GRB 130925A
GCN Circular 15246
Subject
GRB 130925A: Swift detection of a burst
Date
2013-09-25T04:26:41Z (12 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
J. L. Racusin (NASA/GSFC), M. H. Siegel (PSU) and T. N. Ukwatta (MSU)
report on behalf of the Swift Team:
At 04:11:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130925A (trigger=571830). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 41.183, -26.134 which is
RA(J2000) = 02h 44m 44s
Dec(J2000) = -26d 08' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed that the burst
was active during the pre-planned slew before the nominal trigger
with an additional peak extending at least to T+170. The peak count
rate was ~2700 counts/sec (15-350 keV), at ~110 sec after the trigger.
The XRT began observing the field at 04:13:52.3 UT, 147.4 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 41.1766, -26.1544 which is equivalent to:
RA(J2000) = +02h 44m 42.38s
Dec(J2000) = -26d 09' 15.8"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 76 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.
UVOT took a finding chart exposure of 150 seconds with the White
filter starting 156 seconds after the BAT trigger. No credible
afterglow candidate has been found in the initial data products. The
2.7'x2.7' covers 100% of the XRT error circle. The typical 3-sigma
upper limit has been about 19.6 mag. Results from the list of sources
generated on-board are not available at this time. No correction has
been made for the expected extinction corresponding to E(B-V) of
0.02.
Burst Advocate for this burst is A. Y. Lien (yarleen AT gmail.com).
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/too.html.)
GCN Circular 15247
Subject
GRB 130925A: GROND afterglow candidate
Date
2013-09-25T06:05:22Z (12 years ago)
From
Vladimir Sudilovsky at MPE <vsudilov@mpe.mpg.de>
V. Sudilovsky (MPE Garching), D.A. Kann, and J. Greiner
(all MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 130925A (Lien et al., GCN #15246)
simultaneously in g'r'i'z'JHKs with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).
The first epoch observation started at 04:18:52 UT on 25 Sept 2013,
7 minutes after the GRB trigger. They were performed at an average
seeing of 0.7" and at an average airmass of 1.3. We do not find any
sources within the revised 3".6 Swift XRT error circle. However, we do
find an uncataloged red source 2" east of the error circle at position:
RA (J2000.0) = 02:44:42.96 = 41.1790
Dec. (J2000.0) = -26:09:11.16 = -26.1531
with an uncertainty of 0.3" in each coordinate.
Based on a total exposure of 4.4 minutes in g'r'i'z' and 4 minutes in
JHK, we estimate preliminary magnitudes (all in AB) of
g' > 21.5 mag,
r' > 22 mag,
i' = 21.8 � 0.1 mag,
z' = 21.3 � 0.1 mag,
J = 19.6 � 0.1 mag,
H = 18.6 � 0.1 mag, and
K = 18.0 � 0.1 mag.
The source is seen to be brightening in the first images before
fading strongly. We suggest this source to be the afterglow of GRB
130925A.
Given magnitudes are calibrated against GROND zeropoints as well as
2MASS field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V) = 0.02
mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular 15248
Subject
GRB 130925A: MAXI/GSC detection
Date
2013-09-25T08:31:49Z (12 years ago)
From
Satoshi Nakahira at JAXA/MAXI <nakahira.satoshi@jaxa.jp>
K. Suzuki, H. Sakakibara, H. Negoro (Nihon U.),
S. Nakahira, H. Tomida, S. Ueno, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA),
T. Mihara, M. Sugizaki, M. Morii, M. Serino, T. Yamamoto, J. Sugimoto,
T. Takagi, M. Matsuoka (RIKEN),
N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Nakano (AGU),
H. Tsunemi, M. Sasaki (Osaka U.),
M. Nakajima, K. Fukushima, T. Onodera (Nihon U.),
Y. Ueda, M. Shidatsu, T. Kawamuro (Kyoto U.),
Y. Tsuboi, M. Higa (Chuo U.),
M. Yamauchi, K. Yoshidome, Y. Ogawa, H. Yamada (Miyazaki U.),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:
The MAXI/GSC Nova alert system triggered a bright uncatalogued X-ray transient source at
UT 2013-09-25T05:13:41.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(41.38 deg, -25.91 deg) = (02 45 32, -25 54 54)(J2000)
with a 90% C.L. statistical error of 0.2 deg and an additional systematic uncertainty
of 0.1 deg (90% containment radius).
The position is consistent with that of GRB 130925A (Lien et al. GCN #15246),
and apart from GRB 130925A by 0.30 deg.
This detection is, however, about 1 hour after the Swift detection.
The 2-20 keV flux was 290 (-51/+53) mCrab. An absorbed power-law fit to the burst spectrum
gives a photon index 1.62 +/- 0.27.
There was no significant excess flux in the previous transit at 03:41 UT
and in the next transit at 06:47 UT with an upper limit of 20 mCrab for each.
[GCN OPS NOTE(25sep13): Per author's request, the Lien citation of 12526
was changed to 15246.]
GCN Circular 15249
Subject
GRB 130925A: VLT/UVES observations
Date
2013-09-25T10:45:42Z (12 years ago)
From
Paul Vreeswijk at Weizmann Inst of Science <paul.vreeswijk@weizmann.ac.il>
P. M. Vreeswijk (Weizmann), D. Malesani, J. P. U. Fynbo (DARK/NBI),
A. De Cia (Weizmann) and C. Ledoux (ESO) report:
GRB 130925A (Lien et al., GCN 15246; Suzuki et al., GCN 15248) was
observed with UVES at the ESO-VLT, in Rapid Response Mode, starting at
around 5 UT (50 minutes after the Swift trigger). A series of spectra
were taken of the brightest object near the XRT error circle. We
caution that the small field of view of the UVES acquisition camera
and the lack of nearby bright stars does not allow us to identify this
object unambiguously as the optical counterpart discovered by
Sudilovsky et al. (GCN 15247).
