GRB 210726A
GCN Circular 30523
Subject
GRB 210726A: Swift detection of a burst
Date
2021-07-26T19:39:05Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. G. Bernardini (INAF-OAB), M. A. Baer (PSU), P. D'Avanzo (INAF-OAB),
J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII),
S. Laha (GSFC/UMBC/CRESST), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), M. J. Moss (GWU), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 19:19:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210726A (trigger=1061687). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 193.342, +19.185 which is
RA(J2000) = 12h 53m 22s
Dec(J2000) = +19d 11' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a short spike with
a tail with a total duration of about ~3 sec. The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger.
This may be a short GRB.
The XRT began observing the field at 19:20:03.6 UT, 60.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 193.2909,
19.1898 which is equivalent to:
RA(J2000) = 12h 53m 09.81s
Dec(J2000) = +19d 11' 23.2"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 174 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.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.73 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.4
(+2.93/-2.51) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 250 seconds with the U filter starting
276 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 18.0 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.020.
Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.inaf.it).
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 30524
Subject
GRB 210726A: Enhanced Swift-XRT position
Date
2021-07-26T21:21:52Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1692 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 210726A, 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 = 193.29093, +19.19030 which is equivalent
to:
RA (J2000): 12h 53m 9.82s
Dec (J2000): +19d 11' 25.1"
with an uncertainty of 2.4 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 30525
Subject
GRB 210726A: CAHA 2.2m telescope optical limit
Date
2021-07-26T22:25:14Z (4 years ago)
From
Youdong HU at IAA-CSIC <huyoudong072@hotmail.com>
Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado M. D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), A. Gardini and I. Hermelo (CAHA) on behalf of a larger collaboration, report:
Following the detection of GRB210726A by Swift (Bernardini et al. GCNC 30523), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). A series of i-band images were gathered starting on July 26, 20:23 UT (i.e. 1.07 h post trigger). On the co-added image (15 x 60s), no optical object is detected down to 21.9 mag at the X-ray afterglow position reported by Swift/XRT (Osborne et al. GCNC 30524).
We thank the staff at Calar Alto observatory for their excellent support.
GCN Circular 30534
Subject
GRB 210726A: RATIR Optical Upper Limits and Candidate Host Galaxy
Date
2021-07-27T16:14:25Z (4 years ago)
From
Alan M Watson at UNAM <alan@astro.unam.mx>
Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat Butler (ASU), Alexander
Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox
(STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Enrico Ramirez-Ruiz
(UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey Moseley
(GSFC), Rosa L. Becerra (UNAM), Simone Dichiara (UMD), and Oc��lotl L��pez (UNAM)
report:
We observed the field of candidate short GRB 210726A (Bernardini et al., GCN
Circ., 30523) with the Reionization and Transients Infrared Camera (RATIR) on
the 1.5m Harold Johnson Telescope at the Observatorio Astron��mico Nacional on
Sierra San Pedro M��rtir from 2021/07 27.16 to 2021/07 27.22 UTC (8.24 to 9.65
hours after the BAT trigger), obtaining a total of 1.09 hours exposure in the r
and i bands.
For a source within the enhanced Swift-XRT error circle (Osborne et al., GCN
Circ., 30524), in comparison with the SDSS DR9 catalog, we obtain the following
upper limits (3-sigma):
r > 23.0
i > 22.7
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
We note that the SDSS galaxy J125309.63+191127.2 is 3.1 arcsec from the enhanced
XRT position and just outside the error circle. In our observations, it has
r = 22.2 +/- 0.2 and i = 22.2 +/- 0.2, in agreement with the cataloged values.
The cataloged photometric redshift is z = 0.35 +/- 0.15. The probability of a
chance alignment is approximately 3%. Given this low probability, we suggest
that this source might be the host galaxy.
Since this GRB appears to be potentially both short and low-redshift, we
encourage further observations.
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro M��rtir.
