SN2024bch

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General Information

  • Name of the source: SN2024bch
  • Brief description of the source:
    • Object type: CCSN type IIn-L
    • Distance (Mpc): 16.56
    • Redshift: 0.00387
    • Host galaxy: NGC 3206
    • RA: 10:21:49.740 (hh mm ss), Dec: +56:55:40.51 (dd mm ss)
    • RA, Dec in deg (ICRS): 155.45725, +56.927919

People involved

Alphabetical order (corresponding authors)

  • Arnau Aguasca-Cabot
  • Alessandro Carosi
  • Alicia López-Oramas
  • Andrea Simongini (andrea.simongini@inaf.it)

Presentations

Data-taking Information

  • General information:
    • Start observation date: 2024-02-13
    • Total nights: 6
    • Total hours: 14.6
    • Total runs: 53
  • Observation condition: moon and dark
  • Observation mode: wobbles
  • Joint observations with MAGIC?: yes (16845-16863)
  • Joint analysis with MAGIC?: no


SN2024bch observations with LST-1
Run Number Night Run Start Time [UTC] Run Elapsed Time [min] Mean pointing zenith [deg] Wobble Position Used in stacked analysis Conditions ELOG
16771 20240213 00:29 20 32.6 W1 True dark 20240213
16772 20240213 00:49 19 30.5 W2 True dark 20240213
16773 20240213 01:08 24 29.9 W3 True dark 20240213
16774 20240213 01:32 17 28.1 W4 True dark 20240213
16775 20240213 01:49 20 xx W1 True dark 20240213
16776 20240213 02:09 20 xx W2 True dark 20240213
16777 20240213 02:29 20 28.9 W3 True dark 20240213
16778 20240213 02:49 20 xx W4 True dark 20240213
16779 20240213 03:09 22 30.3 W1 True dark 20240213
16780 20240213 03:31 19 32.5 W2 True dark 20240213
16781 20240213 03:50 17 34.3 W3 True dark 20240213
16803 20240214 01:11 26 29.3 W1 True dark 20240214
16804 20240214 01:37 18 28 W2 True dark 20240214
16805 20240214 01:55 15 28.5 W3 True dark 20240214
16806 20240214 02:10 20 27.8 W4 True dark 20240214
16807 20240214 02:30 23 28.5 W1 True dark 20240214
16808 20240214 02:53 18 30 W2 True dark 20240214
16809 20240214 03:11 20 31.4 W3 True dark 20240214
16810 20240214 03:31 21 32.3 W4 True dark 20240214
16811 20240214 03:52 4 34.4 W1 True dark 20240214
16815 20240215 00:14 16 33.3 W1 False dark 20240215
16816 20240215 00:30 20 31.4 W2 False dark 20240215
16817 20240215 00:50 21 30.5 W3 False dark 20240215
16818 20240215 01:11 21 28.7 W4 True dark 20240215
16819 20240215 01:32 18 28.3 W1 True dark 20240215
16820 20240215 01:50 20 28 W2 True dark 20240215
16821 20240215 02:10 22 28.6 W3 True dark 20240215
16822 20240215 02:32 19 28.5 W4 True dark 20240215
16823 20240215 02:51 19 29.7 W1 True dark 20240215
16824 20240215 03:10 22 31.9 W2 True dark 20240215
16825 20240215 03:32 18 33.4 W3 True dark 20240215
16826 20240215 03:50 12 34.6 W4 True dark 20240215
16845 20240216 01:02 21 29.4 W1 False dark 20240216
16846 20240216 01:23 20 28.3 W2 False dark 20240216
16847 20240216 01:43 22 28 W3 False dark 20240216
16848 20240216 02:05 19 27.8 W4 False dark 20240216
16849 20240216 02:24 21 28.6 W1 True dark 20240216
16850 20240216 02:45 20 29.9 W2 True dark 20240216
16851 20240216 03:05 21 31.4 W3 True dark 20240216
16852 20240216 03:26 20 32.5 W2 True dark 20240216
16853 20240216 03:46 14 34.5 W3 True dark 20240216
16863 20240218 03:10 19 32 W1 False moon 20240218
16864 20240218 03:29 18 34.7 W2 False moon 20240218
16866 20240218 03:47 19 36.1 W2 False moon 20240218
16867 20240218 04:06 28 38.1 W3 False moon 20240218
16868 20240218 04:25 3 xx xx False moon 20240218
16869 20240218 04:34 19 41.1 W4 True moon 20240218
16870 20240218 04:53 7 43.4 W1 True moon 20240218
16980 20240306 00:15 20 28 W1 True dark 20240306
16981 20240306 00:35 20 28 W2 True dark 20240306
16982 20240306 00:55 20 28.7 W3 True dark 20240306
16983 20240306 01:15 20 28.7 W4 True dark 20240306
16984 20240306 01:35 8 30 W1 True dark 20240306