Preliminary analysis of the automatically reduced spectra reveals the
presence of a very faint continuum in the red part and a pair of
emission lines at 8845 A and 8873 A. These lines can be identified
with Halpha and [NII] 6585 at a redshift of z=0.347.
We are grateful for the excellent support at Paranal provided by
Jonathan Smoker and Patricia Guajardo, and we thank D. A. Kann and the
GROND team for showing us a finding chart of the afterglow field.
GCN Circular 15250
Subject
GRB 130925A: VLT/X-shooter redshift
Date
2013-09-25T11:07:01Z (12 years ago)
From
Sylvio Klose at TLS Tautenburg <klose@tls-tautenburg.de>
V. Sudilovsky, D.A. Kann, P. Schady (all MPE Garching), S. Klose (TLS
Tautenburg), J. Greiner (MPE Garching), and T. Kruehler (ESO) report:
We observed the optical/NIR afterglow (Sudilovsky et al., GCN 15247) of
GRB 130925A (Swift trigger 571830, Lien et al., GCN 15246) using ESO/VLT
UT2 equipped with the X-shooter spectrograph.
Observations started at 07:42 UT on 2013-09-25, about 3.5 hr after the
Swift trigger. A total exposure of 1.6 hr was obtained, covering the
spectral range from 3000 to 20500 AA.
In the spectrum we detect emission lines, which we interpret as being due
to [O II](3726,3729), H_beta, [O III](4959), [O III](5007) and H_alpha at
a common redshift of z = 0.35, in agreement with Vreeswijk et al. (GCN
15249).
We thank the Paranal staff for excellent support, in particular Linda
Schmidtobreick, Jonathan Smoker and Patricia.
GCN Circular 15251
Subject
GRB 130925A: Enhanced Swift-XRT position
Date
2013-09-25T11:55:00Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 614 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 130925A, 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 = 41.17877, -26.15300 which is equivalent
to:
RA (J2000): 02h 44m 42.91s
Dec (J2000): -26d 09' 10.8"
with an uncertainty of 1.6 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 15252
Subject
GRB 130925A: TAROT La Silla observatory optical observations
Date
2013-09-25T13:27:30Z (12 years ago)
From
Alain Klotz at IRAP-CNRS-OMP <Alain.Klotz@free.fr>
Klotz A. (IRAP-CNRS-OMP), Gendre B. (IRAP-CNRS-OMP),
Boer M., Siellez K., Dereli H., Bardho O. (UNS-CNRS-OCA),
Atteia J.L. (IRAP-CNRS-OMP) report:
We imaged the field of GRB 130925A detected by SWIFT
(trigger 571830) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.
The observations started 88.1s after the GRB trigger
(13.0s after the notice). The elevation of the field increased from
50 degrees above horizon and weather conditions
were good.
We do not detect the afterglow discovered by Sudilovsky
et al. (GCNC 15247, GCNC 15250) and confirmed by Vreeswijk
et al. (GCNC 15249). However, the observations of TAROT
give upper optical limits of the early afterglow.
The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39):
t0+88.1s to t0+148.1s : Rlim = 17.5
We co-added a series of exposures with diurnal drift:
t0+477s to t0+1081s : Rlim = 19.2
Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.
GCN Circular 15253
Subject
GRB 130925A: Initial Similarities to Swift J1644+57
Date
2013-09-25T14:59:41Z (12 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
D. N. Burrows (PSU), D. Malesani (DARK/NBI), A. Y. Lien (NASA/GSFC/ORAU),
S. B. Cenko (NASA/GSFC), and N. Gehrels (NASA/GSFC) report:
At 04:11:24 UT on 25 September 2013, the Swift BAT triggered on an object
denoted as GRB 130925A on the assumption that it is a gamma-ray burst
(Lien et al., GCN 15246). Here we note that this source presents several
unusual features that are atypical of GRBs.
The initial XRT observations show extremely rapid and dramatic flaring
over the first 10^4 s, far in excess of what we typically see in GRBs.
The high X-ray flux at these relatively late times is likely what resulted
in the detection of this source by MAXI ~ 1 hour after the GRB (Suzuki
et al., GCN 15248). The Swift/XRT light curve is available at the
following URL:
http://www.swift.ac.uk/xrt_curves/00571830/
We note that this behavior is at first glance similar to the highly
variable soft X-ray light curve observed from Swift J1644+57 (GRB
110328A), which has been interpreted as a newly formed relativistic jet
resulting from the tidal disruption of a star by a super-massive black
hole (Burrows et al. 2011; Levan et al. 2011; Zauderer et al. 2011; Bloom
et al. 2011). Like Swift J1644+57, GRB 130925A is a BAT image trigger,
is associated with highly absorbed optical/NIR transient emission
(Sudilovsky et al., GCN 15247), and lies at a relatively low redshift
(z = 0.347; Vreeswijk et al., GCN 15249; Sudilovsky et al., GCN 15250).
We encourage observations at all wavelengths to help determine the nature
of this interesting source.
GCN Circular 15254
Subject
GRB 130925A: Swift-XRT refined Analysis
Date
2013-09-25T15:27:05Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans, C. Pagani, K.L. Page, A.P. Beardmore, R.L.C. Starling (U.
Leicester) and A. Y. Lien (NASA/GSFC/ORAU) report on behalf of the
Swift-XRT team:
We have analysed 4.7 ks of XRT data for GRB 130925A (Lien et al. GCN
Circ. 15246), from 151 s to 12.0 ks after the BAT trigger. The data
comprise 3.2 ks in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN. Circ 15251).
The light curve behaviour is dominated by sharp, bright flares. The
initial decay follows a power-law with an index of 2.70 (+/- 0.03) and
then breaks at T0+464 (+9,-6) to a virtually flat segment, with a
formal decay index of 0.16 (+0.11, -0.17). At this point the XRT count
rate is 47 ct/sec (approx 2.1e-9 erg cm^-2 s^-1, 0.3-10 keV). Then at
T0+750 a flare begins, which peaks at T0+1000 s at a count rate of ~100
ct/sec. This flare fades steeply to ~8 ct/sec at T0+1240 s at which
point a second, steep and bright flare begins. This peaks at T0+1380 s
at a count rate of ~150 ct/sec. The Swift observations were interrupted
at T0+1503 s as the GRB entered Earth-eclipse; the count-rate by this
time had fallen to ~50 ct/sec.
