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.55d {+10h 26m 13s}  +13.67d {+13d 40' 07"}
MOON_DIST:        78.32 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [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 18 Apr 24 20:52:30 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.325d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.608d {+23d 36' 31"} (J2000)
ROLL:            45.549d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73731.75 SOD {20:28:51.75} UT,   283.6 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     735164965
X_OFFSET:        776 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       936
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01222885000msuni0317.fits
SUN_POSTN:        27.25d {+01h 49m 00s}  +11.23d {+11d 13' 33"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.56d {+10h 26m 15s}  +13.66d {+13d 39' 53"}
MOON_DIST:        78.31 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [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 18 Apr 24 20:52:40 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     1222885,   Seg_Num: 0
POINT_RA:        239.325d {+15h 57m 18s} (J2000)
POINT_DEC:       +23.608d {+23d 36' 31"} (J2000)
ROLL:            45.549d
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73731.75 SOD {20:28:51.75} UT,   283.6 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     735164965
X_OFFSET:        776 [pixels]
Y_OFFSET:        877 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       936
Y_GRB_POS:       1037
BINNING_INDEX:   1
IM_URL:          sw01222885000msuni0317.fits
SUN_POSTN:        27.25d {+01h 49m 00s}  +11.23d {+11d 13' 34"}
SUN_DIST:        133.00 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.56d {+10h 26m 15s}  +13.66d {+13d 39' 51"}
MOON_DIST:        78.31 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.10 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      230.33, 42.92 [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 18 Apr 24 20:53:56 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     1222885,   Seg_Num: 0
GRB_RA:          239.3734d {+15h 57m 29.61s} (J2000),
                 239.6339d {+15h 58m 32.13s} (current),
                 238.8376d {+15h 55m 21.02s} (1950)
GRB_DEC:         +23.5960d {+23d 35' 45.6"} (J2000),
                 +23.5274d {+23d 31' 38.4"} (current),
                 +23.7389d {+23d 44' 20.2"} (1950)
GRB_ERROR:       1.9 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  20418 TJD;   109 DOY;   24/04/18
IMG_START_TIME:  73577.00 SOD {20:26:17.00} UT,   128.8 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:        27.25d {+01h 49m 00s}  +11.23d {+11d 13' 35"}
SUN_DIST:        132.98 [deg]   Sun_angle= 9.8 [hr] (West of Sun)
MOON_POSTN:      156.57d {+10h 26m 18s}  +13.66d {+13d 39' 35"}
MOON_DIST:        78.35 [deg]
MOON_ILLUM:      78 [%]
GAL_COORDS:       38.83, 48.05 [deg] galactic lon,lat of the burst
ECL_COORDS:      230.40, 42.92 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        This position was enhanced using UVOT field astrometry.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.

GCN Circular #36165
Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International Astronomical Center in Abu Dhabi, UAE) and Nidhal Guessoum (American University of Sharjah, UAE), report:
We observed the field of GRB 240418A (Siegel et al., GCN 36162) with our 0.36m f/7.7 robotic telescope.
We obtained 13x180s images using Ic filter on 18 April 2024, starting at 21:06UT, 42 minutes after the GRB trigger.
We did not detect any credible afterglow candidate within the updated XRT position (Trigger number 1222885), down to the magnitude = 20.0 for the stacked images.
The magnitude was estimated using the Atlas catalogue as a reference, and it is not corrected for galactic extinction.
GCN Circular #36166
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 463 s of XRT Photon Counting mode data and 1 UVOT images for GRB 240418A, 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 = 239.37529, +23.59582 which is equivalent to:
```
RA (J2000): 15h 57m 30.07s
Dec (J2000): +23d 35' 45.0"
```
with an uncertainty of 3.6 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 #36167
D. B. Malesani (DAWN/NBI and Radboud Univ.) and A. C. Casasbuenas (Univ. La Laguna and NOT) report on behalf of a larger collaboration.
We have observed the field of GRB 240418A (Siegel et al., GCN 36162) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out under poor sky transparency, and consisted of images in the SDSS r and z bands (mean epochs 3.19 and 3.37 hr after trigger, respectively).
Within or close to the localization error circle of the X-ray afterglow (Evans et al., GCN 36166), we detect no object in either filter, down to limiting AB magnitudes r > 22, z > 20.4, calibrated against nearby stars from the Pan-STARRS catalog.
GCN Circular #36168
A. Pozanenko (IKI), I. Reva (FAI), N.Pankov (HSE), S. Belkin (IKI) report on behalf of GRB-IKI-FuN:
We have observed the field of GRB 240418A (Siegel et al., GCN 36162) with Zeiss-1000 telescope of Tien Shan Astronomical Observatory starting on 2024-04-18 (UT) 21:47:25.
We do not detect any object within Enhanced Swift-XRT position (Evans et al., GCN 36166) up to R=21.6. Preliminary photometry of the field in a stacked image is following.
