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Observation Date (UT) Observation Lat

Canonical Name:GRB 190829A
TeVCat Name:TeV J0258-089
Other Names:
Source Type:GRB
R.A.:02 58 10.51 (hh mm ss)
Dec.:-08 57 28.1 (dd mm ss)
Gal Long: 187.68 (deg)
Gal Lat: -55.00 (deg)
Distance: z=0.0785
Flux: (Crab Units)
Energy Threshold: GeV
Spectral Index:
Extended:No
Discovery Date:2019-08
Discovered By: H.E.S.S.
TeVCat SubCat:Default Catalog

Source Notes:

Detection Details:

The detection of VHE emission from this GRB was announced in an ATel
by de Naurois et al. (2019). The observations began 4h 20m after
T0 and lasted for 3 hours 34m. A gamma-ray signal at the >5 sigma
level was detected.

From H.E.S.S. Collaboration (2021):
- "We report the detection of very-high-energy (VHE) gamma rays from
the afterglow of GRB 190829A, between 4 and 56 hrs after the trigger,
using the High Energy Stereoscopic System. The low luminosity and
redshift of GRB 190829A reduce both internal and external absorption,
allowing determination of its intrinsic energy spectrum. Between
energies of 0.18 and 3.3 teraelectronvolts, this spectrum is described
by a power law with photon index of 2.07 +/- 0.09, similar to the
X-ray spectrum. The X-ray and VHE gamma-ray light curves also show
similar decay profiles. These similar characteristics in the X-ray and
gamma-ray bands challenge GRB afterglow emission scenarios."
- "The H.E.S.S. observations were on three consecutive nights:
... the first night starting at T0+4.3 hrs for a total of 3.6 hrs,
... the second night at T0+27.2 hrs for 4.7 hrs,
... and the third night at T0+51.2 hrs for 4.7 hrs (16).
Our analysis detected a VHE gamma-ray signal on each of the three
nights, spatially coincident with the GRB position, with
statistical significances of 21.7 sigma, 5.5 sigma and 2.4 sigma."

Source Position:
The position given in TeVCat was reported by Chen et al. (2019):
- R.A. (J2000): 02 58 10.51
- Dec. (J2000): -08 57 28.1

Distance:

The redshift given in TeVCat was reported by Valeev et al. (2019):
- The redshift measurement is based on absorption lines detected in
the GRB afterglow emission and on emission lines of the underlying
galaxy also detected in the afterglow emission, which confirm the
physical association between the GRB and this galaxy, SDSS
J025810.28-085719.2: z = 0.0785 +/- 0.005

From Hu et al. (2021):
- "We present the 10.4 m Gran Telescopio Canarias (GTC) observations
of the afterglow of GRB 190829A and its underlying supernova."
- "The Ca H & K absorption lines doublet (3933.664 and 3968.470 Angstrom)
were identified in the observed spectrum which allowed us to determine
the redshift z = 0.0785 +/- 0.0005 (Valeev et al., 2019)."

Classification:
From The Fermi GBM Team at MSFC (2019):
- "The Fermi GBM team reports the detection of a likely LONG GRB"
From Lesage et al. (2019):
- Further details from the Fermi GBM light curve support the
classification as a long GRB.
- "The GBM light curve shows an initial pulse followed by a brighter
peak, with a duration (T90) of about 63 s (50-300 keV)."

Spectral Properties:
From H.E.S.S. Collaboration (2021):
- "We performed a spectral analysis of the first two nights; the
signal on the third night was too weak to determine the spectrum."
- "We fitted a power-law model to the photon spectrum of the form:
... dN/dE = N0(E/E0)^-A_obs
... where N0 is the spectrum normalisation at photon energy E0,
... A_obs is the spectral index.
We find A_obs:
... 2.59 +/- 0.09 (stat.) +/- 0.23 (syst.) from 0.18 TeV to 3.3 TeV) on the first night
... 2.46 +/- 0.22 (stat.) +/- 0.14 (syst.) from 0.18 TeV to 1.4 TeV on the second night"
- "To characterise the intrinsic GRB spectrum (corrected for EBL
absorption), we fitted an attenuated power-law model of the form:
... dN/dE = N0(E/E0)^A_int.e−T(E,z) to the data.
- The exponential term corresponds to the absorption of photons through
their interaction with the EBL, and T is the energy-dependent optical
depth for a source at redshift z."
- "For the first two observation nights, we determined VHE intrinsic
photon indices of:
... A_int = 2.06 +/- 0.10 (stat.) +/- 0.26 (syst.) (first night)
... A_int = 1.86 +/- 0.26 (stat.) +/- 0.17 (syst.) (second night).
- These values indicate that within the uncertainties, the spectral
shape remains unchanged, so we performed a joint spectral analysis"
- "Combining the three nights of observation data, the photon
index found is:
... A_int = 2.07 +/- 0.09 (stat.) +/- 0.23 (syst.)
... in the energy range 0.18 to 3.3 TeV."
- "These per-night VHE photon indices are consistent, within the
statistical uncertainties, with the photon indices of the x-ray
emission (XRT) we measured from the Swift-XRT data taken during the
same observational periods:
... A_xrt = 2.03 +/- 0.06 (first night)
... A_xrt = 2.04 +/- 0.10 (second night)"

Temporal Properties:
From H.E.S.S. Collaboration (2021):
- "We extracted a light curve of the H.E.S.S. observations in the
energy range 0.2 to 4.0 TeV for the entire temporal coverage up to T0
+56 hours. We split the first observation night into three
subintervals. The gamma-ray energy flux, F_VHE, depends on how much
time t has passed after T0, and the time evolution is characterized by
a power-law model:
... F_VHE(t) propotional to t^-a_vhe,
... with a_vhe = 1.09 +/- 0.05"
- "This VHE gamma-ray flux behavior is similar to the x-ray light curve
derived for the same time period. The flux measured by Swift-XRT can
also be described as a power law, with index a_xrt; using the Swift-XRT
data in the energy interval 0.3 to 10 keV, we find that:
... a_xrt = 1.07 +/- 0.09."

Energetics:
From H.E.S.S. Collaboration (2021):
- "The isotropic energy output measured by Swift-XRT during the
afterglow phase was:
... E_iso approx. 5 x 10e50 erg (t < 10^6 s) with 10% uncertainty.
- This is larger than it was during the prompt phase, a feature that has
rarely been observed (Evans et al., 2014)."


Seen by: H.E.S.S.
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