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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. EP251130a: SAO RAS optical observations
  2. EP251130a: GTC OSIRIS+ redshift z = 4.035 and rebrightening
  3. EP251130a: KAIT optical observations
  4. EP251130A: Optical observation from 1.3m DFOT
  5. EP251130a: refined analysis of the EP-WXT and EP-FXT observations
  6. EP251130a: JinShan optical observations
  7. GRB 251201A: MAXI/GSC detection
  8. Fermi GRB 251130B: Global MASTER-Net observations report
  9. GRB 251127A: SVOM/GRM observation
  10. IceCube Alert 251130.75: Global MASTER-Net observations report
  11. IceCube-251130A - IceCube observation of a high-energy neutrino candidate track-like event
  12. EP251130a: Swift-XRT counterpart detection
  13. GRB 251130B: Fermi GBM Final Localization Correction
  14. EP251130a: Global MASTER-Net observations report
  15. GRB 251130B: Fermi GBM Final Real-time Localization
  16. EP251130a: COLIBRÍ optical counterpart candidate
  17. EP251130a: Einstein Probe detection of an X-ray transient
  18. EP251129a/GRB 251129A: EP-FXT follow-up observations
  19. GRB 251130A: Fermi GBM Final Real-time Localization
  20. GRB 251129A / EP251129a: GTC/OSIRIS+ spectroscopic redshift z = 1.460
  21. GRB 251129A / EP251129a: OSN and CAHA optical follow-up
  22. GRB 251128A: AstroSat CZTI detection
  23. GRB 251129A / EP251129a: SAO RAS optical observations
  24. GRB 251126A: SAO RAS optical observations
  25. GRB 251128A: GECAM-B detection
  26. GRB 251128A: SVOM/GRM observation of a long burst
  27. GRB 251128A: Insight-HXMT/HE detection
  28. SVOM GRB 251129A : MASTER optical counterpart detection
  29. GRB 251129A: Swift-XRT afterglow detection
  30. The EP-WXT trigger 01709248941 is triggered by the known source Perseus Cluster
  31. Swift trigger 1418333 is not an astrophysical source
  32. GRB 251129A: Swift ToO observations
  33. GRB 251129A / EP251129a: SVOM/VT optical fading
  34. EP251129a: Global MASTER-Net observations report
  35. GRB 251129A: Optical Observations via Virtual Telescope Project, Italy
  36. EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient
  37. GRB 251129A: Correction to the position of the optical counterpar
  38. GRB 251129A: SVOM/VT optical counterpart confirmation with VHF data
  39. GRB 251128A: Fermi GBM Observation
  40. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  41. GRB 251129A: SVOM detection of a burst
  42. SVOM GRB251129A: Global MASTER-Net observations report
  43. GRB 251129A: SVOM detection of a burst
  44. GRB 251126A: Swift-BAT refined analysis
  45. GRB 251126A: TShAO, Mondy, and AbAO optical observations
  46. GRB 251128A: Swift/BAT-GUANO localization skymap of a burst
  47. Fermi GRB 251128A: Global MASTER-Net observations report
  48. GRB 251127A: Glowbug gamma-ray detection
  49. GRB 251126A: OHP/T193 optical observations and tentative spectroscopic redshift
  50. GRB 251126A: further SAO RAS optical observations
  51. GRB 250702B: detection of the compact radio counterpart 139 days after the burst
  52. GRB 251126A NUTTelA-TAO Early Measurements
  53. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  54. GRB251126A: MAO/AZT-22 optical observations
  55. GRB 251128A: Fermi GBM Final Real-time Localization
  56. GRB251126A: Continued optical observation from 1.3m DFOT
  57. GRB 251126A: Swift/UVOT Detection
  58. EP251124a: Pan-STARRS ri-band imaging and photometry
  59. GRB 251126A: Mondy and SAO RAS optical observations
  60. GRB 251126A: Swift-XRT refined Analysis
  61. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  62. GRB 251126A: NOT optical observations
  63. GRB 251126A: 1.3m DFOT optical afterglow detection
  64. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  65. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  66. GRB 251125B: GECAM-B detection
  67. Fermi GRB 251127A: Global MASTER-Net observations report
  68. GRB 251127A: Fermi GBM Final Real-time Localization
  69. GRB 251126A: Enhanced Swift-XRT position
  70. GRB 251126A: Kilonova-Catcher optical afterglow detection
  71. GRB 251126A: Asiago i-band detection
  72. GRB 251126A: Nanshan/HMT optical afterglow detection
  73. Swift GRB 251126A: Global MASTER-Net observations report
  74. GRB 251121A: Fermi GBM Observation
  75. GRB 251126A: Prompt enhanced Swift-XRT position
  76. GRB 251126A: GIT discovery of the likely optical afterglow
  77. GRB 251126A: Swift detection of a burst
  78. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  79. EP251124b follow-up observation by EP-FXT
  80. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  81. EP251124b: NOT r- and z-band optical upper limits
  82. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  83. Fermi GRB 251125B: Global MASTER-Net observations report
  84. GRB 251125B: Fermi GBM Final Real-time Localization
  85. EP251124b: Global MASTER-Net observations report
  86. EP251124b: EP-WXT detection of a fast X-ray transient
  87. EP251124a: Xinglong GWAC-F60A optical observation
  88. EP251124a (EP-WXT trigger 01709248862) is triggered by the known source AWM 7
  89. Fermi GRB 251125A: Global MASTER-Net observations report
  90. GRB 251125A: Fermi GBM Final Real-time Localization
  91. EP251124a: NOT r- and z-band optical upper limits
  92. EP251124a: Global MASTER-Net observations report
  93. EP251124a: Swift-XRT observations
  94. GRB 251124A: Fermi GBM Localization by automated pipeline
  95. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  96. EP251124a: Optical upper limit with Kinder observations
  97. GRB 251122B: Fermi GBM Final Localization
  98. EP251118A: 6 GHz VLA Detection
  99. Fermi GRB 251124a: Global MASTER-Net observations report
  100. GRB 251124a: Fermi GBM Final Localization

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