GRB 240615A
GCN Circular 36777
Subject
GRB 240615A: SAI CMO J- band observations
Date
2024-06-28T12:50:00Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>
Via
legacy email
A. Volnova (IKI), A.A. Tatarnikov (SAI MSU), A.M. Tatarnikov (SAI MSU),
N. Pankov (HSE, IKI), A. Pozanenko (IKI), S. Belkin (IKI, HSE) report on
behalf of GRB-IKI-FuN:
We observed the field of GRB 240615A (Fermi GBM team, GCN 36671; DeLaunay
et al, GCN 36672; Evans, GCN 36673; Frederiks et al, GCN 36677; Tan et al,
GCN 36682; Page et al, GCN 36683; Roberts and Meegan, GCN 36685; Kozyrev et
al, GCN 36726) with 2.5-meter SAI-25 telescope of the Caucasian Mountain
Observatory of Sternberg Astronomical Institute (SAI CMO), equipped with
the IR camera ASTRONIRCAM. The observations in the J-filter were carried
out on 2024-06-20, and 2024-06-23. The infrared point source (Busmann et
al, GCN 36706) within XRT S1 localization is well detected in stacked
images of both epochs at coordinates (J2000) 21:44:23.66, +38:34:08.81
with an uncertainty of 0.1 arcsec in both coordinates.
Preliminary photometry of the source is as follows:
Date UT start t-T0 Exp. Filter OT Err. UL(3 sigma)
(mid, days) (s)
2024-06-20 19:39:18 5.10936 46x96.5 J 19.23 0.07 21.1
2024-06-23 21:58:41 8.19335 35x96.5 J 19.76 0.07 21.8
The magnitudes are calibrated against nearby stars of 2MASS and are not
corrected for the Galactic extinction.
The light curve fit yields a power law exponent of about -1.0, which is
typical for a gamma-ray burst afterglow. We suggest the source is an
afterglow of GRB 240615A.
Our photometry is consistent with photometry reported early (Kumar et al,
GCN 36676, Kumar et al, GCN 36680; Karambelkar et al, GCN 36686; Gupta and
Misra, GCN 36696; Busmann et al, GCN 36706; Jiang et al, GCN 36713;
Rastinejad et al, GCN 36746, GCN 36751).
Due to the extremely red color of the source, i.e. marginal detection in
the i-filter by NOT (Jiang et al, GCN 36713) we tentatively set a lower
limit on the redshift of the GRB source of ~4.5. Further observations of
GRB 240615A are encouraged.
GCN Circular 36751
Subject
GRB240615A: Gemini-North observations of the BAT and XRT positions
Date
2024-06-25T02:27:06Z (2 years ago)
From
Jillian Rastinejad at Northwestern Univ. <jillianrastinejad2024@u.northwestern.edu>
Via
legacy email
Jillian Rastinejad, Wen-fai Fong and Charles D. Kilpatrick (Northwestern) report on behalf of a larger collaboration:
We observed the location of the short-duration GRB 240615A (Fermi GBM Team GCN 36671, DeLaunay et al. GCN 36672, Frederiks et al. GCN 36677, Tan et al. GCN 36682) with the 5.5 arcminute square field of view Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-North (PI: Fong). We obtained two epochs of i-band imaging, each consisting of two pointings, at 2.8 and 4.8 days post-burst. Our first pointing was centered at R.A. = 21:44:39.51, Decl. = 38:35:31.2 (J2000), the approximate intersection of the IPN and BAT localizations (DeLaunay et al. GCN 36672, Kozyrev et al. GCN 36726). The second pointing was centered on XRT Source 1 (Page et al. GCN 36683). Observations were taken at a median airmass of 1.1 and in <0.8'' seeing. We perform image subtraction between the two epochs using HOTPANTS (Becker et al. 2015). Following visual inspection, we do not detect a clear optical afterglow in either pointing, though we note the presence of several residuals from saturated stars in the first pointing. Calibrated to Pan-STARRS1, we place an upper limit on an optical afterglow within these pointings at 2.8 days post-burst of i > 25.7 AB mag, not corrected for Galactic extinction.
Our observations covered the location of the optical Source 1 reported in Busmann et al. GCN 36706. We detect the source in both epochs. We do not obtain a significant residual at the position of the source following image subtraction.
We thank Aaron Tohuvavohu for helpful communication on the burst pointings and Jennifer Andrews and Kristin Chiboucas for the rapid planning and execution of these observations.
