GRB 210724A
GCN Circular 30497
Subject
GRB 210724A: Swift detection of a burst
Date
2021-07-24T20:37:28Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
P. D'Avanzo (INAF-OAB), M. G. Bernardini (INAF-OAB),
J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 20:14:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210724A (trigger=1061482). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 227.407d, -6.274d which is
RA(J2000) = 15h 09m 38s
Dec(J2000) = -06d 16' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). Due to a telemetry outage the BAT lightcurve is
not immediately available. However, the trigger information indicates
a duration of at least 4 seconds.
The XRT began observing the field at 20:17:09.0 UT, 179.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 227.4118,
-6.2911 which is equivalent to:
RA(J2000) = 15h 09m 38.83s
Dec(J2000) = -06d 17' 27.8"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). 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 consistent with the Galactic value of 8.23
x 10^20 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 124 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 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag.
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
0.097.
Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT 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 30498
Subject
GRB210724A: MeerLICHT upper limits
Date
2021-07-24T22:56:14Z (4 years ago)
From
Simon de Wet at University of Cape Town <dwtsim002@myuct.ac.za>
S. de Wet (UCT), P.J. Groot (Radboud/UCT/SAAO), A.J. Levan (Radboud),
P.M. Vreeswijk (Radboud), report on behalf of the MeerLICHT consortium:
Following the detection of GRB210724A by Swift and its X-ray
counterpart (D'Avanzo et al., GCN30497), the 0.6m MeerLICHT telescope,
located at Sutherland, South Africa obtained a repeating series of
60s images in the q,u,q,g,q,r,q,i,q,z bands. Observations began at
2021-07-24, 20:25:18.02 UT, 11 minutes after the Swift detection,
and 2 minutes after the distribution of the BAT alert, and continued
untill 21:27:36 UT.
We detect no optical afterglow at the XRT position (D�Avanzo et al.
GCN30497) in our first u,g,q,r,i,z exposures to 5-sigma limiting
magnitudes of:
u > 18.59 at 20:27:37 UT
g > 19.40 at 20:31:01 UT
q > 19.77 at 20:25:49 UT
r > 19.38 at 20:34:31 UT
i > 19.26 at 20:37:45 UT
z > 18.14 at 20:59:12 UT
Full moon conditions limited the depth of our exposures.
We do note that an r=21.5 object is visible within the XRT localisation
in PanSTARRS imaging of the field, and is a plausible host galaxy.
MeerLICHT is built and run by a consortium consisting of Radboud
University, University of Cape Town, the South African Astronomical
Observatory, the University of Oxford, the University of Manchester
and the University of Amsterdam.
Disclaimer - University of Cape Town This email is subject to UCT policies and email disclaimer published on our website at http://www.uct.ac.za/main/email-disclaimer or obtainable from +27 21 650 9111. If this email is not related to the business of UCT, it is sent by the sender in an individual capacity. Please report security incidents or abuse via https://csirt.uct.ac.za/page/report-an-incident.php.
GCN Circular 30511
Subject
GRB 210724A: Afterglow candidate from OSIRIS/GTC
Date
2021-07-25T16:50:29Z (4 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (HETH/IAA-CSIC,DARK/NBI), C. C. Thoene, D. A. Kann, 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), N. Castro-Rodriguez, and A. Marante (GRANTECAN, IAC) report:
We observed the field of GRB 210724A (D'Avanzo et al. GCN 30497) with OSIRIS mounted on the 10.4 m GTC telescope at the Roque de los Muchachos observatory (La Palma, Spain). Observations started at 22:07 UT (1.88 hr after the burst). Observations were affected by strong calima and the full Moon, which resulted in bad transparency and very high background. In a series of short images in r', i' and z' bands we detect a new source, not present in the PanSTARRS catalogue images. The object is located at (J2000 +/- 0.5"):
RA: 15:09:39.44
Dec.: -06:17:26.0
This object had a magnitude of r' = 22.00 +/- 0.15 mag as compared to PanSTARRS field stars. We note that this source is within the early XRT alert error circles but outside the refined one (D'Avanzo et al. GCN 30497). There is no new source detected within this refined error circle. Due to the fact that this source is significantly brighter than the PanSTARRS limit, we propose it as the optical counterpart of GRB 210724A.
GCN Circular 30513
Subject
GRB 210724A: Swift-BAT refined analysis
Date
2021-07-25T19:43:26Z (4 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC),
P. D'Avanzo (INAF-OAB), H. A. Krimm (NSF),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 210724A (trigger #1061482)
(D'Avanzo et al., GCN Circ. 30497). The BAT ground-calculated position is
RA, Dec = 227.425, -6.279 deg which is
RA(J2000) = 15h 09m 41.9s
Dec(J2000) = -06d 16' 42.9"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 34%.
The mask-weighted light curve shows a multi-peaked structure
that starts at ~T-40 s and ends at ~T+25 s. The main peak
occurs at ~T0. T90 (15-350 keV) is 50.57 +- 9.54 sec (estimated
error including systematics).