The MAXI detection (Suzuki et al., GCN Circ. 15248) took place while
the GRB was thus unobservable by Swift and corresponds to an XRT count
rate of ~80 ct/sec.
Swift began observing the GRB again at T0+4.75 ks; the count rate was
~8 ct/sec, but rapidly rising due to another flare which peaked 200 s
later at ~130 ct/sec, and then faded to ~3 ct/sec by T0+6.1 ks. Another
flare began shortly after, at T0+6.6 ks and peaked at T0+7.1 ks at 150
ct/sec. Observations were interrupted soon after this as the GRB again
went into eclipse. The next observation began at T0+10.5 ks at which
time the count rate was ~5 ct/sec but again rising in a flare which
peaked at T0+11.2 ks, at a count rate of ~20 ct/sec. This decayed to ~5
ct/sec by T0+11.6ks and then began to rise again, but the Swift
observations stopped just after this. Further observations are planned.
The time-averaged WT mode spectrum can be modelled with an absorbed
power-law with a photon index of 1.73 (+/-0.02) and an absorption
column of 6.8e21 cm^-2 at z=0.347 (Vreeswijk et al., GCN Circ. 15249)
in addition to the Galactic value of 0.17e21 cm^-2 (Kalberla et al,
2005). However as is typical during flaring episodes, there is strong
spectral evolution during the XRT observations. We therefore extracted
a further 4 spectra, one before the flares and one during each of them.
These spectra were fitted above 0.5 keV to avoid possible instrumental
effects at low energies caused by the accumulation of charge traps due
to radiation damage since the release of the current CALDB WT gain file
(version 13).
In the spectra for the first 2 flares there is evidence for additional
soft emission above the simple power-law. There are known calibration
issues which can cause bumps such as these to appear artificially (see
http://www.swift.ac.uk/analysis/xrt/digest_cal.php#abs) so we extracted
the spectra using only single-pixel events, however the soft component
is still present. It can be well modelled by adding in a thermal
component (reducing the cstat of the fits by ~120). In the first flare
this has a temperature of 33 (+/-3) eV, and in the second flare 45 (+/-
6) eV.
Details of the power-law fits are given below (for the first two flare
spectra these are the fits which include the soft component); note that
it is likely that some spectral evolution occurred during the flares,
thus these are still aggregated values. As for the time-averaged fit,
the Galactic column was fixed to 0.17e21 cm^-2 (Kalberla et al 2005)
and the free absorber was set to have a redshift of z=0.347 (GCN Circ.
15249)
Pre-flare (T0+ 150-500 s):
NH = 1.66 (+/- 0.05) e22 cm^-2
Gamma = 1.70 (+/- 0.04)
Flare 1 (T0+ 1240-1500 s)
NH = 2.2 (+/- 0.1) e22 cm^-2
Gamma = 2.28 (+/- 0.06)
Flare 2 (T0+ 4650-6100 s)
NH = 1.59 (+/- 0.07) e22 cm^-2
Gamma = 2.03 (+/- 0.04)
Flare 3 (T0+ 6700-7300 s)
NH = 1.66 (+/- 0.06) e22 cm^-2
Gamma = 1.79 (+/- 0.03)
Flare 4 (T0+11.5-12.9 ks)
NH = 1.3 (+/- 0.2) e22 cm^-2
Gamma = 2.39 (+/- 0.2)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00571830.
This circular is an official product of the Swift-XRT team.
GCN Circular 15255
Subject
Fermi GBM detection of GRB 130925A and a possible precursor
Date
2013-09-25T16:13:06Z (12 years ago)
From
Gerard Fitzpatrick at UCD <gerard.fitzpatrick@ucdconnect.ie>
Gerard Fitzpatrick (UCD) reports on behalf of the Fermi GBM Team:
At 04:09:26.73 UT on 25 September 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB130925A (trigger 401774969/130925173),
which was also detected approximately 2 minutes later by Swift (Lien et
al., GCN 15246). The on-ground
calculated location is consistent with the Swift location. The GBM data
show that the event
was still in progress at the time of the Swift trigger. The burst was
sufficiently
bright that a Fermi Automatic Repointing Request (ARR) was triggered. This
event may
not actually be a GRB, as indicated by Burrows et al. (GCN 15253). Downlink
of the full data set for
this event was delayed due to the ARR; more details will be provided when
the data are available.
At 03:56:23.29 UT, 15 minutes prior to the GBM detection of GRB130925A,
GBM triggered and located
GBM trigger 401774186/130925164. The on-ground calculated location, using
the GBM trigger
data, is RA = 48.3 , DEC = -21.8 (J2000 degrees,
equivalent to 03h 13m, -21d 42.0'), with an uncertainty
of 12.8 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).
This is also consistent with the Swift location of GRB130925A
(Lien et al., GCN 15246). The temporal and positional coincidence indicate
that this may be
a precursor pulse to GRB130925A.
The GBM light curve for this possible precursor consists of a single peak
with a duration (T90) of about 6.6 s (50-300 keV).
The time-averaged spectrum from T0-4 s to T0+2.5 s is
adequately fit by a simple power law function with index -2.25 +/- 0.07
The event fluence (10-1000 keV) in this time interval is
(6.9 +/- 0.6)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-3 s in the 10-1000 keV band is 3.0 +/- 0.2 ph/s/cm^2.
GCN Circular 15256
Subject
GRB 130925A: Historical non-detection from Rosat-HRI
Date
2013-09-25T17:03:21Z (12 years ago)
From
Jonathan Gelbord at PSU/Swift <jgelbord@gmail.com>
J. M. Gelbord (Eureka Scientific) reports:
Historical X-ray data covering the position of GRB 130925A (Evans et al., GCN Circ 15246) is available from the ROSAT archive at HEASARC. The deepest data set is a 5.5 ks observation with the ROSAT HRI taken 1997-07-01, in which the position of GRB 130925A is 9' off axis. There is no trace of an X-ray source at this position.
