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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: Swift ToO observations
  2. GRB 250917B: Fermi GBM Observation
  3. GRB 250917B: Swift-XRT observations
  4. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  5. Fermi GRB 250917B: Global MASTER-Net observations report
  6. GRB 250917B: Swift detection of a short burst
  7. GRB 250916A: GOTO optical counterpart candidate
  8. GRB 250917B: Fermi GBM Final Real-time Localization
  9. GRB 250917A: Fermi GBM Final Real-time Localization
  10. The EP-WXT trigger 01709241037 is likely a flaring star
  11. GRB 250916A: AstroSat CZTI detection of a bright long burst
  12. GRB 250910A: SVOM/ECLAIRs refined analysis
  13. EP250916a: Einstein Probe detection of an X-ray transient
  14. Fermi GRB 250916A: Global MASTER-Net observations report
  15. GRB 250916A: Fermi GBM Final Real-time Localization
  16. EP250827b: VLA Observations
  17. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  18. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  19. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  20. SVOM/sb25091517: SVOM detection of an X-ray transient
  21. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  22. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  23. GRB 250912A: Swift-XRT observations
  24. GRB250912A: VLT/HAWK-I follow-up observations
  25. GRB 250912A: VLT observations
  26. GRB 250912A: Fermi GBM Observation
  27. GRB 250911A: Insight-HXMT detection
  28. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  29. GRB 250912A:SVOM/VT optical upper limit
  30. GRB 250912A: LCO optical upper limit
  31. The EP-WXT trigger 01709240768 is likely a flaring star
  32. Fermi GRB 250912A: Global MASTER-Net observations report
  33. EP250911a: Global MASTER-Net observations report
  34. GRB 250912A: SVOM detection of a burst
  35. GRB 250912A: Fermi GBM Final Real-time Localization
  36. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  37. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  38. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  39. EP250911a: Upper limit from Fermi-GBM Observations
  40. LIGO/Virgo/KAGRA S250912f: Updated Sky localization
  41. GRB 250911A: GECAM-B detection
  42. GRB 250911A: Swift-BAT refined analysis
  43. EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
  44. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  45. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  46. GRB 250910B: SVOM/GRM observation
  47. EP250911a: SVOM/VT optical observation
  48. GRB 250911A: MASTER optical counterpart observations
  49. EP250911a: SAO RAS optical observations
  50. GRB 250911A: Swift-XRT refined Analysis
  51. GRB 250910C: Fermi GBM Final Localization Correction
  52. EP250911a: Swift-XRT observations
  53. EP250911a: Optical detection with Kinder observations
  54. GRB 250911A: Swift/UVOT Detection
  55. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  56. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  57. GRB 250909B: Insight-HXMT detection
  58. GRB 250909B: SVOM/GRM observation
  59. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  60. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  61. EP250911a: COLIBRÍ optical observations
  62. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  63. Fermi GRB 250910B: Global MASTER-Net observations report
  64. EP250911a: LCO optical counterpart discovery
  65. EP250910a: Global MASTER-Net observations report
  66. EP250911a: Einstein Probe detection of an X-ray transient
  67. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  68. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  69. GRB 250903A: SVOM/ECLAIRs refined analysis
  70. GRB 250911A: Enhanced Swift-XRT position
  71. GRB 250911A: Swift-XRT observations
  72. GRB 250911A: COLIBRÍ optical counterpart candidate
  73. GRB 250911A: Swift detection of a burst
  74. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  75. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  76. GRB 250910B: Fermi GBM Final Real-time Localization
  77. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  78. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  79. GRB 250909B: AstroSat CZTI detection of a long burst
  80. GRB 250910A: SVOM/VT optical upper limit
  81. EP250908C: GROND observation of the fading optical counterpart
  82. GRB 250910A: LCO optical upper limit
  83. GRB 250909A: AstroSat CZTI detection
  84. GRB 250910A: SVOM/MXT possible afterglow detection
  85. GRB 250910A: SVOM detection of a faint burst
  86. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  87. GRB 250702B: Late time Chandra observations
  88. EP250908b/EP#01709240653: Swift/UVOT Detection
  89. EP#01709240653: Swift-XRT observations
  90. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  91. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  92. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  93. EP250908c: SVOM/VT optical observation
  94. EP250908c: VLT/FORS2 optical counterpart identification
  95. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  96. EP250908b: SVOM/VT optical candidate
  97. The EP-WXT trigger EP250908a/01709240652 is not a real source
  98. EP250908c: Global MASTER-Net observations report
  99. Fermi GRB 250909A: Global MASTER-Net observations report
  100. EP250908c: Einstein Probe detection of an X-ray transient

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