The time-averaged spectrum from T-38.55 to T+25.50 sec is best
fit by a simple power-law model. The power law index of the
time-averaged spectrum is 2.30 +- 0.28. The fluence in the
15-150 keV band is 1.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak
photon flux measured from T-0.51 sec in the 15-150 keV band
is 2.5 +- 0.8 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/1061482/BA/
GCN Circular 30515
Subject
GRB 210724A: Swift-XRT refined Analysis
Date
2021-07-25T21:43:29Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &
INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. Tohuvavohu (U. Toronto), B.
Sbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L.
Page (U. Leicester) and P. D'Avanzo report on behalf of the Swift-XRT
team:
We have analysed 2.5 ks of XRT data for GRB 210724A (D'Avanzo et al.
GCN Circ. 30497), from 123 s to 84.6 ks after the BAT trigger. The
data comprise 263 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 331 s of PC mode data and 1 UVOT
image, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
227.41131, -6.29009 which is equivalent to:
RA (J2000): 15h 09m 38.72s
Dec(J2000): -06d 17' 24.3"
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.17 (+0.10, -0.09).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.48 (+/-0.08). The
best-fitting absorption column is 2.08 (+0.23, -0.22) x 10^21 cm^-2,
in excess of the Galactic value of 8.2 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 2.8 x 10^-11 (4.9 x 10^-11) erg
cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
Total column: 2.08 (+0.23, -0.22) x 10^21 cm^-2
Galactic foreground: 8.2 x 10^20 cm^-2
Excess significance: 9.5 sigma
Photon index: 2.48 (+/-0.08)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01061482.
This circular is an official product of the Swift-XRT team.
GCN Circular 30518
Subject
GRB 210724A: Zeiss-1000 of Koshka observatory, optical upper limit
Date
2021-07-26T12:14:12Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
S. Belkin (IKI), A. Novichonok (Petrozavodsk State University, KIAM),
A. Pozanenko (IKI), A. Zhornichenko (KIAM), N. Pankov (HSE) report
on behalf of IKI GRB FuN:
We observed the field of GRB 210724A (D'Avanzo et al. GCN 30497) with
Zeiss-1000 telescope of Koshka observatory starting on July 24 (UT)
20:39:32. We do not detect any object XRT error circle (D'Avanzo et al.
GCN 30497). We also not detect the object at the position of the
afterglow candidate (Ugarte Postigo et al., GCN 30511).
Preliminary photometry of the field is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2021-07-24 20:39:32 0.024919 R 21*60 n/d n/d 18.6
The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
USNO-B1.0_id R2
0837-0267865 15.24
0836-0268753 16.95
0837-0267827 15.54
GCN Circular 30529
Subject
GRB 210724A: Swift/UVOT Upper Limits
Date
2021-07-27T06:17:13Z (4 years ago)
From
Sam LaPorte at PSU <sjl5346@psu.edu>
GRB 210724A: Swift/UVOT Upper Limits
S. J. LaPorte (PSU) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210724A
125 s after the BAT trigger (D'Avanzo et al., GCN Circ. 30497).
No optical afterglow consistent with the XRT position
(D'Avanzo et al. GCN Circ. 30497)
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 125 275 147 >20.8
u_FC 283 513 226 >20.1
white 125 275 147 >20.8
u 283 513 227 >20.1
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.097 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 30547
Subject
GRB 210724A: Corrected Swift-XRT enhanced position
Date
2021-07-29T15:25:48Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester) and P. D'Avanzo (INAF-OAB) report on behalf of
the Swift-XRT team.
The XRT position of GRB 210724A reported in GCN Circ. 30515 was 11" from
the position of the optical candidate found by de Ugarte Postigo et al.
(GCN Circ. 30511). Unusually, this position underwent significant
variation during the normal revisions after each data downlink.
Investigation has revealed a rare local minimum issue during the first
XRT image, which has now been fixed.
The best XRT position is RA, Dec = 227.41461, -6.29070 which is
equivalent to:
RA (J2000): 15h 09m 39.51s
Dec(J2000): -06d 17' 26.5"
with an uncertainty of 3.0 arcsec (radius, 90% confidence). This
position is 1.1" from the optical position of de Ugarte Postigo et al.
We apologise for the confusion caused by this rare glitch, which
coincided with the author's vacation (Murphy et al).
As ever, the most recent version of the position can be found online at:
https://www.swift.ac.uk/xrt_positions/01061482/
This circular is an official product of the Swift-XRT team.
GCN Circular 30551
Subject
GRB 210724A: Early CAHA 2.2m limit
Date
2021-07-30T12:37:10Z (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 in-flight XRT afterglow position (revised in Evans et
al., GCN #30547) of GRB 210724A (D'Avanzo et al., GCN #30497) with CAFOS
mounted at the 2.2m Calar Alto telescope (Almeria, Spain), under very
adverse conditions (high airmass, strong Calima, clouds, bad seeing,
strong moonlight - the works). We obtained 10 x 180 s images in r',
starting on July 24, 21:07:08 UT (0.8831 h after the burst).
At the position of the GTC afterglow candidate (de Ugarte Postigo et
al., GCN #30511), we detect no source down to r' > 22.0 mag (AB
magnitude) against PanSTARRS comparison stars, at midtime 0.0482 d
(1.1569 h) after the burst. This is of similar depth as the detection by
de Ugarte Postigo et al., GCN #30511, perhaps indicating a slowly rising
afterglow, or at least one that is not steeply decaying.