Using a source extraction region of 24" and a concentric annular background region from 80" to 240", formally I find 0.2 +/- 3.6 counts in the HRI band. The three sigma upper limit is 14.8 counts (using the Bayesian approach of Kraft, Burrows & Nousek 1991, ApJ 374, 344). Given the nominal exposure time of 5.5 ks, this translates to 2.7E-03 HRI counts per sec.
We use WebPIMMS ( http://heasarc.gsfc.nasa.gov/Tools/w3pimms.html ) to convert the 3-sigma HRI count rate limit to a limit in the Swift-XRT band. Assuming the auto-generated spectral model for GRB 130925A (available from http://www.swift.ac.uk/xrt_products/00571830 ) fitted to the XRT PC-mode data for GRB 130925A (through T0+29.8 ks; NH (intrinsic) = 9.4E+21, Gamma = 2.61), together with NH (Galactic) = 1.66E+20 and z=0.347 (Vreeswijk et al., GCN Circ 15249 and Sudilovsky et al., GCN Circ 15250), the 3-sigma HRI count rate limit translates to an XRT count rate of 5.7E-3 counts per second. If we instead adopt the harder spectral model resulting from the fit to the WT-mode data (NH (Intrinsic) = 6.8E+21 and Gamma = 1.73), the equivalent XRT count rate would be 7.8E-3 counts per second.
Thus, the Rosat HRI upper limit reveals that GRB 130925A at T0+200s was at least 10^6 times brighter and at T0+30ks was still at least 100 times brighter than any X-ray source at this position in July 1997.
GCN Circular 15257
Subject
GRB 130925A Swift-BAT refined analysis
Date
2013-09-26T00:03:46Z (12 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <james.r.cummings@nasa.gov>
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), D. M. Palmer (LANL),
T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+7152 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 130925A (trigger #571830)
(Lien, et al., GCN Circ. 15246). The BAT ground-calculated position is
RA, Dec = 41.186, -26.146 deg which is
RA(J2000) = 02h 44m 44.5s
Dec(J2000) = -26d 08' 47.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 9%.
The mask-weighted light curve covers only a small part of this exceptionally
long GRB (if indeed it is a GRB at all). As reported by the Fermi-GBM team
(Fitzpatrick, GCN Circ. # 15255) the event may have begun 17 minutes prior to
the BAT trigger, and the source was still detected in BAT at T+2 hours. Thus
we cannot estimate a T90 at this time. There were multiple peaks and several
late-time flares.
In the current analysis, the burst was first detected by BAT at T-59 sec, when
the target entered the BAT field of view already emitting, and last detected by
BAT in a survey interval ending at T+7152 sec.
BAT also detected a flux increase during the first flare detected by XRT (Evans
et al. GCN Circ. # 15254) that peaked at about T+1000 seconds. BAT did not see
a significant increase at the time of the next flare (brightest in XRT), peaking
at about T+1380 seconds, though the source was still detected. BAT did strongly
detect increases during the XRT-observed flares that peaked at approximately
T+4950 and T+7100 seconds. BAT did not detect emission during another, smaller,
flare observed by XRT that peaked at about T+11000 seconds.
BAT has not detected significant flux from this location in the 15-50 keV band
prior to the current event.
The time-averaged spectrum from T-59 to T+903 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.85 +- 0.14,
and Epeak of 33.4 +- 20.0 keV (chi squared 38.18 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 4.1 +- 0.1 x 10^-05 erg/cm2
and the 1-sec peak flux measured from T-35.64 sec in the 15-150 keV band is
7.3 +- 0.6 ph/cm2/sec. A fit to a simple power law gives a photon index
of 2.09 +- 0.04 (chi squared 45.62 for 57 d.o.f.). The flares at T+4950 and
T+7100 seconds have photon indices in simple power-law fits of 2.19 +- 0.36
and 2.34 +- 0.28 respectively. 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/571830/BA/
GCN Circular 15258
Subject
GRB 130925A: RATIR Optical and NIR Observations
Date
2013-09-26T01:55:31Z (12 years ago)
Edited On
2024-11-07T18:57:59Z (7 months ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM),
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC)
report:
We observed the field of GRB 130925A (Lien, et al., GCN 15246) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2013/09 25.27 to 2013/09 25.50 UTC (2.30 to
7.81 hours after the BAT trigger), obtaining a total of 3.67 hours exposure
in the r and i bands and 1.43 hours exposure in the Z, Y, J, and H bands.
We find an uncatalogued source in the enhanced Swift-XRT error circle
(Evans et al., GCN 15251). In comparison with USNO-B1 and 2MASS, we obtain
the following detections and upper limits (3-sigma):
r 22.26 +/- 0.11
i 21.75 +/- 0.10
Z 20.25 +/- 0.06
Y 20.77 +/- 0.14
J 19.98 +/- 0.07
H 19.85 +/- 0.12
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. The source is spatially coincident
and about as bright as the source reported by Sudilovsky et al. (GCN
15247), which was observed minutes rather than hours after the GRB.
Further observations are planned.
We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.
GCN Circular 15260
Subject
Konus-Wind observation of GRB 130925A
Date
2013-09-26T15:36:02Z (12 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline,
on behalf of the Konus-Wind team, report:
The very long GRB 130925A
(Swift-BAT trigger #571830: Lien et al., GCN 15246;
Markwardt et al., GCN 15257;
MAXI/GSC detection: Suzuki et al., GCN 15248;
Fermi/GBM detection: Fitzpatrick, GCN 15255;
INTEGRAL/SPI-ACS observation: Savchenko et al., GCN 15259)
was detected by Konus-Wind in the waiting mode.
