PG 1553 - 2023 ToO data analysis

General information

• Name of the source: PG 1553+113
• Brief description of the source:
  • Object type : AGN
  • Redshift (z) : 0.433 Dorigo Jones et al
  • BL Lac
  • RA: 15 5543.044 (hh mm ss), Dec: +11 11 24.365 (dd mm ss)
  • RA, Dec in deg (ICRS): 238.92934976, 11.19010155

• Analysis by Estelle Pons (LAPP - estelle.pons@lapp.in2p3.fr)

PG 1553+113 - 2023 ToO data analysis (Helena Luciani)

General analysis information

• Source-independent analysis
• lstchain version: lstchain-v0.10.9

Data selection configuration

• Start observation time: 2023-04-26 01:09:52.000
• End observation time: 2023-04-26 05:14:00.000

User input:

• source coordinates: (238.92935002, 11.19010157) (ra, dec) in deg
• date directory: 2023-04-25
• telescope pointings from the source: min_angle = 0.35 deg, max_angle = 0.45 deg
• zenith distance range: 0 deg < zenith < 50 deg
• maximum diffuse NSB: 2.3

---

• Total number of loaded subruns: 1674
• Total number of loaded runs: 15

• Number of runs (% is w.r.t. those in Sky region & zenith range):

   In the requested Sky region and range of dates:	 15
 + zenith in requested range:				 15
 + NSB in requested range:				 15 (100.0%)
 + FF and pedestal interleaved events are present:	 15 (100.0%)
 + Stable pointing:					 15 (100.0%)
 + dR/dI fit P-value ok:				 15 (100.0%)
 + dR/dI LS periodogram ok:				 15 (100.0%)
 + dR/dI index ok:					 15 (100.0%)
 + dR/dI rate ok:					 15 (100.0%)
 + intensity threshold ok:				 15 (100.0%)

• Selected: 15 of 15 runs (in 1 night)
• Total observation time: 3.87 hours

• List of selected runs: [12859 12860 12861 12863 12864 12865 12866 12867 12868 12869 12870 12871 12872 12873 12874]

---

DL1 to DL2

• Random Forest : /fefs/aswg/data/models/AllSky/20240131_allsky_v0.10.5_all_dec_base/dec_931/

• Configuration file: /fefs/aswg/data/models/AllSky/20240131_allsky_v0.10.5_all_dec_base/dec_931/lstchain_config_2024-01-31.json

• DL2 data:

dl2_LST-1.Run12859.h5
dl2_LST-1.Run12860.h5
dl2_LST-1.Run12861.h5
dl2_LST-1.Run12863.h5
dl2_LST-1.Run12864.h5
dl2_LST-1.Run12865.h5
dl2_LST-1.Run12866.h5
dl2_LST-1.Run12867.h5
dl2_LST-1.Run12868.h5
dl2_LST-1.Run12869.h5
dl2_LST-1.Run12870.h5
dl2_LST-1.Run12871.h5
dl2_LST-1.Run12872.h5
dl2_LST-1.Run12873.h5
dl2_LST-1.Run12874.h5

DL3 data and IRFs

• Input gamma:
  

/fefs/aswg/data/mc/DL2/AllSky/20240131_allsky_v0.10.5_all_dec_base/TestingDataset/dec_931/node_theta_*

• Config file :
  

../cta-lstchain/docs/examples/irf_dl3_tool_config.json

• IRFs : GH_efficiency= 0.7, theta_containment= 0.7
  

--point-like --energy-dependent-gh --energy-dependent-theta --gh-efficiency=0.7 --theta-containment=0.7

