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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"

20562 results found.

  1. GRB 250704A: REM detection of the optical afterglow
  2. LIGO/Virgo/KAGRA S250704ab: Coverage and upper limits from MAXI/GSC observations
  3. GRB 250702F: Swift/UVOT Detection
  4. Fermi GBM Analysis of GRB 250702B (formerly B,D,E); dissociation of C burst
  5. Fermi GRB 250703A: Global MASTER-Net observations report
  6. GRB 250702F: Leavitt Observatory optical observations
  7. GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
  8. GRB 250702F: Skynet Optical Observations
  9. GRBs 250702B/C/D/E / EP250702a: Swift XRT localization
  10. EP250702a/GRB 250702B, C, D, E: EP-FXT follow-up observation
  11. GRB 250702F: TRT Optical Observation
  12. GRB 250703A: DDOTI Optical Upper Limit
  13. GRB 250702F: REM optical afterglow detection
  14. EP250702a: Global MASTER-Net observations report
  15. GRB 250702F: DDOTI Optical Observation
  16. GRB 250702B,C,D,E / EP 250702a: MAXI/GSC detection
  17. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  18. GRB 250702F: COLIBRÍ Observations of the Afterglow
  19. EP250702a : an X-ray transient detected by Einstein Probe likely associated with GRB 250702B,C,D,E
  20. Fermi GRB 250702E: Global MASTER-Net observations report
  21. Fermi GRB 250702B: Global MASTER-Net observations report
  22. GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
  23. GRB 250702F: GTC/OSIRIS+ spectroscopic redshift z = 1.520
  24. GRB 250702F: NOT observations of the optical afterglow
  25. Fermi GRB 250702F: Global MASTER-Net observations report
  26. Fermi GRB 250702C: Global MASTER-Net observations report
  27. GRB 250702F: GOTO optical counterpart detection
  28. GRB 250702F: Ondrejov D50 optical afterglow detection
  29. Swift GRB 250702F: Global MASTER-Net observations report
  30. GRB 250628B: Swift-XRT observations
  31. GRB 250628B: SVOM/VT optical upper limit
  32. GRB 250628A: REM optical/NIR upper limits
  33. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  34. GRB 250628A: Swift/UVOT Upper Limits
  35. Fermi GRB 250626A: Global MASTER-Net observations report
  36. Swift GRB 250628A: Global MASTER-Net observations report
  37. GRB 250625A: Leavitt Observatory afterglow detection
  38. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  39. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  40. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  41. GRB 250625A: SVOM/C-GFT upper limit in early phase
  42. GRB 250625A: Swift/UVOT Upper Limits
  43. GRB 250625A: ABObservatory afterglow detection
  44. GRB 250625A: OHP/T193 optical detection
  45. GRB 250625A: COLIBRÍ optical observations
  46. GRB 250625A: JinShan optical observations
  47. Swift GRB 250625A: Global MASTER-Net observations report
  48. GRB 250625A: SAO RAS possible optical afterglow
  49. Fermi GRB 250625A: Global MASTER-Net observations report
  50. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  51. GRB 241018A: Maidanak optical observations
  52. Fermi GRB 250624A: Global MASTER-Net observations report
  53. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  54. Fermi GRB 250623A: Global MASTER-Net observations report
  55. Fermi trigger No 772190032: Global MASTER-Net observations report
  56. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  57. Fermi GRB 250621A: Global MASTER-Net observations report
  58. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  59. GRB 250506A - SVOM/ECLAIRs Refined analysis
  60. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  61. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  62. Fermi trigger No 772128434: Global MASTER-Net observations report
  63. EP-WXT trigger 01709179036: a new outburst of GRS 1739-278
  64. GRB 250617B: Nickel telescope optical observations
  65. Fermi trigger No 772058337: Global MASTER-Net observations report
  66. GRB 250615A: Kilonova-Catcher optical upper limits
  67. GRB 250617B: Assy AZT-20 Optical Observations
  68. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  69. Fermi GRB 250617A: Global MASTER-Net observations report
  70. GRB 250615A/EP250615a: FTW optical and NIR observations
  71. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  72. GRB 250617B: Swift/UVOT Detection
  73. GRB 250617B: Kilonova-Catcher optical afterglow detection
  74. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  75. GRB 250617B: COLIBRÍ optical observations
  76. GRB 250617B: NOT NIR observations of the afterglow
  77. GRB 250617B: NUTTelA-TAO early time optical observations
  78. Fermi trigger No 771886893: Global MASTER-Net observations report
  79. Swift GRB 250617B: Global MASTER-Net observations report
  80. GRB 250617B: GOTO optical upper limit
  81. GRB 250617B: SAO RAS optical observations
  82. GRB 250615A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  83. EP#01709178975: Swift-XRT counterpart detection
  84. EP-WXT trigger 01709178975: GOTO optical upper limit
  85. SVOM sb25061207: AbAO AS-32 Optical Upper Limit
  86. GRB 250615A: DDOTI Optical Upper Limit
  87. GRB 250615A: Swift/UVOT Upper Limits
  88. Fermi trigger No 771752663: Global MASTER-Net observations report
  89. Swift GRB 250615A: Global MASTER-Net observations report
  90. Fermi trigger No 771718064: Global MASTER-Net observations report
  91. sb25061207: Mephisto optical upper limits
  92. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  93. Fermi trigger No 771494087: Global MASTER-Net observations report
  94. sb25061218: Swift-XRT observations
  95. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  96. GRB 250610B: J band upper limit by SYSU 80cm infrared telescope
  97. Fermi trigger No 771424081: Global MASTER-Net observations report
  98. EP250612a: Global MASTER-Net observations report
  99. sb25061207: Swift-XRT observations
  100. EP250612a/GRB 250612B: JinShan optical upper limit

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