The light curve shows several multi-peaked pulses separated
by long periods of a low-level emission with a total duration of ~4500 s.
At least three major emission episodes can be distingushed:
the first one, which triggered BAT, started at ~T0(BAT)-130 s
and lasted until ~T0(BAT)+170 s; the second, more fluent episode,
from ~T0(BAT)+1750 s to ~T0(BAT)+2950 s;
and the third, the weakest one, which onset corresponds
to the MAXI detection, from ~T0(BAT)+3730 s to ~T0(BAT)+4360 s.
The possible precursor detected by GBM is clearly seen
at ~T0(BAT)-900 s in the softest KW energy band.
As observed by Konus-Wind, the burst had a fluence of
(5.0 � 0.1)x10^-4 erg/cm2 and a 2.944-s peak energy flux,
measured from T0(BAT)+2548.858, of (1.0 � 0.03)x10^-6 erg/cm2
(both in the 20 - 10000 keV energy range).
The emission shows no signs of strong spectral variability.
Modeling the KW 3-channel time-integrated spectrum
(from T0(BAT)-120 s to T0(BAT)+4340 s) by a power law
with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.42 � 0.04, and Ep = 181 � 10 keV.
Assuming z = 0.347 (Vreeswijk et al., GCN 15249) and a
standard cosmology model with H_0 = 71 km/s/Mpc, Omega_M = 0.27,
Omega_Lambda = 0.73,
the isotropic energy release E_iso = (1.50 � 0.03)x10^53 erg,
the peak isotropic luminosity L_iso = (4.0 � 0.1)x10^50 erg,
and Ep_rest is 244 � 13 keV.
Thus, the prompt gamma-ray emission properties of this GRB: fluence, Ep,
and E_iso are similar to those observed in other long energetic GRBs;
the only outstanding feature of the burst is its huge duration.
In that, it resembles other ultra-long bursts: GRB 111209A at z=0.677
(with total duration of ~10000 s: Golenetskii et al., GCN 12663)
and GRB 121027A at z=1.77 (with a total duration of >4000 s: Starling et al.,
in preparation).
Therefore, we suggest that the extremely rapid and dramatic X-ray flaring
observed over the first 10^4 s after the BAT trigger (Evans et al., GCN 15254)
at least partially corresponds to the burst prompt emission.
All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.
The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB130925A/
GCN Circular 15261
Subject
GRB 130925A: Fermi GBM Detection
Date
2013-09-26T15:42:20Z (12 years ago)
From
Peter Jenke at MSFC <peter.a.jenke@nasa.gov>
P. Jenke (UAH) reports on behalf of the Fermi GBM Team:
"At 04:09:26.73 UT on September 25 2013, the Fermi Gamma-Ray
Burst Monitor triggered and located
GRB 130925A (trigger 401774969/130925173),
which was also detected by Swift (Lien et al. GCN 15246)
and MAXI (Suzuki et al., GCN 15248).
The trigger resulted in an Autonomous Repoint Request (ARR)
that was accepted and the LAT slewed to the GBM in-flight
location which was consistent with the Swift/XRT position
(Evans et al. GCN 15251). The angle from the Fermi LAT boresight
is 22 deg from Swift/XRT position.
The GBM light curve consists of multiple peaks with a
duration (T90) of about 212 s (50-300 keV).
The time-averaged spectrum from T0-6 s to T0+288 s is
best fit with a power law function with an exponential high-energy
cutoff parameterized as Epeak = 107 +/- 3 keV and
an Index = -1.50 +/- 0.05.
The event fluence (10-1000 keV) in this time interval is
(2.83 +/- 0.06)E-07 erg/cm^2. The 1.0-sec peak photon flux
measured starting from T0+83 s in the 10-1000 keV band
is 11.5 +/- 0.3 ph/s/cm^2.
This event, although initially classified as a GRB, has been
shown to exhibit behavior consistent with a Tidal Disruption
Event (Burrows et al. GCN 15253). Its location suggests that
it is the same source as
GBM trigger 401774186/130925164 (G. Fitzpatrick GCN 15255).
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 15262
Subject
GRB 130925A: Continued RATIR Optical and NIR Observations
Date
2013-09-26T17:50:25Z (12 years ago)
Edited On
2024-11-07T19:51:02Z (7 months ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM),
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC)
report:
We observed the field of GRB 130925A (Lien, et al., GCN 15246) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2013/09 26.28 to 2013/09 26.51 UTC (26.43 to
31.98 hours after the BAT trigger), obtaining a total of 3.66 hours
exposure in the r and i bands and 1.12 hours exposure in the Z, Y, J, and H
bands.
For the uncatalogued source in the enhanced Swift-XRT error circle (Evans
et al., GCN 15251) reported previously (Butler et al., GCN 15258), in
comparison with 2MASS, we obtain the following detections and upper limit
(3-sigma):
r 22.29 +/- 0.16
i 21.36 +/- 0.13
Z > 21.5
Y 21.28 +/- 0.29
J 19.69 +/- 0.06
H 20.02 +/- 0.17
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. Compared to our observations the
night before (GCN 15258), the source has apparently remained approximately
constant in flux in all bands. We cannot determine, as did Sudilovsky et
al. (GCN 15247), that the source is fading.
We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.