GCN Circular 36746
Subject
GRB240615A: Gemini-North observations of the BAT and XRT positions
Date
2024-06-24T19:59:01Z (2 years ago)
From
Jillian Rastinejad at Northwestern Univ. <jillianrastinejad2024@u.northwestern.edu>
Via
email
Jillian Rastinejad, Wen-fai Fong and Charles D. Kilpatrick (Northwestern) report on behalf of a larger collaboration:
We observed the location of the short-duration GRB 240615A (Fermi GBM Team GCN 36671, DeLaunay et al. GCN 36672, Frederiks et al. GCN 36677, Tan et al. GCN 36682) with the 5.5 arcminute square field of view Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-North (PI: Fong). We obtained two epochs of i-band imaging, each consisting of two pointings, at 2.8 and 4.8 days post-burst. Our first pointing was centered at R.A. = 21:44:39.51, Decl. = 38:35:31.2 (J2000), the approximate intersection of the IPN and BAT localizations (DeLaunay et al. GCN 36672, Kozyrev et al. GCN 36726). The second pointing was centered on XRT Source 1 (Page et al. GCN 36683). Observations were taken at a median airmass of 1.1 and in <0.8'' seeing. We perform image subtraction between the two epochs using HOTPANTS (Becker et al. 2015). Following visual inspection, we do not detect a clear optical afterglow in either pointing, though we note the presence of several residuals from saturated stars in the first pointing. Calibrated to Pan-STARRS1, we place an upper limit on an optical afterglow within these pointings at 2.8 days post-burst of i > 25.7 AB mag, not corrected for Galactic extinction.
Our observations covered the location of the optical Source 1 reported in Busmann et al. GCN 36706. We detect the source in both epochs. We do not obtain a significant residual at the position of the source following image subtraction.
We thank Aaron Tohuvavohu for helpful communication on the burst pointings and Jennifer Andrews and Kristin Chiboucas for the rapid planning and execution of these observations.
GCN Circular 36726
Subject
IPN triangulation of GRB 240615A (short)
Date
2024-06-21T17:27:05Z (2 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
legacy email
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The short-duration GRB 240615A
(Fermi-GBM detection: The Fermi GBM team, GCN 36671;
Swift-BAT/GUANO detection and localization: DeLaunay et al., GCN 36672;
Konus-Wind detection: Frederiks et al., GCN 36677;
GECAM-C detection: Tan et al., GCN 36682)
was detected by Fermi (GBM trigger 740166710), Swift (BAT),
Konus-Wind, INTEGRAL (SPI-ACS), GECAM-C, and Mars-Odyssey (HEND)
at about 64305 s UT (17:51:45).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
326.163 (21h 44m 39s) +38.634 (+38d 38' 02")
Corners:
326.204 (21h 44m 49s) +38.689 (+38d 41' 21")
326.141 (21h 44m 34s) +38.735 (+38d 44' 07")
326.122 (21h 44m 29s) +38.578 (+38d 34' 42")
326.186 (21h 44m 45s) +38.532 (+38d 31' 56")
---------------------------------------------
The error box area is 31 sq. arcmin, and its maximum
dimension is 12 arcmin (the minimum one is 3.3 arcmin).
The Sun distance was 95 deg.
The IPN localization is consistent with, but reduces the area of,
the Swift-BAT/GUANO localization. All the sources reported by Swift-XRT (GCN 36683) are outside the IPN box.
This localization may be improved.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB240615_T64306/IPN
The HEALPix triangulation map is the multi-order HEALPix in units of probability density.
GCN Circular 36713
Subject
GRB 240615A: NOT optical observations
Date
2024-06-20T13:43:59Z (2 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, S.Y. Fu, X. Liu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), Z.P. Zhu, J. An, D. Xu (NAOC), B. Gompertz (Birmingham), M. A. Diaz Teodori (NOT), report on behalf of a large collaboration:
We observed the Swift/BAT-GUANO field of GRB 240615A detected by Fermi/GBM (Fermi GBM team, GCN 36671), Swift/BAT-GUANO (DeLaunay et al., GCN 36672), Konus-Wind (Frederiks et al., GCN 36677) and GECAM (Tan et al., GCN 36682) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.
Observations were carried out in the r band on 2024-06-16 and in the r and z bands on 2024-06-20. A red optical source is detected in the z-band of the second NOT epoch at the Wendelstein position (Busmann et al., GCN GCN 36706), which is consistent with the XRT Source #1 position (Page et al., GCN 36683). Preliminary photometry for the optical transient is as follows:
Tmid(UT) Tmid-T0(hr) Mag MagErr UL(5-sigma) Filter
2024-06-16T03:50:07 9.98 - - >23.9 r
2024-06-20T01:23:48 103.53 - - >22.8 r
2024-06-20T01:41:45 103.83 21.95 0.14 - z
calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction.
