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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 251126A NUTTelA-TAO Early Measurements
  2. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  3. GRB251126A: MAO/AZT-22 optical observations
  4. GRB 251128A: Fermi GBM Final Real-time Localization
  5. GRB251126A: Continued optical observation from 1.3m DFOT
  6. GRB 251126A: Swift/UVOT Detection
  7. EP251124a: Pan-STARRS ri-band imaging and photometry
  8. GRB 251126A: Mondy and SAO RAS optical observations
  9. GRB 251126A: Swift-XRT refined Analysis
  10. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  11. GRB 251126A: NOT optical observations
  12. GRB 251126A: 1.3m DFOT optical afterglow detection
  13. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  14. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  15. GRB 251125B: GECAM-B detection
  16. Fermi GRB 251127A: Global MASTER-Net observations report
  17. GRB 251127A: Fermi GBM Final Real-time Localization
  18. GRB 251126A: Enhanced Swift-XRT position
  19. GRB 251126A: Kilonova-Catcher optical afterglow detection
  20. GRB 251126A: Asiago i-band detection
  21. GRB 251126A: Nanshan/HMT optical afterglow detection
  22. Swift GRB 251126A: Global MASTER-Net observations report
  23. GRB 251121A: Fermi GBM Observation
  24. GRB 251126A: Prompt enhanced Swift-XRT position
  25. GRB 251126A: GIT discovery of the likely optical afterglow
  26. GRB 251126A: Swift detection of a burst
  27. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  28. EP251124b follow-up observation by EP-FXT
  29. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  30. EP251124b: NOT r- and z-band optical upper limits
  31. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  32. Fermi GRB 251125B: Global MASTER-Net observations report
  33. GRB 251125B: Fermi GBM Final Real-time Localization
  34. EP251124b: Global MASTER-Net observations report
  35. EP251124b: EP-WXT detection of a fast X-ray transient
  36. EP251124a: Xinglong GWAC-F60A optical observation
  37. EP251124a (EP-WXT trigger 01709248862) is triggered by the known source AWM 7
  38. Fermi GRB 251125A: Global MASTER-Net observations report
  39. GRB 251125A: Fermi GBM Final Real-time Localization
  40. EP251124a: NOT r- and z-band optical upper limits
  41. EP251124a: Global MASTER-Net observations report
  42. EP251124a: Swift-XRT observations
  43. GRB 251124A: Fermi GBM Localization by automated pipeline
  44. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  45. EP251124a: Optical upper limit with Kinder observations
  46. GRB 251122B: Fermi GBM Final Localization
  47. EP251118A: 6 GHz VLA Detection
  48. Fermi GRB 251124a: Global MASTER-Net observations report
  49. GRB 251124a: Fermi GBM Final Localization
  50. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  51. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  52. EP251124a: GROWTH-India Telescope optical upper limits
  53. EP251124a: Einstein Probe detection of an X-ray transient
  54. GRB 251116C: Swift-XRT confirmation of fading
  55. GRB 251122A/EP251122a: FTW optical and NIR observations
  56. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  57. The EP-WXT trigger 01709248783 is likely a flaring star
  58. GRB 251122A / EP251122a: Xinglong 2.16m optical observation
  59. EP251118A: 3.6m DOT optical afterglow detection
  60. GRB 251122A / EP251122a: EP-FXT counterpart detection
  61. EP251122a: refined analysis of the EP-WXT and EP-FXT observations
  62. GRB 251122A / EP251122a: WFST optical observations
  63. GRB 251122A/EP251122a: SVOM/VT optical observations with VHF data
  64. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  65. GRB 251122A / EP251122a: LCO optical upper limits
  66. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  67. EP251122a: Global MASTER-Net observations report
  68. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  69. GRB 251122A / EP251122a: SVOM detection of a long burst
  70. EP251122a: Einstein Probe detection of an X-ray transient
  71. EP251118a: Continued Optical Detection with Kinder observations
  72. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
  73. LIGO/Virgo/KAGRA S251112cm: SOAR spectroscopy of three TROVE TNS candidates
  74. GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst
  75. GRB 251121A: Glowbug gamma-ray detection of a likely short burst
  76. EP251118a: Xinglong-2.16m optical observation
  77. GRB 251115A: Fermi GBM Observation
  78. The EP-WXT trigger 01709248635 is likely a flaring star
  79. GRB 251121A: Fermi GBM Final Real-time Localization
  80. Fermi Gamma-ray Burst Monitor trigger 785388351 / 251121143 is not a GRB
  81. Fermi trigger No 785388351: Global MASTER-Net observations report
  82. EP251118A: 1.3m DFOT optical afterglow detection
  83. GRB 251118A: Swift/UVOT Detection
  84. EP251118a / GRB 251118C: SAO RAS optical observations
  85. GRB 251118A: Glowbug gamma-ray detection
  86. GRB 251118A: Fermi GBM Observation
  87. GRB 251118A: Swift-XRT afterglow detection
  88. GRB 251103A: SVOM/ECLAIRs and SVOM/GRM joint refined analysis
  89. EP251118a: Optical detection with Kinder observations
  90. GRB 251118A: GECAM-B detection
  91. EP-WXT trigger 01709248403: confirmation of a stellar flare by SVOM/VT
  92. LIGO/Virgo/KAGRA S251112cm: SVOM/VT optical observations and preliminary results
  93. EP251118a / GRB 251118C: SVOM/VT optical observation
  94. The EP-WXT trigger 01709248403 is likely a flaring star
  95. GRB 251118A: NuSTAR detection of bright prompt emission
  96. EP251118a / GRB 251118C: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at CTIO
  97. GRB 251116C: NOT optical observations
  98. GRB 251118C: Glowbug gamma-ray detection of the fast X-ray transient EP251118A
  99. GRB 251118C: Swift/BAT rates detection of a burst with a possible association with EP 251118A
  100. GRB 251018A: FRAM-Auger optical detection

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