GCN Circular 15263
Subject
GRB 130925A: optical upper limit
Date
2013-09-27T10:43:49Z (12 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Volnova (IKI), N. Minikulov (Institute of Astrophysics), S. Abdulaev
(Institute of Astrophysics), I. Molotov (KIAM), A. Pozanenko (IKI)
report on behalf of larger GRB follow-up collaboration:
We observed the field of GRB 130925A (Lien, et al., GCN 15246) with
AZT-8 (0.7m) telescope of Gissar observatory in R filter starting on
Sep. 25 (UT) 22:15. We do not detect optical afterglow (Sudilovsky et
al., GCN 15247). A preliminary photometry of combined image is following
T_start T0+ Filter, Exposure, OT, UL(3 sigma)
(UT) (mid, d) (s)
2013-09-25T22:16:55 0.7766 R 60x60 n/d 19.9
The photometry is based on the reference star USNO-B1.0 0638-0038928
RA 02:45:02.36 Dec -26:10:50.2 (J2000), assuming R = 17.07
GCN Circular 15264
Subject
GRB 130925A: sub-mm non-detection with SMA
Date
2013-09-27T10:47:02Z (12 years ago)
From
Ashley Zauderer at CfA <bevinashley@gmail.com>
A. Zauderer, E. Berger (Harvard), and G. Petitpas (SMA) report on behalf of
a larger collaboration:
"We observed the position of GRB 130925A (Lien et al., GCN 15246) beginning
2013 Sep 26.31 UT
(dt = 1.1 d) with the SMA at a mean frequency of 230 GHz. We find no
significant radio emission
at the position of the enhanced Swift-XRT position (Evans et al., GCN
15250) to a 3-sigma limit of 1.89 mJy.
Observations are ongoing.
We thank the SMA staff for prompt execution of these observations."
GCN Circular 15266
Subject
GRB 130925A: Swift/UVOT Upper Limits
Date
2013-09-27T11:37:03Z (12 years ago)
From
Stephen Holland at STScI <sholland@stsci.edu>
S. T. Holland (STScI) and
A. Y. Lien (NASA/GSFC/ORAU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB
130925A 157 s after the BAT trigger (Lien et al. 2013, GCNC 15246).
We do not detect any new source consistent with the GROND afterglow
position (Sudilovsky et al. 2013, GCNC 15247) in any of the UVOT
exposures. Preliminary 3-sigma upper limits, using the UVOT
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373),
for the finding chart and summed exposures are presented below.
---------------------------------------------------
Filter TSTART TSTOP Exposure Mag
---------------------------------------------------
white (FC) 157 306 147 >21.4
u (FC) 315 564 246 >20.6
---------------------------------------------------
v 645 7269 381 >20.0
b 571 6121 170 >20.6
u 719 5983 274 >20.4
uvw1 5579 11,956 701 >21.1
uvm2 5374 11,436 1082 >21.2
uvw2 4964 7136 393 >20.7
white 595 6929 618 >22.0
---------------------------------------------------
The quoted upper limits have not been corrected for the expected
extinction due to the Galactic reddening along the line of sight to
this burst of E(B-V) = 0.02 mag (Schlafly et al. 2011, ApJS, 737,
103).
GCN Circular 15267
Subject
GRB 130925A: Swift/UVOT Detection of the Host Galaxy
Date
2013-09-27T18:22:43Z (12 years ago)
From
Stephen Holland at STScI <sholland@stsci.edu>
S. T. Holland (STScI)
reports on behalf of the Swift/UVOT team:
Deep Swift/UVOT imaging taken between 157 s and 184.8 ks after
the BAT trigger (Lien et al, 2013, GCNC 15246) shows a faint source at
the location of the GROND detection (Sudilovsky et al. 2013, GCNC
15247). This source has a preliminary magnitude, on the UVOT
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373),
of white = 22.9 +/- 0.3 mag and is detected with a significance of 4.7
sigma. This magnitude has not been corrected for the expected
extinction due to the Galactic reddening along the line of sight to
this burst of E(B-V) = 0.02 mag (Schlafly et al. 2011, ApJS, 737,
103). The total white exposure time is 18 ks. There is no evidence
for variability.
The probability of finding a galaxy of this apparent luminosity
within the UVOT-enhanced XRT error circle (Evans et al. 2013, GCNC
15251) is 0.01 using the method of Bloom et al. (2002, AJ, 423, 1111).
The positional coincidence and lack of variability suggest that this
is the host galaxy of GRB 130925A. There is no evidence in the UVOT
data that this source has any extended structure.
GCN Circular 15268
Subject
Fermi LAT Upper Limits on GRB 130925A
Date
2013-09-28T00:03:12Z (12 years ago)
From
Daniel Kocevski at SLAC <dankocevski@gmail.com>
D. Kocevski, J. Racusin (NASA/GSFC), G. Vianello (Stanford), M. Axelsson
(Stockholm University), Nicola Omodei (Stanford) report on behalf of the
Fermi-LAT team:
A preliminary examination of the Fermi LAT data of the field containing GRB
130925A (Lien, et al., GCN 15246) has revealed no significant emission
above 40 MeV. The GRB was located ~22 degrees away from the LAT boresight
at the time of the first GBM detected emission associated with this burst
at 03:56:23.29 UT on 25 September 2013 (GCN 15255), hereafter T0(GBM), and
the subsequent autonomous repoint ensured that the source remained in the
field-of-view for the next ~2000s until it was occulted by the Earth.
Using an unbinned likelihood analysis, we estimate the following LAT upper
limits at 95% confidence for three separate time intervals, one covering
the entire 2000s that the source stayed in the LAT field-of-view, and two
of which correspond to the first and third emission episodes detected by
INTEGRAL/SPI-ACS (GCN 15259) and Konus-Wind (GCN 15260). We note that the
source was not in the LAT field-of-view during the second interval reported
in GCNs 15259 & 15260.
Interval 1: T0(GBM) to T0(GBM)+2000 = 7.3e-07 photons cm-2 s-1 (4.8e-10
ergs cm-2 s-1)
Interval 2: T0(GBM)+900s to T0(GBM)+1100s = 5.5e-06 photons cm-2 s-1
(3.6e-09 ergs cm-2 s-1)
Interval 3: T0(GBM)+4900 to T0(GBM)+5400 = 2.5e-06 photons cm-2 s-1
(1.6e-09 ergs cm-2 s-1)
This analysis covers an energy range of 0.1 to 10 GeV with a 12 deg
extraction region centered on the best known source position (GCN 15246).
The upper limits are computed using the P7SOURCE_V6 instrument response
functions, where we assume a power-law source spectrum fixed to a photon
index of -2.1, reflecting a typical value for high-energy emission in GRBs.
For reference, T0(GBM) = T0(BAT)-900s.
