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

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