GRB 190828B

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

At 12:59:59 UT on 28 Aug 2019, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 190828B (trigger 588690004.456526 / 190828542).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 246.6, Dec = 24.6 (J2000 degrees, equivalent to J2000 16h 26m, 24d 36'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 17.0 degrees.

The skymap can be found here:
http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn190828542/quicklook/glg_skymap_all_bn190828542.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/bn190828542/quicklook/glg_healpix_all_bn190828542.fit

The GBM light curve can be found here:
http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn190828542/quicklook/glg_lc_medres34_bn190828542.gif

S. Dichiara (NASA/GSFC/UMCP), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), M. G. Bernardini (INAF-OAB),
A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), P. A. Evans (U Leicester), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), K. L. Page (U Leicester), B. Sbarufatti (PSU),
M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 12:59:59.42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190828B (trigger=922808).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 251.818, 27.237 which is 
   RA(J2000) = 16h 47m 16s
   Dec(J2000) = +27d 14' 12"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 40 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~10 sec after the trigger. 

The XRT began observing the field at 13:00:54.1 UT, 54.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
251.8317, 27.2808 which is equivalent to:
   RA(J2000)  = 16h 47m 19.60s
   Dec(J2000) = +27d 16' 50.9"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 163 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 6.84
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 2.12e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 63 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
0.10. 

Burst Advocate for this burst is S. Dichiara (dichiara AT umd.edu). 
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/)

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

Using 1594 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 190828B, 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 = 251.83127, +27.28091 which is equivalent
to:

RA (J2000): 16h 47m 19.51s
Dec (J2000): +27d 16' 51.3"

with an uncertainty of 1.7 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.

B.Y. Yu, X. Liu, D. Xu, Z.P. Zhu (NAOC), J.H. Liu (XAO), X. Gao (Urumqi 
No.1 Senior High School), Z.B. Zhang (XJTS) report:

We observed the field of GRB 190828B (Dichiara et al., GCN 25517
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 ) using 
the Half-Meter Telescope (HMT-0.5m) located at Dabancheng, Xinjiang, 
China. We obtained 5x60 s unfiltered frames, started at 13:56:32 UT on 
2019-08-28, i.e., 56.5 min after the burst.

No optical source is detected at the XRT position (Dichiara et al., 
GCN25517
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 ) in our stacked image, down to a limiting magnitude of R~17.8, 
calibrated with the nearby SDSS field.

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), S. Dichiara (NASA/GSFC/UMCP),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+962 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 190828B (trigger #922808)
(Dichiara et al., GCN Circ. 25517
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 ).  The BAT ground-calculated position is
RA, Dec = 251.838, 27.287 deg which is
   RA(J2000)  =  16h 47m 21.2s
   Dec(J2000) = +27d 17' 12.9"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a multi-peak structure that starts
at ~T-40 s and ends at ~T+50 s. There are roughly three main peaks
that occurs at ~T0, ~T+11 s, and ~T+31 s, respectively.
T90 (15-350 keV) is 66.6 +- 6.2 sec (estimated error including systematics).

The time-averaged spectrum from T-42.4 to T+53.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.29 +- 0.07.  The fluence in the 15-150 keV band is 4.2 +- 0.2 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T+10.74 sec in the 15-150 keV band
is 2.3 +- 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/922808/BA/

O.J. Roberts (USRA/MSFC), E. Bissaldi (INFN Bari) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 12:59:59.46 UT on 28 August 2019, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 190828B (trigger 588690004 / 190828542),
which was also detected by Swift (Dichiara et al. 2019, GCN 25517
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  )

The Fermi GBM Final Real-time Localization (GCN 25516
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 ) is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 18 degrees.

The GBM light curve consists of multiple, bright peaks with a
duration (T90) of about 55 s (50-300 keV).
The time-averaged spectrum from T0-34 s to T0+46 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.99 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 237 +/- 22 keV

The event fluence (10-1000 keV) in this time interval is
(1.24 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+10.6 s in the 10-1000 keV band
is 3.9 +/- 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/"

S. R. Oates (U.Warwick) and S. Dichiara (NASA/GSFC/UMCP)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190828B
63 s after the BAT trigger (Dichiara et al., GCN Circ. 25517
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 ).
No optical afterglow consistent with the XRT position
(Beardmore et al. GCN Circ. 25521
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 )
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            63          213          147         >20.8
u_FC               275          525          246         >20.1
white               63         1717          411         >21.4
v                  605         1767          136         >19.1
b                  530         1693          117         >20.0
u                  275         1668          363         >20.4
w1                 654         1644          117         >19.2
m2                 630         5626          259         >19.4
w2                 580         1743          136         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.10 in the direction of the burst
(Schlegel et al. 1998).