The Fermi LAT point of contact for this burst is Magnus Axelsson (
magnusa@astro.su.se).
The Fermi LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 15278
Subject
IPN Observations of GRB 130925A
Date
2013-09-30T22:05:33Z (12 years ago)
From
Kevin Hurley at UCBerkeley/SSL <khurley@ssl.berkeley.edu>
K. Hurley, on behalf of the IPN team,
S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline, on behalf of the Konus-Wind team,
I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on
behalf of the GRS-Odyssey GRB team,
D. M. Smith, J. McTiernan, R. Schwartz, W.
Hajdas, and A. Zehnder, on behalf of the RHESSI GRB team,
A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C.
Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
K. Yamaoka, M. Ohno, Y. Hanabata, Y. Fukazawa, T. Takahashi, M. Tashiro,
Y. Terada, T. Murakami, and K. Makishima on behalf of the Suzaku WAM team,
S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of
the Swift-BAT team,
J. Goldsten, on behalf of the MESSENGER NS GRB team, and
V. Connaughton, M. S. Briggs, C. Meegan, and V. Pelassa, on behalf of the Fermi
GBM team, report:
Eight IPN spacecraft observed GRB 130925A (Lien et al. GCN 15246,
Markwardt et al. 15247). When the responses of all the spacecraft are
considered, the IPN had an uninterrupted view of this event from
roughly 900 s before the Swift BAT trigger, to ~7100 s after it.
Constraints on the arrival directions of the four main emission
episodes strengthen the case for their common origin, as suggested by
Savchenko et al. (GCN 15259). The following table details the
observations. The times are relative to the BAT trigger at 15084 s UT
(04:11:24). N/O means the episode was not observable.
----------------------------------------------------------------------------
Instrument/ | Precursor | 1st | 2nd | 3rd
spacecraft | -900 s | episode | episode | episode*
| | -130 -> +170 s|+1750 -> +2950 s|+3730 -> +4360 s
----------------------------------------------------------------------------
Swift BAT No Trig N/O No
Fermi GBM Trig Trig N/O No
INTEGRAL SPI-ACS No Yes Yes Yes
Konus Wind Yes Yes Yes Yes
MESSENGER No Yes Yes No
Mars Odyssey No N/O Yes No
Suzaku WAM No No Yes No
RHESSI Yes Yes N/O No
------------------------------------------------------------------------------
*also observed and localized by MAXI (Suzuki et al. GCN 15248)
We conclude from these observations that the total duration of this
event in >25 keV gamma-rays above the IPN flux/fluence threshold was
at least 5260 s, and ~7150 s long when the later episodes, observed only
by BAT (GCN 15257), are included.
GCN Circular 15280
Subject
GRB 130925A: continuing Swift/XRT monitoring
Date
2013-10-01T17:52:33Z (12 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. Malesani (DARK/NBI), S. B. Cenko (NASA/GSFC), D. N. Burrows (PSU), A.
Y. Lien (NASA/GSFC/ORAU), P. A. Evans (U. Leicester), and N. Gehrels
(NASA/GSFC) report:
Swift has been continuously monitoring the X-ray counterpart of GRB
130925A (Lien et al., GCN 15246), with data currently extending up to
512 ks after the trigger. The intense X-ray flaring activity reported by
Burrows et al. (GCN 15253) and Evans et al. (GCN 15254) ceased between
12 and 28 ks after the trigger. The X-ray light curve from 27.9 to 512.4
ks can be modelled with an initial power-law decay with an index of
alpha = 0.84 +/- 0.03, followed by a possible break at 310 (+60, -50) ks
to an alpha of 1.38 (+0.47, -0.23). The updated X-ray light curve is
available at the following URL:
http://www.swift.ac.uk/xrt_curves/00571830/
While the duration of the prompt emission and the flaring activity are
extraordinary among GRBs (Suzuki et al., GCN 15248; Fitzpatrick, GCN
15255; Markwardt et al., GCN 15257; Savchenko et al., GCN 15259;
Golenetskii et al., GCN 15260; Jenke, GCN 15261; Hurley et al., GCN
15278), the late-time behaviour is typical of long-duration GRB
afterglows, and quite different from that of the TDE Swift J1644+57,
which showed continuous flares and dips, with no regular power-law decay
(e.g. Burrows et al. 2011, Nat, 476, 421). There is also no prior
detection of the source in BAT before the trigger (Markwardt et al., GCN
15257).
The extremely long-lived high-energy emission coupled with the
relatively steady power-law X-ray decay at t > 20 ks is reminiscent of
the so-called "ultra-long" GRBs (Levan et al. 2013, arXiv:1302.2352),
including GRB 101225A (Thoene et al. 2011, Nat, 480, 72; Campana et al.
2011, Nat, 480, 69), GRB 111209A (Gendre et al. 2013, ApJ, 766, 30), and
GRB 121027A. The origin of these events and their relation to
traditional long-duration GRBs (i.e., the core-collapse of a massive
star) remain controversial, so we encourage continued multi-wavelength
follow-up of this object.
GCN Circular 15286
Subject
NuSTAR observations of GRB 130925A
Date
2013-10-02T15:16:42Z (12 years ago)
From
Eric Bellm at Caltech <ebellm@caltech.edu>
E. C. Bellm, F. A. Harrison, K. Forster, K. K. Madsen, V. Rana
(Caltech), S. E. Boggs, J. Tomsick (U.C. Berkeley), J. M. Miller
(Michigan), and S. B. Cenko (NASA/GSFC) report on behalf of the NuSTAR
collaboration:
NuSTAR observed the unusual ultra-long GRB/TDE candidate GRB 130925A
(GCN 15246) beginning 44.3 hours after the Swift trigger for a total
of 39.2 ksec exposure time.
NuSTAR detects the source to >20 keV; the average 3-20 keV flux over
the interval was 1.3E-12 erg/cm^-2/s^-1. The data may be fit with an
absorbed power law with spectral index Gamma ~ 3.