Photometry of the Pan-STARRS archival images yields r > 23.2 (5-sigma) and z > 22.1 (5-sigma). We notice that the NOT z-band magnitude is not significantly brighter than the Pan-STARRS limit, hence our data alone do not allow to robustly claim the detection of a new source.
GCN Circular 36706
Subject
GRB 240615A: possible transient detection from Wendelstein observations
Date
2024-06-19T22:11:12Z (2 years ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Via
Web form
Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.), Antonella Palmese (Carnegie Mellon U.), Christoph Ries (LMU), Arno Riffeser (LMU/MPE) report:
With the 3KK optical-NIR imager at the 2m Fraunhofer telescope at Wendelstein Observatory, Germany, we have followed up the GRB 240615A reported by GCN 36671, 36672. Our observations began at ~3.2 days after the GRB.
We detect one source at 10sigma significance that is consistent with the location (90% error of ~9") of the Swift-XRT uncatalogued X-ray source reported in GCN 36683. We report the following photometric measurements and 3-sigma upper limits for this source (hereafter referred to as Source 1):
Name RA(J2000) dec(J2000) UTC mag_r mag_i mag_J
Source 1 21:44:23.63 +38:34:08.89 2024-06-18T22:44:19 >24.0 24.0 +/- 0.5 20.36 +/- 0.09
We also obtained a tentative detection of Source 1 in images taken about 22 h before this detection (~2.3 days after the GRB). There is evidence at the 3sigma level that Source 1 was brightening between the two epochs. We note that Source 1 is extremely red in color with i-J>3 mag.
A second source (Source 2) is marginally detected at RA, dec (J2000) = 21:44:23.8, +38:34:03.4 in both r and i-bands. We note the marginal detection of an underlying source in PS1 imaging at both of these locations (Source 1 and Source 2).
Further observations are scheduled and additional follow-up is encouraged.
Magnitudes are in the AB system and not corrected for the significant Milky Way extinction along this line of sight.
GCN Circular 36696
Subject
GRB240615A: 1.3m DFOT optical upper limit
Date
2024-06-19T06:22:27Z (2 years ago)
Edited On
2024-06-19T15:06:32Z (2 years ago)
From
ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of ANSHIKA GUPTA at ARIES <anshika05180@gmail.com>
Via
Web form
Anshika Gupta, Kuntal Misra (ARIES) report:
We observed the field of GRB 240615A detected by Fermi GBM (GCN #36671) and Swift/BAT-GUANO (GCN #36672) and using the 1.3m Devasthal Fast Optical Telescope (DFOT) located at the Devasthal observatory of Aryabhatta Research Institute of observational sciencES (ARIES), Nainital, India. The observation started on 2024-06-16 at 20:07:06 UTC, i.e., ~ 26.25 hours after the trigger. 24 frames of 300 sec exposure were acquired in the R band. We do not detect the optical afterglow (earlier reported in #GCN 36676, #GCN 36680) in the stacked image down to a limiting magnitude of 22.8. The photometric calibration is performed using the standard stars from the USNO-B1.0 catalog.
GCN Circular 36686
Subject
GRB 240615A: J-band upper limits from WINTER
Date
2024-06-17T15:22:28Z (2 years ago)
From
Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197@gmail.com>
Via
legacy email
Viraj Karambelkar (Caltech), Geoffrey Mo (MIT), Robert Stein (Caltech),
Danielle Frostig (MIT), Tomas Ahumada (Caltech), Nathan Lourie (MIT),
Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the Swift-GUANO localization region of short GRB 240615A (GCN
36671, 36672, 36673, 36676, 36680, 36682, 36683) in the near-infrared
J-band with the Palomar 1-m telescope, equipped with the 1-square degree
WINTER camera (Lourie et al. 2020).
Our observations began at 2024-06-16T06:06:34 UTC (~12 hours after the GRB
trigger) and lasted for an hour. The images were processed using the WINTER
data reduction pipeline (https://github.com/winter-telescope/mirar,
https://doi.org/10.5281/zenodo.10888436), with image subtraction performed
relative to J-band images from the UKIRT Hemisphere survey (Dye et al.,
2017).
We do not detect the XRT source (reported by GCN 36683) in our stacked and
subtracted images to a depth of J~19 mag (AB). No other new sources are
identified in our subtracted images, to a depth of J~19 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between
MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF
AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute
for Astrophysics and Space Research.
