GRB 191011A

The Fermi GBM team reports the detection of a likely LONG GRB

At 04:35:58 UT on 11 Oct 2019, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 191011A (trigger 592461363.582334 / 191011192).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 207.9, Dec = 57.8 (J2000 degrees, equivalent to J2000 13h 51m, 57d 47'), with a statistical uncertainty of 4.0 degrees.

The angle from the Fermi LAT boresight is 169.0 degrees.

The skymap can be found here:
http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn191011192/quicklook/glg_skymap_all_bn191011192.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn191011192/quicklook/glg_healpix_all_bn191011192.fit

The GBM light curve can be found here:
http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn191011192/quicklook/glg_lc_medres34_bn191011192.gif

S. L Laha (GSFC/UMBC/CRESST), C. Gronwall (PSU), J.D. Gropp (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
E. Troja (NASA/GSFC/UMCP) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 04:35:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 191011A (trigger=928924).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 44.724, -27.845 which is 
   RA(J2000) = 02h 58m 54s
   Dec(J2000) = -27d 50' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex peak
structure with a duration of about 20 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 04:37:11.1 UT, 74.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 44.72679, -27.84594 which is equivalent
to:
   RA(J2000)  = 02h 58m 54.43s
   Dec(J2000) = -27d 50' 45.4"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 9.5 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 (1.54 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 5.8
(+3.35/-2.89) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	02:58:54.80 =  44.72832
  DEC(J2000) = -27:50:43.5  = -27.84541
with a 90%-confidence error radius of about 0.83 arc sec. This position is 6.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
20.20 with a 1-sigma error of about  0.19. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is S. L Laha (sib.laha 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/)

D. B. Malesani (DTU Space), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), D. A. Kann (HETH/IAA-CSIC), V. D'Elia (SSDC), J. P. U. Fynbo 
(DAWN/NBI), and G. Pugliese (Univ. Amsterdam) report on behalf of the 
Stargate Consortium:

We observed the localization of the Swift GRB 191011A (Laha et al., GCN 
25988
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 ) with X-shooter on the VLT in RRM mode. The optical afterglow 
(Laha et al., GCN 25988
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 , Lipunov et al., GCN 25989
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 ) is well-detected, 
and we measure a magnitude of r' = 19.18 +/- 0.06 mag (AB) from the 15 s 
acquisition image obtained starting at 2019-10-11T04:59:12.540, 23.28 
min after the trigger, measured against PanSTARRS field stars.

In the first spectrum (integration time 175 s) we detect Ly-a, SII, OI, 
SiII, CII, SiIV, CIV, FeII, CI, AlII, AlIII, MnII, MgII, MgI, and FeII*, 
all at a common redshift z=1.722. We consider this the redshift of GRB 
191011A. We furthermore report the presence of an intervening MgII 
system at z=1.2072.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Chiara Mazzucchelli, Rodrigo Palominos, and 
Camila Navarrete.

NB: We note the detection of a Fermi GRB (The Fermi GBM team, GCN 25987
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 ) 
at essentially the same time and with similar light curve structure, 
however, this GRB is localized to the northern hemisphere.

A. Nicuesa Guelbenzu (TLS Tautenburg) and P. Schady (Univ. of Bath)
report:

We observed the field of GRB 191011A (Swift trigger 928924; Laha et al.,
GCN 25988
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 ) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 04:38 UT on 2019-10-11, around 2 minutes after the
GRB trigger and lasted for about 5 minutes. They were performed at an
average seeing of 1.14" and at an average airmass of 1.1.

We detect the optical afterglow candidate reported by Laha et al. (GCN
25988
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 ) and measure the following preliminary magnitudes and upper limits
(AB magnitudes):

r' = 19.52 +/- 0.1 mag,
i' = 18.46 +/- 0.05 mag,
z' = 18.62 +/- 0.1 mag,
J  = 17.89 +/- 0.1 mag,
H  = 17.21 +/- 0.1 mag.

The optical afterglow is also visible in g' band.

