GRB 240402B
GCN Circular 36385
Subject
LXT 240402A / GRB 240402B: VLT X-shooter redshift of host
Date
2024-05-03T15:23:10Z (a year ago)
From
nrt3@le.ac.uk
Via
Web form
N. R. Tanvir (U. Leicester), J. Palmerio (GEPI/Obs. de Paris), D. B. Malesani (DAWN/NBI & Radboud U.), A. J. Levan (Radboud U.), A. Saccardi (GEPI/Obs. de Paris), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud U.), K. Wiersema (U. Hertfordshire), Y. Julakanti (U. Leicester) report on behalf of the Stargate collaboration:
We obtained observations of the location of the X-ray transient LXT 240402A (Xu et al., GCN 36016; Jia et al., GCN 36022; Levan et al., GCN 36025), coincident with GRB 240402B detected by GECAM-C (Xue et al., GCN 36017) and Konus-Wind (Ridnaia et al., GCN 36028), using the X-shooter spectrograph at the VLT. Observations began at 04:04 (UT) on 03 May 2024, approximately 31 days after the trigger. The spectrum covers a wavelength range roughly 0.31 to 2.1 mum, with a total integration time of 4800 s.
A weak continuum is seen throughout the spectrum, and we clearly detect emission lines of [O II], H-beta, [O III], H-alpha, and tentatively Ly-alpha, at a common redshift of z = 1.551. We propose that these lines are from the host of the transient. Based on the gamma-ray fluence seen by Konus-Wind in the 20 keV - 10 MeV band (Ridnaia et al., GCN 36028) we conclude an isotropic-equivalent energy release in gamma-rays of 4.7x10^52 erg. This places it very close to the mean Amati relationship (Amati et al. 2006 MNRAS 372 233), and thus is consistent with a long-GRB origin.
We thank ESO support staff Zahed Wahhaj and Francisco Caceres for undertaking these observations.
GCN Circular 36253
Subject
LXT240402A/GRB240402B: Chandra X-ray detection
Date
2024-04-23T12:55:40Z (2 years ago)
From
muskan.yadav@students.uniroma2.eu
Via
Web form
M. Yadav, E. Troja, Y. -H. Yang, and R. L. Becerra (U. Rome) report:
Following the detection of the fast X-ray transient LXT 240402A (Xu et al., GCN 36016) associated with GRB 240402B (Wang et al., GCN 36017), we performed observations of the field with the Chandra X-ray Observatory starting at UT 00:48 on April 15, 2024 for a total exposure of 16 ks.
An X-ray source is detected with high significance at the location of the optical counterpart (Yang at al., GCN 36094).
Using the spectral parameters of the EP-FXT detection (Jia et al., GCN 36022) we derive an X-ray flux of 8*10^-14 erg s^-1 cm^-2 (0.5-10 keV), consistent with the Swift/XRT observations (Martin-Carrillo et al., GCN 36114).
We thank Pat Slane and the CXO staff for quickly arranging and executing the observations.
GCN Circular 36114
Subject
LXT 240402A/GRB 240402B: Swift follow-up observations
Date
2024-04-15T13:21:33Z (2 years ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
A. Martin-Carrillo (UCD), S. Campana (INAF/Brera), D. B. Malesani (DAWN/NBI & Radboud Univ.), A. J. Levan (Radboud Univ.), G. Pugliese (Amsterdam), D. Xu (NAOC/CAS), N. R. Tanvir (Leicester), P. G. Jonker (Radboud Univ.), A. Rossi (INAF-OAS), P. O’Brien (Leicester) report on behalf of the Stargate collaboration:
Following up the LEIA trigger LXT 240402A (Xu et al., GCN 36016) associated with the Konus-Wind GRB 240402B (Ridnaia et al., GCN 3628) and the detection of its X-ray counterpart (Jia et al., GCN 36022) a series of Swift follow-up observations (PI Xu, ID: 203030 and PI Martin-Carrillo, ID: 20382) were performed between April 7 and April 14, with a total exposure time of 8 ks.
