| Summary table |
|---|
| Variable |
Value |
Source |
| T0 |
20:24:08 UTC |
GCN_circulars,Swift Det |
| ra |
239.3752° |
Swift |
| decl |
23.5958° |
Swift |
| pos_error |
4.66e-04° |
Swift |
| GBM_located |
False |
|
| mjd |
60418.85009259259 |
GCN_circulars,Swift Det |
| IPN table |
|---|
| GRB_name |
GRB240418A |
| ra |
239.3208° |
| decl |
23.6000° |
| pos_error |
5.00e-02° |
| Swift table |
|---|
| GRB_name |
GRB240418A |
| t_trigger |
20:24:08 UTC |
| ra |
239.3752° |
| decl |
23.5958° |
| pos_error |
4.66e-04° |
| GCN 36162 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36162 |
| Detection_method |
Swift Det |
| t_trigger |
20:24:08 UTC |
| ra |
239.3220° |
| decl |
23.6070° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36162
SUBJECT: GRB 240418A: Swift detection of a burst
DATE: 24/04/18 20:36:44 GMT
FROM: Simone Dichiara at Pennsylvania State University
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 36165 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36165 |
| Detection_method |
Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36165
SUBJECT: GRB 240418A: AKO Upper Limit
DATE: 24/04/18 21:54:58 GMT
FROM: Mohammad Odeh at Al Khatim Observatory M44
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 36166 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36166 |
| Detection_method |
Swift-XRT Det |
| ra |
239.3753° |
| decl |
23.5958° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36166
SUBJECT: GRB 240418A: Enhanced Swift-XRT position
DATE: 24/04/19 00:11:49 GMT
FROM: Phil Evans at U of Leicester
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 36167 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36167 |
| Detection_method |
Optical |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36167
SUBJECT: GRB 240418A: NOT optical upper limits
DATE: 24/04/19 00:50:40 GMT
FROM: Daniele B. Malesani at IMAPP / Radboud University
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 36168 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36168 |
| Detection_method |
Optical |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36168
SUBJECT: GRB 240418A: TSHAO Zeiss-1000 optical upper limit
DATE: 24/04/19 01:36:41 GMT
FROM: Alexei Pozanenko at IKI, Moscow
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 36177 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36177 |
| Detection_method |
Swift Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36177
SUBJECT: GRB240418A: YAHPT Upper Limits
DATE: 24/04/19 11:15:10 GMT
FROM: Tianrui Sun at Purple Mountain Obs,CAS
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 36181 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36181 |
| Detection_method |
Swift-XRT Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36181
SUBJECT: GRB 240418A: Swift-XRT refined Analysis
DATE: 24/04/19 15:17:47 GMT
FROM: Phil Evans at U of Leicester
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 36184 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36184 |
| Detection_method |
Swift-UVOT Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36184
SUBJECT: GRB 240418A: Swift/UVOT Upper Limits
DATE: 24/04/19 16:06:19 GMT
FROM: Sam Shilling at Lancaster University
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 36199 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36199 |
| Detection_method |
Optical |
| ra |
239.3744° |
| decl |
23.5961° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36199
SUBJECT: GRB240418A - Candidate afterglow from NIRES
DATE: 24/04/20 19:35:35 GMT
FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay
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 36254 table |
|---|
| GRB_name |
GRB240418A |
| GCN_number |
36254 |
| Detection_method |
Swift-BAT Det |
| ra |
239.3420° |
| decl |
23.6320° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 36254
SUBJECT: GRB 240418A: Swift-BAT refined analysis
DATE: 24/04/23 12:59:27 GMT
FROM: Mike Moss at NASA GSFC
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 |