SGR1935+2154

General Information

• Name of the source: SGR 1935+2154
• Brief description of the source:
  • Object type : Soft Gamma Repeater, Galactic Magnetar
  • Other relevant information: Its simultaneous X-ray bursts (INTEGRAL, AGILE) and Fast radio Bursts (CHIME) on April 28th, 2020 were associated, providing the first evidence that FRBs can originate from magnetars.
  • RA: 19 35 00.0 (hh mm ss), Dec: +21 53 59.1 (dd mm ss)
  • RA, Dec in deg (ICRS): 293.75, 21.90
  • Galactic Coordinates l=57.26, b=0.81

SGR 1935+2154 is a Galactic magnetar that presents two types of high-energy emission:

• the persistent emission at few keV
• the transient emission of short nonthermal bursts at keV−MeV. The transient emission is characterized by occasional activity period lasting days-weeks with tens-hundreds of random, short (≈0.1s) and irregular bursts.

Repository for the Burst Analysis: gabriele-panebianco-inaf/BurstAnalysis (Please contact me to be added if not visible.)

Paper and Review Links: CDS Paper, CTAO Wiki, CTA Indico Review

People involved

• Gabriele Panebianco (gabriele.panebianco@inaf.it)
• Rubén López-Coto
• Andrea Bulgarelli
• Pol Bordas
• Tarek Hassan
• Alicia López-Oramas (PI of the MAGIC proposal that triggered the LST-1 observations)
• Ambra Di Piano
• Nicolò Parmiggiani
• Irene Jimenez Martinez
• Andrea Simongini
• Alessandro Carosi

Presentations

• 2023-06-05 LST Analysis Call (reco meeting): pdf on first standard analysis
• 2023-06-19 LST General Meeting: link to pdf
• 2023-07-21 LST Galactic Group Meeting: pdf on standard analysis
• 2023-11-08 LST General Meeting: link to pdf
• 2024-01-15 Contributed talk at VHEGAM Conference: link to SAPO XWiki
• 2024-02-19 LST Analysis Call (reco meeting): pdf on first burst analysis
• 2024-03-22 LST Galactic Group Meeting: pdf on burst analysis development
• 2024-04-15 Contributed poster at CTAO Symposium: link to XWiki
• 2024-06-17 LST Analysis Call (reco meeting): pdf on burst analysis
• 2024-06-21 LST Galactic Group Meeting: pdf on burst analysis update
• 2024-07-25 LST Galactic Group Meeting: pdf on results discussion
• 2024-07-29 LST Analysis Call (reco meeting): cross-check results
• 2024-09-02 Contributed poster at Gamma2024: link to XWiki
• 2024-09-26 LST Galactic Group Meeting: pdf on paper status
• 2024-11-13 LST General Meeting: link to pdf
• 2024-11-21 CTAO Consortium Galactic SWG Call: CTAO Consortium presentation

Data-taking Information

SGR 1935+2154 was observed during July 2021, September 2021, June 2022, October 2022 as follow up to external science alerts. SGR 1935+2154 was observed for a total of 37.7 hours over 118 runs in 17 nights.

Roughly half of the observations were conducted with MAGIC.

Observations are quasi-simultaneous to other facilities observations, both at VHE and MWL. Observations are simultaneous to 9 time of alerts of high-energy satellites triggered by SGR 1935+2154 bursts. See March 2024 slides for comparison between LST-1, MAGIC observations and the Time of Alerts published by external facilities in GCN and ATels (they trace SGR 1935 activity periods). All the available science alerts and time of alerts (trigger times) are recorded here

Most observations are in Wobble mode, though some runs (about 5 hours) were taken in ON mode but without OFF observations (this is the case for all October 2022 runs and 4 July 2021 runs).