GCN Circular 30535
Subject
GRB 210726A: Likely a short burst
Date
2021-07-27T16:59:24Z (4 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
GRB 210726A, detected by Swift BAT and XRT (GCN 30523) appears likely
to be a short burst, despite the real time duration estimate (~3s)
reported in the discovery circular using limited data products. The
T90 estimate derived from the full downlinked Swift/BAT event data is
less than 0.5 seconds.
Follow-up is encouraged.
GCN Circular 30536
Subject
GRB 210726A: Swift-BAT refined analysis
Date
2021-07-27T19:36:05Z (4 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 210726A (trigger #1061687)
(Bernardini et al., GCN Circ. 30523). The BAT ground-calculated position is
RA, Dec = 193.333, 19.211 deg which is
RA(J2000) = 12h 53m 19.9s
Dec(J2000) = +19d 12' 38.9"
with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
The mask-weighted light curve shows a short spike that starts at ~T0,
peaks at ~T+0.2 s, and ends at ~T+0.4 s. Some tail emission from the
raw light curves was mentioned in the original circular (Bernardini et al.,
GCN Circ. 30523), and this potential weak tail can be seen in the 1-s
binned
light curve (15-350 keV) as well. However, image analyses from ~T+0.5 s
to ~T+2 s do not find any significant detections that are >~ 2 sigma.
Therefore, this signal is also consistent with noise fluctuation.
T90 (15-350 keV) is 0.39 +- 0.11 sec (estimated error including
systematics).
The time-averaged spectrum from T-0.00 to T+0.42 sec is best fit by
a simple power-law model. The power law index of the time-averaged
spectrum is 1.54 +- 0.47. The fluence in the 15-150 keV band is
4.5 +- 1.1 x 10^-8 erg/cm2. The 1-sec peak photon flux measured from
T-0.29 sec in the 15-150 keV band is 0.7 +- 0.3 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1061687/BA/
GCN Circular 30537
Subject
GRB 210726A: Swift-XRT refined Analysis
Date
2021-07-27T19:57:58Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A.
Tohuvavohu (U. Toronto), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), T.
Sbarrato (INAF-OAB) and M.G. Bernardini report on behalf of the
Swift-XRT team:
We have analysed 5.9 ks of XRT data for GRB 210726A (Bernardini et al.
GCN Circ. 30523), from 79 s to 75.9 ks after the BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Osborne et al. (GCN Circ. 30524).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.49 (+0.22, -0.26).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+/-0.3). The
best-fitting absorption column is 3.3 (+1.3, -1.2) x 10^21 cm^-2, in
excess of the Galactic value of 1.7 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 3.3 x 10^-11 (5.7 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.3 (+1.3, -1.2) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 4.5 sigma
Photon index: 2.2 (+/-0.3)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01061687.
This circular is an official product of the Swift-XRT team.
GCN Circular 30540
Subject
Fermi GBM Sub-Threshold Detection of GRB 210726A
Date
2021-07-28T15:21:41Z (4 years ago)
From
Peter Veres at UAH <veresp@gmail.com>
P. Veres (UAH) reports on behalf of the Fermi-GBM Team:
"Swift-BAT detected GRB 210726A at 19:19:03 UT (GCN 30523). There was
no Fermi-GBM
onboard trigger around the event.
The GBM targeted search [1], the most sensitive, coherent search for
GRB-like signals was run from +/-30 s around the BAT trigger time. A
transient source was identified whose most significant timescale according
to the search is 512 ms, and a location consistent with the Swift-BAT
event. The GBM targeted search event was found with the highest
significance with a "soft" spectral template (Band function with Epeak = 70
keV, alpha = -1.9, beta = -3.7).
The GBM light curve consists of a single peak. The time-averaged spectrum
from T0+0.6 s to T0+1.4 s is best fit by a power law function with index
-2.03 +/- 0.3 (T0 is 2021-07-26 19:19:03 UT). A power law function with an
exponential high-energy cutoff fits equally well, but it is not
statistically preferred over the power law; the fit measures the power law
index 0.23 +/- 1.67 and the cutoff energy, parameterized as Epeak, is 41
+/- 10 keV.
