TITLE: GCN CIRCULAR
NUMBER: 34753
SUBJECT: GRB 230918B: VLT/X-shooter classification of AT 2023tbf (GOTO23aky) as a dwarf nova
DATE: 23/09/20 22:32:36 GMT
FROM: Daniele B. Malesani at IMAPP / Radboud University <d.malesani(a)astro.ru.nl>
A. Saccardi (GEPI/Paris Obs.), L. Izzo (INAF/OACn & DARK/NBI), J. T. Palmerio (GEPI/Paris Obs. & IAP), D. B. Malesani (Radboud Univ. & DAWN/NBI), P. D'Avanzo (INAF-OABr), V. D’Elia (ASI-SSDC & INAF-OAR), M. Della Valle (INAF/OAC), D. H. Hartmann (Clemson Univ.), K. E. Heintz (DAWN/NBI), P. Jakobsson (U. of Iceland), L. Kaper (U. of Amsterdam), G. Leloudas (DTU Space), A. J. Levan (Radboud Univ.), A. Martin-Carrillo (UCD), B. Schneider (MIT), S. Schulze (OKC), A. de Ugarte Postigo (OCA), and K. Wiersema (U. of Hertfordshire) report on behalf of the Stargate collaboration:
We observed the transient AT 2023tbf (GOTO23aky; Gompertz et al., GCN 34738), spatially and temporally consistent with the Fermi GBM GRB 230918B (Fermi GBM team; GCN 34734). We used the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph, starting on 2023 September 20.093 UT. Our data cover the wavelength range 3000-24800 AA and consist of 4 exposures of 600 s each.
In the acquisition image, taken on 2023 Sep 20.086 UT, we measure for the transient a magnitude r = 19.64 +- 0.05 AB (calibrated against a single nearby star from the SkyMapper catalog).
A strong continuum is detected in the blue end of the spectrum, with a decreasing signal towards the VIS and NIR arms. The UVB shows several broad undulations, not seen in GRB afterglow spectra; in the VIS and NIR arms, the continuum is smoother.
The source shows narrow absorption from Ca H and K a z = 0, as well as broad features in correspondence of the Balmer lines, at least H-beta to H-eta, all at z = 0. No features are identified at z > 0. Comparison with template spectra (e.g. Morales-Rueda & Marsh, 2002, MNRAS, 332, 814) allows us to classify AT 2023tbf as a dwarf nova. We thus conclude that AT 2023tbf is not a GRB afterglow and is not associated with GRB 230918B.
We acknowledge excellent support from the observing staff at Paranal, in particular Ditte Slumstrup, Xavier Haubois, Francisco Caceres and Paulina Venegas.
View this GCN Circular online at https://gcn.nasa.gov/circulars/34753.
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TITLE: GCN CIRCULAR
NUMBER: 34752
SUBJECT: IPN triangulation of GRB 230919A (short)
DATE: 23/09/20 21:46:04 GMT
FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru>
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
A. Ridnaia, D. Frederiks, D. Svinkin, 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,
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 230919A
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 34737;
Scotton et al., GCN Circ. 34750;
AstroSat CZTI detection: Navaneeth et al., GCN Circ. 34742;
Swift/BAT-GUANO detection: DeLaunay et al., GCN Circ. 34747)
has been detected by Fermi (GBM trigger 716835508), Konus-Wind,
Mars-Odyssey (HEND), Swift (BAT), and AstroSat (CZTI),
so far, at about 61103 s UT (16:58:23).
The burst was outside the coded field of view of the BAT.
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
71.620 (04h 46m 29s) +44.076 (+44d 04' 35")
Corners:
70.812 (04h 43m 15s) +45.562 (+45d 33' 43")
70.802 (04h 43m 12s) +45.703 (+45d 42' 10")
72.402 (04h 49m 37s) +42.484 (+42d 29' 04")
72.411 (04h 49m 39s) +42.324 (+42d 19' 28")
---------------------------------------------
The error box area is 543 sq. arcmin, and its maximum
dimension is 3.6 deg (the minimum one is 3 arcmin).
The Sun distance was 100 deg.
The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM final localization (GCN Circ. 34737).
