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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"

5401 results found.

  1. GRB 250925A/EP250925a: EP-WXT detection
  2. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  3. GRB 250924A: Swift/UVOT Detection
  4. GRB 250924A: COLIBRÍ optical observations
  5. GRB 250924A: Swift detection of a burst with an optical counterpart
  6. Fermi GRB 250922B: Global MASTER-Net observations report
  7. Fermi trigger No 780156732: Global MASTER-Net observations report
  8. GRB 250922A: Fermi GBM Final Localization
  9. GRB 250920B: Enhanced Swift-XRT position
  10. GRB 250920C: GOTO optical counterpart candidate
  11. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  12. EP250919a: Global MASTER-Net observations report
  13. EP250916a: EP-FXT follow-up observation
  14. GRB 250916A: GOTO optical counterpart candidate
  15. GRB250912A: VLT/HAWK-I follow-up observations
  16. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  17. EP250910a: Global MASTER-Net observations report
  18. GRB 250910A: LCO optical upper limit
  19. EP250908c: Global MASTER-Net observations report
  20. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  21. EP250905a: Liverpool Telescope i-band upper limits
  22. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  23. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  24. IceCube Alert 250905.84: Global MASTER-Net observations report
  25. GRB 250905A: KAIT optical upper limit
  26. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  27. GRB 250904A: Prompt enhanced Swift-XRT position
  28. GRB 250904A: Swift detection of a burst
  29. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  30. GRB 250903A: LCO optical observation
  31. GRB 250903A: LCO optical afterglow detection
  32. EP250903a: LCO candidate counterpart discovery
  33. GRB 250903A: TRT optical counterpart detection
  34. EP250903a: Global MASTER-Net observations report
  35. EP250903a: TRT optical observations
  36. EP250903a: Einstein Probe detection of an X-ray transient
  37. EP 250827B: Detection of supernova counterpart by LCO.
  38. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  39. EP250827b: continued Liverpool Telescope observations
  40. Fermi GRB 250902B: Global MASTER-Net observations report
  41. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  42. GRB 250901A: EP-FXT follow-up observation
  43. EP250901a: Swift-XRT observations
  44. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  45. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  46. EP250901a: Mephisto optical upper limits
  47. EP250901a: Einstein Probe detection of an X-ray transient
  48. GRB 250831A: Swift-XRT counterpart detection
  49. GRB 250830B: MAXI/GSC detection
  50. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  51. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  52. Fermi GRB 250827A: Global MASTER-Net observations report
  53. EP250827a: Global MASTER-Net observations report
  54. Fermi GRB 250824B: Global MASTER-Net observations report
  55. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  56. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  57. GRB 250812A: SVOM/ECLAIRs refined analysis
  58. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  59. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  60. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  61. IPN triangulation of GRB 250814C (short)
  62. GRB 250818B: Liverpool Telescope optical detections
  63. GRB 250818B: Swift/UVOT Detection
  64. GRB 250818B: NOT optical observations
  65. Fermi trigger No 776849714: Global MASTER-Net observations report
  66. GRB 250818B: GOTO optical counterpart candidate
  67. sb25081602: Swift-XRT observations
  68. SVOM/sb25081602: detection of a likely X-ray transient
  69. GRB 250813B: Liverpool Telescope optical upper limits
  70. GRB 250814A: Further COLIBRÍ optical upper limit
  71. GRB 250814A: P200/WIRC observations of the afterglow candidate
  72. Fermi trigger No 776818276: Global MASTER-Net observations report
  73. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  74. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  75. EP250812a: Liverpool Telescope upper limits
  76. EP250812a: SVOM/VT optical counterpart
  77. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  78. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  79. IceCube Alert 250813.14: Global MASTER-Net observations report
  80. EP 250812a: GOTO optical upper limit
  81. EP250812a: Swift-XRT counterpart detection
  82. GRB 250812A: SVOM/VT optical afterglow confirmation
  83. GRB 250812A: SVOM detection of a faint long burst
  84. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  85. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  86. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  87. EP250806a: Liverpool telescope optical upper limit
  88. GRB 250807A: Swift detection of a burst with an optical counterpart
  89. EP250802a: additional Liverpool Telescope upper limits
  90. Fermi Gamma-ray Burst Monitor trigger 775945985/250803856 is not a GRB
  91. EP250802a: Liverpool Telescope optical upper limits
  92. EP250802a: Global MASTER-Net observations report
  93. EP250802a: GROWTH-India Telescope optical upper limit
  94. EP250730a: Global MASTER-Net observations report
  95. GRB 250728A: COLIBRÍ optical upper limit
  96. GRB 250727A: Swift-XRT observations
  97. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  98. GRB 250725A: Swift detection of a burst
  99. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  100. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits

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