The magnitudes are calibrated against GROND zeropoints and 2MASS field
stars and are not corrected for the Galactic foreground extinction
corresponding to a reddening of E_(B-V)= 0.02 mag in the direction of the
burst (Schlegel et al. 1998).

We acknowledge the excellent support from Regis Lachaume in La Silla
in acquiring these observations.

J. Burgess, F. Kunzweiler, B. Biltzinger, F. Berlato,  & J. Greiner (all MPE Garching) report:

The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
592461363 at 04:35:58 on 11 Oct. 2019 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).

The best-fit position (1 sigma statistical errors) is:
RA(2000.0) = 46.4+/-4.6 deg
Decl.(2000.0) = -32.5+/-5.6 deg
We estimate an additional systematic error of 2 deg.

Further details are available at:
https://grb.mpe.mpg.de/grb/GRB191011192/

The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB191011192/healpix

The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB191011192/json

A. Nicuesa Guelbenzu (TLS Tautenburg) reports:

An error occurred in the previous data reduction. Corrected AB magnitudes
are (midtime of the observations: 04:42 UT, Oct. 11):

g' = 19.97 +/- 0.08 mag,
r' = 19.46 +/- 0.05 mag,
i' = 19.08 +/- 0.07 mag,
z' = 18.79 +/- 0.10 mag,
J  = 18.79 +/- 0.06 mag, and
H  = 18.61 +/- 0.06 mag,

calibrated against PanSTARRS and 2MASS field stars.

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 4075 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 191011A, 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 = 44.72800, -27.84540 which is equivalent
to:

RA (J2000): 02h 58m 54.72s
Dec (J2000): -27d 50' 43.4"

with an uncertainty of 1.5 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.

V. Lipunov
Sternberg Astronomical Institute, Moscow State University

The GRB 191011A optical transient candidate  published by us in (Lipunov 
et. al. GCN 25989
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 ) is a group of hot pixels on a CCD matrix. This is not 
a real GRB afterglow candidate. We sorry for this mistake.

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (ASDC), V. D'Elia
(ASDC), J.A. Kennea (PSU), B. Sbarufatti (PSU), D.N. Burrows (PSU) and
S.L Laha report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 191011A (L Laha et al. GCN
Circ. 25988
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 ), from 84 s to 23.3 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Evans et al. (GCN Circ. 25995
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 ).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.15 (+0.15, -0.20), followed by a break at T+855 s to
an alpha of 1.34 (+/-0.12).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.83 (+/-0.15). The
best-fitting absorption column is  5.3 (+3.5, -3.1) x 10^21 cm^-2, at a
redshift of 1.722, in addition to the Galactic value of 1.5 x 10^20
cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 3.6 x
10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.5 x 10^20 cm^-2
Intrinsic column:    5.3 (+3.5, -3.1) x 10^21 cm^-2 at z=1.722
Photon index:	     1.83 (+/-0.15)

If the light curve continues to decay with a power-law decay index of
1.34, the count rate at T+24 hours will be 1.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.7 x
10^-14 (4.2 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/00928924.

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

E. Bissaldi (Politecnico and INFN Bari) and P. Veres (UAH)
report on behalf of the Fermi GBM Team:

"At 04:35:58.58 UT on 11 October 2019, the Fermi Gamma-Ray Burst Monitor
(GBM) triggered and located GRB 191011A (trigger 592461363 / 191011192), which
was also detected by the Swift/BAT (Laha et al. 2019, GCN 25988
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 ).

The GBM localization statistic exhibited two minima, one of which is
consistent with the Swift location (75% containment).  The localization
centroid in the Real-time Localization notice (GCN 25987
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 ) is for the other
minimum, which is near the Earth limb and is inconsistent with the Swift
location.

The angle from the Fermi LAT boresight at the GBM trigger time is 39
degrees.

The GBM light curve shows several pulses
with a duration (T90) of about 13 s (50-300 keV).
The time-averaged spectrum from T0-2.0 s to T0-0.38 s is
adequately fit by a simple power law function with index -1.76 +/- 0.08.

