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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 250813B: SVOM/ECLAIRs refined analysis
  2. GRB 250818A: Fermi GBM Observation
  3. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  4. GRB 250818B: SVOM/VT optical observation
  5. GRB 250814A: Further GRAWITA TNG NIR observations
  6. GRB 250818B: Swift-XRT afterglow detection
  7. GRB 250818B: GOTO optical counterpart candidate
  8. GRB 250818B: SVOM detection of a short burst
  9. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  10. GRB 250818A: Swift detection of a burst
  11. GRB 250818A: Fermi GBM Final Real-time Localization
  12. sb25081602: Swift-XRT observations
  13. GRB 250816A: SVOM/GRM observation of a short burst
  14. SVOM/sb25081602: detection of a likely X-ray transient
  15. Fermi GRB 250814B: Global MASTER-Net observations report
  16. GRB 250816A: Fermi GBM Final Real-time Localization
  17. GRB 250814A: Swift-BAT refined analysis
  18. GRB 250815A: Fermi GBM Final Localization
  19. GRB 250813B: Liverpool Telescope optical upper limits
  20. GRB 250814A: Further COLIBRÍ optical upper limit
  21. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  22. GRB 250814A: GRAWITA TNG NIR observations
  23. GRB 250812A: SVOM/VT optical continued observation
  24. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  25. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  26. GRB250814A: TRT optical upper limits
  27. GRB 250814B: SVOM/GRM observation
  28. GRB 250814C: SVOM/GRM observation of a short burst
  29. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  30. GRB 250813B: SVOM/GRM observation
  31. GRB 250814A: P200/WIRC observations of the afterglow candidate
  32. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  33. GRB 250814A: KAIT optical upper limit
  34. GRB 250814A: Swift-XRT refined Analysis
  35. GRB 240814A: Fermi GBM Observation
  36. GRB 250814A: Possible afterglow candidate from P200/WIRC
  37. GRB 250813B: Fermi GBM Observation
  38. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  39. Fermi trigger No 776818276: Global MASTER-Net observations report
  40. Swift GRB250814.32: Global MASTER-Net observations report
  41. GRB 250814A: J-band upper limit from WINTER
  42. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  43. GRB 250813B: NOT observations of the optical afterglow
  44. GRB 250813B: SVOM/VT optical observations
  45. Subject GRB 250813B: SVOM/MXT refined analysis
  46. GRB 250814A: COLIBRÍ optical upper limit
  47. GRB 250814B: Fermi GBM Final Real-time Localization
  48. GRB 250813A: AstroSat CZTI detection
  49. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  50. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  51. GRB 250814A: DDOTI Optical Upper Limit
  52. GRB 250813B: EP-FXT counterpart detection
  53. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  54. GRB 250813B: Swift-XRT afterglow detection
  55. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  56. GRB 250814A: Fermi GBM Final Real-time Localization
  57. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  58. GRB 250813B: Ondrejov D50 fast decay
  59. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  60. GRB 250813B: Ondrejov D50 optical afterglow detection
  61. GRB 250813B: SVOM detection of a bright long burst
  62. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  63. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  64. EP250812a: Nickel optical upper limit
  65. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  66. GRB 250812A: NTT spectroscopic redshift z = 2.57
  67. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  68. EP250812a: NOT, NTT, and GS observations
  69. GRB 250812A: Swift/UVOT Detection
  70. GRB 250813A: Fermi GBM Final Localization
  71. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  72. EP250812a: Liverpool Telescope upper limits
  73. EP250812a: SVOM/VT optical counterpart
  74. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  75. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  76. IceCube Alert 250813.14: Global MASTER-Net observations report
  77. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  78. GRB 250812A: EP-FXT counterpart detection
  79. GRB 250812A: Swift ToO observations
  80. GRB 250807B: Swift-BAT refined analysis
  81. EP 250812a: GOTO optical upper limit
  82. GRB 250812A: Kilonova-Catcher optical afterglow detection
  83. EP250812a: Swift-XRT counterpart detection
  84. Fermi Gamma-ray Burst Monitor trigger 776705265/250812644 is not a GRB
  85. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  86. EP250812a: Einstein Probe detection of an X-ray transient
  87. GRB 250812A: SVOM/VT optical afterglow confirmation
  88. GRB 250812A: Swift-XRT afterglow detection
  89. GRB 250812A: TRT likely optical counterpart detection
  90. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  91. GRB 250812A: SVOM detection of a faint long burst
  92. GRB 250809A: Swift-BAT refined analysis
  93. Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB
  94. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  95. GRB 250807A: Swift-BAT refined analysis
  96. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  97. GRB 250809A: Swift/UVOT Detection
  98. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  99. Corrected Swift-XRT Refined Analysis of GRB 250809A
  100. GRB 250809A: Swift-XRT refined Analysis

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