```
Date       UT start t-T0    Filter  Exp.   OT  Err. UL(3 sigma)
                     (mid, days)     (s)
2024-04-18 21:47:25  -      R       21*120 n/d n/d  21.6
```
The photometry is based on nearby USNO-B1.0 stars. Non detection of the OT is in agreement with the observations (Lipunov et al., GCN 36163; Odeh et al., GCN 36165; Malesani et al., GCN 36167).
GCN Circular #36177
Tian-Rui Sun, Jin-Jun Geng, Jian Chen, Yan-Long Hua and Lei Hu report on behalf of the YAHPT team:
Following the detection of GRB 240418A by SWIFT (Siegel et al., GCN 36162; Evans et al., GCN 36166), we use the Yaoan High Precision Telescope at Yaoan Astronomy Observation Station (Yunnan province, China) to search and follow up its afterglow at XRT position.
We observed the target position with 180s exposure in V-band starting from 2024-04-18T20:32:14.600 about 486.6 seconds after the burst. We took 25 images with total exposure time of 4500 seconds from 20:32:14 to 21:48:29.4. We did not detect any object up to V = 22.2 with the stacked images within the Enhanced Swift XRT position This non-detection results of the gamma-ray bursts is in agreement with the previous circulars (Lipunov et al., GCN 36163; Odeh et al., GCN 36165; Malesani et al., GCN 36167; Pozanenko et al. GCN 36168;).
We used the UCAC4 catalog (Vmag) as the magnitude reference for calibration.
GCN Circular #36181
A. Tohuvavohu (U. Toronto), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), D.N. Burrows (PSU), J. D. Gropp (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.1 ks of XRT data for GRB 240418A, from 107 s to 44.9 ks after the BAT trigger. The data comprise 7 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=2.9 (+0.3, -0.4).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+0.6, -0.4). The best-fitting absorption column is consistent with the Galactic value of 5.3 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 (3.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     5 (+/-12) x 10^20 cm^-2
Galactic foreground: 5.3 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.0 (+0.6, -0.4)
```
If the light curve continues to decay with a power-law decay index of 2.9, the count rate at T+24 hours will be 1.2 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x 10^-19 (4.1 x 10^-19) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01222885.
This circular is an official product of the Swift-XRT team.
GCN Circular #36184
S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.), A. A. Breeveld (UCL-MSSL), N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 240418A 126 s after the BAT trigger (Siegel et al., GCN Circ. 36162). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 36166) 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           126          276          147         >20.6
u_FC               284          533          246         >19.4
white              126         5282          347         >21.1
v                 4072         4272          197         >19.3
b                  539         5093          216         >20.2
u                  284         4888          442         >19.9
w1                4482         4682          197         >19.7
m2                4276         4476          197         >19.5
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.057 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #36199
Viraj Karambelkar (Caltech), Kaew Tinyanont (NARIT), Sam Rose (Caltech), Tomas Ahumada (Caltech), Robert Stein (Caltech), Nathan Lourie (MIT), Danielle Frostig (MIT), Geoffrey Mo (MIT), Robert Simcoe (MIT), Mansi Kasliwal (Caltech)
We observed the field of the long GRB 240418A (GCN 36162; GCN 36166; GCN 36177; GCN 36184) in the near-infrared K-prime band with the NIRES acquisition camera on the Keck II telescope starting at UTC 2024-04-19T09:56:00 (~14 hours since trigger). The observations lasted for 300 sec. (25 sec, 12 coadds).
We find an uncataloged source at RA = 239.3744, Dec = 23.5961 that is 3.1 arcsec from the centroid of the GRB position and within its 3.6 arcsec localization (from GCN 36166). This source has m_Kp ~ 20.9 +/- 0.1 mag (AB). There is no source at this location in an archival Ks-band image from the UKIRT hemisphere survey (Lucas et al. 2008), and a deep optical image from the Legacy Survey. However, we note that our NIRES observations are more sensitive than the archival UKIRT observations, so it is possible that the NIRES source is an unrelated background source.
We also observed this source in the J-band with the WINTER camera on the Palomar 40-inch telescope (Lourie et al. 2021) on 2024-04-19T09:00:14 and did not detect it to a limiting magnitude of m_J ~ 19 mag.
Further observations are encouraged.
GCN Circular #36254
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), T. Parsotan (GSFC), T. Sakamoto (AGU), M. H. Siegel (PSU) (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 240418A (trigger #1222885) (Siegel, et al., GCN Circ. 36162). The BAT ground-calculated position is RA, Dec = 239.342, 23.632 deg which is
```
   RA(J2000)  =  15h 57m 22.0s
   Dec(J2000) = +23d 37' 54.4"
```
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 79%.
The mask-weighted light curve shows a single, dim pulse peaking at T0+5 s. The T90 (15-350 keV) is 12.00 +- 3.61 sec (estimated error including systematics).
The time-averaged spectrum from T-0.47 to T+12.53 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.99 +- 0.31. The fluence in the 15-150 keV band is 2.3 +- 0.5 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+4.53 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/1222885

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Jochen Greiner, last update: 18-Aug-2025 [Disclaimer]