NuSTAR observes a broad absorption feature centered near 6 keV.
Simultaneous Swift-XRT spectra support the existence of this feature
at lower SNR. An F-test of a Gaussian absorption feature fit to the
combined data sets yields a detection significance of 5.5 sigma.
Preliminary searches for features in the early-time XRT data have not
identified any clear signatures; additional tests are ongoing.
Further observations are in progress; we encourage continued
monitoring of this interesting event at all wavelengths.
We thank the NuSTAR Mission Operations Team for the rapid turnaround
that enabled this observation.
GCN Circular 15299
Subject
GRB 130925A/Sw J0244-2609: mm observations at PdBI
Date
2013-10-03T20:02:01Z (12 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
A. J. Castro-Tirado (IAA-CSIC Granada and Univ. de M�laga), M. Bremer,
J.-M. Winters and S. Koenig (IRAM Grenoble), on behalf of a large
collaboration, report:
"Following the detection of the extraordinarily long event GRB 130925A/Sw
J0244-2609 by Swift (Lien et al. 2013, GCN 15247) we attempted on Oct 1
(00:30 UT) millimetre observations with the Plateu de Bure Interferometer
(PdBI) in the French Alps, in 6-antenna compact D configuration. Due to
the low declination, the source was lost for two antennas due to shadowing
effects by other antenna. No mm source is detected, with a 3 sigma limit
of 0.58 mJy at 86 GHz. This value is a factor of 30 times less than the
measured flux density for the tidal disruption flare candidate GRB
110328A/Sw J1644+5734 with PdBI one week post burst (Castro-Tirado et al.
2013, RMxAC 42, 36)."
GCN Circular 15301
Subject
GRB 130925A: 3mm observations with CARMA
Date
2013-10-04T16:39:51Z (12 years ago)
From
Ashley Zauderer at CfA <bevinashley@gmail.com>
B. A. Zauderer, E. Berger, T. Laskar (Harvard) report on behalf of a larger
collaboration
as part of the CARMA Key Project "A Millimeter View of the Transient
Universe":
"We observed the position of GRB 130925A (Lien et al., GCN 15246) with the
Combined Array for Research in Millimeter Astronomy (CARMA) beginning
2013 Sep 26.36 (dt = 1.19 d) at a mean frequency of 93 GHz. Observations
were
conducted in the compact E configuration, with significant flagging for
shadowed
antennas required. We do not detect any significant radio emission to a
3-sigma
limit of 0.6 mJy at the position of the Swift-XRT position (Evans et al.,
GCN 15251).
We thank the CARMA observers and staff for prompt execution of these
observations."
GCN Circular 15322
Subject
GRB 130925A: Possible signatures of binary nature in the afterglow - Request for observations
Date
2013-10-10T14:57:27Z (12 years ago)
From
Remo Rufinni at ICRA <ruffini@icra.it>
R. Ruffini, C.L. Bianco, M. Enderli, M. Muccino, A.V. Penacchioni, G.B.
Pisani, J.A. Rueda, N. Sahakyan, Y. Wang, L.Izzo report:
The observed X-ray emission in the afterglow of GRB 130925A (Lien et al., GCN 15247; Fitzpatrick et al., GCN 15255) presents an unprecedented sequence of flares departing from the canonical single power law decay (L \propto t^{-1.5}) observed in energetic GRBs-SNe (the "golden sample", Pisani et al. 2013, A&A 552, L5, arXiv:1304.1764). Correspondingly the X-ray Luminosity after 2*10^4 s in the rest-frame of the burst is almost constant (L \propto t^{-0.3}) and the energy emitted is a factor 30 larger than in the golden sample.
In the Induced Gravitational Collapse (IGC) paradigm, after the "input" due to a supernova explosion and the Black Hole formation (Ruffini 2013, IJMPD, 22, 1360009, arXiv:1310.1836), the "output" of a newly born Neutron Star from the Supernova and the Black Hole may remain bound in an elliptical orbit. This can explain the repeated flaring activity and the source of the larger observed energy.
In the canonical IGC scenario at z = 0.35 (Sudilovsky et al., GCN 15250, Vreeswijk et al., GCN 15249), assuming a 1998bw-like SN, a supernova should be expected to peak around the 10 - 16 October. It is crucial to perform optical observations in order to find out if the presence of the above mentioned binary nature in the "output" can modify the canonical scenario. Periodicities on time scales down to few minutes should be explored.
GCN Circular 15489
Subject
GRB 130925A: HST imaging
Date
2013-11-16T09:22:23Z (12 years ago)
From
Nial Tanvir at U.Leicester <nrt3@star.le.ac.uk>
N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick), R. Hounsell,
A. S. Fruchter (STScI), S. B. Cenko (NASA/GSFC), D. A. Perley (Caltech),
P. T. O'Brien (U. Leicester) report:
We imaged the location of GRB 130925A (Evans et al. GCN 15251;
Sudilovsky et al. GCN 15247) with HST at two epochs, at 20 days and
47 days post-burst respectively, in the F814W (I-band), F110W (J-band)
and F160W (H-band) filters.
The host galaxy is well resolved and appears to be an almost edge-on spiral.
The galaxy shows signs of disturbance: specifically the disk shows asymmetry
and the bulge appears to be extended perpendicular to the disk, suggestive
of a polar-ring morphology.
Image subtraction reveals evidence of faint transient light in the first epoch
in all three filters. The location is in good agreement with that from prior
ground-based imaging of the GRB. The transient position is close to the disk
plane, which likely accounts for the high extinction and X-ray column for this
event (Evans et al. GCN 15254). It is, however, slightly offset from the
nucleus of the galaxy by about 0.12 arcsec (~600pc in projection). This
would initially seem to be in conflict with a possible tidal disruption origin
for this event, although if the galaxy morphology is indicative of a recent
major merger, then it is plausible that the system currently contains more
than one super-massive black hole.
Further analysis is ongoing.
We thank the staff at STScI for approving and expediting
these ToO observations.