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GRB 180904A

GCN Circular 23194

Subject
GRB 180904A: Swift detection of a burst
Date
2018-09-04T21:42:57Z (7 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
A. D'Ai (INAF-IASFPA), J.D. Gropp (PSU), J. A. Kennea (PSU),
S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
M. J. Moss (George Washington University), D. M. Palmer (LANL),
B. Sbarufatti (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 21:28:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180904A (trigger=859282).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 274.250, +46.623 which is 
   RA(J2000) = 18h 17m 00s
   Dec(J2000) = +46d 37' 24"
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 20 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 21:30:35.3 UT, 123.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 274.2495,
46.6298 which is equivalent to:
   RA(J2000)  = 18h 16m 59.87s
   Dec(J2000) = +46d 37' 47.4"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 24 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 http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.37 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.3
(+3.26/-2.80) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.47e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 131 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
0.04. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT ifc.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/too.html.)

GCN Circular 23195

Subject
GRB 180904A: NOT optical observations, candidate host galaxy
Date
2018-09-04T23:04:27Z (7 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
Daniele Malesani (DAWN/NBI and DARK/NBI), Kasper Elm Heintz (Univ. 
Iceland and DAWN/NBI), Sune Dyrbye (NOT), report on behalf of a largert 
collaboration:

We observed the field of GRB 180904A (D'Ai' et al., GCN 23194) with the 
Nordic Optical Telescope (NOT) equipped with the AlFOSC camera.

In an image of 300 s exposure taken with the SDSS r filter and 
commencing on Sep 4.9057 UT (15.6 min after the GRB), we detect a single 
object consistent with the currently available XRT position 
(http://www.swift.ac.uk/xrt_positions/). Its coordinates are (J2000):

RA = 18:16:59.74
Dec = +46:37:47.1

Compared to nearby stars from the Pan-STARRS survey, we measure for this 
object a magnitude r = 22.56 +- 0.08 AB.

We note that the same object is visible in the archival Pan-STARRS image 
of this field, with a measured magnitude r = 22.84 +- 0.15 AB. There is 
thus only marginal indication of excess flux in the NOT image. If this 
object is related to GRB 180904A, as suggested by the spatial 
coincidence with the X-ray position, it is largely or entirely dominated 
by the host galaxy.

Further observations are planned.

GCN Circular 23196

Subject
GRB 180904A: Enhanced Swift-XRT position
Date
2018-09-04T23:19:01Z (7 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 468 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180904A, 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 = 274.24978, +46.62971 which is equivalent
to:

RA (J2000): 18h 16m 59.95s
Dec (J2000): +46d 37' 46.9"

with an uncertainty of 1.8 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 23197

Subject
GRB 180904A: OSN observations
Date
2018-09-05T00:16:23Z (7 years ago)
From
Luca Izzo at IAA-CSIC <Luca.Izzo@ICRA.it>
L. Izzo, D. A. Kann, A. de Ugarte Postigo, C.C. Thoene (all HETH/IAA-CSIC), and F. Aceituno (IAA-CSIC) report:

We observed the field of GRB 180904A (D���Ai et al., GCN #23194) with the 1.5-m OSN telescope in Granada, Spain. We obtained 12 x 300 s images in the Ic band centered at 1.23 hours after the GRB.

At the enhanced XRT position of the GRB (Osborne et al., GCN #23196), we find no source inside the Swift-XRT error circle down to a limit of Ic (AB) > 22.4. We note, however, that the object reported in Malesani et al., GCN #23195, lies just outside the XRT position reported by Osborne et al., and may therefore be unrelated to the GRB.

The calibration was performed using i-band magnitudes of nearby stars in the Pan-STARRS catalog, transformed into Ic magnitudes according to the Lupton (2005) transformations.

GCN Circular 23198

Subject
GRB 180904A: SAO RAS optical observations
Date
2018-09-05T00:46:37Z (7 years ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
Moskvitin, A. S., Spiridonova O. I., Maslennikova O. A. (SAO RAS),
report on behalf of larger GRB follow-up team.

We observed the field of the GRB 180904A (D'Ai et al., GCNC 23194)
with the Zeiss-1000 telescope of SAO RAS (+ CCD UBVRcIc photometer)
on the 2018 September, 4.926 (mid. time).

