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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. IceCube Alert 251130.75: Global MASTER-Net observations report
  2. IceCube-251130A - IceCube observation of a high-energy neutrino candidate track-like event
  3. EP251130a: Swift-XRT counterpart detection
  4. GRB 251130B: Fermi GBM Final Localization Correction
  5. EP251130a: Global MASTER-Net observations report
  6. GRB 251130B: Fermi GBM Final Real-time Localization
  7. EP251130a: COLIBRÍ optical counterpart candidate
  8. EP251130a: Einstein Probe detection of an X-ray transient
  9. EP251129a/GRB 251129A: EP-FXT follow-up observations
  10. GRB 251130A: Fermi GBM Final Real-time Localization
  11. GRB 251129A / EP251129a: GTC/OSIRIS+ spectroscopic redshift z = 1.460
  12. GRB 251129A / EP251129a: OSN and CAHA optical follow-up
  13. GRB 251128A: AstroSat CZTI detection
  14. GRB 251129A / EP251129a: SAO RAS optical observations
  15. GRB 251126A: SAO RAS optical observations
  16. GRB 251128A: GECAM-B detection
  17. GRB 251128A: SVOM/GRM observation of a long burst
  18. GRB 251128A: Insight-HXMT/HE detection
  19. SVOM GRB 251129A : MASTER optical counterpart detection
  20. GRB 251129A: Swift-XRT afterglow detection
  21. The EP-WXT trigger 01709248941 is triggered by the known source Perseus Cluster
  22. Swift trigger 1418333 is not an astrophysical source
  23. GRB 251129A: Swift ToO observations
  24. GRB 251129A / EP251129a: SVOM/VT optical fading
  25. EP251129a: Global MASTER-Net observations report
  26. GRB 251129A: Optical Observations via Virtual Telescope Project, Italy
  27. EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient
  28. GRB 251129A: Correction to the position of the optical counterpar
  29. GRB 251129A: SVOM/VT optical counterpart confirmation with VHF data
  30. GRB 251128A: Fermi GBM Observation
  31. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  32. GRB 251129A: SVOM detection of a burst
  33. SVOM GRB251129A: Global MASTER-Net observations report
  34. GRB 251129A: SVOM detection of a burst
  35. GRB 251126A: Swift-BAT refined analysis
  36. GRB 251126A: TShAO, Mondy, and AbAO optical observations
  37. GRB 251128A: Swift/BAT-GUANO localization skymap of a burst
  38. Fermi GRB 251128A: Global MASTER-Net observations report
  39. GRB 251127A: Glowbug gamma-ray detection
  40. GRB 251126A: OHP/T193 optical observations and tentative spectroscopic redshift
  41. GRB 251126A: further SAO RAS optical observations
  42. GRB 250702B: detection of the compact radio counterpart 139 days after the burst
  43. GRB 251126A NUTTelA-TAO Early Measurements
  44. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  45. GRB251126A: MAO/AZT-22 optical observations
  46. GRB 251128A: Fermi GBM Final Real-time Localization
  47. GRB251126A: Continued optical observation from 1.3m DFOT
  48. GRB 251126A: Swift/UVOT Detection
  49. EP251124a: Pan-STARRS ri-band imaging and photometry
  50. GRB 251126A: Mondy and SAO RAS optical observations
  51. GRB 251126A: Swift-XRT refined Analysis
  52. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  53. GRB 251126A: NOT optical observations
  54. GRB 251126A: 1.3m DFOT optical afterglow detection
  55. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  56. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  57. GRB 251125B: GECAM-B detection
  58. Fermi GRB 251127A: Global MASTER-Net observations report
  59. GRB 251127A: Fermi GBM Final Real-time Localization
  60. GRB 251126A: Enhanced Swift-XRT position
  61. GRB 251126A: Kilonova-Catcher optical afterglow detection
  62. GRB 251126A: Asiago i-band detection
  63. GRB 251126A: Nanshan/HMT optical afterglow detection
  64. Swift GRB 251126A: Global MASTER-Net observations report
  65. GRB 251121A: Fermi GBM Observation
  66. GRB 251126A: Prompt enhanced Swift-XRT position
  67. GRB 251126A: GIT discovery of the likely optical afterglow
  68. GRB 251126A: Swift detection of a burst
  69. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  70. EP251124b follow-up observation by EP-FXT
  71. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  72. EP251124b: NOT r- and z-band optical upper limits
  73. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  74. Fermi GRB 251125B: Global MASTER-Net observations report
  75. GRB 251125B: Fermi GBM Final Real-time Localization
  76. EP251124b: Global MASTER-Net observations report
  77. EP251124b: EP-WXT detection of a fast X-ray transient
  78. EP251124a: Xinglong GWAC-F60A optical observation
  79. EP251124a (EP-WXT trigger 01709248862) is triggered by the known source AWM 7
  80. Fermi GRB 251125A: Global MASTER-Net observations report
  81. GRB 251125A: Fermi GBM Final Real-time Localization
  82. EP251124a: NOT r- and z-band optical upper limits
  83. EP251124a: Global MASTER-Net observations report
  84. EP251124a: Swift-XRT observations
  85. GRB 251124A: Fermi GBM Localization by automated pipeline
  86. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  87. EP251124a: Optical upper limit with Kinder observations
  88. GRB 251122B: Fermi GBM Final Localization
  89. EP251118A: 6 GHz VLA Detection
  90. Fermi GRB 251124a: Global MASTER-Net observations report
  91. GRB 251124a: Fermi GBM Final Localization
  92. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  93. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  94. EP251124a: GROWTH-India Telescope optical upper limits
  95. EP251124a: Einstein Probe detection of an X-ray transient
  96. GRB 251116C: Swift-XRT confirmation of fading
  97. GRB 251122A/EP251122a: FTW optical and NIR observations
  98. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  99. The EP-WXT trigger 01709248783 is likely a flaring star
  100. GRB 251122A / EP251122a: Xinglong 2.16m optical observation

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