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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 251129A: Swift ToO observations
  2. GRB 251129A / EP251129a: SVOM/VT optical fading
  3. EP251129a: Global MASTER-Net observations report
  4. GRB 251129A: Optical Observations via Virtual Telescope Project, Italy
  5. EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient
  6. GRB 251129A: Correction to the position of the optical counterpar
  7. GRB 251129A: SVOM/VT optical counterpart confirmation with VHF data
  8. GRB 251128A: Fermi GBM Observation
  9. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  10. GRB 251129A: SVOM detection of a burst
  11. SVOM GRB251129A: Global MASTER-Net observations report
  12. GRB 251129A: SVOM detection of a burst
  13. GRB 251126A: Swift-BAT refined analysis
  14. GRB 251126A: TShAO, Mondy, and AbAO optical observations
  15. GRB 251128A: Swift/BAT-GUANO localization skymap of a burst
  16. Fermi GRB 251128A: Global MASTER-Net observations report
  17. GRB 251127A: Glowbug gamma-ray detection
  18. GRB 251126A: OHP/T193 optical observations and tentative spectroscopic redshift
  19. GRB 251126A: further SAO RAS optical observations
  20. GRB 250702B: detection of the compact radio counterpart 139 days after the burst
  21. GRB 251126A NUTTelA-TAO Early Measurements
  22. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  23. GRB251126A: MAO/AZT-22 optical observations
  24. GRB 251128A: Fermi GBM Final Real-time Localization
  25. GRB251126A: Continued optical observation from 1.3m DFOT
  26. GRB 251126A: Swift/UVOT Detection
  27. EP251124a: Pan-STARRS ri-band imaging and photometry
  28. GRB 251126A: Mondy and SAO RAS optical observations
  29. GRB 251126A: Swift-XRT refined Analysis
  30. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  31. GRB 251126A: NOT optical observations
  32. GRB 251126A: 1.3m DFOT optical afterglow detection
  33. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  34. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  35. GRB 251125B: GECAM-B detection
  36. Fermi GRB 251127A: Global MASTER-Net observations report
  37. GRB 251127A: Fermi GBM Final Real-time Localization
  38. GRB 251126A: Enhanced Swift-XRT position
  39. GRB 251126A: Kilonova-Catcher optical afterglow detection
  40. GRB 251126A: Asiago i-band detection
  41. GRB 251126A: Nanshan/HMT optical afterglow detection
  42. Swift GRB 251126A: Global MASTER-Net observations report
  43. GRB 251121A: Fermi GBM Observation
  44. GRB 251126A: Prompt enhanced Swift-XRT position
  45. GRB 251126A: GIT discovery of the likely optical afterglow
  46. GRB 251126A: Swift detection of a burst
  47. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  48. EP251124b follow-up observation by EP-FXT
  49. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  50. EP251124b: NOT r- and z-band optical upper limits
  51. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  52. Fermi GRB 251125B: Global MASTER-Net observations report
  53. GRB 251125B: Fermi GBM Final Real-time Localization
  54. EP251124b: Global MASTER-Net observations report
  55. EP251124b: EP-WXT detection of a fast X-ray transient
  56. EP251124a: Xinglong GWAC-F60A optical observation
  57. EP251124a (EP-WXT trigger 01709248862) is triggered by the known source AWM 7
  58. Fermi GRB 251125A: Global MASTER-Net observations report
  59. GRB 251125A: Fermi GBM Final Real-time Localization
  60. EP251124a: NOT r- and z-band optical upper limits
  61. EP251124a: Global MASTER-Net observations report
  62. EP251124a: Swift-XRT observations
  63. GRB 251124A: Fermi GBM Localization by automated pipeline
  64. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  65. EP251124a: Optical upper limit with Kinder observations
  66. GRB 251122B: Fermi GBM Final Localization
  67. EP251118A: 6 GHz VLA Detection
  68. Fermi GRB 251124a: Global MASTER-Net observations report
  69. GRB 251124a: Fermi GBM Final Localization
  70. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  71. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  72. EP251124a: GROWTH-India Telescope optical upper limits
  73. EP251124a: Einstein Probe detection of an X-ray transient
  74. GRB 251116C: Swift-XRT confirmation of fading
  75. GRB 251122A/EP251122a: FTW optical and NIR observations
  76. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  77. The EP-WXT trigger 01709248783 is likely a flaring star
  78. GRB 251122A / EP251122a: Xinglong 2.16m optical observation
  79. EP251118A: 3.6m DOT optical afterglow detection
  80. GRB 251122A / EP251122a: EP-FXT counterpart detection
  81. EP251122a: refined analysis of the EP-WXT and EP-FXT observations
  82. GRB 251122A / EP251122a: WFST optical observations
  83. GRB 251122A/EP251122a: SVOM/VT optical observations with VHF data
  84. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  85. GRB 251122A / EP251122a: LCO optical upper limits
  86. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  87. EP251122a: Global MASTER-Net observations report
  88. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  89. GRB 251122A / EP251122a: SVOM detection of a long burst
  90. EP251122a: Einstein Probe detection of an X-ray transient
  91. EP251118a: Continued Optical Detection with Kinder observations
  92. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
  93. LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates
  94. GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst
  95. GRB 251121A: Glowbug gamma-ray detection of a likely short burst
  96. EP251118a: Xinglong-2.16m optical observation
  97. GRB 251115A: Fermi GBM Observation
  98. The EP-WXT trigger 01709248635 is likely a flaring star
  99. GRB 251121A: Fermi GBM Final Real-time Localization
  100. Fermi Gamma-ray Burst Monitor trigger 785388351 / 251121143 is not a GRB

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