SGR 1935+2154 Observations with LST-1

Run Number	Night	Run Start Time [UTC]	Run Elapsed Time [s]	Source Offset [deg]	Mean pointing azimuth [deg]	Mean pointing zenith [deg]	Used in stacked analysis	mode
5154	20210706	2021-07-06 21:35:40.008366	967.415	0.348	81.331	56.930	False	wobble
5155	20210706	2021-07-06 21:55:39.538852	1016.190	0.451	83.681	51.829	False	wobble
5156	20210706	2021-07-06 22:18:14.314086	1053.514	0.372	85.327	47.133	True	wobble
5157	20210706	2021-07-06 22:41:17.329760	1205.443	0.434	88.929	42.344	True	wobble
5158	20210706	2021-07-06 23:03:40.273986	1205.356	0.357	90.827	37.672	True	wobble
5161	20210706	2021-07-06 23:38:21.458475	1206.221	0.443	96.226	29.316	True	wobble
5162	20210706	2021-07-07 00:00:21.764677	1205.398	0.442	100.261	24.532	True	wobble
5163	20210706	2021-07-07 00:25:00.965802	1443.322	0.368	104.802	19.462	True	wobble
5164	20210706	2021-07-07 00:49:25.963768	1145.974	0.436	116.293	14.803	True	wobble
5165	20210706	2021-07-07 01:10:44.258733	1203.290	0.365	127.337	10.904	True	wobble
5166	20210706	2021-07-07 01:32:50.001943	1203.480	0.437	158.649	7.453	True	wobble
5167	20210706	2021-07-07 01:54:27.456639	1206.198	0.367	195.814	6.820	True	wobble
5168	20210706	2021-07-07 02:16:10.395605	1205.429	0.436	224.205	9.957	True	wobble
5169	20210706	2021-07-07 02:38:19.418482	1205.540	0.370	241.561	13.290	True	wobble
5170	20210706	2021-07-07 02:59:59.232267	1205.947	0.432	252.307	18.372	True	wobble
5171	20210706	2021-07-07 03:22:42.369718	1203.333	0.367	258.984	22.682	True	wobble
5175	20210706	2021-07-07 04:15:42.475526	1205.977	0.434	266.547	34.509	True	wobble
5176	20210706	2021-07-07 04:35:08.352232	905.936	0.377	269.512	38.264	True	wobble
5192	20210707	2021-07-08 01:19:53.546984	1204.101	0.022	142.520	8.584	False	ON
5193	20210707	2021-07-08 01:41:14.972905	1205.786	0.021	177.694	6.946	False	ON
5194	20210707	2021-07-08 02:02:34.873506	1204.280	0.020	214.208	8.269	False	ON
5195	20210707	2021-07-08 02:16:24.810369	292.236	0.019	230.309	10.271	False	ON
5196	20210707	2021-07-08 02:25:59.058815	605.461	0.381	236.500	11.662	True	wobble
5197	20210707	2021-07-08 02:38:06.497275	606.417	0.418	245.497	14.658	True	wobble
5198	20210707	2021-07-08 02:51:02.354297	602.274	0.398	251.387	16.760	True	wobble
5199	20210707	2021-07-08 03:03:00.516614	605.874	0.402	252.977	19.611	True	wobble
5211	20210709	2021-07-09 22:50:58.651400	1205.470	0.370	90.657	37.872	True	wobble
5212	20210709	2021-07-09 23:15:16.868188	1205.343	0.428	94.403	31.785	True	wobble
5213	20210709	2021-07-09 23:46:33.454934	1205.261	0.399	98.543	25.197	True	wobble
5214	20210709	2021-07-10 00:10:33.631798	1201.304	0.402	106.053	20.354	True	wobble
5215	20210709	2021-07-10 00:34:57.851661	1204.504	0.376	112.827	15.470	True	wobble
5216	20210709	2021-07-10 01:00:10.746264	1206.832	0.422	131.291	10.101	True	wobble
5217	20210709	2021-07-10 01:24:30.383948	1205.869	0.398	160.492	6.922	True	wobble
5218	20210709	2021-07-10 01:49:41.124249	1206.164	0.403	205.604	8.073	True	wobble
5253	20210712	2021-07-13 00:58:23.075673	1205.001	0.379	138.150	9.080	True	wobble
5254	20210712	2021-07-13 01:23:14.131849	1206.654	0.420	184.029	6.975	True	wobble
5255	20210712	2021-07-13 01:47:16.445606	1203.150	0.398	221.435	8.531	True	wobble
5256	20210712	2021-07-13 02:11:20.228025	1201.871	0.403	239.169	13.172	True	wobble