This localization may be improved.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB230919_T61103/IPN/
The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.
View this GCN Circular online at https://gcn.nasa.gov/circulars/34752.
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TITLE: GCN CIRCULAR
NUMBER: 34751
SUBJECT: LIGO/Virgo/KAGRA S230904n: Classification of the candidate AT2023rkw with DBSP
DATE: 23/09/20 21:02:04 GMT
FROM: Shreya Anand at GROWTH Caltech <sanand(a)caltech.edu>
Shreya Anand (Caltech), Jannis Necker (DESY), Nicholas Earley (Caltech), Yu-Jing Qin (Caltech), Simeon Reusch (DESY), Joel Johansson (SU), Tomas Ahumada (Caltech), and Christoffer Fremling (Caltech) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We observed the candidate AT2023rkw [1,2] with the Double Beam Spectrograph (DBSP) mounted on the Palomar 200-in telescope on 2023-09-16 (UTC), using a setup with a red grating of 316/7500, a blue grating of 600/400, a D55 dichroic, and a slitmask of 1.5". The data were reduced using a custom DBSP pipeline relying on Pypeit [3,4]. The spectrum exhibits narrow host galaxy lines at a redshift of z=0.113. We observe weak Si II lines characteristic of a SN Ia (91T-like), which is re-affirmed by the astrodash best match template. Therefore, we conclude that AT2023rkw is unrelated to the event S230904n.
We thank the Palomar observatory staff for making these observations possible.
[1] ZTF and GROWTH Collaborations, GCN 34688
[2] ZTF and GROWTH Collaborations, GCN 34717
[3] Prochaska et al. 2019
[4] Roberson et al. 2021
ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). GROWTH India telescope is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). GROWTH-India project is supported by SERB and administered by IUSSTF, under grant number IUSSTF/PIRE Program/GROWTH/2015-16 and IUCAA.
View this GCN Circular online at https://gcn.nasa.gov/circulars/34751.
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TITLE: GCN CIRCULAR
NUMBER: 34750
SUBJECT: GRB 230919A: Fermi GBM Observation
DATE: 23/09/20 20:49:41 GMT
FROM: Lorenzo Scotton at UAH <lscottongcn(a)outlook.com>
L. Scotton (UAH), C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 16:58:23.86 UT on 19 September 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230919A (trigger 716835508/230919707).
which was also detected by AstroSat (Navaneeth et al. 2023, GCN 34742)
and Swift/BAT-GUANO (DeLaunay et al. 2023, GCN 34747).
The Fermi GBM Final Real-time Localization was reported in GCN 34737.
The angle from the Fermi LAT boresight is 120 degrees.
The GBM light curve consists of multiple peaks
with a duration (T90) of about 2.9s. The time-averaged spectrum
from T0-0.06 to T0+1.34 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.74 +/- 0.06 and the cutoff energy,
parameterized as Epeak, is 2023 +/- 271 keV.
A Band function fits the spectrum equally well with
Epeak = 1617 +/- 352 keV, alpha = -0.68 +/- 0.08 and beta = -2.43 +/- 0.32.
The event fluence (10-1000 keV) in this time interval is
(3.3 +/- 0.1)E-06 erg/cm^2. The 64-msec peak photon flux measured
starting from T0+0.58 s in the 10-1000 keV band is 12 +/- 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/"
View this GCN Circular online at https://gcn.nasa.gov/circulars/34750.
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TITLE: GCN CIRCULAR
NUMBER: 34749
SUBJECT: Correction to Fermi GBM Statement for Trigger 716527670/230916144
DATE: 23/09/20 19:18:23 GMT
FROM: Oliver J Roberts at USRA/NASA <oliver.roberts(a)nasa.gov>
We reported previously in GCN 34748 that Fermi-GBM trigger 716527670/230916144 was followed up by GOTO (Vail et al., GCN 34730), where a candidate afterglow (AT 2023sva) was identified and suggested it was the counterpart to the Fermi-GBM trigger.
This statement is incorrect. The afterglow reported in (Vail et al., GCN 34730) was not discovered in follow-up observations, but blindly via a search for fast transients in ZTF optical-survey data and not GOTO. The reported afterglow was checked against the GBM archive for any possible high-energy counterpart, where trigger 716527670/230916144 was inferred as a possible counterpart.
