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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"

27075 results found.

  1. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  2. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  3. GRB 250824B: Fermi GBM Final Real-time Localization
  4. The EP-WXT trigger 01709200707 is likely a flaring star
  5. GRB 250823A: COLIBRÍ optical observations
  6. The EP-WXT trigger 01709200706 is likely a flaring star
  7. GRB 250823A: SVOM/VT optical observation
  8. GRB 250824A: Fermi GBM Final Real-time Localization
  9. GRB 250823A: Swift/UVOT Detection
  10. GRB 250823A: NOT optical observations
  11. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  12. GRB 250823A: Fermi GBM Observation
  13. GRB 250823A: LCOGT Optical Detection
  14. GRB 250823A: BOOTES6/DPRT early optical detection
  15. GRB 250823A: Liverpool Telescope optical detection
  16. GRB 250823A: Swift detection of a burst
  17. GRB 250823A: Fermi GBM Final Real-time Localization
  18. Swift GRB250823.84: Global MASTER-Net observations report
  19. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  20. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  21. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  22. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  23. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  24. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  25. IPN triangulation of GRB 250821B (long/bright)
  26. GRB 250821A: Kilonova-Catcher optical upper limits
  27. GRB 250812A: SVOM/ECLAIRs refined analysis
  28. GRB 250821A: Swift-BAT refined analysis
  29. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  30. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  31. GRB 250821A: VLT/FORS2 Optical Observation
  32. GRB 250821A: GECAM-B detection
  33. GRB 250821B: SVOM/GRM observation
  34. EP250821a: SVOM/VT optical observation
  35. Fermi GRB 250821B: Global MASTER-Net observations report
  36. GRB 250821A: NOT z-band upper limit
  37. GRB 250821C: Fermi GBM Final Real-time Localization
  38. GRB 250821A: Swift-XRT refined Analysis
  39. Swift GRB 250821A: Global MASTER-Net observations report
  40. GRB 250821B: Fermi GBM Detection
  41. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  42. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  43. GRB 250821A: Swift/UVOT Upper Limits
  44. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  45. EP250821a: Swift XRT and UVOT counterpart detection
  46. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  47. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  48. GRB 250821A: LCOGT Optical Upper Limits
  49. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  50. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  51. GRB 250821A: Swift detection of a burst
  52. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  53. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  54. EP250821a: Einstein Probe detection of an X-ray transient
  55. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  56. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  57. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  58. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  59. GRB 250814A: Swift/UVOT Upper Limits
  60. GRB 250813B: Swift/UVOT Upper Limit
  61. IPN triangulation of GRB 250816A (short)
  62. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  63. GRB 250818B: Kilonova-Catcher optical afterglow detection
  64. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  65. GRB 250818B: Liverpool Telescope optical detections
  66. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  67. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  68. GRB 250818B: Swift/UVOT Detection
  69. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  70. GRB 250820A: Fermi GBM Final Real-time Localization
  71. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  72. Fermi GRB 250816A: Global MASTER-Net observations report
  73. Swift GRB 250818A: Global MASTER-Net observations report
  74. GRB 250818B: NOT optical observations
  75. GRB 250818A: Swift-XRT refined Analysis
  76. GRB 250818B: EP-FXT counterpart detection
  77. GRB 250818A: Swift-BAT refined analysis
  78. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  79. GRB 250818C: Fermi GBM Final Real-time Localization
  80. Fermi trigger No 776849714: Global MASTER-Net observations report
  81. GRB 250818B: KAIT optical observations
  82. GRB 250818A: Swift/UVOT Upper Limits
  83. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  84. GRB 250813B: SVOM/ECLAIRs refined analysis
  85. GRB 250818A: Fermi GBM Observation
  86. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  87. GRB 250818B: SVOM/VT optical observation
  88. GRB 250814A: Further GRAWITA TNG NIR observations
  89. GRB 250818B: GOTO optical counterpart candidate
  90. GRB 250818B: SVOM detection of a short burst
  91. GRB 250818A: Swift detection of a burst
  92. GRB 250818A: Fermi GBM Final Real-time Localization
  93. sb25081602: Swift-XRT observations
  94. GRB 250816A: SVOM/GRM observation of a short burst
  95. SVOM/sb25081602: detection of a likely X-ray transient
  96. Fermi GRB 250814B: Global MASTER-Net observations report
  97. GRB 250816A: Fermi GBM Final Real-time Localization
  98. GRB 250814A: Swift-BAT refined analysis
  99. GRB 250815A: Fermi GBM Final Localization
  100. GRB 250813B: Liverpool Telescope optical upper limits

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