5257	20210712	2021-07-13 02:33:55.047752	1205.168	0.383	250.357	17.114	True	wobble
5258	20210712	2021-07-13 02:58:36.310374	1206.582	0.415	258.359	23.067	True	wobble
5281	20210716	2021-07-17 01:58:45.359084	606.296	0.382	241.680	13.200	True	wobble
5284	20210716	2021-07-17 02:56:34.882860	1205.573	0.414	261.193	26.029	True	wobble
5285	20210716	2021-07-17 03:20:04.027781	1205.415	0.399	265.644	30.642	True	wobble
5286	20210716	2021-07-17 03:37:31.978401	486.510	0.401	266.766	34.734	True	wobble
5294	20210717	2021-07-18 00:00:54.795768	1205.661	0.376	111.738	15.997	False	wobble
5295	20210717	2021-07-18 00:24:54.352744	1205.205	0.422	127.894	10.745	False	wobble
5299	20210717	2021-07-18 01:13:54.687818	1206.271	0.398	200.712	6.971	True	wobble
5300	20210717	2021-07-18 01:37:59.408685	1206.359	0.403	229.105	10.732	True	wobble
5301	20210717	2021-07-18 02:03:47.384962	1205.794	0.383	246.089	14.978	True	wobble
5320	20210718	2021-07-19 00:20:59.428245	1206.284	0.378	125.137	11.347	False	wobble
5321	20210718	2021-07-19 00:45:18.481347	1206.659	0.421	157.894	7.455	False	wobble
5322	20210718	2021-07-19 01:10:06.164715	1203.304	0.398	200.913	6.987	False	wobble
5326	20210718	2021-07-19 01:53:36.855329	1206.637	0.402	242.509	14.294	True	wobble
5327	20210718	2021-07-19 02:18:57.552751	1202.194	0.384	253.242	18.914	True	wobble
5328	20210718	2021-07-19 02:43:21.359871	1201.198	0.414	260.142	24.866	True	wobble
5329	20210718	2021-07-19 03:07:08.815895	1206.109	0.399	264.874	29.535	True	wobble
5330	20210718	2021-07-19 03:30:44.162188	1206.552	0.401	266.901	34.969	True	wobble
6125	20210907	2021-09-07 20:59:10.755258	1205.524	0.378	124.154	11.577	True	wobble
6126	20210907	2021-09-07 21:23:12.990901	1205.299	0.421	155.315	7.588	True	wobble
6127	20210907	2021-09-07 21:47:15.248035	1205.164	0.398	196.709	6.816	True	wobble
6128	20210907	2021-09-07 22:10:35.035322	1205.448	0.403	226.375	10.253	True	wobble
6129	20210907	2021-09-07 22:33:47.974373	1205.418	0.383	243.388	13.879	True	wobble
6198	20210910	2021-09-10 21:00:37.748895	1157.028	0.421	139.966	8.843	True	wobble
6199	20210910	2021-09-10 21:22:28.734336	1159.121	0.398	171.222	6.611	True	wobble
6200	20210910	2021-09-10 21:43:20.062237	1172.043	0.403	207.669	8.199	True	wobble
6201	20210910	2021-09-10 22:06:16.572737	1400.066	0.382	232.938	10.951	True	wobble
6202	20210910	2021-09-10 22:38:58.567869	1208.935	0.416	251.895	18.029	True	wobble
6203	20210910	2021-09-10 23:00:16.579873	1166.859	0.398	258.398	22.026	True	wobble
6204	20210910	2021-09-10 23:21:18.495585	1202.413	0.402	260.967	26.864	True	wobble
6205	20210910	2021-09-10 23:42:55.358996	1211.386	0.387	265.112	31.062	True	wobble
6206	20210910	2021-09-11 00:02:55.673674	1217.310	0.411	268.387	36.205	False	wobble
6208	20210910	2021-09-11 00:47:32.362278	1206.405	0.399	272.881	45.754	True	wobble
6223	20210911	2021-09-11 22:47:39.440023	1188.808	0.384	254.708	19.958	True	wobble
6224	20210911	2021-09-11 23:09:07.997514	1188.388	0.414	260.555	25.306	True	wobble
6225	20210911	2021-09-11 23:30:04.701359	1148.914	0.399	264.754	29.356	True	wobble
6226	20210911	2021-09-11 23:49:53.932634	1204.881	0.401	266.265	33.963	True	wobble
6227	20210911	2021-09-12 00:12:02.313915	1172.191	0.390	269.596	38.313	False	wobble
6228	20210911	2021-09-12 00:30:34.922076	866.843	0.408	272.167	43.141	False	wobble