GCN Circular 36685
Subject
GRB 240615A: Fermi GBM Observation
Date
2024-06-17T14:47:05Z (2 years ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
Via
Web form
O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 17:51:45.05 UT on 15 June 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240615A (trigger 740166710/240615744), which was
also detected by Swift BAT GUANO (DeLaunay et al. 2024, GCN 36672),
KONUS-WIND (Frederiks et al. 2024, GCN 36677) and GECAM (Tan et al. 2024, GCN 36682).
The Fermi-GBM Final Real-time location (Fermi GBM Team 2024, GCN 36671)
is consistent with the Swift BAT-GUANO position.
The angle from the Fermi LAT boresight is 23 degrees.
The GBM light curve consists of bright, overlapping emission episodes with a
duration (T90) of about 0.10 s (50-300 keV). The time-averaged spectrum
from T0-0.03 to T0+0.09 s is best fit by a power law function with an
exponential high-energy cutoff. The power law index is -0.52 +/- 0.07
and the cutoff energy, parameterized as Epeak, is 933 +/- 105 keV.
A Band function fits the spectrum equally well with Epeak= 858 +/- 110 keV,
alpha = -0.48 +/- 0.08 and beta = -3.04 +/- 0.76.
The event fluence (10-1000 keV) in this time interval is
(1.56 +/- 0.06)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band is 45 +/- 2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 36683
Subject
GRB 240615A: Swift-XRT observations
Date
2024-06-17T09:09:22Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
K.L. Page (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi
(INAF-IASFPA), M. Perri (SSDC & INAF-OAR), J. D. Gropp (PSU), S.
Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Swift/BAT-GUANO-detected burst GRB 240615A, collecting 5.0 ks of Photon
Counting (PC) mode data between T0+78.9 ks and T0+92.0 ks.
One uncatalogued X-ray source has been detected consistent with being
within 394 arcsec of the Swift/BAT-GUANO position, it is below the RASS
limit and shows no definitive signs of fading. Therefore, at the
present time we cannot confirm this as the afterglow. Details of this
source are given below:
Source 1:
RA (J2000.0): 326.0968 = 21:44:23.22
Dec (J2000.0): +38.5681 = +38:34:05.1
Error: 8.9 arcsec (radius, 90% conf.)
Count-rate: (3.6 [+9.7, -3.6])e-4 ct s^-1
Distance: 157 arcsec from Swift/BAT-GUANO position.
Flux: (8.5 [+23.2, -8.5])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)
Four uncatalogued sources were also detected too far from the GRB
position to be likely afterglow candidates.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021696.
This circular is an official product of the Swift-XRT team.
GCN Circular 36682
Subject
GRB 240615A: GECAM detection
Date
2024-06-17T07:34:20Z (2 years ago)
From
tanwj@ihep.ac.cn
Via
Web form
Wen-Jun Tan, Ce Cai，Shao-Lin Xiong report on behalf of the GECAM team:
GECAM-C was triggered by a short burst, GRB 240615A, during the routine ground search at 2024-06-15T17:51:45.100 UTC (T0), which was also detected by Fermi/GBM (GCN #36671), Swift/BAT-GUANO arcminute localization(GCN #36672) and Konus-Wind (GCN #36677) .
According to the GECAM-C light curve, this burst shows one single pulse with a total duration of ~0.1 sec.
We note that these results are very preliminary. 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).
GCN Circular 36680
Subject
GRB 240615A: FLWO-1.2m optical upper limits
Date
2024-06-17T02:24:03Z (2 years ago)
From
Harsh Kumar at Center for Astrophysics | Harvard & Smithsonian <harshkosli13@gmail.com>
Via
Web form
H. Kumar (CFA) D. Hiramatsu (CFA), and E. Berger (CFA) report on behalf of the FLWO team:
We observed GRB 240615A detected by Fermi GBM (GCN #36671)and Swift/BAT-GUANO (GCN #36672), with the FLWO 1.2m (48”) robotic telescope. We obtained multiple 300-sec exposures in the g, r, and i filters and did not detect any new source in our stacked images within 4 arcmin of BAT position: RA (J2000) = 21:44:33.91, Dec(J2000) = 38:35:41.3. We obtained the following upper limits:
---------------------------------------------------------------------------------
JD (mid) | T-T0(hrs) | Exposure (sec) | Filter | Lim_mag (5-sigma)
---------------------------------------------------------------------------------
2460477.78778 | 13.04 | 900 (stacked) | r | > 21.92
2460477.79915 | 13.32 | 900 (stacked) | g | > 21.33
2460477.81047 | 13.59 | 900 (stacked) | i | > 21.47
---------------------------------------------------------------------------------
The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
We thank the FLWO staff for their support.
GCN Circular 36677
Subject
Konus-Wind detection of GRB 240615A (short/hard)
Date
2024-06-16T16:36:40Z (2 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
legacy email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The short GRB 240615A (The Fermi GBM team, GCN 36671;
Swift/BAT-GUANO arcminute localization: DeLaunay et al., GCN 36672).
triggered Konus-Wind (KW) at T0=64306.225 s UT (17:51:46.225).
The burst light curve shows a single pulse,
which starts at ~T0-0.02 s and has a duration of ~0.1 s.
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240615_T64306/
As observed by Konus-Wind, the burst had the total fluence
of 1.85(-0.49,+0.65)x10^-6 erg/cm^2 and a 16-ms peak energy flux,
measured from T0, of 3.21(-0.89,+1.15)x10^-5 erg/cm^2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst (measured from T0 to T0+0.128 s)
is best fit in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.55(-0.27,+0.37) and Ep = 878(-281,+441) keV (chi2 = 24.4/28 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -2.15 (chi2 = 24.5/27 dof).
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 36676
Subject
GRB 240615A: GOTO optical upper limits
Date
2024-06-16T08:59:28Z (2 years ago)
From
Amit Kumar at University of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar; B. P. Gompertz; G. Ramsay; S. Belkin; R. Starling; D. K. Galloway; K. Ackley; M. J. Dyer; J. Lyman; K. Ulaczyk; F. Jimenez-Ibarra; D. O'Neill; D. Steeghs; V. Dhillon; P. O'Brien; K. Noysena; R. Kotak; R. P. Breton; L. K. Nuttall; E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) in response to the Fermi GBM detected GRB 240615A (Fermi GBM Team, GCN 36671). Targeted observations also covered the Swift/BAT-GUANO updated localisation (DeLaunay, et al., GCN 36672) with GOTO-N on 2024-06-16 from UT 01:39:52 to 03:56:07 (from ~7.80 to 10.07 hours after trigger, respectively) distributed over four epochs. Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using recent survey observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.
No significant optical counterpart is detected within the Swift/BAT-GUANO localisation region to a 5-sigma limiting L-band magnitude range of 19.8-20.4 (AB) across 4 epochs of observations.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 36673
Subject
GRB 240615A: Swift ToO observations
Date
2024-06-16T04:54:26Z (2 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT-GUANO GRB 240615A.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021696
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Swift/BAT-GUANO event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a
GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular 36672
Subject
GRB 240615A: Swift/BAT-GUANO arcminute localization of a short burst
Date
2024-06-16T01:36:09Z (2 years ago)
From
Aaron Tohuvavohu at University of Toronto <aaron.tohu@gmail.com>
Via
Web form
James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea
(PSU), Samuele Ronchini (PSU), Gayathri Raman (PSU), Tyler Parsotan (GSFC) report:
Swift/BAT did not localize GRB 240615A onboard (T0: 2024-06-15T17:51:45 UTC, Fermi GCN 36671).
The Fermi/GBM notice, distributed in near real-time, triggered the
Swift Mission Operations Center operated Gamma-ray Urgent Archiver for
Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst
Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from
[-50,+150] seconds around the time of the burst. All the requested
event mode data was delivered to the ground.
The burst is detected in BAT with a duration of < 0.1 seconds.
The burst occurred during a Swift slew.
A confident location is found for the burst with SNR of 12.
The BAT position is
RA, Dec = 326.1413, +38.5948 deg which is
RA(J2000) = 21h 44m 33.91s
Dec(J2000) = +38d 35’ 41.3″
with an estimated uncertainty of 4 arcmin.
This position is consistent with the Ferm/GBM localization (GCN 33023).
XRT and UVOT follow-up has been requested. Results of follow-up
observations will be reported in future circulars.
GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be
found at: https://www.swift.psu.edu/guano/
GCN Circular 36671
Subject
GRB 240615A: Fermi GBM Final Real-time Localization
Date
2024-06-15T18:02:18Z (2 years ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely SHORT GRB
At 17:51:45 UT on 15 Jun 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240615A (trigger 740166710.052962 / 240615744).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 335.4, Dec = 42.5 (J2000 degrees, equivalent to J2000 22h 21m, 42d 30'), with a statistical uncertainty of 1.8 degrees.
The angle from the Fermi LAT boresight is 17.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240615744/quicklook/glg_skymap_all_bn240615744.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240615744/quicklook/glg_healpix_all_bn240615744.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2024/bn240615744/quicklook/glg_lc_medres34_bn240615744.gif