P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), E. Ambrosi	(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M.
Perri (ASDC), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp
(PSU) and S. Dichiara report on behalf of the Swift-XRT team:

We have analysed 5.8 ks of XRT data for GRB 190828B (Dichiara et al.
GCN Circ. 25517
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 ), from 60 s to 74.7 ks after the  BAT trigger. The data
comprise 90 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Beardmore et al. (GCN Circ. 25521
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.4 (+/-0.4). At T+98.4 s	the decay
flattens to an alpha of -1.5 (+0.0, -1.4). The light curve breaks again
at T+110 s to a decay with alpha=3.5 (+0.7, -0.4),  and  again at T+217
s s to alpha=-0.24 (+0.16, -0.20),  before a final break at T+1028 s s
after which the decay index is 0.96 (+/-0.04).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.56 (+0.11, -0.09). The
best-fitting absorption column is  7.8 (+3.8, -1.0) x 10^20 cm^-2,
consistent with the Galactic value of 6.8 x 10^20 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 1.91 (+/-0.10)
and a best-fitting absorption column of 1.25 (+0.29, -0.27) 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 (4.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.25 (+0.29, -0.27) x 10^21 cm^-2
Galactic foreground: 6.8 x 10^20 cm^-2
Excess significance: 3.4 sigma
Photon index:	     1.91 (+/-0.10)

If the light curve continues to decay with a power-law decay index of
0.96, the count rate at T+24 hours will be 0.035 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 x
10^-12 (1.6 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00922808.

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

A. Brosio (Oss. Astr. Savelli), A. Melandri (INAF-OAB), E. Palazzi (INAF-OAS), L. Nicastro (INAF-OAS), M.A. Tripodi (Oss. Astr. Savelli), S. Savaglio (UniCal) on behalf of a larger collaboration report:


We observed the field of GRB 190828B (Dichiara et al., GCN 25517
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 ) with the 0.5m Savelli Robotic Telescope (SRT) located at the Osservatorio Astronomico Lilio (Savelli, Italy). The observations were performed starting on 2019 August 28 at 19:19:22 UT (i.e. about 6.3 hours after the burst) and consisted of 24x300s exposures in the r-sdss band. 

No optical counterpart is detected nearby the XRT enhanced position (Beardmore et al., GCN 25521
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 ) in our stacked image, down to a 5sigma limiting magnitude of r>20.5, at a mean time of about 7.48 hours after the GRB. Calibration was performed against the SDSS catalog.

J. P. U. Fynbo (DAWN/NBI), K. E. Heintz (Univ. of Iceland), D. B. Malesani (DTU space), and D. A. Perley (LJMU), report on behalf of the Stargate collaboration:

We imaged the field of the Swift (Dichiara et al., GCN 25517
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 ) and Fermi-GBM (Roberts et al., GCN 25536
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 ) detected GRB 190828B with the ESO-VLT/X-shooter acquisition camera between 00:03:44 and 00:22:49 UT on August 29 (i.e. 11.15 hr after the trigger). From the combined images, obtained with a total integration time of 210 sec, we identify a faint source within the XRT error circle with magnitude r = 23.55 +/- 0.15 AB mag, calibrated from the photometry of nearby field stars as listed in the Pan-STARRS archival data. To verify whether this source is the afterglow or host galaxy of the GRB, a second epoch of images is required.

We acknowledge the ESO observing staff at Paranal, especially Alain Smette, Camila Navarrete and Linda Schmidtobreick.

[GCN OPS NOTE(31aug19): Per author's request, the "Title:" string was removed from the SUBJECT: line.]

R. Gaikwad, V. Sharma, D. Bhattacharya and A. Vibhute (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed the detection of a GRB 190828B, which was also detected by Fermi GBM Final Real-time Localization (GCN #25516
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 ), Swift (S. Dichiara. et al., GCN # 25517), Swift-XRT (Beardmore A. et al., GCN # 25521), Swift-BAT (Krimm H. et al., GCN # 25534), Fermi GBM (Roberts J. et al., GCN # 25535),.

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple pulses of emission with the strongest peak at 2019-08-28 12:59:59.0 UT. The measured peak count rate associated with the burst is 297 cts/s above the background in the combined data of four quadrants, with a total of 3424 cts. The local mean background count rate was 611 cts/s. Using cumulative rates, we measure a T90 of 31.9 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.