{"bundle_type":"pith_open_graph_bundle","bundle_version":"1.0","pith_number":"pith:2026:6VDIWPRNVJTMYUTFVZ6SECSM5E","short_pith_number":"pith:6VDIWPRN","canonical_record":{"source":{"id":"2604.06399","kind":"arxiv","version":2},"metadata":{"license":"http://creativecommons.org/licenses/by/4.0/","primary_cat":"astro-ph.IM","submitted_at":"2026-04-07T19:32:57Z","cross_cats_sorted":[],"title_canon_sha256":"8532f44ee3aa0a449b021b710ced0c9cbf76f062b94a9943fe2ebaf88d02fd14","abstract_canon_sha256":"8456be65bd8bcc4fa66626a52a7b8dd43737e16e033c78868021944eb845df12"},"schema_version":"1.0"},"canonical_sha256":"f5468b3e2daa66cc5265ae7d220a4ce92e2cfd689d59bcdf6395648a54b6353a","source":{"kind":"arxiv","id":"2604.06399","version":2},"source_aliases":[{"alias_kind":"arxiv","alias_value":"2604.06399","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"arxiv_version","alias_value":"2604.06399v2","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"doi","alias_value":"10.48550/arxiv.2604.06399","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"pith_short_12","alias_value":"6VDIWPRNVJTM","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"pith_short_16","alias_value":"6VDIWPRNVJTMYUTF","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"pith_short_8","alias_value":"6VDIWPRN","created_at":"2026-05-25T02:01:19Z"}],"events":[{"event_type":"record_created","subject_pith_number":"pith:2026:6VDIWPRNVJTMYUTFVZ6SECSM5E","target":"record","payload":{"canonical_record":{"source":{"id":"2604.06399","kind":"arxiv","version":2},"metadata":{"license":"http://creativecommons.org/licenses/by/4.0/","primary_cat":"astro-ph.IM","submitted_at":"2026-04-07T19:32:57Z","cross_cats_sorted":[],"title_canon_sha256":"8532f44ee3aa0a449b021b710ced0c9cbf76f062b94a9943fe2ebaf88d02fd14","abstract_canon_sha256":"8456be65bd8bcc4fa66626a52a7b8dd43737e16e033c78868021944eb845df12"},"schema_version":"1.0"},"canonical_sha256":"f5468b3e2daa66cc5265ae7d220a4ce92e2cfd689d59bcdf6395648a54b6353a","receipt":{"kind":"pith_receipt","key_id":"pith-v1-2026-05","algorithm":"ed25519","signed_at":"2026-05-25T02:01:19.017005Z","signature_b64":"X6jOHNibdzR4Qzs7mDGoBsfqXyRT2bLo3nSJDNd6E7ZDBNPDOL34glFD1CLJrCxFFMGEDQoHBKnXCL8GdPbRDg==","signed_message":"canonical_sha256_bytes","builder_version":"pith-number-builder-2026-05-17-v1","receipt_version":"0.3","canonical_sha256":"f5468b3e2daa66cc5265ae7d220a4ce92e2cfd689d59bcdf6395648a54b6353a","last_reissued_at":"2026-05-25T02:01:19.016207Z","signature_status":"signed_v1","first_computed_at":"2026-05-25T02:01:19.016207Z","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54"},"source_kind":"arxiv","source_id":"2604.06399","source_version":2,"attestation_state":"computed"},"signer":{"signer_id":"pith.science","signer_type":"pith_registry","key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54"},"created_at":"2026-05-25T02:01:19Z","supersedes":[],"prev_event":null,"signature":{"signature_status":"signed_v1","algorithm":"ed25519","key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54","signature_b64":"o719Icvq0k1nmjOooKAxx16Qk5IyMHp6VaYdlYn+TbOTvC99FQrqsOAg1JzfJ2Woj4KiVvK/6WRVmIkybNZBCw==","signed_message":"open_graph_event_sha256_bytes","signed_at":"2026-06-26T20:45:23.551339Z"},"content_sha256":"1a30a6358ee7eeba1988c38f8f8a348d16191bd4a3382e3ad69b2446a3321c4b","schema_version":"1.0","event_id":"sha256:1a30a6358ee7eeba1988c38f8f8a348d16191bd4a3382e3ad69b2446a3321c4b"},{"event_type":"graph_snapshot","subject_pith_number":"pith:2026:6VDIWPRNVJTMYUTFVZ6SECSM5E","target":"graph","payload":{"graph_snapshot":{"paper":{"title":"Reliability of uGMRT Band-4 Polarimetry: Results from a Quadrature Hybrid Polarizer Bypass Experiment","license":"http://creativecommons.org/licenses/by/4.0/","headline":"Bypassing the quadrature hybrid polarizer in uGMRT Band 4 eliminates the dominant source of polarimetric instability and enables accurate sub-GHz polarization measurements.","cross_cats":[],"primary_cat":"astro-ph.IM","authors_text":"Arpan Pal, Ganesh Kumbhar, Sanjeet Rai","submitted_at":"2026-04-07T19:32:57Z","abstract_excerpt":"Polarimetric observations at sub-GHz frequencies offer unique access to the magnetized universe through Faraday rotation and depolarization studies, but achieving reliable polarization calibration at these frequencies remains challenging. We report the identification and resolution of a systematic polarization calibration instability in the upgraded Giant Metrewave Radio Telescope (uGMRT) Band 4 (550--750\\,MHz). Through diagnostic observations of multiple calibrators, we discovered that the cross-hand phase response varies with the fractional polarization of the observed source, violating the "},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"These results establish that the QH polarizer is the dominant source of polarimetric instability in uGMRT Band 4 and demonstrate that its removal enables reliable sub-GHz polarimetry.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"That the bypass experiment isolates the QH polarizer as the sole cause of the observed instability without introducing new systematics in the frontend signal chain or calibration process.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Bypassing the quadrature hybrid polarizer in uGMRT Band-4 reduces instrumental leakage from 10-15% to 2-5%, stabilizes cross-hand phases, and allows accurate polarization angle measurements across the band.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Bypassing the quadrature hybrid polarizer in uGMRT Band 4 eliminates the dominant source of polarimetric instability and enables accurate sub-GHz polarization measurements.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"57dff9ef3f1965bbbb92d59ebad2c89f47bc9be1dc9abaafaca5c3cf4f0232ea"},"source":{"id":"2604.06399","kind":"arxiv","version":2},"verdict":{"id":"36b02aa3-34d1-4940-a94a-9318c8acfd6d","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-10T18:00:21.844415Z","strongest_claim":"These results establish that the QH polarizer is the dominant source of polarimetric instability in uGMRT Band 4 and demonstrate that its removal enables reliable sub-GHz polarimetry.","one_line_summary":"Bypassing the quadrature hybrid polarizer in uGMRT Band-4 reduces instrumental leakage from 10-15% to 2-5%, stabilizes cross-hand phases, and allows accurate polarization angle measurements across the band.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"That the bypass experiment isolates the QH polarizer as the sole cause of the observed instability without introducing new systematics in the frontend signal chain or calibration process.","pith_extraction_headline":"Bypassing the quadrature hybrid polarizer in uGMRT Band 4 eliminates the dominant source of polarimetric instability and enables accurate sub-GHz polarization measurements."},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2604.06399/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":2,"snapshot_sha256":"eba777f4fac3be5f521877e76a13f25199f6c945d20e8051559450fdcede0e3b"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"},"verdict_id":"36b02aa3-34d1-4940-a94a-9318c8acfd6d"},"signer":{"signer_id":"pith.science","signer_type":"pith_registry","key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54"},"created_at":"2026-05-25T02:01:19Z","supersedes":[],"prev_event":null,"signature":{"signature_status":"signed_v1","algorithm":"ed25519","key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54","signature_b64":"NFS/zJOF8LqwZdnAbmW6uy0QWUPbT4//gVTMuSDM9poWZDepYgEwd3F1NukoL6C1uxNog4eUpdtuUiaglsWSCA==","signed_message":"open_graph_event_sha256_bytes","signed_at":"2026-06-26T20:45:23.551789Z"},"content_sha256":"a8d7f19c6b039eac6f821d26b2b29babddd8c0d6bfd490ef6309b13dfe203567","schema_version":"1.0","event_id":"sha256:a8d7f19c6b039eac6f821d26b2b29babddd8c0d6bfd490ef6309b13dfe203567"}],"timestamp_proofs":[],"mirror_hints":[{"mirror_type":"https","name":"Pith Resolver","base_url":"https://pith.science","bundle_url":"https://pith.science/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E/bundle.json","state_url":"https://pith.science/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E/state.json","well_known_bundle_url":"https://pith.science/.well-known/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E/bundle.json","status":"primary"}],"public_keys":[{"key_id":"pith-v1-2026-05","algorithm":"ed25519","format":"raw","public_key_b64":"stVStoiQhXFxp4s2pdzPNoqVNBMojDU/fJ2db5S3CbM=","public_key_hex":"b2d552b68890857171a78b36a5dccf368a953413288c353f7c9d9d6f94b709b3","fingerprint_sha256_b32_first128bits":"RVFV5Z2OI2J3ZUO7ERDEBCYNKS","fingerprint_sha256_hex":"8d4b5ee74e4693bcd1df2446408b0d54","rotates_at":null,"url":"https://pith.science/pith-signing-key.json","notes":"Pith uses this Ed25519 key to sign canonical record SHA-256 digests. Verify with: ed25519_verify(public_key, message=canonical_sha256_bytes, signature=base64decode(signature_b64))."}],"merge_version":"pith-open-graph-merge-v1","built_at":"2026-06-26T20:45:23Z","links":{"resolver":"https://pith.science/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E","bundle":"https://pith.science/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E/bundle.json","state":"https://pith.science/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E/state.json","well_known_bundle":"https://pith.science/.well-known/pith/6VDIWPRNVJTMYUTFVZ6SECSM5E/bundle.json"},"state":{"state_type":"pith_open_graph_state","state_version":"1.0","pith_number":"pith:2026:6VDIWPRNVJTMYUTFVZ6SECSM5E","merge_version":"pith-open-graph-merge-v1","event_count":2,"valid_event_count":2,"invalid_event_count":0,"equivocation_count":0,"current":{"canonical_record":{"metadata":{"abstract_canon_sha256":"8456be65bd8bcc4fa66626a52a7b8dd43737e16e033c78868021944eb845df12","cross_cats_sorted":[],"license":"http://creativecommons.org/licenses/by/4.0/","primary_cat":"astro-ph.IM","submitted_at":"2026-04-07T19:32:57Z","title_canon_sha256":"8532f44ee3aa0a449b021b710ced0c9cbf76f062b94a9943fe2ebaf88d02fd14"},"schema_version":"1.0","source":{"id":"2604.06399","kind":"arxiv","version":2}},"source_aliases":[{"alias_kind":"arxiv","alias_value":"2604.06399","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"arxiv_version","alias_value":"2604.06399v2","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"doi","alias_value":"10.48550/arxiv.2604.06399","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"pith_short_12","alias_value":"6VDIWPRNVJTM","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"pith_short_16","alias_value":"6VDIWPRNVJTMYUTF","created_at":"2026-05-25T02:01:19Z"},{"alias_kind":"pith_short_8","alias_value":"6VDIWPRN","created_at":"2026-05-25T02:01:19Z"}],"graph_snapshots":[{"event_id":"sha256:a8d7f19c6b039eac6f821d26b2b29babddd8c0d6bfd490ef6309b13dfe203567","target":"graph","created_at":"2026-05-25T02:01:19Z","signer":{"key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54","signer_id":"pith.science","signer_type":"pith_registry"},"payload":{"graph_snapshot":{"author_claims":{"count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","strong_count":0},"builder_version":"pith-number-builder-2026-05-17-v1","claims":{"count":4,"items":[{"attestation":"unclaimed","claim_id":"C1","kind":"strongest_claim","source":"verdict.strongest_claim","status":"machine_extracted","text":"These results establish that the QH polarizer is the dominant source of polarimetric instability in uGMRT Band 4 and demonstrate that its removal enables reliable sub-GHz polarimetry."},{"attestation":"unclaimed","claim_id":"C2","kind":"weakest_assumption","source":"verdict.weakest_assumption","status":"machine_extracted","text":"That the bypass experiment isolates the QH polarizer as the sole cause of the observed instability without introducing new systematics in the frontend signal chain or calibration process."},{"attestation":"unclaimed","claim_id":"C3","kind":"one_line_summary","source":"verdict.one_line_summary","status":"machine_extracted","text":"Bypassing the quadrature hybrid polarizer in uGMRT Band-4 reduces instrumental leakage from 10-15% to 2-5%, stabilizes cross-hand phases, and allows accurate polarization angle measurements across the band."},{"attestation":"unclaimed","claim_id":"C4","kind":"headline","source":"verdict.pith_extraction.headline","status":"machine_extracted","text":"Bypassing the quadrature hybrid polarizer in uGMRT Band 4 eliminates the dominant source of polarimetric instability and enables accurate sub-GHz polarization measurements."}],"snapshot_sha256":"57dff9ef3f1965bbbb92d59ebad2c89f47bc9be1dc9abaafaca5c3cf4f0232ea"},"formal_canon":{"evidence_count":2,"snapshot_sha256":"eba777f4fac3be5f521877e76a13f25199f6c945d20e8051559450fdcede0e3b"},"integrity":{"available":true,"clean":true,"detectors_run":[],"endpoint":"/pith/2604.06399/integrity.json","findings":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938","summary":{"advisory":0,"by_detector":{},"critical":0,"informational":0}},"paper":{"abstract_excerpt":"Polarimetric observations at sub-GHz frequencies offer unique access to the magnetized universe through Faraday rotation and depolarization studies, but achieving reliable polarization calibration at these frequencies remains challenging. We report the identification and resolution of a systematic polarization calibration instability in the upgraded Giant Metrewave Radio Telescope (uGMRT) Band 4 (550--750\\,MHz). Through diagnostic observations of multiple calibrators, we discovered that the cross-hand phase response varies with the fractional polarization of the observed source, violating the ","authors_text":"Arpan Pal, Ganesh Kumbhar, Sanjeet Rai","cross_cats":[],"headline":"Bypassing the quadrature hybrid polarizer in uGMRT Band 4 eliminates the dominant source of polarimetric instability and enables accurate sub-GHz polarization measurements.","license":"http://creativecommons.org/licenses/by/4.0/","primary_cat":"astro-ph.IM","submitted_at":"2026-04-07T19:32:57Z","title":"Reliability of uGMRT Band-4 Polarimetry: Results from a Quadrature Hybrid Polarizer Bypass Experiment"},"references":{"count":0,"internal_anchors":0,"resolved_work":0,"sample":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"2604.06399","kind":"arxiv","version":2},"verdict":{"created_at":"2026-05-10T18:00:21.844415Z","id":"36b02aa3-34d1-4940-a94a-9318c8acfd6d","model_set":{"reader":"grok-4.3"},"one_line_summary":"Bypassing the quadrature hybrid polarizer in uGMRT Band-4 reduces instrumental leakage from 10-15% to 2-5%, stabilizes cross-hand phases, and allows accurate polarization angle measurements across the band.","pipeline_version":"pith-pipeline@v0.9.0","pith_extraction_headline":"Bypassing the quadrature hybrid polarizer in uGMRT Band 4 eliminates the dominant source of polarimetric instability and enables accurate sub-GHz polarization measurements.","strongest_claim":"These results establish that the QH polarizer is the dominant source of polarimetric instability in uGMRT Band 4 and demonstrate that its removal enables reliable sub-GHz polarimetry.","weakest_assumption":"That the bypass experiment isolates the QH polarizer as the sole cause of the observed instability without introducing new systematics in the frontend signal chain or calibration process."}},"verdict_id":"36b02aa3-34d1-4940-a94a-9318c8acfd6d"}}],"author_attestations":[],"timestamp_anchors":[],"storage_attestations":[],"citation_signatures":[],"replication_records":[],"corrections":[],"mirror_hints":[],"record_created":{"event_id":"sha256:1a30a6358ee7eeba1988c38f8f8a348d16191bd4a3382e3ad69b2446a3321c4b","target":"record","created_at":"2026-05-25T02:01:19Z","signer":{"key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54","signer_id":"pith.science","signer_type":"pith_registry"},"payload":{"attestation_state":"computed","canonical_record":{"metadata":{"abstract_canon_sha256":"8456be65bd8bcc4fa66626a52a7b8dd43737e16e033c78868021944eb845df12","cross_cats_sorted":[],"license":"http://creativecommons.org/licenses/by/4.0/","primary_cat":"astro-ph.IM","submitted_at":"2026-04-07T19:32:57Z","title_canon_sha256":"8532f44ee3aa0a449b021b710ced0c9cbf76f062b94a9943fe2ebaf88d02fd14"},"schema_version":"1.0","source":{"id":"2604.06399","kind":"arxiv","version":2}},"canonical_sha256":"f5468b3e2daa66cc5265ae7d220a4ce92e2cfd689d59bcdf6395648a54b6353a","receipt":{"algorithm":"ed25519","builder_version":"pith-number-builder-2026-05-17-v1","canonical_sha256":"f5468b3e2daa66cc5265ae7d220a4ce92e2cfd689d59bcdf6395648a54b6353a","first_computed_at":"2026-05-25T02:01:19.016207Z","key_id":"pith-v1-2026-05","kind":"pith_receipt","last_reissued_at":"2026-05-25T02:01:19.016207Z","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54","receipt_version":"0.3","signature_b64":"X6jOHNibdzR4Qzs7mDGoBsfqXyRT2bLo3nSJDNd6E7ZDBNPDOL34glFD1CLJrCxFFMGEDQoHBKnXCL8GdPbRDg==","signature_status":"signed_v1","signed_at":"2026-05-25T02:01:19.017005Z","signed_message":"canonical_sha256_bytes"},"source_id":"2604.06399","source_kind":"arxiv","source_version":2}}},"equivocations":[],"invalid_events":[],"applied_event_ids":["sha256:1a30a6358ee7eeba1988c38f8f8a348d16191bd4a3382e3ad69b2446a3321c4b","sha256:a8d7f19c6b039eac6f821d26b2b29babddd8c0d6bfd490ef6309b13dfe203567"],"state_sha256":"68f79d18fd67d832ed6c546a25e615beb8f0ab1055587f75e0219db0055424af"},"bundle_signature":{"signature_status":"signed_v1","algorithm":"ed25519","key_id":"pith-v1-2026-05","public_key_fingerprint":"8d4b5ee74e4693bcd1df2446408b0d54","signature_b64":"WzZQNWJ52beUWQNYzh1TX8YSzhLLE3tzyQdfrAIlavEr+GnbT67s70QiV67PSICdcQ9GbF8zMJ/VTewOESLhCg==","signed_message":"bundle_sha256_bytes","signed_at":"2026-06-26T20:45:23.553976Z","bundle_sha256":"d4f921ca84639a17c746fb54808223af9cf8be4f462a44ab8b77d9c549cbea65"}}