GRB 210725A
GCN Circular 30501
Subject
GRB 210725A: Swift detection of a burst
Date
2021-07-25T04:07:21Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),
N. J. Klingler (GSFC/UMBC/CRESSTII), A. Y. Lien (GSFC/UMBC),
A. Melandri (INAF-OAB), D. M. Palmer (LANL) and T. Sbarrato (INAF-OAB)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 03:47:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210725A (trigger=1061511). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 215.363, -1.177 which is
RA(J2000) = 14h 21m 27s
Dec(J2000) = -01d 10' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a complex
structure with a duration of about 10 sec. The peak count rate
was ~1800 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 03:48:53.6 UT, 110.7 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 215.3742,
-1.1934 which is equivalent to:
RA(J2000) = 14h 21m 29.81s
Dec(J2000) = -01d 11' 36.2"
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 in excess of the Galactic value (4.09 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9
(+2.81/-2.40) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 114 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 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.046.
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 30503
Subject
GRB 210725A: KAIT Optical Upper Limit
Date
2021-07-25T05:20:35Z (4 years ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 210725A (Bernardini et al.,
GCN 30501) starting at 56 minutes after the burst. A total of
30x60s images were obtained in the clear (roughly R) filters.
We do not detect any optical afterglow candidate within the XRT
position error circle (Bernardini et al., GCN 30501), neither in
single image, nor in the co-add images. The typical limiting magnitude
of our single clear image is about 18.5 mag calibrated to the PS1 catalog.
GCN Circular 30507
Subject
GRB 210725A: CALET Gamma-Ray Burst Monitor detection
Date
2021-07-25T10:59:46Z (4 years ago)
From
Valentin Pal'shin at AGU <val@phys.aoyama.ac.jp>
S. Torii (Waseda U),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
Y. Asaoka (ICRR), Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC),
M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The long GRB 210725A (Swift detection: Bernardini et al., GCN Circ. 30501;
https://gcn.gsfc.nasa.gov/other/210725A.gcn3) triggered the CALET
Gamma-ray Burst Monitor (CGBM) at 03:47:01.565 UTC on 25 July 2021
(http://cgbm.calet.jp/cgbm_trigger/flight/1311219774/index.html).
The burst signal was seen only by the SGM detector.
The burst light curve shows a single weak pulse which starts at T+1.4 sec,
peaks at T+1.5 sec,and ends at T+6.9 sec. The T90 and T50 durations
measured by the SGM data are 5.0 +- 0.7 sec and 3.0 +- 0.9 sec
(40-1000 keV), respectively.
The ground processed light curve is available at
http://cgbm.calet.jp/cgbm_trigger/ground/1311219774/
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at the Waseda University.
GCN Circular 30509
Subject
GRB 210725A: MITSuME Akeno optical upper limits
Date
2021-07-25T14:19:34Z (4 years ago)
From
Masafumi Niwano at Tokyo Institute of Tech <niwano@hp.phys.titech.ac.jp>
M. Niwano, R. Hosokawa, K. L. Murata, N. Ito, H. Takamatsu, Y. Imai, R.
Noto, S. Sato, M. Takaku, R. Yamaguchi, Y. Yatsu, and N. Kawai
(TokyoTech) report on behalf of the MITSuME collaboration:
We observed the field of GRB 210725A (Bernardini et al. GCN Circular
#30501, WeiKang Zheng et al. GCN Circular #30503, S. Torii et al. GCN
Circular #30507) with the optical three color (g', Rc, and Ic) CCD
cameras attached to the MITSuME 50 cm telescope Akeno. The observation
with a series of 60 sec exposures started at 2021-07-25 10:26:07 UT (6.7
hours after Swift BAT trigger). We stacked the images with good
conditions. We did not detect any uncatalogued sources within the XRT
error region (Bernardini et al. GCN Circular #30501). We obtained the
5-sigma limits of the stacked images as follows.
T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
6.7 2021-07-25 11:21:56.58 900 g'>18.6, Rc>18.9, Ic>18.4
------------------------------------------------------------------------------------------------
T-EXP: Total Exposure time
We used PS1 catalog for flux calibration.
The magnitudes are expressed in the AB system.
The images were processed in real-time through the MITSuME GPU
reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages
4-24; https://github.com/MNiwano/Eclaire).
GCN Circular 30514
Subject
GRB 210725A: Swift-BAT refined analysis
Date
2021-07-25T20:06:04Z (4 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
M. G. Bernardini (INAF-OAB), H. A. Krimm (NSF),
S. Laha (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-239 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 210725A (trigger #1061511)
(Bernardini et al., GCN Circ. 30501). The BAT ground-calculated position is
RA, Dec = 215.381, -1.177 deg which is
RA(J2000) = 14h 21m 31.4s
Dec(J2000) = -01d 10' 37.2"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.
