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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"

20963 results found.

  1. GRB 250818B: Swift/UVOT Detection
  2. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  3. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  4. GRB 250818B: TRT Optical Observation
  5. Fermi GRB 250816A: Global MASTER-Net observations report
  6. GRB 250818B: SAO RAS optical observations
  7. Swift GRB 250818A: Global MASTER-Net observations report
  8. GRB 250818B: NOT optical observations
  9. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  10. Fermi trigger No 776849714: Global MASTER-Net observations report
  11. GRB 250818B: KAIT optical observations
  12. GRB 250818A: Swift/UVOT Upper Limits
  13. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  14. GRB 250813B: SVOM/ECLAIRs refined analysis
  15. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  16. GRB 250818B: SVOM/VT optical observation
  17. GRB 250814A: Further GRAWITA TNG NIR observations
  18. GRB 250818B: Swift-XRT afterglow detection
  19. GRB 250818B: GOTO optical counterpart candidate
  20. sb25081602: Swift-XRT observations
  21. Fermi GRB 250814B: Global MASTER-Net observations report
  22. GRB 250813B: Liverpool Telescope optical upper limits
  23. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  24. GRB 250814A: GRAWITA TNG NIR observations
  25. GRB 250812A: SVOM/VT optical continued observation
  26. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  27. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  28. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  29. GRB 250814A: P200/WIRC observations of the afterglow candidate
  30. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  31. GRB 250814A: Possible afterglow candidate from P200/WIRC
  32. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  33. Fermi trigger No 776818276: Global MASTER-Net observations report
  34. Swift GRB250814.32: Global MASTER-Net observations report
  35. GRB 250814A: J-band upper limit from WINTER
  36. GRB 250813B: NOT observations of the optical afterglow
  37. GRB 250813B: SVOM/VT optical observations
  38. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  39. GRB 250814A: DDOTI Optical Upper Limit
  40. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  41. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  42. GRB 250813B: Ondrejov D50 fast decay
  43. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  44. EP250812a: Nickel optical upper limit
  45. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  46. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  47. EP250812a: NOT, NTT, and GS observations
  48. GRB 250812A: Swift/UVOT Detection
  49. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  50. EP250812a: SVOM/VT optical counterpart
  51. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  52. IceCube Alert 250813.14: Global MASTER-Net observations report
  53. GRB 250812A: Swift ToO observations
  54. EP 250812a: GOTO optical upper limit
  55. GRB 250812A: Kilonova-Catcher optical afterglow detection
  56. EP250812a: Swift-XRT counterpart detection
  57. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  58. GRB 250812A: SVOM/VT optical afterglow confirmation
  59. GRB 250812A: Swift-XRT afterglow detection
  60. GRB 250812A: TRT likely optical counterpart detection
  61. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  62. GRB 250809A: Swift/UVOT Detection
  63. GRB 250702B: Chandra X-ray Detection
  64. EP250807a: Global MASTER-Net observations report
  65. Fermi GRB 250808A: Global MASTER-Net observations report
  66. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  67. GRB 250808A: Swift-XRT candidate counterpart detection
  68. GRB 250807A: SVOM/VT optical continued observation
  69. EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
  70. GRB 250807B: Swift/UVOT Detection
  71. GRB 250807B: Kilonova-Catcher optical afterglow detection
  72. GRB 250807A: Swift/UVOT Detection
  73. EP250807a: NTT z-band optical upper limit
  74. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  75. Swift GRB250807.45: Global MASTER-Net observations report
  76. GRB 250807B: NTT optical observations
  77. EP250807a: EP-WXT detection of a fast X-ray transient
  78. EP 250807.979: GOTO optical upper limit
  79. GRB 250807A: SVOM/VT optical observation
  80. EP250806a: Upper limit from Fermi-GBM Observations
  81. Swift GRB250807.65: Global MASTER-Net observations report
  82. GRB 250805A: Kilonova-Catcher optical upper limits
  83. GRB 250805A: Swift/UVOT Upper Limits
  84. GRB 250806A: Swift/UVOT U-band detection
  85. IceCube Alert 250804.84: Global MASTER-Net observations report
  86. EP#01709198415/EP250806a: Swift-XRT observations
  87. EP250806a: Global MASTER-Net observations report
  88. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  89. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  90. GRB 250806A: J-band upper limit from WINTER
  91. GRB 250806A: KAIT optical upper limit
  92. GRB 250806A: Kilonova-Catcher optical upper limits
  93. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  94. GRB 250805A: ESO/VLT observations
  95. GRB 250804B: Swift-XRT observations
  96. GRB 250805A: TRT optical upper limits
  97. GRB 250805A: Swift-XRT observations
  98. Swift GRB250805.26: Global MASTER-Net observations report
  99. GRB 250804B: Tiled Swift observations
  100. Fermi trigger No 776041355: Global MASTER-Net observations report

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