OP313 Dec2023 Jan2024 LST1 analysis details

LST analysis OP313 Dec 2023 and Jan 2024

Wiki page with general information on all results for the paper: December_January_paper

LST-1 analyzers:

• Seiya Nozaki (MPP)
• Jorge Otero-Santos (IAA-CSIC)
• Mireia Nievas-Rosillo (IAC)
• Daniel Morcuende (IAA-CSIC)

Links to presentation of the LST-1 analysis in several analysis and OP313 meetings

To be added

Data-taking information

• NSB level: all data was taken in dark NSB conditions
• Zenith angles: 15-54 deg (December 2023 data have zenith angle > 30 deg)

Good-quality selected dataset

The list of data runs below was obtained using the notebook https://github.com/cta-observatory/cta-lstchain/blob/main/notebooks/data_quality.ipynb.

We used default settings, but min_drdi_at_422pe = 1.2 instead of the default 1.5 to recover 1.7 h from January 2024 where low statistics limit us. Still, the data selected have a relative light yield above ~80%.

Also, short data runs (< 5 min) were excluded, because usually short runs are a symptom of problems during data acquisition.

'2023-12-09': [15942, 15943, 15944, 15945],
'2023-12-10': [15975, 15976, 15977, 15978],
'2023-12-11': [16007, 16008, 16009, 16010],
'2023-12-12': [16042, 16043, 16044, 16045],
'2023-12-13': [16079, 16080, 16081, 16082, 16083],
'2023-12-14': [16114, 16116, 16117, 16118, 16119],
'2023-12-15': [16150, 16151, 16152, 16153, 16154, 16155, 16156],
'2023-12-16': [16188, 16189, 16191, 16192, 16193],
'2023-12-17': [16220, 16221, 16222, 16223, 16224, 16225],
'2023-12-18': [16240, 16241, 16242, 16243, 16244, 16246],
'2024-01-09': [16293, 16294, 16295],
'2024-01-13': [16350, 16351, 16352, 16353, 16354, 16356, 16357, 16358, 16359],
'2024-01-17': [16391, 16392],
'2024-01-19': [16412, 16413, 16414, 16415],
'2024-01-21': [16418, 16419, 16420]

In total, there are 19.8 hours effective time.

• Relative light yield of the selected data:

lstchain settings

• lstchain version: v0.10.7
• MC production: 20230901_v0.10.4_allsky_base_prod
• RF models: /fefs/aswg/data/models/AllSky/20230901_v0.10.4_allsky_base_prod/dec_3476/
• DL2 MC for IRF calculation: /fefs/aswg/data/mc/DL2/AllSky/20230901_v0.10.4_allsky_base_prod/TestingDataset/dec_3476
• Used IRF interpolation
• Selection cuts IRF and DL3: 70% efficiency in both gammaness and theta gamma-ray selection cuts (Mireia used 68% theta containment instead). Intensity > 50 p.e.
• Energy threshold: ~ 40 GeV. Calculated from DL2 testing gamma MC (several nodes with similar zenith as the bulk of the telescope pointing positions: 32.059_az_102.217, 37.814_az_90, 43.197_az_87.604, 47.952_az_90, 52.374_az_110.312), weighting the default MC spectrum by a log parabola calculated from OP313 (alpha: -3.7, beta: -1.1, amplitude: 3.0e-09 TeV s-1 cm-2, E_0: 100 GeV) and assuming the same selection cuts as in the DL3 files (intensity>50 p.e., 70% efficiency in gammaness cut, and 70% efficiency in theta cut). Treatment of the DL2 MC was done using functions from lstchain.mc module

Gammapy settings

• Gammapy version: v1.1
• Energy binning:

reco energy axis: 5 GeV - 10 TeV, 5 bins per decade
true energy axis: 1 GeV - 20 TeV, 10 bins per decade

• 3 off positions for SED and LC calculation
• Safe mask: 5% of max. Aeff
• Energy range for spectral fitting: 70 GeV - 1 TeV (In Mireia's analysis, the fit range starts at around 60 GeV, because uses a slightly different reconstructed energy binning)
• redshift: 0.997

Analysis cross-check

Cross-checks of different LST-1 analysis results.

Cross-check of LST-1 SED from OP313 during high-flux period (Dec 2023).

Cross-check of LST-1 LC from OP313 (Dec 9th 2023 to Jan 21th 2024).

Best-fit spectral parameters

Analyzer	Analysis method	Spectral model	EBL model	Index	Amplitude [x 10-8 TeV-1 s-1 cm-2]	E_ref [GeV]	alpha_norm
Seiya	source-dependent	PWL+EBL	Saldana-Lopez 2021	2.37 ± 0.88	0.82 ± 0.14	100	1.0
Jorge	source-independent	PWL+EBL	Saldana-Lopez 2021	2.07 ± 0.51	1.15 ± 0.13	100	1.0
Mireia	source-independent	PWL+EBL	Dominguez 2011	1.86 ± 0.50	0.93 ± 0.11	100	1.0
Daniel	source-independent	PWL+EBL	Saldana-Lopez 2021	2.00 ± 0.45	1.14 ± 0.13	100	1.0

Test on background normalization systematics

The relative difference between the background counts in two off-source regions at the same distance from the center of the field of view (0.4 deg), and equidistant from the OP313 location is 0.31% ± 0.14% (counts in the OFF region at 90 deg: 487702 ± 698, and in the OFF region at 270 deg: 486203 ± 697). Therefore we tested the effect that a factor ±0.5% in the background normalization has in the SED calculation (see best-fit model spectral parameters calculated after considering the change in background normalization for source-independent analysis, assuming PWL+EBL Saldana-Lopez 2021 model).

Best-fit spectral parameters after scaling the background normalization ±0.5%

Background normalization	Index	Amplitude [x 10-8 TeV-1 s-1 cm-2]	E_ref [GeV]	alpha_norm
+0.5%	2.12 ± 0.58	0.89 ± 0.14	100	1.0
-0.5%	1.86 ± 0.37	1.39 ± 0.14	100	1.0