6229	20210911	2021-09-12 00:47:58.089294	906.975	0.401	274.398	46.445	True	wobble
6244	20210912	2021-09-12 21:53:20.006110	1284.220	0.382	228.547	10.084	False	wobble
6245	20210912	2021-09-12 22:15:07.177227	1181.297	0.417	245.585	14.756	False	wobble
6246	20210912	2021-09-12 22:36:24.544463	1197.066	0.398	254.190	18.612	False	wobble
6247	20210912	2021-09-12 22:58:01.640121	1232.768	0.402	257.764	23.537	False	wobble
6248	20210912	2021-09-12 23:19:36.515968	1208.833	0.386	262.595	27.689	False	wobble
6249	20210912	2021-09-12 23:50:33.302675	1328.482	0.411	267.791	35.214	True	wobble
6250	20210912	2021-09-13 00:05:53.763888	328.248	0.400	270.158	38.076	True	wobble
6251	20210912	2021-09-13 00:19:51.266180	1236.984	0.400	270.625	41.402	True	wobble
6252	20210912	2021-09-13 00:41:51.959164	1153.771	0.393	273.459	45.724	True	wobble
6253	20210912	2021-09-13 00:57:51.387474	595.861	0.405	275.503	49.979	True	wobble
6269	20210913	2021-09-13 22:58:57.497780	1562.563	0.385	259.350	24.064	False	wobble
6271	20210913	2021-09-13 23:30:41.016183	312.418	0.387	265.064	30.965	False	wobble
6272	20210913	2021-09-13 23:49:12.585701	28.083	0.388	267.697	35.026	False	wobble
6273	20210913	2021-09-14 00:00:57.099488	1229.859	0.410	269.620	38.362	False	wobble
6288	20210914	2021-09-15 00:04:45.977484	1164.339	0.400	269.760	39.817	False	wobble
6289	20210914	2021-09-15 00:25:30.855964	1163.854	0.392	272.532	43.863	False	wobble
6290	20210914	2021-09-15 00:46:18.103774	1208.983	0.406	275.120	49.172	False	wobble
6291	20210914	2021-09-15 01:08:00.772730	1193.965	0.402	277.627	53.399	False	wobble
8607	20220602	2022-06-03 02:18:17.116211	1168.144	0.375	100.131	24.574	True	wobble
8608	20220602	2022-06-03 02:39:12.544475	1189.029	0.423	106.122	19.362	True	wobble
8610	20220602	2022-06-03 03:12:23.674925	1175.487	0.399	117.749	12.744	True	wobble
8611	20220602	2022-06-03 03:32:43.771255	1134.869	0.402	137.193	9.706	True	wobble
8612	20220602	2022-06-03 03:52:58.185166	1134.483	0.380	161.859	7.264	True	wobble
8613	20220602	2022-06-03 04:12:50.695077	1130.355	0.418	204.330	7.555	True	wobble
8614	20220602	2022-06-03 04:28:44.929503	630.429	0.398	225.667	8.973	True	wobble
8891	20220624	2022-06-25 01:38:48.786781	1239.415	0.402	116.787	14.563	True	wobble
8892	20220624	2022-06-25 02:04:18.557745	1173.345	0.379	131.935	9.980	True	wobble
8893	20220624	2022-06-25 02:24:22.669043	1151.907	0.419	164.241	7.185	True	wobble
8894	20220624	2022-06-25 02:44:34.480588	1152.283	0.398	199.396	6.903	True	wobble
8895	20220624	2022-06-25 03:04:38.363385	1154.168	0.402	224.591	9.965	True	wobble
8896	20220624	2022-06-25 03:22:02.053649	841.338	0.383	239.084	12.399	True	wobble
9722	20221019	2022-10-19 20:30:27.600677	1794.876	0.015	257.908	22.698	False	ON
9723	20221019	2022-10-19 21:00:12.800844	1206.477	0.012	263.753	29.174	False	ON
9724	20221019	2022-10-19 21:21:36.919730	1205.612	0.011	266.964	33.859	False	ON
9725	20221019	2022-10-19 21:43:03.569971	1206.730	0.009	269.741	38.567	False	ON
9726	20221019	2022-10-19 22:04:13.933069	1206.449	0.008	272.208	43.217	False	ON
9727	20221019	2022-10-19 22:26:16.460377	1205.381	0.006	274.589	48.049	False	ON
9728	20221019	2022-10-19 22:43:13.303530	605.614	0.004	276.339	51.755	False	ON
9752	20221020	2022-10-20 21:02:33.395669	5316.643	0.012	264.317	30.563	False	ON