• DL3 creation using IRF nearest node

 "EventSelector": {
   "filters": {
     "intensity": [50, Infinity],
     "width": [0, Infinity],
     "length": [0, Infinity],
     "r": [0, 1],
     "wl": [0.01, 1],
     "leakage_intensity_width_2": [0, 1],
     "event_type": [32, 32]
   }
 },
 "DL3Cuts": {
   "min_event_p_en_bin": 100,
   "global_gh_cut": 0.7,
   "gh_efficiency": 0.7,
   "min_gh_cut": 0.1,
   "max_gh_cut": 0.98,
   "global_alpha_cut": 10,
   "global_theta_cut": 0.2,
   "theta_containment": 0.7,
   "alpha_containment": 0.7,
   "min_theta_cut": 0.1,
   "max_theta_cut": 0.32,
   "fill_theta_cut": 0.32,
   "min_alpha_cut": 1,
   "max_alpha_cut": 20,
   "fill_alpha_cut": 20,
   "allowed_tels": [1]

High-level analysis

• Gammapy version: 1.1

• 1D analysis

Analysis Results

Livetime : 3.67 h

Significance : 15.68σ

Theta2 plot

• Theta2 cut for signal extraction: 0.04 deg2

• Energy range: 10 GeV - 10 TeV

• Significance: 15.68σ

---

Light-curve

Energy threshold: 50 GeV

Time binning: 20 min

---

SED

Energy range: 10 GeV - 10 TeV

Best fit model: Log Parabola + EBL (Dominguez 2011)

600px

PG 1553+113 - 2023 ToO data analysis 2 (Arshia Ruina)

General analysis information

• Source-independent analysis
• lstchain version: lstchain-v0.10.9

Data selection configuration

• Source coordinates (ra, dec): (238.92935002°, 11.19010157°)
• Telescope pointings around source: [0.35°, 0.45°]
• Zenith distance range: [0°, 52°]
• Maximum diffuse NSB std: 2.3
• first_date = 20191101
• last_date = 20231231

Number of runs (% is w.r.t. those in Sky region & zenith range):

   In the requested Sky region and range of dates:	 125
 + zenith in requested range:				 120
 + NSB in requested range:				 116 (96.7%)
 + FF and pedestal interleaved events are present:	 116 (96.7%)
 + Stable pointing:					 116 (96.7%)
 + dR/dI fit P-value ok:				 116 (96.7%)
 + dR/dI LS periodogram ok:				 113 (94.2%)
 + dR/dI index ok:					 103 (85.8%)
 + dR/dI rate ok:					 90 (75.0%)
 + intensity threshold ok:				 90 (75.0%)

• Selected: 90 of 8196 runs
• Total observation time (elapsed time): 22.75 h
• Total ontime 22.52 hrs
• Total livetime 21.38 hrs

• List of runs:

   * 20210321 [4207]
   * 20210407 [4335 4336]
   * 20210408 [4343 4344]
   * 20210410 [4363 4364 4365 4366 4367 4368 4369 4370]
   * 20210508 [4652 4653 4654]
   * 20210604 [4902 4903 4904 4905]
   * 20220228 [7153 7154]
   * 20220501 [8059 8060 8061 8062 8063 8064]
   * 20220520 [8377 8378 8379]
   * 20220523 [8424 8425]
   * 20220602 [8600 8601 8602]
   * 20230120   [11748 11749 11750 11751]
   * 20230123 [11809 11810 11811 11812 11813]
   * 20230126 [11903 11904 11906]
   * 20230224 [12080 12081 12082 12083 12084 12085]
   * 20230226 [12096 12097 12098 12099]
   * 20230317 [12234 12235 12236 12237]
   * 20230321 [12362 12363 12364 12365 12366]
   * 20230414 [12697 12698 12699 12700]
   * 20230418 [12755 12756 12757 12758]
   * 20230426 [12859 12860 12861 12863 12864 12865 12866 12867 12868 12869 12870 12871 12872 12873 12874] <<-- flare night

DL1 to DL2 conversion

• RF Model: /fefs/aswg/data/models/AllSky/20240131_allsky_v0.10.5_all_dec_base/dec_931
• Config file: Github link

• File list: File:Dl2 filelist AR.pdf

Creating IRFs

lstchain_create_irf_files -g ${file} -c ${config_file} -o ${irf_file} --point-like --energy-dependent-gh --energy-dependent-theta