Combining all the data, a source is well detected with a count rate of 1.9 (+0.7, -0.6) x 10^-3 count s^-1 at the coordinates (J2000):
RA: 16:21:47.75 (245.4490);
Dec: +25:45:45.9’ (25.7627);
Error: 5.8” (90% confidence).
Using the spectral parameters of the EP-FXT detection (Jia et al., GCN 36022), this corresponds to an observed flux of 7.7*10^-14 erg cm^-2 s^-1. Assuming a mid-point for the Swift observations of 8.5 days after the LEIA trigger, and using a single power-law decay, the X-ray flux decays with an approximate index -1.2, typical for a GRB afterglow.
The source centroid lies within 1.5" from the optical counterpart reported by Levan et al. (GCN 36025) and Yang et al. (GCN 36027). The reduced localisation error strengthens its association with the proposed optical counterpart.
We thank the Neil Gehrels Swift Observatory team for making these ToO observations possible.
GCN Circular 36041
Subject
LXT 240402A/GRB 240402B: rest-frame energetics from Konus-Wind observation
Date
2024-04-06T14:54:45Z (2 years ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
Assuming the spectrum and the observer-frame energetics of GRB 240402B
measured by KW (GCN 36028); the redshift of the probable host galaxy
z=0.047 (Xu et al., GCN 36016; Levan et al., GCN 36025; Xue at al., GCN 36034);
and a standard cosmology with H_0 = 67.3 km/s/Mpc,
Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014);
we estimate the burst isotropic energy release E_iso to (4.06 ± 0.27)x10^49 erg,
the isotropic peak luminosity L_iso to (2.85 ± 0.38)x10^49 erg/s,
the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (90 ± 5) keV.
With the obtained estimates, GRB 240402B is a low-luminosity outlier
in both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs
with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB240402_T31668/GRB240402B_rest_frame.pdf
All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.
GCN Circular 36034
Subject
LXT 240402A/GRB 240402B: GECAM-C refined analysis
Date
2024-04-05T01:59:44Z (2 years ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Wangchen Xue, Shaolin Xiong, Chenwei Wang, Chengkui Li, Shuxu Yi on behalf of GECAM team
Following our initial analysis reported in GCN 36017, here we analyzed the Amati relation for this burst.
We find that, if this burst had a redshift of z~0.047 (Levan et al.; GCN 36025, Xu et al., GCN 36016),
it falls in the short burst region, supporting the compact object merger origin as also evident by the large offset from the galaxy (Levan et al., GCN 36025).
The small spectral lag compared to its luminosity also indicates the compact object merger origin.
The associated gravitational wave would likely have been observed if LVK was observing at the time of this burst.
The gravitational wave of such kind of GRB with small redshift would be potentially observed in O4b of LVK.
With the probable compact object merger origin of this GRB, follow-up observations are encouraged.
GCN Circular 36030
Subject
LXT 240402A/GRB 240402B: Glowbug gamma-ray detection
Date
2024-04-04T19:13:46Z (2 years ago)
From
C.C. Cheung at Naval Research Lab <Teddy.Cheung@nrl.navy.mil>
Via
Web form
C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The Glowbug gamma-ray telescope [1,2], operating on the International Space Station, reports the detection of LXT 240402A/GRB 240402B, which was also detected by LEIA (GCN 36016), GECAM-C (GCN 36017), and Konus/Wind (GCN 36028).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2024-04-02 08:47:45.240 with a duration of 4.1 s and a total significance of about 18.3 sigma. The light curve comprises two primary peaks at ~T0+0.5s and ~T0+3s.
The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS. The detector comprises 12 large-area (15 cm x 15 cm) CsI:Tl panels covering the surface of a half cube, and two hexagonal (5-cm diameter, 10-cm length) CLLB scintillators, giving it a large field of view (instantaneous FoV ~2/3 sky) over a wide energy band of 50 keV to >2 MeV.
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv :1909.03006
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 36028
Subject
Konus-Wind detection of LXT 240402A/GRB 240402B
Date
2024-04-04T15:59:11Z (2 years ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 240402B
(GECAM-C detection: Xue et al., GCN 36017)
associated with the LEIA fast X-ray transient
LXT 240402A (Xu et al., GCN 36016)
triggered Konus-Wind at T0=31668.797 s UT (08:47:48.797).
The burst light curve shows a multipeaked structure
which starts at ~T0-0.2 s and has a total duration of ~5.1 s.
The emission is seen up to ~3 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240402_T31668/
As observed by Konus-Wind, the burst
had a fluence of 7.56(-0.43,+0.50)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+2.704 s,
of 5.07(-0.66,+0.68)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 4 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.71(-0.17,+0.19),
the high energy photon index beta = -3.58(-1.30,+0.44),
the peak energy Ep = 86(-4,+5) keV
(chi2 = 57/68 dof).
This spectrum is nearly-well fitted
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.78(-0.15,+0.16)
and Ep = 88(-4,+4) keV (chi2 = 61/69 dof).
All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.
GCN Circular 36018
Subject
GRB 240402B: GWAC-F50A optical upper limit
Date
2024-04-03T22:56:22Z (2 years ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
legacy email
L.P.Xin(NAOC), Y.G.Yang(HNU), C.WU(NAOC), Y.L.Qiu(NAOC), J.Wang(GXU/NAOC),
L.H.Li(NAOC), C.Wu(NAOC), E.W.Liang(GXU), X.H.Han (NAOC), X.M.Lu(NAOC),
R.S.Zhang(NAOC), Y.Xu(NAOC), Y.J.Xiao(NAOC), P.P.Zhang(NAOC), L.Lan(NAOC),
J.Y.Wei(NAOC) on behalf of the SVOM/GWAC team:
We began to observe X-ray transient LXT 240402A (Xu et all., GCN 36106) detected by LEIA,
which was also detected by GECAME-C as GRB 240402B (Xue et al., GCN 36107),
with GWAC-F50A telescope, at Xinglong station, China, at 19:22:13 (UT), 03. April. 2024,
about 34.57 hours after the burst. The weather was not good.
After stacking 5*200 seconds, no any new sources were detected in our stacked image
down to a limit magnitude of 18.0 mag in R band comparing to several nearby USNO B1.0 stars.
We acknowledge the excellent support from observation assistant Yangtong Zheng.
GCN Circular 36017
Subject
GRB 240402B: GECAM-C detection
Date
2024-04-03T17:01:02Z (2 years ago)
Edited On
2024-04-03T18:46:19Z (2 years ago)
From
Kai <wcxuemail@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Kai <wcxuemail@gmail.com>
Via
Web form
Wang-Chen Xue, Shao-Lin Xiong, Chao Zheng, Yanqiu Zhang, and Chengkui Li,
report on behalf of the GECAM team:
GECAM-C observed a long burst, GRB 240402B at
2024-04-02T08:47:46 UTC (denoted as T0), which has been
detected by LEIA (GCN 36016) and Konus-Wind.
According to the observation data of GECAM-C, this burst mainly consists
of two peaks with a duration (T90) of 6.55 +/- 0.52 sec (15-350 keV).
The GECAM-C localization is consistent with the LEIA localization
(GCN 36016) within the error.
The time-averaged spectrum of GECAM-C data from T0-7.0 to T0+7.0 s could be
adequately fit by a cut-off power-law with photon index alpha of -0.62 (-0.14, +0.13),
and peak energy Ep of 66 (-3, +3) keV. The corresponding burst fluence is
7.69 (-0.24, +0.25) * 10^-7 erg/cm^2 in 15-350 keV.
We note that these results are preliminary and refined analysis will be reported later.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor
(GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B)
launched in Dec. 2020. As the third member of GECAM constellation,
GECAM-C was launched onboard SATech-01 experimental satellite in July 2022.
GECAM mission is funded by the Chinese Academy of Sciences (CAS).