The event fluence (10-1000 keV) in this time interval is
(4.33 +/- 0.50)E-7 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-1.8 s in the 10-1000 keV band is 3.29 +/- 0.30 ph/s/cm^2.

A power law function with an exponential high-energy cutoff
fits the spectrum equally well. The power law index is -1.24 +/- 0.29 and
the cutoff energy, parameterized as Epeak, is 89 +/- 23 keV.

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/"

Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), William H.
Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska
(UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Diego Gonz��lez (UNAM),
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 191011A (Laha et al., GCN Circ. 25988
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 ) 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 2019/10 11.26 to 2019/10 11.48 UTC (1.60 to 6.94 hours after
the BAT trigger), obtaining a total of 1.64 hours exposure in the i band and
0.49 hours exposure in the Z, Y, J, and H bands.

For a source within the Swift-XRT error circle, in comparison with the USNO-B1
and 2MASS catalogs, we obtain the following detections and upper limits
(3-sigma):

  i	= 21.59 +/- 0.13
  Z	= 21.22 +/- 0.21
  Y	> 21.76
  J	> 19.81
  H	> 20.54

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.

N. P. M. Kuin (UCL-MSSL) and Laha (GSFC/UMBC/CRESST)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 191011A
78 s after the BAT trigger (Laha et al., GCN Circ. 25988
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 ).  A source
consistent with the XRT position (Evans et al. GCN Circ. 25995
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 )
is detected in the initial UVOT exposures. This GRB was also detected
by Fermi/GBM (GCN Circ. 25987
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 ,26000
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 ) and Insight-HXMT-HE(Yi et al, GCN
Cir. 25997). A redshift was reported using the VLT/Xshooter (Kahn et al,
GCN Circ.25991
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 ), while the optical afterglow was reported from Master
(Lipunov et al, GCN Circ. 25990
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 ; GROND (Nicuesa Guelbenzu et al.,
GCN Circ. 25992
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 ).

The preliminary UVOT position is:
    RA  (J2000) =  02:58:54.79 =  44.72829 (deg.)
    Dec (J2000) = -27:50:43.4  = -27.84540 (deg.)
with an estimated uncertainty of 0.73 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric
system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white               78          228          147         20.27 +/- 0.16
v                  620        11672         1211        >20.2
b                  545         7080          510         21.03 +/- 0.27
u                  290         6875          697         20.86 +/- 0.27
w1                 670         6670          510        >20.3
m2                1073        12198          767        >21.1
w2                1024         7491          432        >20.9

The afterglow is seen to be nearly constant in the white filter until
about 1000s, whereafter a decay is observed.  The magnitudes in the table
are
not corrected for the Galactic extinction due to the reddening of E(B-V) =
0.02
in the direction of the burst (Schlegel et al. 1998).

T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU) (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 191011A (trigger #928924)
(Laha et al., GCN Circ. 25988
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 ).  The BAT ground-calculated position is
RA, Dec = 44.729, -27.853 deg which is
   RA(J2000)  =  02h 58m 55.0s
   Dec(J2000) = -27d 51' 12.4"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.

The mask-weighted light curve shows a short pulse that starts and peaks
at ~T0, and ends at ~T+2 s. The short pulse is followed by some weak
emission
that lasts until ~T+8 s. T90 (15-350 keV) is 7.37 +- 0.95 sec (estimated
error
including systematics).

The time-averaged spectrum from T-0.21 to T+8.04 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.94 +- 0.17.  The fluence in the 15-150 keV band is 3.3 +- 0.4 x 10^-7
erg/cm2.
The 1-sec peak photon flux measured from T+0.18 sec in the 15-150 keV band
is 1.8 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

Using the 16-ms binned light curve, the spectral lag of the short pulse
is 30 (+45, -34) ms for the 50-100 keV to 15-25 keV bands, and 20 (+40,
-44) ms
for the 25-50 keV to 15-25 keV bands. These values are consistent with
both short and long GRBs due to the large uncertainties.


The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/928924/BA/