Data quality cuts

We performed a standard source independent analysis for this source. The data quality is performed using the data_quality.ipynb notebook from the 2024-LST-School.

  • Source selection:
    • zenith_range = [0, 90]
    • min_angle_to_source = 0.35
    • max_angle_to_source = 0.45
  • Global cuts:
    • max_diffuse_nsb_std = 2.3
    • max_pointing_dec_std = 0.01
    • min_mean_fit_p = -3.
    • max_LS_periodogram_maxamplitude = 1e-2
    • min_drdi_index = -2.35
    • max_drdi_index = -2.1
    • min_drdi_at_422pe = 1.4
    • min_fraction_around_mode = 0.8
    • max_intensity_at_half_peak_rate = 70
  • Data quality plots:

Quality cuts.png

  • Relative light yield of the selected nights:

Light yield SN2024bch.png

  • Results:
    • Good quality runs: 41/53(77%)
    • Total time: 12.1 h
  • Extra notes:
    • 16868 is a very short run (3.4939323 min) due to data taking interruption by shifters
    • 16815 16816 16817 16847 16848 16867 were removed due to different NSB level

Data analysis

MC production

According to the data_quality.ipynb, the NSB level in the FoV of SN2024bch is low enough to consider the standard MC.

  • MC used:
    • 20240131_allsky_v0.10.5_all_dec_base
  • Declination line:
    • dec_6166 (4.8 deg away from SN 2024bch)

Declination map SN2024bch.png

Pointing issues

We could not fit 3 OFF positions in several runs due to small offset angular distance of the wobbles.

  • Possible solutions (applied in this analysis):
    • Reduce the max_theta_cut to 0.26 deg
    • Use only 1 OFF position

DL3 production

The DL3 are produced using the following standard parameters:

  • Intensity cut: [50GeV, infty]
  • w1: [0.01, 1]
  • r: [0, 1]
  • leakage_intensity_width_2: [0, 1]
  • event_type: [32, 32]
  • theta_containment: 0.7
  • gh_efficiency: 0.7
  • min_livetime: 300
  • max_zenith: 90

DL3 data are stored here:

  • /fefs/aswg/workspace/andrea.simongini/Analysis/SN2024bch/DL3

Theta-squared plots

  • We produced theta-squared plots with all good quality data:
    • n_wobbles: 4
    • theta2_cut: 0.04
    • energy bounds: [50GeV-100GeV]; [100GeV-1TeV]; [1TeV-10TeV]
    • gammaness_cut: 0.7
    • theta2_cut: 0.07 deg2
  • Plots:

Theta2 plots SN2024bch.png

  • Results:
    • [50GeV-100GeV]: N_on = 287155; N_off = 6220812; Significance = -0.572341
    • [100GeV-1TeV]: N_on = 107335; N_off = 2284060; Significance = -1.255360
    • [1TeV-10TeV]: N_on = 267; N_off = 6189; Significance = -1.701900

No significant excess coming from this source! We go for upper-limits

High-level analysis

For the high-level analysis we set:

  • n_off_regions: 1
  • safe_mask_method: aeff-max (5%)
  • e_reco: [35GeV - 10TeV]
  • e_true: [1GeV - 50TeV]
  • n_reco_bin_p_dec: 3.5
  • n_true_bin_p_dec: 10

Note that the energy treshold (Eth) is ~30GeV. As discussed in the LST analysis call (see presentation from 2024-06-10) the safest and most conservative way to integrate fluxes is to set the lower energy bound of the reconstructed energy to 100GeV.