The observations started since 7.2 minutes after the Swift trigger
(21:35:44--22:46:03 UT). 12 x 300 sec. exposures in Rc band
were obtained. We can not see any object inside the XRT enhanced
1".8 error circle (Osborne et al., GCNC 23196) down to
the limiting magnitude of R_lim = 22.7, but at the edge
of the circle we detected the object mentioned by Malesani et al.
(GCNC 23195). The preliminary magnitude of the object is
R = 21.9 +/- 0.2 (Vega system) compared to nearby USNO-B1 stars.

The finding chart can be found at
ftp://ftp.sao.ru/pub/grb/GRB/GRB180904A_SAORAS.png

GCN Circular 23199

Subject
GRB 180904A: LT early observations
Date
2018-09-05T09:57:11Z (7 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell 
(U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a 
large collaboration report:

The 2-m robotic Liverpool Telescope automatically began observing Swift 
GRB 180904A (D'Ai et al. GCN 23194) with the polarimeter RINGO3 and the 
IO:O camera on September 04, 21:32:12 UT (219 seconds from the GRB 
trigger time). Within the enhanced Swift-XRT error circle (Osborne et 
al. GCN 23196) we do not detect any object down to a limit of r' > 21.2 
mag in a 6x10s exposure at a mid time of 37 minutes post burst, as 
calibrated against nearby Pan-STARRS objects, in agreement with previous 
reports (Malesani et al. GCN 23195; Izzo et al. GCN 23197; Moskvitin et 
al. GCN 23198).

GCN Circular 23200

Subject
GRB 180904A: Swift-XRT refined Analysis
Date
2018-09-05T13:04:23Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), A. Tohuvavohu (PSU), P.A. Evans (U.
Leicester) and A. D'Ai report on behalf of the Swift-XRT team:

We have analysed 6.5 ks of XRT data for GRB 180904A (D'Ai et al. GCN
Circ. 23194), from 129 s to 45.0 ks after the  BAT trigger. The data
comprise 91 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Osborne et al. (GCN Circ. 23196).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.9 (+0.4, -0.6). At T+179 s  the decay
steepens to an alpha of 7.84 (+0.16, -1.21) before breaking again at
T+247 s to a final decay with index alpha=1.19 (+/-0.15).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.61 (+0.24, -0.22). The
best-fitting absorption column is  4.6 (+1.0, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 3.4 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.19 (+0.26, -0.24)
and a best-fitting absorption column of 4.3 (+1.2, -1.1) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (6.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.3 (+1.2, -1.1) x 10^21 cm^-2
Galactic foreground: 3.4 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     2.19 (+0.26, -0.24)

If the light curve continues to decay with a power-law decay index of
1.19, the count rate at T+24 hours will be 7.3 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x
10^-14 (4.6 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00859282.

This circular is an official product of the Swift-XRT team.

GCN Circular 23203

Subject
GRB 180904A: Swift-BAT refined analysis
Date
2018-09-05T15:28:50Z (7 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), A. D'Ai (INAF-IASFPA),
H. A. Krimm (NSF/USRA), 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-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180904A (trigger #859282)
(D'Ai et al., GCN Circ. 23194).  The BAT ground-calculated position is
RA, Dec = 274.260, 46.640 deg which is
  RA(J2000)  =  18h 17m 02.4s
  Dec(J2000) = +46d 38' 23.3"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 56%.

The mask-weighted light curve shows a weak structure that starts at ~T0
and ends at ~T+6 s. T90 (15-350 keV) is 5.40 +- 0.89 sec (estimated error
including systematics).

The time-averaged spectrum from T+0.28 to T+6.18 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.02 +- 0.30.  The fluence in the 15-150 keV band is 2.4 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+5.14 sec in the 15-150 keV band
is 0.5 +- 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/859282/BA/

GCN Circular 23204

Subject
GRB 180904A: RATIR Optical and NIR Observations
Date
2018-09-05T15:49:17Z (7 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora
Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes��s
Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report:

We observed the field of GRB 180904A (D'Ai, et al., GCN 23194) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astron��mico Nacional on
Sierra San Pedro M��rtir from 2018/09 5.13 to 2018/09 5.32 UTC (5.66 to
10.26 hours after the BAT trigger), obtaining a total of 2.91 hours
exposure in the r and i bands and 1.33 hours exposure in the Z, Y, J, and H
bands.