We apologize for this inaccurate reporting and thank the co-authors of Vail et al. for bringing this to our attention.
View this GCN Circular online at https://gcn.nasa.gov/circulars/34749.
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TITLE: GCN CIRCULAR
NUMBER: 34748
SUBJECT: Fermi GBM Statement for Trigger 716527670/230916144
DATE: 23/09/20 18:05:31 GMT
FROM: Oliver J Roberts at USRA/NASA <oliver.roberts(a)nasa.gov>
O.J. Roberts (USRA/NASA-MSFC), S. Bala (USRA), C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 03:27:45.98 UT on 16 September 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered on trigger 716527670/230916144 as a GRB with 64% confidence). This trigger
was later followed up by GOTO (Vail et al., GCN 34730), identifying a candidate afterglow
(AT 2023sva) and suggested it was the counterpart.
Careful inspection of the GBM trigger by the Fermi-GBM Team identified a weak
C1-class solar flare occurring contemporaneously at the trigger time, which dominates
the spectrum below 50 keV. There is approximately several hundred counts in the
50-300 keV band over 12s, which the Team was able to localize. The on-ground calculated
location using the Fermi GBM trigger data over this energy range is
RA = 143.0, Dec = 70.5 (J2000 degrees, equivalent to J2000 9h 32m, +/- 70d 30'), with a
statistical uncertainty of 8.0 degrees (radius, 1-sigma containment, statistical only; there
is additionally a systematic error which we have characterized as a core-plus-tail model,
with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).
We note that this localization is 71 degrees from the Sun, and is quite far from the
RA and Dec of the afterglow candidate reported by Vail et al. in GCN 34730. We therefore
believe these two events to be unrelated and suggest that AT2023sva is an orphan afterglow.
We also note that this weak burst is contaminated by the solar flare and that any meaningful
data regarding the nature of this transient is likely unrecoverable.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230916144/…
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230916144/…
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230916144/…"
View this GCN Circular online at https://gcn.nasa.gov/circulars/34748.
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TITLE: GCN CIRCULAR
NUMBER: 34747
SUBJECT: GRB 230919A: Swift/BAT-GUANO detection of a possibly short burst outside the coded FOV
DATE: 23/09/20 17:51:55 GMT
FROM: Jimmy DeLaunay at University of Alabama <delauj2(a)gmail.com>
James DeLaunay (U Alabama), Aaron Tohuvavohu (U Toronto), Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 230919A onboard (T0: 2023-09-19T16:58:23.86 UTC, Fermi trig 716835508, AstroSat CZTI GCN 34742)
The Fermi 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 90 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 BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 16.6 in a 1.5 s analysis time bin, starting at T0 - 0.2 s.
NITRATES results are consistent with a burst coming from outside the FOV, with DeltaLLHOut of -0.6 and are consistent with Fermi GBM's localization (GCN 34737).
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
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/
View this GCN Circular online at https://gcn.nasa.gov/circulars/34747.
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TITLE: GCN CIRCULAR
NUMBER: 34746
SUBJECT: LIGO/Virgo/KAGRA S230920al: Updated Sky localization
DATE: 23/09/20 17:06:10 GMT
FROM: naresh.adhikari(a)ligo.org
The LIGO Scientific Collaboration, the Virgo Collaboration, and the
KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory
(H1) and LIGO Livingston Observatory (L1) data around the time of the
compact binary merger (CBC) candidate S230920al (GCN Circular 34741). Parameter estimation has been
performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0,
distributed via GCN Notice, is available for retrieval from the
GraceDB event page:
https://gracedb.ligo.org/superevents/S230920al
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is
2180 deg2. Marginalized over the whole sky, the a posteriori
luminosity distance estimate is 3139 +/- 1003 Mpc (a posteriori mean
+/- standard deviation).
For further information about analysis methodology and the contents of
this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide
https://emfollow.docs.ligo.org/userguide/.
[1] Ashton et al. ApJS 241, 27 (2019)
View this GCN Circular online at https://gcn.nasa.gov/circulars/34746.
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