Data analysis Information

SGR 1935+2154 is a Galactic magnetar that presents two types of high-energy emission: the persistent emission and the transient emission, hence we performed two types of analysis.

Common starting point are the DL1b produced by lstosa.

To reconstruct the events properties and obtain DL2 data, we employed a set of Random Forests trained with Monte Carlo (MC) simulations tuned to the Night Sky background (NSB) level of our data.

• Monte Carlo simulations of DL2 and trained RF were requested to lstmcpipe team, NSB tuned. MC prod name: 20230428_src_dec2276_tuned_nsb_az_tel
• lstchain version: 0.9.13

NSB Tuning and MC production

• We evaluated the NSB on a sub-sample of our data and obtained the following image modifier parameters:

"image_modifier":{
"increase_nsb": true,
"extra_noise_in_dim_pixels": 1.309,
"extra_bias_in_dim_pixels": 0.54,
"transition_charge": 8,
"extra_noise_in_bright_pixels": 1.79}

We use these parameters for the whole dataset. The true distribution of the parameters of the dataset is shown in the images below:

Parameter distribution for every subrun of the dataset

Parameter distribution for subruns of the good runs (no moon, no bad weather, only wobble)

We produced the configuration files for the lstMCpipe and lstchain, added the image modifier parameters and produced the Monte Carlo simulations as described in the links below.

(Preliminary) MC production = 20230315_src_dec2276_tuned_nsb

... Then we figured out we used sin_az_tel instead of az_tel so the RF would not work with our data, and we had to update the MC production just for this parameter...

Final MC production = 20230428_src_dec2276_tuned_nsb_az_tel

Types of analysis

• The persistent emission analysis is a "standard" stacked spectral analysis.
  • We obtained DL3 and IRFs with a set of "standard" cuts (details below).
  • We selected "good quality" runs (25h of data).
  • Results are upper limits on the SED and Light Curve on 3 time scales: all stacked data (25h), night-wise (approx 2h), run-wise (approx 20m)

• The transient analysis is energy-integrated due to poor statistics, and focuses on 100ms time scale.
  • The cuts were chosen to optimise the short-scale sensitivity (details below). This method can be used for the detection of other short transients too.
  • We obtained a new set of DL3 and IRFs with the short scale cuts. We placed upper limits to SGR flux on the 9 time intervals (100ms) centered around the 9 simultaneous Time of Alerts, plus the stacked upper limit
  • We searched for non-simultaneous bursts in all our data, without any detection.

Analysis of Persistent Emission

Bad quality runs and runs taken in ON mode were discarded from the analysis.

The SGR 1935+2154 analysis covers 25.8 hours of observations over 83 runs and 13 nights.

Plots can be found in early presentation pdf.

Low Level Analysis

1 - The DL1 were processed into DL2 sbatching one job per run, using the same path-models and config.

• We used long jobs and mem-per-cpu 120g:

conda activate lstchain-v0.9.13
lstchain_dl1_to_dl2 \
 --input-files /fefs/aswg/data/real/DL1/20210706/v0.9/tailcut84/dl1_LST-1.Run05163.h5 \
 --path-models /fefs/aswg/data/models/AllSky/20230428_src_dec2276_tuned_nsb_az_tel/dec_2276 \
 --config /fefs/aswg/data/models/AllSky/20230428_src_dec2276_tuned_nsb_az_tel/dec_2276/lstchain_config.json \
 --output-dir /fefs/aswg/workspace/gabriele.panebianco/analysis/SGRJ1935+2154/DL2 

2 - We prepared a DL2->DL3 configuration file (energydep_intensity80_gheff0.7_thetacont0.68.json) to get IRFs and DL3 data.

• We modified a template existing in lstchain docs by setting:
  • GH-efficiency: 0.7.
  • Theta Containment: 0.68
  • Event selector filter: INTENSITY>80 P.E.

