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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 250818A: Swift-XRT refined Analysis
  2. GRB 250818B: EP-FXT counterpart detection
  3. GRB 250818A: Swift-BAT refined analysis
  4. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  5. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  6. GRB 250818C: Fermi GBM Final Real-time Localization
  7. GRB 250818B: Keck redshift of the optical afterglow
  8. Fermi trigger No 776849714: Global MASTER-Net observations report
  9. GRB 250818B: KAIT optical observations
  10. GRB 250818A: Swift/UVOT Upper Limits
  11. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  12. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  13. GRB 250818A: Enhanced Swift-XRT position
  14. GRB 250813B: SVOM/ECLAIRs refined analysis
  15. GRB 250818A: Fermi GBM Observation
  16. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  17. GRB 250818B: SVOM/VT optical observation
  18. GRB 250814A: Further GRAWITA TNG NIR observations
  19. GRB 250818B: Swift-XRT afterglow detection
  20. GRB 250818B: GOTO optical counterpart candidate
  21. GRB 250818B: SVOM detection of a short burst
  22. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  23. GRB 250818A: Swift detection of a burst
  24. GRB 250818A: Fermi GBM Final Real-time Localization
  25. sb25081602: Swift-XRT observations
  26. GRB 250816A: SVOM/GRM observation of a short burst
  27. SVOM/sb25081602: detection of a likely X-ray transient
  28. Fermi GRB 250814B: Global MASTER-Net observations report
  29. GRB 250816A: Fermi GBM Final Real-time Localization
  30. GRB 250814A: Swift-BAT refined analysis
  31. GRB 250815A: Fermi GBM Final Localization
  32. GRB 250813B: Liverpool Telescope optical upper limits
  33. GRB 250814A: Further COLIBRÍ optical upper limit
  34. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  35. GRB 250814A: GRAWITA TNG NIR observations
  36. GRB 250812A: SVOM/VT optical continued observation
  37. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  38. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  39. GRB250814A: TRT optical upper limits
  40. GRB 250814B: SVOM/GRM observation
  41. GRB 250814C: SVOM/GRM observation of a short burst
  42. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  43. GRB 250813B: SVOM/GRM observation
  44. GRB 250814A: P200/WIRC observations of the afterglow candidate
  45. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  46. GRB 250814A: KAIT optical upper limit
  47. GRB 250814A: Swift-XRT refined Analysis
  48. GRB 240814A: Fermi GBM Observation
  49. GRB 250814A: Possible afterglow candidate from P200/WIRC
  50. GRB 250813B: Fermi GBM Observation
  51. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  52. Fermi trigger No 776818276: Global MASTER-Net observations report
  53. Swift GRB250814.32: Global MASTER-Net observations report
  54. GRB 250814A: J-band upper limit from WINTER
  55. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  56. GRB 250813B: NOT observations of the optical afterglow
  57. GRB 250813B: SVOM/VT optical observations
  58. Subject GRB 250813B: SVOM/MXT refined analysis
  59. GRB 250814A: COLIBRÍ optical upper limit
  60. GRB 250814B: Fermi GBM Final Real-time Localization
  61. GRB 250813A: AstroSat CZTI detection
  62. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  63. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  64. GRB 250814A: DDOTI Optical Upper Limit
  65. GRB 250813B: EP-FXT counterpart detection
  66. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  67. GRB 250813B: Swift-XRT afterglow detection
  68. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  69. GRB 250814A: Fermi GBM Final Real-time Localization
  70. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  71. GRB 250813B: Ondrejov D50 fast decay
  72. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  73. GRB 250813B: Ondrejov D50 optical afterglow detection
  74. GRB 250813B: SVOM detection of a bright long burst
  75. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  76. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  77. EP250812a: Nickel optical upper limit
  78. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  79. GRB 250812A: NTT spectroscopic redshift z = 2.57
  80. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  81. EP250812a: NOT, NTT, and GS observations
  82. GRB 250812A: Swift/UVOT Detection
  83. GRB 250813A: Fermi GBM Final Localization
  84. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  85. EP250812a: Liverpool Telescope upper limits
  86. EP250812a: SVOM/VT optical counterpart
  87. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  88. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  89. IceCube Alert 250813.14: Global MASTER-Net observations report
  90. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  91. GRB 250812A: EP-FXT counterpart detection
  92. GRB 250812A: Swift ToO observations
  93. GRB 250807B: Swift-BAT refined analysis
  94. EP 250812a: GOTO optical upper limit
  95. GRB 250812A: Kilonova-Catcher optical afterglow detection
  96. EP250812a: Swift-XRT counterpart detection
  97. Fermi Gamma-ray Burst Monitor trigger 776705265/250812644 is not a GRB
  98. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  99. EP250812a: Einstein Probe detection of an X-ray transient
  100. GRB 250812A: SVOM/VT optical afterglow confirmation

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