Within the XRT error circle (Osborne, et al., GCN 23196), we detect the
source reported by Malesani, et al. (GCN 23195) at a consistent brightness
level.  In comparison with the USNO-B1 and 2MASS catalogs, we obtain the
following detections and upper limit (3-sigma):

 r = 22.61 +/- 0.08
 i = 22.06 +/- 0.05
 Z = 22.13 +/- 0.16
 Y = 21.64 +/- 0.18
 J = 21.72 +/- 0.21
 H > 21.86

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

GCN Circular 23205

Subject
GRB 180904A: Swift/UVOT Upper Limits
Date
2018-09-05T15:58:34Z (7 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180904A
131 s after the BAT trigger (D'Ai et al., GCN Circ. 23194).
No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 23196)
is detected in the initial UVOT exposures, consistent with the non-detections
of Malesani et al. (GCN Circ. 23195), Izzy et al. (GCN Circ 23197), 
Moskvitin et al. (GCN Circ. 23198) and Guidorzi et al. (GCN Circ. 23199).
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           131          281          147         >21.1
u_FC               289          539          246         >20.1
white              131          589          167         >21.1
v                  620          640           19         >20.1
b                  545          565           19         >19.4
u                  289          539          246         >20.1
w1                 670          690           19         >18.1
w2                 595          615           19         >18.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).

GCN Circular 23206

Subject
GRB 180904A: AbAO optical upper limit
Date
2018-09-05T16:18:22Z (7 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Volnova  (IKI),  A. Pozanenko (IKI), R. Inasaridze (AbAO),  E. 
Mazaeva (IKI),  V. Ayvazian  (AbAO),  O. Kvaratskhelia (AbAO), G. 
Kapanadze (AbAO),  I. Molotov (KIAM) report on behalf of larger GRB 
follow-up collaboration:

We observed the field of the Swift GRB 180904A (D'Ai et al., GCN 23194) 
with AS-32 (0.7m) telescope of Abastumani Observatory starting on 
September 04 (UT) 21:52:23.   We do not detect any object within 
enhanced XRT position (Osborne et al., GCN 23196). Preliminary 
photometry of the field is following:

Date        UT start   t-T0      Filter Exp.   OT    Err. UL
                      (mid, days)        (s)

2018-09-04  21:52:23   0.05731   CR     70*60  n/d   n/d  21.5

The photometry is based on nearby USNO-B1.0 stars (R2 magnitude)
USNO-B.1_id    R2
1366-0296056   14.72
1366-0296068   15.43
1365-0287325   15.62
1366-0296106   15.21
1366-0296088   14.95
1366-0296093   14.37

GCN Circular 23209

Subject
GRB 180904A: BOOTES-2/TELMA early observations
Date
2018-09-05T22:11:32Z (7 years ago)
From
Youdong HU at IAA-CSIC, UGR <youdong@iaa.es>
C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), Y.-D. 
Hu, E. Fernandez-Garcia, J. C. Tello, A. Ayala, A. J. Castro-Tirado 
(IAA-CSIC), and M. Jelinek (ASU-CAS), on behalf of a larger 
collaboration, report:

The 60cm BOOTES-2/TELMA robotic telescope at IHSM La Mayora (UMA-CSIC) 
in Algarrobo Costa (Spain) automatically responded in 56s (and 116s 
after the GRB onset) to the Swift trigger of GRB 180904A (D'Ai et al. 
GCNC 23194). The first image (11s exposure, unfiltered) was obtained at 
21:30:28 UT. At the position of the enhanced Swift X-ray afterglow 
(Osborne et al. GCNC 23196), no optical afterglow is detected down to 19 
mag at a mid time of 6 minutes post burst. This is consistent with the 
limits reported by Malesani et al. (GCNC 23195), Izzo et al. (GCNC 
23197), Moskvitin et al. (GCNC 23198, Guidorzi et al. (GCNC 23199), 
Butler et al. (GCNC 23204), Siegel et al. (GCNC 23205), Volnova et al. 
(GCNC 23206).

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