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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"

3036 results found.

  1. GRB 251007B: SVOM/VT optical candidate
  2. EP251003a: LCO and VST fading optical counterpart
  3. Fermi GRB 251006B: Global MASTER-Net observations report
  4. EP250821a: iTelescope T-59 possible detection of the optical counterpart
  5. Fermi GRB 251002A: Global MASTER-Net observations report
  6. Swift GRB 251001B: Global MASTER-Net observations report
  7. GRB 251001A: Fermi GBM Detection
  8. GRB 250925A: COLIBRÍ photometric redshift
  9. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  10. GRB 250920C: COLIBRÍ optical observations
  11. Fermi GRB 250922B: Global MASTER-Net observations report
  12. GRB 250916A: CrAO ZTSh R-band optical observations
  13. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  14. GRB 250920B: Swift/UVOT Detection
  15. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  16. GRB 250919A/EP250919a: SVOM/VT optical observation
  17. Fermi GRB 250918A: Global MASTER-Net observations report
  18. GRB 250919A: Fermi GBM Final Real-time Localization
  19. Fermi GRB 250910B: Global MASTER-Net observations report
  20. EP250910a: Global MASTER-Net observations report
  21. GRB 250905A: Swift-BAT refined analysis
  22. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  23. GRB250904A: Liverpool Telescope upper limits
  24. GRB 250905A: Enhanced Swift-XRT position
  25. GRB 250905A: Swift detection of a burst
  26. GRB 250903A: Swift-XRT observations
  27. GRB 250903A: TRT optical counterpart detection
  28. GRB 250902B: AstroSat CZTI detection
  29. Fermi GRB 250902B: Global MASTER-Net observations report
  30. EP250827b: Liverpool Telescope observations
  31. Fermi GRB 250827A: Global MASTER-Net observations report
  32. GRB 250827A: Fermi GBM Final Real-time Localization
  33. EP250827a: BOOTES-7 early optical dectection
  34. EP250827a: Global MASTER-Net observations report
  35. Fermi GRB 250826A: Global MASTER-Net observations report
  36. Fermi trigger No 777883624: Global MASTER-Net observations report
  37. Fermi GRB 250824B: Global MASTER-Net observations report
  38. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  39. IPN triangulation of GRB 250821B (long/bright)
  40. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  41. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  42. GRB 250820A: Fermi GBM Final Real-time Localization
  43. Fermi trigger No 776849714: Global MASTER-Net observations report
  44. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  45. sb25081602: Swift-XRT observations
  46. SVOM/sb25081602: detection of a likely X-ray transient
  47. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  48. Fermi trigger No 776818276: Global MASTER-Net observations report
  49. Subject GRB 250813B: SVOM/MXT refined analysis
  50. EP250812a: SVOM/VT optical counterpart
  51. IceCube Alert 250813.14: Global MASTER-Net observations report
  52. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  53. GRB 250807A: AstroSat CZTI detection of bright long burst
  54. GRB 250807A: SVOM/VT optical observation
  55. GRB 250807A: Swift detection of a burst with an optical counterpart
  56. EP250730a: SVOM/VT optical upper limit
  57. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  58. EP250730a: Global MASTER-Net observations report
  59. GRB 250725A: Swift-BAT refined analysis
  60. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  61. GRB 250725A: SVOM/VT optical candidate
  62. GRB 250725A: Enhanced Swift-XRT position
  63. GRB 250725A: Swift detection of a burst
  64. Fermi GRB 250725A: Global MASTER-Net observations report
  65. GRB 250717B: SVOM/GRM observation
  66. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  67. GRB 250717B: Swift-XRT observations
  68. GRB 250716A: Fermi GBM Observation
  69. Fermi GRB 250715A: Global MASTER-Net observations report
  70. Fermi GRB 250714A: Global MASTER-Net observations report
  71. Fermi GRB 250711A: Global MASTER-Net observations report
  72. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  73. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  74. IPN triangulation of GRB 250703A
  75. GRB 250702B / EP2050702a: FTW optical and NIR observations
  76. Fermi GRB 250703A: Global MASTER-Net observations report
  77. GRB 250702F: Leavitt Observatory optical observations
  78. Fermi GRB 250702F: Global MASTER-Net observations report
  79. GRB 250628A: Swift-XRT refined Analysis
  80. Fermi GRB 250626A: Global MASTER-Net observations report
  81. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  82. Fermi trigger No 772190032: Global MASTER-Net observations report
  83. Konus-Wind detection of GRB 250620C
  84. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  85. GRB250620C: Fermi GBM Observation
  86. GRB 250620A: Fermi GBM Final Real-time Localization
  87. EP-WXT trigger 01709178975: GOTO optical upper limit
  88. Fermi trigger No 771752663: Global MASTER-Net observations report
  89. sb25061218: Swift-XRT observations
  90. GRB 250605A: Swift-BAT refined analysis
  91. GRB 250609A: Fermi GBM Observation
  92. Fermi trigger No 771072240: Global MASTER-Net observations report
  93. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  94. GRB 250609A: Fermi GBM Final Real-time Localization
  95. GRB 250605A: Enhanced Swift-XRT position
  96. Fermi GRB 250606A: Global MASTER-Net observations report
  97. The EP-WXT trigger 01709177873 is likely a flaring star
  98. GRB 250605A: LT optical observations
  99. GRB 250605A: Swift detection of a burst
  100. Fermi GRB 250601A: Global MASTER-Net observations report

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