Analysis BLLac Aug 2021 Emery

Main page for the analysis of the observations of BL Lacertae of August 2021 by the LST1 using the likelihood reconstruction method.

LST data analysis responsible : Gabriel Emery using the LH fit reconstruction pipeline.

Other analysis : See the common page for links to each analysis BLLac

Context : BL Lacertae is a know blazar (and more precisely an IBL) located at a redshift of 0.069 with relatively low luminosity in quiescent state. It was active on multiple occasion in 2021 and in particular in July and August. An elevated state was reported in optical, X-rays and at high energy (see e.g. ATel #14773 , ATel #14774 and ATel #14777). This was followed in July by a detection of the source by LST reported in an astronomer telegram ATel #14783. Further observations of a new flux increase at the end of July/start of August (ATel #14820) lead to additional MAGIC follow up (ATel #14826), along with piggyback observations with LST-1.

The dataset analysed in this page is the August dataset from August 2nd to August 13th.

Current analysis status :

Clear detection and variability are obtained. The brightest night allows for the extraction of a spectrum with a threshold around 20-30 GeV.

Both a source independent and source dependent analysis are used with the likelihood method (and standard reconstruction crosscheck).

Run list

August 2nd to 13th :

5443,5444,5447,5448,5449,5450, 5454,5455,5456,5457,5458,5460,5466, 5481,5482, 5486,5488, 5546,5547, 5552,5553,5554,5555,5556,5557,5558,5559, 5592,5593,5594,5595, 5688,5689,5690, 5705,5706, 5732,5733,5734,5735,5736

August 8th : 5552,5553,5554,5555,5556,5557,5558,5559

LH-fit analysis (Shown at the LST general meeting Fall 2021)

MC	it-cluster : /fefs/aswg/data/mc/DL0/20200629_prod5_trans_80/particle/zenith_20deg/south_pointing/
Code	https://github.com/gabemery/cta-lstchain/tree/lhfit_wl_less1_and_numexpr
Config r0-dl1	it-cluster : /home/gabriel.emery/cta/lstchaindev/cta-lstchain-lhfit/lstchain/data/lstchain_lhfit_config_data_v15.json
Processed DL1 files	it-cluster : /fefs/aswg/workspace/gabriel.emery/lhfit_withasymetry_rebasemaster17052021/data/DL1/v15/merged/

Analysis results

Presentation at LST general meeting (19/11/2021) https://indico.cta-observatory.org/event/3671/contributions/31294/attachments/20338/28385/LHfit_BLlac_flare_analysis_LSTGeneralMeetingFall2021.pdf

Main results :

Nice spectra extending to quite low energy (down to a couple of tens of GeV depending on the time window and analysis) and connecting, even if imperfectly, with the contemporaneous data from Fermi-LAT. MWL lightcurves display common and independent variability features. Analysis in source independent/dependent mode with LHfit/standard shown compatible spectra and similar light curves on the 8th. The spectra are also compatible with the simultaneous MAGIC data. Only in slides : ~3 minutes binned LC of the LST-1 LHfit analysis of the 8th shows similar variability as the run wise LC. LC below and above 100 GeV don't differ significantly.

- 2-13th of August MWL :