3 - We computed the IRFs for every node as point-like and with energy-dependent cuts.

MCDL2DIRECTORY=/fefs/aswg/data/mc/DL2/AllSky/20230428_src_dec2276_tuned_nsb_az_tel/TestingDataset/dec_2276
lstchain_create_irf_files \
 -g "$MCDL2DIRECTORY/node_theta_23.630_az_100.758_/dl2_20230315_src_dec2276_tuned_nsb_node_theta_23.630_az_100.758__merged.h5" \
 -o "/fefs/aswg/workspace/gabriele.panebianco/analysis/SGRJ1935+2154/IRF/energydep_intensity80_gheff0.7_thetacont0.68/pointlike_Theta23.630_Az100.758/irf.fits.gz" \
 --point-like \
 --energy-dependent-gh \
 --energy-dependent-theta \
 --config "/home/gabriele.panebianco/Workspace/SGRJ1935+2154/DL3configurations/energydep_intensity80_gheff0.7_thetacont0.68.json" 

4 - We processed DL2 files into DL3 with the same configuration file used for the IRFs and associated every run with its closest IRF (in terms of azimuth and zenith).

IRFDIRECTORY=/fefs/aswg/workspace/gabriele.panebianco/analysis/SGRJ1935+2154/IRF
lstchain_create_dl3_file \
 -d "/fefs/aswg/workspace/gabriele.panebianco/analysis/SGRJ1935+2154/DL2/dl2_LST-1.Run05163.h5" \
 -o "/fefs/aswg/workspace/gabriele.panebianco/analysis/SGRJ1935+2154/DL3/energydep_intensity80_gheff0.7_thetacont0.68/pointlike/Run05163/" \
 --input-irf "$IRFDIRECTORY/energydep_intensity80_gheff0.7_thetacont0.68/pointlike_Theta23.630_Az100.758/irf.fits.gz" \
 --source-name "SGRJ1935+2154" \
 --source-ra "293.75deg" \
 --source-dec "21.9deg" \
 --overwrite \
 --config "/home/gabriele.panebianco/Workspace/SGRJ1935+2154/DL3configurations/energydep_intensity80_gheff0.7_thetacont0.68.json" 

5 - We created the DL3 index files to take advantage of gammapy DataStore class in the High Level Analysis.

lstchain_create_dl3_index_files \
 --input-dl3-dir "/fefs/aswg/workspace/gabriele.panebianco/analysis/SGRJ1935+2154/DL3/energydep_intensity80_gheff0.7_thetacont0.68/pointlike" \
 --file-pattern "Run*/dl3*.fits" \
 --overwrite

High Level Analysis

We processed every run in the Low Level Analysis, but we used only a subset for the High Level Analysis made up by good runs.

• Runs exclusion criteria (info taken from long-term data check files):
  • Source offset not in [0.35,0.45] deg (use only wobble runs, no on runs).
  • Rate of cosmics < 2500 evt/s (avoid problematic runs due to calima or other environmental/instrumental problems).
  • Pedestal charge standard deviation > 2 P.E. (avoid Moon runs).
  • Run 6253 has an asymmetric telescope response (probably due to a humidity patch?)

We performed High-level analysis with gammapy v1.0.

• Standard Wobble Analysis was performed with 1 off region. Region size is energy dependent and set in the RADMAX IRF.
• Safe Mask method: aeff-max with aeff-percent=1.
• Flux Points upper limits were obtained for the source under different conditions:
  • SED ULs in [0.1, 10] TeV, 5 bins per energy decade.
    • 1 set of stacked ULs for total integrated livetime.
    • 13 sets of night-wise ULs.
  • Light Curve UL run-wise and night-wise, energy integrated in [0.1, 50] TeV
• Flux points obtained with power law spectrum, index=2.4.

Main results: theta2 plot and upper limits on the stacked emission. The Nightly SEDs and the Light Curve can be seen in the presentation PDFs. The Source is never detected.

Theta2 plot for the stacked analysis (25.8 h)

Stacked SED ULs DNDE (25.8 h). HESS is taken from their 2021 paper on SGR1935+2154 (2h data, 5 stereo telescopes).