The mask-weighted light curve shows a multi-peaked structure that
starts at ~T0 and ends at ~T+60 s. The main peak occurs at ~T+1 s.
T90 (15-350 keV) is 53.54 +- 11.25 sec (estimated error including
systematics).
The time-averaged spectrum from T-0.82 to T+59.86 sec is best fit
by a simple power-law model. The power law index of the time-averaged
spectrum is 1.42 +- 0.32. The fluence in the 15-150 keV band
is 8.1 +- 1.2 x 10^-7 erg/cm2. The 1-sec peak photon flux measured
from T+1.01 sec in the 15-150 keV band is 1.0 +- 0.2 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/1061511/BA/
GCN Circular 30517
Subject
GRB 210725A: Swift-XRT refined Analysis
Date
2021-07-26T00:09:08Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai
(INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp
(PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P.
Beardmore (U. Leicester) and M.G. Bernardini report on behalf of the
Swift-XRT team:
We have analysed 6.3 ks of XRT data for GRB 210725A (Bernardini et al.
GCN Circ. 30501), from 114 s to 64.8 ks after the BAT trigger. The
data comprise 74 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 1409 s of PC mode data and 2 UVOT
images, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
215.37414, -1.19268 which is equivalent to:
RA (J2000): 14h 21m 29.79s
Dec(J2000): -01d 11' 33.6"
with an uncertainty of 1.9 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.99 (+/-0.08).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.48 (+0.21, -0.19). The
best-fitting absorption column is 8.0 (+6.8, -3.9) x 10^20 cm^-2,
consistent with the Galactic value of 4.1 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 4.5 x 10^-11 (4.9 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 8.0 (+6.8, -3.9) x 10^20 cm^-2
Galactic foreground: 4.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.48 (+0.21, -0.19)
If the light curve continues to decay with a power-law decay index of
1.99, the count rate at T+24 hours will be 1.2 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.6 x
10^-16 (6.1 x 10^-16) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01061511.
This circular is an official product of the Swift-XRT team.
GCN Circular 30519
Subject
GRB 210725A: Fermi GBM detection
Date
2021-07-26T16:48:00Z (4 years ago)
From
Suraj Poolakkil at UAH <sp0076@uah.edu>
S. Poolakkil (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 03:47:03.54 UT on 25 July 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210725A (trigger 648877628 / 210725158)
which was also detected by the Swift/BAT (Bernardini et al. 2021, GCN
30501).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 78
degrees.
The GBM light curve consists of a single peak followed by some
extended emission with a duration (T90) of about 47 s (50-300 keV).
The time-averaged spectrum from T0-1.02 s to T0+9.21 s
is best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.37 +/- 0.22 and
the cutoff energy, parameterized as Epeak, is 460 +/- 104 keV.
The event fluence (10-1000 keV) in this time interval is
(3.14 +/- 0.35)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.64 s in the 10-1000 keV band
is 2.0 +/- 0.2 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 30527
Subject
GRB 210725A: Swift/UVOT Upper Limits
Date
2021-07-27T00:40:13Z (4 years ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
M. H. Siegel (PSU) and M. G. Bernardini (INAF-OAB)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210725A
114 s after the BAT trigger (Bernardini et al., GCN Circ. 30501).
No optical afterglow consistent with the XRT position (Perri et al. GCN Circ. 30517)
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) 114 264 147 >20.7
u (fc) 273 523 246 >20.2
white 114 1545 392 >21.0
v 603 1595 117 >19.1
b 529 1519 97 >20.4
u 273 1495 343 >20.4
w1 653 1470 97 >19.2
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.047 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 30530
Subject
GRB 210725A: AbAO optical upper limit
Date
2021-07-27T06:54:14Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI),
S. Belkin (IKI), V. R. Ayvazian (AbAO), G. V. Kapanadze (AbAO), report
on behalf of GRB IKI FuN:
We observed the field of GRB 210725A (Bernardini et al. GCN 30501;
Torii et al. GCN 30507; Poolakkil et al. GCN 30519) with AS-32
telescope of Abastumani observatory (AbAO) in R-filter starting on July,
25 (UT) 19:11:58. We do not detect any object in the enhanced XRT
position (Perri et al. GCN 30517). The non detection is consistent with
optical observations (Zheng et al. GCN 30503; Niwano et al., GCN 30509;
Siegel et al. GCN 30527).
Preliminary photometry of the field is following
Date UT start t-T0 Filter Exp. OT Err. UL(3sigma)
(mid, days) (s)
2021-07-25 19:11:58 0.65481 R 36*60 n/d n/d 20.8
The photometry is based on the nearby stars:
USNO-B1.0 R2
USNO_B10_id R2
0888-00234198 14.31
0888-00234167 15.25