Spectral Energy Distribution

We are fitting our data with a simple power law distribution with the following parameters:

  • Gamma: -2.5
  • amplitude: 2e-12 cm−2s−1TeV−1
  • bounds: [1e-18, 1e-5] cm−2s−1TeV−1
  • ref_energy: 2TeV

We use all good quality data

SN2024bch sed upper limits.png

Light curves

We produced run-wise and night-wise light curves between 100GeV and 10TeV.

SN2024bch light curves.png

Cross-check

SN2024bch SED Xcheck.png SN2024bch light curve Xcheck.png

Crab check

  • General information:
    • we applied the same data-quality cuts as SN2024bch
    • we used the same period of data taking (Feb-Mar 2024)
    • we applied the same max_theta_cut for IRF production
    • we employed a different Monte Carlo production
    • the DL3 and DL4 files are produced with the same specifications as SN2024bch
  • Data saved:
    • 29/33 runs (88%)
    • 8.5h
  • Relative light yield:

Light yield Crab SN2024bch.png


  • Monte Carlo production:
    • We used a different production with respect to SN2024bch
    • 20230927_v0.10.4_crab_tuned
    • dec_2276
  • Theta-squared plots:

Theta squared Crab SN2024bch.png


  • High-level analysis:

We fitted the spectral energy distribution using:

    • spectral_model = LogParabolaSpectralModel
    • index = 2.5
    • amplitude = 2e-12cm-2 s-1 TeV-1
    • ref = 0.7TeV
    • lambda_ = 0.1TeV-1

Both the spectral energy distribution and the light curves are built between 100GeV and 10TeV.

SN2024bch crab check final results.png

Progenitor analysis

We performed a 4-steps analysis to investigate the progenitor star of SN2024bch. The data employed are:

  • LST-1 data:
    • telescope: LST-1 in mono configuration
    • type: light curves upper limits
    • range: 100GeV-10TeV
    • availability: proprietary data
  • Optical data:
    • telescope: many, Cafos, Mistral
    • type: light curves and spectra
    • range: B, V, R, I filters; 4000-9000 A
    • availability: public at WISeREP and AAVSO
  • Optical spectrum:
    • telescope: Liverpool Telescope
    • type: spectrum
    • range: 4000-9000 A
    • availability: proprietary data
  • Pre-explosion images:
    • telescope: Hubble Space Telescope
    • type: images
    • range: optical
    • availability: public at HLA

The analysis is performed with our own written python codes and with CASTOR (Simongini et al. 2024), an open access software for CCSN data analysis.


Theoretical modeling

VHE photons are thought to be produced from the non-thermal interaction between the fast-moving shock-wave of the supernova ejecta and a dense circumstellar medium (CSM) surrounding a massive progenitor. As the CSM density decreases moving away from the progenitor, the potential gamma-ray signal is expected to peak shortly after the explosion as a dense CSM enhances p-p interaction}. However, during the first tens to hundreds of days after the explosion, the putative VHE signal is significantly attenuated by the gamma-gamma absorption with the optical photons emitted by the supernova photosphere. Several parameters need to be taken into account for a detailed description of the gamma absorption. Among them, the mass-loss rate and the wind velocity of the progenitor star before the onset of the explosion, play a key role is suppressing the VHE signal by up to several orders of magnitude.

To model the gamma flux we use the model from Dwarkadas 2013:

Optical analysis

Pre-explosion images

We collected one image of the host galaxy (NGC 3206) taken with the Hubble Space Telescope on the 14th of May 2001. Some sources are identified within the coordinates of the events:


Candidate progenitor stars
Catalog RA [deg] DEC [deg] MAG Log (L/L0)
DAOphot 155.45741 56.92795 21.59 3.80
DAOphot 155.45735 56.92793 21.57 3.81
SExtractor 155.45735 56.92800 20.50 4.24
GSCII 155.45735 56.92793 19.76 4.53
HSC 155.45730 56.92801 21.84 3.70
PS1 155.45735 56.92794 19.32 4.71

SN2024bch Hubble map.png

Thanks to this image we are able to identify the luminosity of the progenitor star, either in a direct or indirect way:

    • if the progenitor star is identified by the catalogs, then we have its luminosity
    • if the progenitor star is not identified by the catalogs, then we have an upper limit to its luminosity.


Classification

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