• Config file: Github link
• gh_efficiency= 0.7, theta_containment= 0.7

DL2 to DL3

lstchain_create_dl3_file --overwrite --use-nearest-irf-node --config ${config_file} --input-dl2 ${file} --input-irf-path ${irfs}  --source-name=PG1553+113 --source-ra=238.92935002deg --source-dec=11.19010157deg --output-dl3-path ${OUTPUT_DIR}/

• Config file: Github link
• gh_efficiency= 0.7, theta_containment= 0.7

The default version of the analysis used "nearest node IRF". Later, I also tried using "interpolation IRF".

lstchain_create_dl3_file --overwrite --config ${config_file} --input-dl2 ${file} --input-irf-path ${irfs}  --source-name=PG1553+113 --source-ra=238.92935002deg --source-dec=11.19010157deg --output-dl3-path ${OUTPUT_DIR}/

High level analysis

Selecting runs only for the flaring night

• For PG1553+113, intra-night variability is looked for using the longest data collection period available i.e. data from the night of 26-04-2023 (nearly 4 hours of data).

• Number of runs selected: 15
• Run list (flare night): [12859 12860 12861 12863 12864 12865 12866 12867 12868 12869 12870 12871 12872 12873 12874]
• Start observation time: 2023-04-26 01:09:56.663
• End observation time: 2023-04-26 05:13:44.526
• Total ontime of flare night observations: 3.86 hrs
• Total livetime of flare night observations: 3.67 hrs

Note: Only observations with a minimum livetime of 30 seconds were selected.

Theta-squared plot

Excess counts plot

600px

Light curve

• LC is estimated from 50 GeV to 10 TeV
• Energy binning:

e_reco_min = 10 * u.GeV
e_reco_max = 10 * u.TeV
e_true_min = 10 * u.GeV
e_true_max = 100 * u.TeV
e_reco_bin_p_dec = 5
e_true_bin_p_dec = 100

• The LC is made in varying time bins, ranging from 5 min to 40 min

LCs with nearest node IRFs (default)

• LC with 20 min time bins, and energy threshold 50 GeV

• LC with 20 min time bins, and energy threshold 150 GeV

Cross-check of LC with Helena Luciani

LCs with interpolation IRFs

• LC with 20 min time bins, and energy threshold 50 GeV

• LC with 20 min time bins, and energy threshold 150 GeV

SED

Energy range: 10 GeV - 10 TeV Best fit model: Log Parabola + EBL (Dominguez 2011)

With neareast node IRFs (default)

It is a match with Helena Luciani (see above). We will upload a comparison plot with both SEDs overlayed on one another soon.

With interpolation IRFs

Differential Spectrum

With neareast node IRFs (default)

It is a match with Helena Luciani (see above). We will upload a comparison plot with both spectra overlayed on one another soon.

With interpolation IRFs

Constraints on the emitting region radius

• We characterise the variations in the flux by using the normalised RMS variability amplitude, F_var, defined as

F_{\text{var}} = \sqrt{\frac{S^{2}- \langle \sigma^{2}_{\text{err}} \rangle }   {{\langle F \rangle}^{2} } }

where S^2 is the sample variance, σ^2 is the mean square error (MSE) and <F> is the mean flux. We obtain S^2 > MSE and F_var (%) = 24.04 ± 6.93 (3.47σ significance) which hints towards the presence of IDV.

Method: Gammapy compute_fvar

• We compute the shortest variability timescale using the flux halving/doubling timescales as follows

F(t_{1}) = F(t_{2}) 2^{(t_{1}-t_{2})/\tau}

where τ is a characteristic halving/doubling time-scale and F(t1) and F(t2) are the fluxes of the LC at times t1 and t2, respectively.

Method 1: Gammapy compute_lightcurve_doublingtime

Method 2: Gammapy compute_flux_doubling

Both methods give same results.

• Using this shortest variability timescale, we compute an upper limit on the radius of the emission region using the formula

R \leq \frac{c t_{\text{var}} \delta}{1+z}

where the Doppler factor, δ, ranges from 11 to 35.

• The procedure followed here is inspired from sections 3.1 and 3.2 of the XMM paper by Dhiman et al. 2021

• Results: