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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  2. GRB 250916A: Swift-XRT observations
  3. EP250916a: EP-FXT follow-up observation
  4. GRB 250916A: MAO/AZT-22 optical observations
  5. GRB 250916A: SAO RAS optical observations
  6. GRB 250916A : GIT optical observations
  7. LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
  8. LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
  9. GRB 250916A: Glowbug gamma-ray detection
  10. GRB250917B: WFST optical observations
  11. GRB 250916A: Swift ToO observations
  12. GRB 250917B: Fermi GBM Observation
  13. GRB 250917B: Swift-XRT observations
  14. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  15. Fermi GRB 250917B: Global MASTER-Net observations report
  16. GRB 250917B: Swift detection of a short burst
  17. GRB 250916A: GOTO optical counterpart candidate
  18. GRB 250917B: Fermi GBM Final Real-time Localization
  19. GRB 250917A: Fermi GBM Final Real-time Localization
  20. The EP-WXT trigger 01709241037 is likely a flaring star
  21. GRB 250916A: AstroSat CZTI detection of a bright long burst
  22. GRB 250910A: SVOM/ECLAIRs refined analysis
  23. EP250916a: Einstein Probe detection of an X-ray transient
  24. Fermi GRB 250916A: Global MASTER-Net observations report
  25. GRB 250916A: Fermi GBM Final Real-time Localization
  26. EP250827b: VLA Observations
  27. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  28. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  29. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  30. SVOM/sb25091517: SVOM detection of an X-ray transient
  31. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  32. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  33. GRB 250912A: Swift-XRT observations
  34. GRB250912A: VLT/HAWK-I follow-up observations
  35. GRB 250912A: VLT observations
  36. GRB 250912A: Fermi GBM Observation
  37. GRB 250911A: Insight-HXMT detection
  38. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  39. GRB 250912A:SVOM/VT optical upper limit
  40. GRB 250912A: LCO optical upper limit
  41. The EP-WXT trigger 01709240768 is likely a flaring star
  42. Fermi GRB 250912A: Global MASTER-Net observations report
  43. EP250911a: Global MASTER-Net observations report
  44. GRB 250912A: SVOM detection of a burst
  45. GRB 250912A: Fermi GBM Final Real-time Localization
  46. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  47. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  48. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  49. EP250911a: Upper limit from Fermi-GBM Observations
  50. LIGO/Virgo/KAGRA S250912f: Updated Sky localization
  51. GRB 250911A: GECAM-B detection
  52. GRB 250911A: Swift-BAT refined analysis
  53. EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
  54. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  55. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  56. GRB 250910B: SVOM/GRM observation
  57. EP250911a: SVOM/VT optical observation
  58. GRB 250911A: MASTER optical counterpart observations
  59. EP250911a: SAO RAS optical observations
  60. GRB 250911A: Swift-XRT refined Analysis
  61. GRB 250910C: Fermi GBM Final Localization Correction
  62. EP250911a: Swift-XRT observations
  63. EP250911a: Optical detection with Kinder observations
  64. GRB 250911A: Swift/UVOT Detection
  65. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  66. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  67. GRB 250909B: Insight-HXMT detection
  68. GRB 250909B: SVOM/GRM observation
  69. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  70. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  71. EP250911a: COLIBRÍ optical observations
  72. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  73. Fermi GRB 250910B: Global MASTER-Net observations report
  74. EP250911a: LCO optical counterpart discovery
  75. EP250910a: Global MASTER-Net observations report
  76. EP250911a: Einstein Probe detection of an X-ray transient
  77. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  78. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  79. GRB 250903A: SVOM/ECLAIRs refined analysis
  80. GRB 250911A: Enhanced Swift-XRT position
  81. GRB 250911A: Swift-XRT observations
  82. GRB 250911A: COLIBRÍ optical counterpart candidate
  83. GRB 250911A: Swift detection of a burst
  84. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  85. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  86. GRB 250910B: Fermi GBM Final Real-time Localization
  87. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  88. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  89. GRB 250909B: AstroSat CZTI detection of a long burst
  90. GRB 250910A: SVOM/VT optical upper limit
  91. EP250908C: GROND observation of the fading optical counterpart
  92. GRB 250910A: LCO optical upper limit
  93. GRB 250909A: AstroSat CZTI detection
  94. GRB 250910A: SVOM/MXT possible afterglow detection
  95. GRB 250910A: SVOM detection of a faint burst
  96. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  97. GRB 250702B: Late time Chandra observations
  98. EP250908b/EP#01709240653: Swift/UVOT Detection
  99. EP#01709240653: Swift-XRT observations
  100. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg

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