The event fluence (10-1000 keV) in this time interval for the power law
with the exponential cutoff is (6.4 +/- 1.7)E-08 erg/cm^2. Using the
photometric redshift z=0.35 reported by Watson et al. (GCN 30534), we
derive an isotropic equivalent energy in the 1-10,000 keV range of (2.1 +/-
0.5)E+49 erg.
This analysis is preliminary.
[1] Goldstein et al. 2019 arXiv:1903.12597
"
GCN Circular 30542
Subject
GRB 210726A: 6 GHz VLA radio upper limit
Date
2021-07-28T22:38:02Z (4 years ago)
From
Genevieve Schroeder at Northwestern University <genevieveschroeder2023@u.northwestern.edu>
G. Schroeder, W. Fong, A. Rouco Escorial, (Northwestern), T. Laskar (U. of
Bath), E. Berger (Harvard) report:
"We observed the position of short GRB 210726A (Bernardini et al., GCN
30523; Veres et al., GCN 30540; Palmer et al., GCN 30536; Tohuvavohu et
al., GCN 30535) with the Karl G. Jansky Very Large Array (VLA) under
program 20B-057 (PI: Fong) beginning on 2021 July 27.81 UT (1.00 days
post-burst) at a mean frequency of 6 GHz.
Based on preliminary analysis, in 1 hour of observations we do not detect
any radio emission at or near the position of the XRT afterglow (Osborne et
al., GCN 30524) to a 3-sigma limit of 15 microJy. Additional, detailed
analysis is ongoing.
We thank the VLA staff for quickly approving and executing these
observations."
GCN Circular 30543
Subject
GRB 210726A: Deep CAHA 2.2m limit
Date
2021-07-29T00:01:25Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all
HETH/IAA-CSIC), A. Gardini, and I. Hermelo (both CAHA) report:
We observed the XRT afterglow position (Osborne et al., GCN #30524) of
GRB 210726A (Bernardini et al., GCN #30523), classified as a short GRB
(Tohuvavohu, GCN #30535; Palmer et al., GCN #30536; Veres, GCN #30540)
with CAFOS mounted at the 2.2m Calar Alto telescope (Almeria, Spain),
under good conditions but at high airmass, starting July 26, 20:52:13
UT, 1.553 h after the GRB. We obtained 15 x 180 s images in r'.
Within the XRT error circle, we do not detect any source down to r' >
24.2 mag (AB magnitude) at 0.081518 d (1.956 h) after the burst, in
agreement with but deeper than limits presented by Hu et al., GCN
#30525; Watson et al., GCN #30534.
Watson et al. suggest an object about 3" away as a possible host-galaxy
candidate. We clearly detect this object and measure r' = 22.26 +/- 0.06
mag. This value is in agreement with detections from the PanSTARRS and
SDSS surveys, and therefore there is no evidence of excess emission that
could be an afterglow superposed on the host galaxy.
GCN Circular 30545
Subject
GRB 210726A: OSIRIS/GTC observations
Date
2021-07-29T12:54:52Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all
HETH/IAA-CSIC), J. P. U. Fynbo (DAWN/NBI), L. Izzo (DARK/NBI), N. R.
Tanvir (U. Leicester), and G. Gomez Velarde (GRANTECAN) report:
We observed the XRT afterglow position (Osborne et al., GCN #30524) of
GRB 210726A (Bernardini et al., GCN #30523), classified as a short GRB
(Tohuvavohu, GCN #30535; Palmer et al., GCN #30536; Veres, GCN #30540)
with OSIRIS mounted on the 10.4m Gran Telescopio Canarias (Observatorio
Astrof��isco Roque de Los Muchachos, La Palma, Canary Islands, Spain),
under mediocre conditions and at high airmass, starting July 26,
21:21:31 UT, 2.041 h after the GRB. We obtained a sequence of 30, 30,
60, 30 s images in r' for a total integration time of 150 s.