Stacked SED ULs E2DNDE (25.8 h). HESS is taken from their 2021 paper on SGR1935+2154 (2h data, 5 stereo telescopes).

Cuts optimization for a short-scale emission

See June 2024 slides for the full process.

Optimisation process in a nutshell

• For a grid of cuts: estimate background rate from an OFF region → get N_5σ, the number of counts needed to reject the background (null) hypothesis at 5σ level
• For a grid of cuts: estimate the cut efficiency on a Monte Carlo file ε_MC.
• Divide N_5σ by ε_MC (this is proportional to the sensitivity of the analysis) and find the region with lowest values.

Cuts optimisation. Optimisation region in lower left part of the map.

Note: this plot was made using runs with average rates under 20 deg of zenith and efficiencies with PL index=2. Namely, we used runs: 5163, 5164, 5165, 5166, 5167, 5170, 5196, 5197, 5198, 5199, 5217, 5218, 5253, 5254, 5281, 5300, 5301, 5326, 5327, 6126, 6127, 6128, 6129, 6198, 6202, 6223, 8612, 8613, 8614, 8891, 8893, 8894, 8895, 8896, for the background, and their closest MC nodes for the efficiency. We also tried with other zenith bands and PL indexes.

• Cuts optimised to detect a 100ms burst above a Poisson background in a single energy bin (>30 GeV):
  • Intensity > 50 p.e.
  • Global Theta2 cut 0.08 deg^2
  • Global Gammaness cut 0.75

Analysis of Transient Emission

VHE Flux Upper Limits on simultaneous X bursts

See June 2024 slides for details.

1 - We obtained a new set of DL3 and IRFs for the transient analysis.

• We used the IRFs to obtain the effective area and the exposure in a 100ms time bin in the energy range [100 GeV; 10 TeV] assuming a power law with index=2 (also 2.4,3,4).
• We counted the ON photons in a 100ms time window centred on the Time of Alert (ToA) provided by ATels/GCNs. The ON radius is given by the theta2 global cut.
• These counts are either 0 or 1. They are not enough to claim a detection (the threshold is N_5σ) → No TeV counterpart of the X bursts was observed.

2 - We can use the ON counts to estimate the upper limit on the transient emission flux.

• According to Cowan 2007 (eq. 6), Patrignani 2016 (eq 39.59->39.61, Table 39.3), if we suppose the ON counts are due to a signal Poisson distribution with unknown expected value μ, the ON counts constrain the 95% upper limit on μ (we are estimating the Bayesian upper limit for a Poisson likelihood and uniform prior). In particular:
  • ON = 0 → μ_UL=3.00
  • ON = 1 → μ_UL=4.74
  • ON = 2 → μ_UL=6.30
  • Note: the background must then be subtracted to get the counts upper limit, according to the equation.
• The Flux upper limit can be found by dividing μ_UL over the bin exposure.
• The Burst fluence can be found converting photon flux into energy flux and then integrating for the burst duration

3 - We can stack the counts to estimate the total upper limit on the transient emission of SGR 1935+2154 (over a 0.9s livetime).

Link to pdf with results

Search for non-simultaneous bursts

See June 2024 slides for details.

We selected the DL3 (with short time scale cuts) in SGR 1935+2154 ON region and binned them in 0.1s bins from the start of every run.

The number of counts in a bin follow the background Poisson distribution -> no detection of non-simultaneous bursts.

In order to claim a detection in a bin, we need a number of counts>N_5σ corrected by the number of trials.

We used approx 1E6 trials (because we use 118 runs of approx 20 mins in 0.1s bins).

The post-trial N_5σ is the number of counts with a post-trial p-value of 2.87E-7. We convert it first into a pre-trial pvalue, then into a N_5σ. Maths is explained in March 2024 slides.

LST-1 rates in the short time scale cuts ranges from 0.2 to 2 cts/s, that imply pre-trial N_5σ from 3 to 5, and post-trial N_5σ from 6 to 9.

Results recap

• Persistent Emission Analysis:

1. SGR 1935+2154 is not detected.
2. We placed Upper Limits on the SED.

• Transient Emission Analysis:

1. No burst is detected in coincidence to the 9 external ToAs.
2. We placed integrated flux TeV 2sigma upper limits in coincidence to simultaneous X bursts.
3. No burst is detected in the rest of our dataset (non-simultaeous bursts).