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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 250725A: BOOTES-7 early optical detection
  2. GRB 250725A: SVOM/VT optical candidate
  3. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  4. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  5. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  6. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  7. GRB 250725A: Enhanced Swift-XRT position
  8. GRB 250725A: Swift detection of a burst
  9. Swift GRB 250725A: Global MASTER-Net OT detection
  10. GRB 250725A: Fermi GBM Final Real-time Localization
  11. Fermi GRB 250725A: Global MASTER-Net observations report
  12. Swift GRB 250725A: Global MASTER-Net observations report
  13. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  14. SVOM J195836+32283 is not a real source
  15. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  16. SVOM J195836+32283/sb25072103: Second VT observation
  17. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  18. GRB 250723B: Fermi GBM Final Real-time Localization
  19. GRB 250721A: Fermi GBM Observation
  20. GRB 250723A: Fermi GBM Final Real-time Localization
  21. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  22. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  23. Swift-BAT trigger 1334535 is not a GRB
  24. GRB 250721A: Swift-XRT observations
  25. GRB 250722A: Fermi GBM Final Real-time Localization
  26. GRB 250713A : SVOM/ECLAIRs refined analysis
  27. GRB 250717B: SVOM/GRM observation
  28. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  29. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  30. GRB 250721A: Tiled Swift observations
  31. GRB 250721A: MAXI/GSC detection
  32. GRB 250721A: Fermi GBM Final Localization
  33. GRB 250720B: Fermi GBM Final Localization Correction
  34. GRB 250720A: Fermi GBM Final Localization
  35. Fermi trigger No 774730635: Global MASTER-Net observations report
  36. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  37. Fermi Gamma-ray Burst Monitor trigger 774670514/250720094 is not a GRB
  38. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  39. GRB 250717B: COLIBRÍ optical upper limit
  40. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  41. GRB 250717B: Swift-XRT observations
  42. GRB 250718B: Fermi GBM Final Localization Correction
  43. GRB 250718B: Fermi GBM Final Real-time Localization
  44. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  45. Swift Trigger 1334535: a possible GRB 250718A
  46. Swift GRB250718.01: Global MASTER-Net observations report
  47. GRB 250717B: Swift ToO observations
  48. GRB 270713A: Kitab and AbAO Optical Observations
  49. GRB 250717B: Fermi GBM Observation
  50. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  51. Konus-Wind detection of GRB 250716A
  52. GRB 250716A: Swift-XRT afterglow detection
  53. GRB 250717B: Fermi GBM Final Real-time Localization
  54. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  55. GRB 250717A: Fermi GBM Final Real-time Localization
  56. GRB 250716A: Swift ToO observations
  57. GRB 250716A: GOTO tentative optical counterpart candidate
  58. GRB 250716A: Fermi GBM Observation
  59. GRB 250714A: SVOM/GRM observation
  60. Fermi GRB 250716A: Global MASTER-Net observations report
  61. GRB 250716A: Fermi GBM Final Real-time Localization
  62. Fermi GRB 250715A: Global MASTER-Net observations report
  63. GRB 250715A: Fermi GBM Final Real-time Localization
  64. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  65. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  66. GRB 250713A: Mephisto optical upper limits
  67. Fermi GRB 250714A: Global MASTER-Net observations report
  68. GRB 250713A: SVOM/VT optical upper limit
  69. GRB 250713A: NOT optical upper limits
  70. GRB 250713A: OHP/T193 upper limit
  71. GRB 250713A: SVOM/C-GFT upper limit
  72. GRB 250714A: Fermi GBM Final Real-time Localization
  73. GRB 250706B/C: 7DT Follow-up Observations
  74. GRB 250713A: Swift-XRT observations
  75. GRB 250713A: EP-FXT counterpart detection
  76. EP250711a: COLIBRÍ continuous optical observations
  77. GRB 250706A: Swift-BAT refined analysis
  78. GRB 250702F: Swift-BAT refined analysis
  79. GRB 250628A: Swift-BAT refined analysis
  80. LIGO/Virgo/KAGRA S250712cd: Updated Sky localization
  81. GRB 250713A: JinShan optical upper limits
  82. GRB 250713A: SVOM detection of a long burst
  83. EP250711a: Global MASTER-Net observations report
  84. GRB 250711A: DDOTI Optical Upper Limit
  85. LIGO/Virgo/KAGRA S250712cd: Identification of a GW compact binary merger candidate
  86. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate (duplicate submission)
  87. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  88. GRB 250711A: SVOM/GRM observation
  89. EP250711a: NOT optical counterpart candidate
  90. EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  91. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  92. Fermi GRB 250711A: Global MASTER-Net observations report
  93. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  94. GRB 250704A: GRANDMA observations
  95. GRB 250711A: BALROG localization (Fermi Trigger 773937617 / GRB 250711611)
  96. GRB 250711A: Fermi GBM Final Real-time Localization
  97. GRB 250704A: SVOM/ECLAIRs refined analysis
  98. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  99. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  100. GRB 250704B / EP250704a: 1.3 GHz MeerKAT Detection

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