Within the XRT error circle, we do not detect any source down to r' >
24.4 mag (AB magnitude), measured against a nearby PanSTARRS fiel star,
at 0.088533 d (2.125 h) after the burst, in agreement with Kann et al.,
GCN #30543.
The possible host galaxy (Watson et al., GCN #30534, Kann et al., GCN
#30543) is found at r' = 22.04 +/- 0.05 mag, again in agreement with
detections from the PanSTARRS and SDSS surveys.
GCN Circular 30558
Subject
GRB 210726A: Chandra detection of the X-ray afterglow
Date
2021-07-30T23:26:02Z (4 years ago)
From
Alicia Rouco Escorial at CIERA <alicia.rouco.escorial@northwestern.edu>
A. Rouco Escorial, W. Fong, K. Paterson (Northwestern University), R. Margutti (UC Berkeley) and E. Berger (Harvard University) report:
���We initiated observations with the Chandra X-ray Observatory of the short-duration GRB 210726A (Bernardini et al., GCN 30523; Tohuvavohu, GCN 30535; Palmer, GCN 30536) starting on 2021 July 29 16:04:38 UT, with a median observation time of ~3 days post-trigger. We obtained one ACIS-S observation under the Proposal 22400461 (ObsID 23445; PI: Fong), with an effective exposure time of ~24.6 ks.
We obtain a ~7sigma detection of GRB 210726A with a total net source counts of 76+/-10 (0.5-7 keV). The Chandra position of the short GRB is fully consistent with the enhanced Swift-XRT position (90% confidence; XRT GRB catalogue, Evans et al., 2009). The Chandra position is:
RA(J2000)= 12h53m09.7s
Dec(J2000)=19d11m24.6s
with a total positional uncertainty of 0.81 arcsec (largely dominated by Chandra's absolute astrometric uncertainty).
Based on our MCMC modeling, the XRT and Chandra afterglow flux, starting at ~120.89 s post-burst, can be modeled with a broken power-law decline characterized by a second segment with a decay index (F~t^alpha) of alpha2=-0.62 (-0.05,+0.04) starting at ~418 s post-burst. In particular, the Chandra detection roughly follows the latest decline rate based on XRT data alone..
Further Chandra observations are planned. We thank the Chandra Director, Pat Slane, and staff for the rapid planning and scheduling of these observations.���
GCN Circular 30658
Subject
GRB 210726A: VLA radio afterglow detection
Date
2021-08-18T20:48:40Z (4 years ago)
From
Genevieve Schroeder at Northwestern University <genevieveschroeder2023@u.northwestern.edu>
G. Schroeder, K. D. Alexander, W. Fong, A. Rouco Escorial, (Northwestern),
T. Laskar (U. of Bath), E. Berger (Harvard) report:
"We re-observed the position of short GRB 210726A (Bernardini et al., GCN
30523; Veres et al., GCN 30540; Palmer et al., GCN 30536; Tohuvavohu et
al., GCN 30535) with the Karl G. Jansky Very Large Array (VLA) under
program 20B-057 (PI: Fong) beginning on 2021 August 07.02 UT (11.21 days
post-burst) at a mean frequency of 6 GHz.
In 1.5 hour of observations we detect a radio source with a preliminary
flux density of ~40 uJy. The position of this radio source is fully
consistent with the position of the X-ray afterglow (Osborne et al., GCN
30524; Rouco Escorial et al., GCN 30558) at:
RA(J2000): 12:53:09.8
Dec(J2000): +19:11:25.1
with an uncertainty of 0.6 arcsec in each coordinate.
We obtained further VLA observations at 6 GHz and 10 GHz beginning on 2021
August 14.75 UT (18.94 days post-burst) and detect the source at both
frequencies. We find a significant brightening at 6 GHz, confirming this
source as the radio afterglow of GRB210726A. We note that this radio
afterglow is among the brightest ever detected for a short GRB to date.
Further observations are planned. We thank the VLA staff for quickly
approving and executing these observations."